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BEHAVIORAL PHARMACOLOGY
Departments of Pharmacology and Toxicology (M.L.H., J.F.B., H.C.D., M.C.O., J.N.R.), Psychology (A.E.M., H.C.D., M.C.O.), and The Centre for Neuroscience Studies (J.F.B., H.C.D., M.C.O., J.N.R.), Queen's University, Kingston, Ontario, Canada
Received August 29, 2003; accepted October 30, 2003.
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Abstract |
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; Clarren and Smith, 1978; Abel, 1995). In particular, in offspring CPEE can induce brain injury that manifests as lifelong learning and cognitive deficits.
Animal models have been used to gain insight into the neurobehavioral deficits that result from CPEE. In particular, the effects of CPEE on learning and memory have received a great deal of attention. In the rat (Blanchard et al., 1987; Reyes et al., 1989; Matthews and Simson, 1998) and the guinea pig (Richardson et al., 2002; Iqbal et al., 2003), CPEE impairs spatial learning in postnatal offspring. Similarly, in tests of operant learning, CPEE has been reported to produce impairments in performance (Riley et al., 1980; Driscoll et al., 1990), the magnitude of which may be dependent on the complexity of the task (Mihalick et al., 2001).
Among brain regions adversely affected by CPEE, the hippocampus appears to be especially vulnerable (West and Pierce, 1986). Brain imaging studies have revealed gross hippocampal dysmorphology in children with fetal alcohol syndrome (Riikonen et al., 1999; Mattson et al., 2001), and animal models of the disorder have demonstrated selective loss of CA1 pyramidal cells (Gibson et al., 2000), altered mossy fiber and pyramidal cell arrangement (Sakata-Haga et al., 2003), and decreased dendritic spine density (Ferrer et al., 1988) in the hippocampus. CPEE induces deficits in spatial learning tasks that are sensitive indicators of hippocampal injury (Berman and Hannigan, 2000; Richardson et al., 2002) and impairs synaptic plasticity in the CA1 region of the hippocampus (Richardson et al., 2002) and in the perforant path-dentate gyrus granule cell pathway (Sutherland et al., 1997).
Synaptic plasticity arises from temporally coordinated changes in both presynaptic neurotransmitter release and postsynaptic receptor function, which cause long-lasting changes in the efficiency of synaptic communication. Direct imaging has confirmed that presynaptic function is enhanced during long-term potentiation (LTP) in the CA1 region of mammalian hippocampal slices (Zakharenko et al., 2001). At present, however, only a few studies have been conducted to investigate the potential role of neurotransmitter release in CPEE-induced alterations in synaptic plasticity (Savage et al., 1998, 2002), and none have examined endogenous glutamate and GABA release simultaneously. The purpose of this study was to determine the effects of CPEE, via daily maternal administration of ethanol, on electrically stimulated amino acid neurotransmitter release in the hippocampus of the adult guinea pig. In addition, we compared the effects of CPEE on performance in two different learning paradigms, spatial navigation in the water maze and conditioned responding in a lever pressing task, which may be adversely affected by CPEE.
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Materials and Methods |
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) was used to mate nulliparous female Dunkin-Hartley strain guinea pigs (500–600 g body weight; Charles River Canada, Montreal, PQ, Canada) with male guinea pigs of the same strain. The last day of full vaginal membrane opening was defined as gestational day (GD) 0 (term, about GD 68). On GD 2, pregnant animals were housed individually in large, stainless steel cages. Lighting was on a 12-h light/dark cycle, with lights on at 7:00 AM. Animals were monitored daily for general health, body weight, food consumption, and vaginal membrane status. On the day of parturition [postnatal day (PD) 0], litters were placed in large plastic bins with wood-chip bedding. Offspring were weighed and monitored for general health daily starting at PD 1 and were weaned and separated by gender on PD 17.
Chronic Treatment Regimens
Pregnant guinea pigs were assigned to one of three treatment groups: 1) 3 g ethanol/kg of maternal body weight/day with ad libitum access to pellet food and water; 2) isocaloric, isovolumetric sucrose with pair-feeding and ad libitum access to water; or 3) isovolumetric water with ad libitum access to food and water. Treatment solutions were 30% ethanol (v/v, in tap water), 42% sucrose (w/v, in tap water), or plain tap water, respectively. The pair-feeding regimen involved pairing each sucrose-treated animal with an ethanol-treated animal; each day, the sucrose-treated guinea pig received food equal to the amount eaten by its ethanol pair on the same gestational day. Daily treatments were given by intubation into the oral cavity from GD 2 to GD 67. All treatments were administered in two equally divided doses 2 h apart, beginning between 8:00 and 9:30 AM each day. At GD 57, a 200-µl sample of blood was taken from an ear blood vessel of each ethanol-treated animal 1 h after the second divided dose, and a gas-liquid chromatographic method (Steenaart et al., 1985) was used to determine blood ethanol concentration. Blood also was taken from the sucrose-treated and water-treated guinea pigs to control for the stress induced by the procedure.
Morris Water Maze
The Morris water maze consisted of a circular pool 180 cm in diameter. Water, made opaque by the addition of a nontoxic white paint, was used to fill the maze. A hidden escape platform, 30 cm in diameter, was located in the center of one of the quadrants of the pool 2 cm below the surface of the water. The water temperature of the maze was maintained at 21–22°C.
Beginning at approximately PD 50 (range, PD 45–55), male and female offspring were trained in the water maze for 7 consecutive days (acquisition phase). Four trials were administered on each day, given in two blocks of two trials with a 5-min rest period between the blocks. For each trial, the animal was placed into one quadrant of the pool, facing the wall. Animals were allowed a maximum of 45 s to swim to the hidden escape platform; animals that failed to locate and mount the platform within this time limit were retrieved from the pool and placed on the platform. Once on the platform, the animal was allowed to remain on it for 15 s. The time to reach the hidden platform was recorded for each trial. Four different start positions, one from each quadrant of the pool, were used in a randomized order for the four trials administered each day. All trials were videotaped using a camera mounted above the pool.
Seven days after the last day of training, a probe trial was administered to test retention performance. This involved removing the escape platform from the pool and allowing the animal to explore the pool for 60 s. The time spent in the quadrant where the platform was located during training was recorded.
Conditioned Responding
Subjects. The subjects were male and female guinea pig offspring from mothers in one of the three chronic maternal treatment regimens: ethanol, isocaloric-sucrose/pair-fed, and water treatments. Where possible, subjects were chosen such that there was a male and female animal from each litter in each treatment group. When litters did not contain a male and female, either two offspring of the same sex were chosen or a single member was included, to make the male/female ratio as uniform as possible. The number of subjects in each group were: four females and seven males from the ethanol treatment group (ethanol, n = 11 offspring obtained from eight litters), seven females and five males from the isocaloric-sucrose/pair-fed treatment group (sucrose, n = 12 offspring obtained from eight litters), and six females and six males from the water treatment group (water, n = 12 offspring obtained from eight litters). Training in the operant paradigm began on average at about PD 63 (S.E.M. = ±0.40).
Animals were kept on a 12-h light/dark cycle, with lights on at 7:00 AM. Before the start of operant training, subjects were given ad libitum access to both food and water; during operant training, animals were food-deprived for approximately 7 h before each session. Subjects had ad libitum access to water at all times. On the day before training began, subjects were exposed to sucrose by adding approximately 16 g of sucrose pellets to their food.
Apparatus. Training occurred in operant boxes (26.5 cm long x 22.0 cm wide x 20.0 cm high), with each animal housed individually in a sound-attenuating chamber. The operant chamber was fitted with two retractable levers (4-cm wide), positioned on one wall, 13 cm apart and 5 cm above the Plexiglas floor. A food magazine was located between the two levers. Sucrose pellets (45 mg; Bio-Serv, Frenchtown, NJ) were delivered to the magazine via a pellet dispenser (MED Associates, St. Albans, VT). Pellet delivery was signaled by a dim light located 4 cm above the magazine, and infrared sensors detected pellet collection. An IBM-type computer controlled the operant equipment and was used to collect data (software written in-house).
Habituation. Habituation to the operant chambers occurred for 30 min per day. During habituation sessions, animals were placed in the operant chambers. Levers remained retracted for these sessions, and 20 sucrose pellets were delivered at random intervals. Subjects were required to make a minimum of 20 nosepokes to the magazine in at least one of two sessions to progress to the next stage of training. Subjects who did not reach criterion after 8 days were removed from training. Five females and six males from the water group (n = 11), seven females and two males from the sucrose group (n = 9), and all animals from the ethanol group (n = 11) completed this phase of training.
Continuous Reinforcement (CRF) Training. During CRF training, both levers were extended into the chamber. One lever was designated the reinforced lever, and one pellet was delivered for each press on this lever. The depression of the other lever had no consequences. Levers were counterbalanced such that half the animals in each group had the right lever reinforced and the other half the left lever reinforced. Subjects completed one session per day. A maximum of 50 sucrose pellets could be obtained in a 30-min session, and if the maximum was reached before 30 min, the session was terminated. The number of reinforced and nonreinforced lever presses was recorded. To complete the CRF schedule, an animal had to receive at least 45 rewards and make at least 75% of their responses on the reinforced lever on 2 consecutive days. Subjects who did not reach this criterion after 20 days were removed from training. Twenty days is approximately 2 standard deviations higher than the average number of days required by the subjects who successfully reached criterion. Four females and five males in the water group (n = 9), four females and two males in the sucrose group (n = 6), and three females and five males in the ethanol group (n = 8) completed this phase of training.
Increasing Fixed Ratio (FR) Schedules. Subjects reaching the CRF schedule criterion were moved onto a FR schedule. Session parameters and lever designations were the same as those used during the CRF training. Criterion to complete a given FR schedule was 2 consecutive days in which the animal received at least 45 sucrose pellets and made at least 75% of their responses on the reinforced lever. The schedule increased by increments of two (e.g., FR-3, FR-5, FR-7) to a maximum of FR-33. Subjects that did not reach criterion for a given schedule after 8 days were removed from training. Eight days is approximately two standard deviations higher than the average number of days taken for the remaining subjects to reach criterion at each FR step. Three animals (two from the water group and one from the ethanol group) completed FR-33. Data for the first two-thirds of subjects not reaching criterion were organized into six blocks, as shown in Table 1. Analyses by likelihood ratio 
2 tests of the drop-out rates revealed no differences between treatment groups (p > 0.05). Therefore, the remaining subjects, two from the water group, four from the sucrose group, and five from the ethanol group, were also moved from FR training to extinction sessions.
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Extinction. All subjects tested under increasing FR schedules were tested in extinction. Animals completed 3 consecutive days of CRF sessions before extinction sessions. During extinction, there were no consequences for pressing either lever. Responses on the previously reinforced and nonreinforced levers were recorded over four 30-min sessions.
Hippocampal Slice Preparation
Between PD 70 and PD 100, male and female guinea pig offspring were weighed, anesthetized with halothane, and euthanized by decapitation. The brain was quickly excised, weighed, and placed in ice-cold buffered saline (118 mM NaCl, 4.8 mM KCl, 1.2 mM KH2PO4, 1.3 mM CaCl2, 1.2 mM MgSO4, 25 mM NaHCO3, and 10 mM glucose, pH 7.4, saturated with 95% O2/5% CO2). A vibrating microtome (TSE Systems, Hamburg, Germany) was used to cut 400-µm-thick coronal slices containing dorsal hippocampus. In a small Petri dish filled with ice-cold, oxygenated, buffered saline, the hippocampal tissue was carefully isolated using fine-tipped brushes, and the left and right hippocampi in each slice were separated by scalpel cut. The hippocampal slices were randomly separated into two sets and used for determination of either the input-output relationship between electrical stimulation and amino acid neurotransmitter release or the effects of tetanic stimulation on electrically stimulated amino acid neurotransmitter release.
Basal and Electrically Stimulated Amino Acid Neurotransmitter Efflux
A superfusion system (BSC-440; Warner Instruments, Hamden, CT) was used to determine basal and electrically stimulated release of glutamate and GABA in the hippocampus. The superfusion system was coupled to a bipolar pulse generator (BTS-404; Warner Instruments) for electrical stimulation of hippocampal slices in the four perfusion chambers. A single hippocampal slice was placed into each chamber of the apparatus, which then was submerged in a 37°C water bath, and slices were perfused throughout the experiment with oxygenated, buffered saline at a flow rate of 0.8 ml/min. After a 2-h equilibration period, two 3-min perfusate fractions were collected and used to determine baseline neurotransmitter release. In half of the chambers, sequential, increasing stimulation strengths of 25, 50, 60, and 75 mA (20 Hz, 5-ms pulse width, 3-min duration) were delivered. For each stimulus applied, three consecutive 3-min perfusate fractions were used to capture the evoked neurotransmitter release. Collection of the first fraction began simultaneously with initiation of electrical stimulation, and delivery of the next stimulus began after collection of the third fraction (interpulse interval of 6 min). Pilot studies showed that this time interval was sufficient for the release of amino acid neurotransmitter substances to return to baseline (data not shown). The remaining chambers were used for the tetanus-induced potentiation paradigm. A control, submaximal stimulus of 50 mA (20 Hz, 5-ms pulse width, 3-min duration) was given, and three 3-min fractions were collected as described for the input-output paradigm. After completion of collection of the third fraction, a tetanizing stimulus was applied to the chamber (five trains of stimulation at 99 mA, 100 Hz, 2-ms pulse width, interstimulus interval of 5 s). At 5 and 15 min after the end of the tetanus, a 50 mA submaximal stimulation identical to the pretetanus control stimulus was administered, and three 3-min fractions were collected as previously described. After experimentation, the hippocampal slice in each chamber was digested in 1 N NaOH, and the amount of protein was determined using a modified Lowry assay (Lowry et al., 1951).
Amino Acid Analysis
Glutamate and GABA in the perfusate fractions were quantified using reverse-phase high-performance liquid chromatography with fluorescence detection of their thiol-substituted isoindole derivatives (Butters et al., 2000). The individual hippocampal slices were considered viable and included in data analysis if the amount of neurotransmitter release in the perfusate was stable over the two basal fractions (<30% variation) and the 50-mA stimulation increased neurotransmitter amount by at least 1.5-fold above basal value.
Glutamate and GABA content values in the individual 3-min perfusate fractions were calculated by dividing the amount of respective neurotransmitter in the perfusate by the amount of protein in the respective hippocampal slice. Basal neurotransmitter efflux was calculated by averaging the values for the two prestimulus basal fractions. Stimulated neurotransmitter efflux was calculated as the sum of total efflux minus basal efflux for each of the three fractions collected for that stimulus, and expressing the data as the fold-increase above basal efflux.
Statistical Analyses
The data are presented as group means ± S.E.M. Pregnancy-outcome parameters were analyzed by one-way analysis of variance (ANOVA) coupled with Newman-Keuls test for multiple comparisons. There was no evidence of sex differences, and sex did not interact with treatment on any behavioral measure. Thus, the data for male and female subjects in a treatment group were combined for all statistical analyses. Morris water maze data were analyzed by repeated-measures two-way ANOVA with day as the within-subject factor. For the conditioned responding experiments, the number of days to reach criterion for the CRF schedule was analyzed using a one-way ANOVA with treatment as the between-subjects factor. Extinction data were analyzed in a three-way repeated measures ANOVA with treatment group (ethanol, sucrose, water) as the between-subjects variable, and day of training (1–4) and lever (reinforced, nonreinforced) as within-subjects variables. When the assumption of sphericity was violated, a Huynh-Feldt correction was used to adjust the degrees of freedom. All statistically significant effects and interactions of interest were analyzed further using an estimated marginal means procedure with a Bonferroni correction for multiple comparisons. Stimulated neurotransmitter efflux data were analyzed by two-way ANOVA for effects of treatment and stimulus (intensity or temporal relationship to tetanus), followed by two-tailed, unpaired t tests (95% confidence interval) at each stimulus value. A p value less than 0.05 was considered to be statistically significant.
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Results |
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Morris Water Maze
The chronic maternal ethanol regimen did not affect task acquisition in the Morris water maze (Fig. 1). Probe trials administered 7 days after completion of the training (acquisition) phase did not reveal differences among the offspring of the three treatment groups (Fig. 1).
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Conditioned Responding
CRF Training. The mean number of days to reach criterion for offspring in the ethanol, sucrose, and water treatment groups was 9.88 ± 1.81, 11.17 ± 3.59, and 10.17 ± 1.96, respectively. There was no difference in this measure among the three groups (F(2, 20) = 0.07, p > 0.05).
Extinction. Figure 2 shows the number of reinforced and nonreinforced lever presses across 4 days of extinction for animals in each of the three treatment groups. The ANOVA revealed a day-by-lever-by-group interaction (F(5, 47) = 3.06, p < 0.05). Lever responding decreased over the 4 days of training in all groups (F(3, 51) = 8.39, p < 0.05); however, the effect interacted with lever (F(2, 47) = 9.38, p < 0.05). Post hoc tests showed that this lever-by-day interaction was due to the fact that nonreinforced lever presses did not change across days, whereas reinforced lever presses were higher on days 1 and 2 than on days 3 and 4 (p < 0.05).
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All offspring responded more on the previously reinforced lever than on the nonreinforced lever (F(1, 20) = 35.78, p < 0.05), an effect that interacted with treatment (F(2, 20) = 4.61, p < 0.05). Post hoc tests for this lever-by-treatment interaction revealed that the offspring of the ethanol group had a higher number of presses on the previously reinforced lever compared with the water and sucrose groups (p < 0.05). The offspring of the water and sucrose groups did not differ in the number of previously reinforced lever presses, and there were no group differences in responding on the nonreinforced lever.
During extinction sessions, responses of animals in the three treatment groups were different (F(2, 20) = 4.04, p < 0.05), and this effect interacted with day (F(5, 51) = 3.74, p < 0.05). Post hoc analyses revealed that, on the first day of extinction, offspring of the ethanol group responded more than the animals of both the sucrose and water groups (p < 0.05), whereas there was no difference in responding for offspring in the water group and sucrose group. On the second day of testing, animals in the ethanol group responded more than those in the water group (p < 0.05). There was no difference in the rate of responding between offspring in the sucrose and water groups or between offspring in the sucrose and ethanol groups. Responses of animals in the three treatment groups for the third and fourth days of extinction were not different.
Amino Acid Neurotransmitter Efflux in Hippocampal Slices
The basal efflux of glutamate and GABA was not different among the treatment groups (Table 3). The data for the isocaloric-sucrose/pair-fed and water treatment groups were not different for any of the parameters measured; hence, these control treatment groups were collapsed into a single control group for the purpose of data analysis. The relationship between the strength of the electrical stimulus and the efflux of glutamate and GABA (input-output relationship) is shown in Fig. 3. Neither the glutamate input-output relationship nor the GABA input-output relationship was affected by CPEE. High-frequency, stimulus-induced potentiation of glutamate efflux in hippocampal slices (Fig. 4A) obtained from CPEE offspring was not different from that in control hippocampal slices (F(1,52) = 2.76, p = 0.103). However, high-frequency, stimulus-induced potentiation of GABA efflux (Fig. 4B) was higher in hippocampal slices obtained from CPEE offspring compared with control animals (F(1,48) = 9.74, p = 0.003). This difference was most evident at the 5-min time point, although evoked GABA efflux was still elevated at 15 min after high-frequency stimulation of the tissue.
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Discussion |
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). The timing of brain development is species-dependent, and therefore, putative critical periods of vulnerability to ethanol exposure probably vary across different animal species. The most rapid period of brain growth and development, the brain growth spurt, is one such putative critical period of vulnerability to ethanol. The brain growth spurt is a perinatal event in the human, a prenatal event in the guinea pig and sheep, and a postnatal event in the rat and mouse (Dobbing and Sands, 1979). The guinea pig, therefore, is an appropriate animal model for human prenatal ethanol exposure, in which brain development may be affected by maternal oral ingestion of ethanol and subsequent transfer of ethanol across the placenta into the fetal compartment. The guinea pig has a placenta that is most similar to that of the human among rodent species and has a trimester-equivalent type of gestation that is similar to that of the human (Martensson, 1984).
CPEE, via maternal ethanol ingestion, results in persistent alterations in brain morphology, neurochemistry, and behavior. Offspring exposed to ethanol during gestation demonstrate deficits in spatial tasks sensitive to hippocampal damage, such as the Morris water maze (see review, Berman and Hannigan 2000), suggesting that CPEE perturbs synaptic plasticity in the hippocampus. In our laboratory, previous studies have demonstrated that CPEE can induce deficits in both Morris water maze performance and LTP in the CA1 region of the hippocampus (Richardson et al., 2002; Iqbal et al., 2003). Coincident pre- and postsynaptic activity is required for the generation of LTP, and recent studies have provided evidence that the increased excitability in hippocampal circuits that characterize LTP requires changes in both excitatory and inhibitory mechanisms (Lu et al., 2000). Specifically, an N-methyl-D-aspartate receptor-dependent inhibition of GABAA receptor-mediated inhibitory postsynaptic potentials may be a required step in LTP induction (Lu et al., 2000). Furthermore, enhancement of GABAergic function in the hippocampus can inhibit LTP induction (Levkovitz et al., 1999).
In this study, we report for the first time that CPEE induces alterations in the evoked release of the inhibitory neurotransmitter GABA in the hippocampus of postnatal guinea pig offspring. An increase in post-tetanic potentiation of electrically stimulated GABA release could explain, at least in part, the deficits in hippocampal LTP previously observed in CPEE offspring (Richardson et al., 2002). Interestingly, chronic ethanol exposure in the adult rat that is associated with long-lasting deficits in hippocampal LTP also increases electrically stimulated GABA release in the hippocampus (Tremwell et al., 1994; Peris et al., 1997). This increase in hippocampal GABA release after chronic ethanol exposure has been attributed to a deficit in presynaptic inhibition of GABA release mediated by GABAB receptor activation (Peris et al., 1997). Thus, one possible explanation for the observations made in this study is that CPEE results in decreased GABAB receptor-dependent presynaptic inhibition of GABA release from interneurons in the hippocampus of postnatal offspring. This deficit would be most evident during periods of high-frequency stimulation, such as during the induction of LTP, when GABAB receptor-mediated inhibition of GABA release plays an important role in facilitating N-methyl-D-aspartic acid receptor activation. Future studies will be aimed at elucidating the effects of CPEE on the expression and function of GABAB receptors in the guinea pig hippocampus.
For the maternal ethanol regimen used in this study, CPEE did not alter task acquisition in the Morris water maze. Previous studies conducted in our laboratory have demonstrated that a higher daily dose of ethanol administered throughout gestation (4 g of ethanol/kg of maternal body weight/day) reliably induces deficits in task acquisition in the fixed-platform version of the Morris water (Richardson et al., 2002; Iqbal et al., 2003). Abdollah et al. (1993) demonstrated that CPEE at 4 g of ethanol/kg of maternal body weight/day resulted in greater behavioral dysfunction, manifesting as increased spontaneous locomotor activity, compared with 3 g of ethanol/kg of maternal body weight/day, suggesting that CPEE-induced deficits in performance in spatial learning tasks may be dose-dependent. Similar dose-dependent effects of CPEE on spatial task performance also have been observed in the rat (Savage et al., 2002). In adult rat offspring exposed to ethanol during prenatal development at a maternal blood ethanol concentration of 83 mg/dl, performance in the fixed-platform version of the Morris water maze was unaffected, whereas learning in a "moving-platform" version of the test was markedly impaired (Savage et al., 2002). It will be of interest to determine whether the moving-platform version of the Morris water maze reveals performance deficits in guinea pig offspring exposed to the lower chronic maternal ethanol regimen used in this study. Indeed, one of the goals of the current study was to determine whether a chronic maternal ethanol regimen, which is lower than that used in previous studies, would induce neurobehavioral deficits in our animal model that would be revealed by more sophisticated operant-learning paradigms.
In contrast to the spatial navigation task, CPEE induced a pronounced behavioral deficit in an operant-conditioning paradigm that manifested as high magnitude of responding on the previously reinforced lever during extinction trials. This result is remarkably consistent across multiple learning paradigms that measure adaptive response inhibition in experimental animals (Riley et al., 1979, 1980; Abel, 1982; Driscoll et al., 1990) and children with fetal alcohol spectrum disorder (Streissguth et al., 1984; Nanson and Hiscock, 1990; Mattson and Riley, 1998), indicating that common neuroanatomical structures and/or neurophysiological processes may be involved. Our data suggest that CPEE alters the regulation of presynaptic GABA release, resulting in increased release of this neurotransmitter, in the hippocampus during periods of high-frequency stimulation that would be consistent with deficits in the expression of synaptic plasticity in this brain region. However, other brain structures that also are affected by CPEE may contribute to the behavioral deficits observed in the present study. In particular, a recent study in the rat (Mihalick et al., 2001) showed that CPEE produced neuronal cell loss in the medial prefrontal cortex that was correlated with deficits in a reversal learning paradigm. Such an effect also may account for, or contribute to, the resistance to extinction observed in CPEE guinea pig offspring. It is likely that CPEE-induced injury of multiple brain structures contributes to the learning deficits, alterations in organizational skills, and poor response to changing environments that characterize individuals exposed to ethanol during prenatal life. Moreover, the results of this study support the idea that CPEE regimens, which do not induce gross impairment in motor and spatial learning skills, nevertheless produce learning deficits that are directly dependent on the complexity of the task.
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Footnotes |
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ABBREVIATIONS: CPEE, chronic prenatal ethanol exposure; LTP, long-term potentiation; GD, gestational day; PD, postnatal day; CRF, continuous reinforcement; FR, fixed ratio; ANOVA, analysis of variance.
Address correspondence to: Dr. J. N. Reynolds, Pharmacology and Toxicology, Botterell Hall Room 535, Queen's University, Kingston, Ontario, Canada, K7L 3N6. E-mail: jnr{at}post.queensu.ca
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References |
|---|
|
TopAbstractMaterials and MethodsResultsDiscussionReferences |
|---|
Abdollah S, Catlin MC, and Brien JF (1993) Ethanol neurobehavioural teratogenesis in the guinea pig: Behavioural dysfunction and hippocampal morphological change. Can J Physiol Pharmacol 71: 776–782.[Medline]
Abel EL (1982) In utero alcohol exposure and developmental delay of response inhibition. Alcoholism Clin Exp Res 6: 369–376.[Medline]
Abel EL (1995) An update on incidence of FAS: FAS is not an equal opportunity birth defect. Neurotoxicol Teratol 17: 437–443.[CrossRef][Medline]
Berman RF and Hannigan JH (2000) Effects of prenatal exposure on the hippocampus: spatial behavior, electrophysiology and neuroanatomy. Hippocampus 10: 94–110.[CrossRef][Medline]
Blanchard BA, Riley EP, and Hannigan JH (1987) Deficits on a spatial navigation task following prenatal exposure to ethanol. Neurotoxicol Teratol 9: 253–258.[CrossRef][Medline]
Butters NS, Gibson MAS, Reynolds JN, and Brien JF (2000) Effects of chronic prenatal ethanol exposure on hippocampal glutamate release in the postnatal guinea pig. Alcohol 21: 1–9.[CrossRef][Medline]
Clarren SK and Smith DW (1978) The fetal alcohol syndrome. N Engl J Med 298: 1063–1067.[Medline]
Dobbing J and Sands J (1979) Comparative aspects of the brain growth spurt. Early Hum Dev 3: 79–83.[CrossRef][Medline]
Driscoll CD, Streissguth AP, and Riley EP (1990) Prenatal alcohol exposure: comparability of effects in humans and animal models. Neurotoxicol Teratol 12: 231–237.[CrossRef][Medline]
Elvidge H (1972) Production of dated pregnant guinea pigs without post-partum matings. J Inst Anim Technol 23: 111–117.
Ferrer I, Galofre E, Lopez-Tejero D, and Llobera M (1988) Morphological recovery of hippocampal pyramidal neurons in the adult rate exposed in utero to ethanol. Toxicology 48: 191–197.[CrossRef][Medline]
Gibson MAS, Butters NS, Reynolds JN, and Brien JF (2000) Effects of chronic prenatal ethanol exposure on locomotor activity, hippocampal weight, neurons and nitric oxide synthase activity of the young postnatal guinea pig. Neurotoxicol Teratol 22: 183–192.[CrossRef][Medline]
Iqbal U, Dringenberg HC, Brien JF, and Reynolds JN (2003) Chronic prenatal ethanol exposure alters hippocampal GABAA receptors and impairs spatial learning in the guinea pig. Behav Brain Res, in press.
Jones KL and Smith DW (1973) Recognition of the fetal alcohol syndrome in early infancy. Lancet 2: 999–1001.[Medline]
Levkovitz Y, Avignone E, Groner Y, and Segal M (1999) Upregulation of GABA neurotransmission suppresses hippocampal excitability and prevents long-term potentiation in transgenic superoxide dismutase-overexpressing mice. J Neurosci 19: 10977–10984.
Lowry OH, Rosebrough NJ, Farr AL, and Randall RJ (1951) Protein measurement with the Folin phenol reagent. J Biol Chem 193: 265–275.
Lu YM, Mansuy IM, Kandel ER, and Roder J (2000) Calcineurin-mediated LTD of GABAergic inhibition underlies the increased excitability of CA1 neurons associated with LTP. Neuron 26: 197–205.[CrossRef][Medline]
Martensson L (1984) The pregnant rabbit, guinea pig, sheep and rhesus monkey as models in reproductive physiology. Eur J Obstet Gynecol Reprod Biol 18: 169–182.[CrossRef][Medline]
Matthews DB and Simson PE (1998) Prenatal exposure to ethanol disrupts spatial memory: effect of the training-testing delay period. Physiol Behav 64: 63–67.[CrossRef][Medline]
Mattson SN and Riley EP (1998) A review of the neurobehavioral deficits in children with fetal alcohol syndrome or prenatal exposure to alcohol. Alcoholism Clin Exp Res 22: 279–294.[CrossRef][Medline]
Mattson SN, Schoenfeld AM, and Riley EP (2001) Teratogenic effects of alcohol on brain and behaviour. Alcohol Res Health 25: 185–191.[Medline]
Mihalick SM, Crandall JE, Langlois JC, Krienke JD, and Dube WV (2001) Prenatal ethanol exposure, generalized learning impairment and medial prefrontal cortical deficits in rats. Neurotoxicol Teratol 23: 453–462.[CrossRef][Medline]
Nanson JL and Hiscock M (1990) Attention deficits in children exposed to alcohol prenatally. Alcoholism Clin Exp Res 14: 656–661.[CrossRef][Medline]
Peris J, Eppler B, Hu M, Walker DW, Hunter BE, Mason K, and Anderson KJ (1997) Effects of chronic ethanol exposure on GABA receptors and GABAB receptor modulation of 3H-GABA release in the hippocampus. Alcoholism Clin Exp Res 21: 1047–1052.[Medline]
Reyes E, Wolfe J, and Savage DD (1989) The effects of prenatal alcohol exposure on radial arm maze performance in adult rats. Physiol Behav 46: 45–48.[CrossRef][Medline]
Richardson DP, Byrnes ML, Brien JF, Reynolds JN, and Dringenberg HC (2002) Impaired acquisition in the water maze and hippocampal long-term potentiation after chronic prenatal ethanol exposure in the guinea-pig. Eur J Neurosci 16: 1593–1598.[CrossRef][Medline]
Riikonen R, Salonen I, Partanen K, and Verho S (1999) Brain perfusion SPECT and MRI in foetal alcohol syndrome. Dev Med Child Neurol 41: 652–659.[CrossRef][Medline]
Riley EP, Lochry EA, and Shapiro NR (1979) Lack of response inhibition in rats prenatally exposed to alcohol. Psychopharmacology (Berl) 62: 47–52.[CrossRef][Medline]
Riley EP, Shapiro NR, Lochry EA, and Broida JP (1980) Fixed-ratio performance and subsequent extinction in rats prenatally exposed to ethanol. Physiol Psychol 8: 27–50.
Sakata-Haga H, Sawada K, Ohta K, Cui C, Hisano S, and Fukui Y (2003) Adverse effects of maternal ethanol consumption on development of dorsal hippocampus in rat offspring. Acta Neuropathol (Berl) 105: 30–36.[Medline]
Savage DD, Becher M, de la Torre AJ, and Sutherland RJ (2002) Dose-dependent effects of prenatal ethanol exposure on synaptic plasticity and learning in mature offspring. Alcoholism Clin Exp Res 26: 1752–1758.[Medline]
Savage DD, Cruz LL, Duran LM, and Paxton LL (1998) Prenatal ethanol exposure diminishes activity-dependent potentiation of amino acid neurotransmitter release in adult rat offspring. Alcoholism Clin Exp Res 22: 1771–1777.[Medline]
Steenaart NAE, Clarke DW, and Brien JF (1985) Gas-liquid chromatographic analysis of ethanol and acetaldehyde in blood with minimal artifactual acetaldehyde formation. J Pharmacol Methods 14: 199–212.[CrossRef][Medline]
Streissguth AP, Martin DC, Barr HM, and MacGregor-Sandman B (1984) Intrauterine alcohol and nicotine exposure: attention and reaction time in 4-year-old children. Dev Psychol 20: 533–541.[CrossRef]
Sutherland RJ, McDonald RJ, and Savage DD (1997) Prenatal exposure to moderate levels of ethanol can have long-lasting effects on hippocampal synaptic plasticity in adult offspring. Hippocampus 7: 232–238.[CrossRef][Medline]
Tremwell MF, Hunter BE, and Peris J (1994) Chronic ethanol exposure enhances [3H]GABA release and does not affect GABAA receptor mediated 36Cl uptake. Synapse 17: 149–154.[CrossRef][Medline]
West JR and Pierce DR (1986) Perinatal alcohol exposure and neuronal damage. In: Alcohol and Brain Development (West JR ed) pp 120–157, Oxford University Press, New York.
Zakharenko SS, Zablow L, and Siegelbaum SA (2001) Visualization of changes in presynaptic function during long-term synaptic plasticity. Nat Neurosci 4: 711–717.[CrossRef][Medline]
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