Persistent blockade of potassium-evoked serotonin release from rat frontocortical terminals after fluoxetine administration

doi:10.1016/0006-8993(91)90530-9

Brain Research

Volume 540, Issues 1–2, 1 February 1991, Pages 325-330

https://doi.org/10.1016/0006-8993(91)90530-9 Get rights and content

Abstract

We examined 5-HT and 5-HIAA release from frontal cortex evoked by high potassium chloride concentrations in rats pretreated for 3 days with high doses of the 5-HT uptake blocker fluoxetine or of dexfenfluramine, which both releases 5-HT and blocks its reuptake. The standard fluoxetine dose (30 mg/kg i.p.) was about 4 times the drug's ED₅₀ in producing a serotonin-related behavioral effect, anorexia, while the dexfenfluramine dose (7.5 mg/kg i.p.) was about 6 times its ED₅₀. These high doses were chosen in order to elucidate the mechanism by which similar doses of fluoxetine and dexfenfluramine had been found to produce long-term changes in serotonin dynamics. Fluoxetine decreased the basal release of both compounds; dexfenfluramine decreased basal 5-HIAA efflux without affecting the release of 5-HT release. Potassium-evoked 5-HT release was unchanged after dexfenfluramine pretreatment but was suppressed by fluoxetine doses as low as 7.5 mg per kg per day. Basal release of 5-HT and 5-HIAA returned to normal after 7 days of fluoxetine pretreatment, but evoked relase continued to be suppressed. These data suggest that long-term changes in brain serotonin dynamics after high doses of dexfenfluramine or fluoxetine are related to the drug's mechanisms of action, specifically their blockade of 5-HT reuptake.

References (37)

AuerbachS.B. et al.
Extracellular serotonin and 5-hydroxyindolacetic acid in hypothalamus of the unaesthetized rat measured by in vivo dialysis coupled to high-performance liquid chromatography with electrochemical detection: dialysate serotonin reflects neuronal release
Brain Research
(1989)
CarboniE. et al.
Serotonin release estimated by transcortical dialysis in freely-moving rats
Neuroscience
(1989)
ChastainJ.E. et al.
Kainic acid-induced seizures: changes in brain extracellular ions as assessed by intracranial microdialysis
Life Sci.
(1989)
DuhaultJ. et al.
Fenfluramine long-term administration and brain serotonin
Eur. J. Pharmacol.
(1977)
FullerR.W. et al.
Reversible and irreversible phases of serotonin depletion by 4-chloroamphetamine
Eur. J. Pharmacol.
(1975)
FullerR.W. et al.
Fluoxetine enantiomers as antagonists ofP-chloroamphetamine effects in rats
Pharmacol. Biochem. Behav.
(1986)
GuanX.M. et al.
Fluoxetine increases the extracellular levels of serotonin in the nucleus accumbens
Brain Res. Bull.
(1988)
HrdinaP.D.
Regulation of high and low affinity³H-imipramine recognition sites in rat brain by chronic treatment with antidepressants
Eur. J. Pharmacol.
(1987)
KawasakiK. et al.
Prolonged exposure to high potassium concentrations results in irreversible loss of synaptic transmission in hippocampal tissue slices
Brain Research
(1988)
KlevenM.S. et al.
d-,l- anddl-fenfluramine cause long-lasting depletions of serotonin in rat brain
Brain Research
(1989)

LaferrereB. et al.

Effect ofd-fenfluramine on serotonin release in brain of anesthetized rats

Brain Research

(1989)

MarsdenC.A. et al.

Monitoring 5-hydroxytryptamine release in the brain of the freely moving unanesthetized rat using in vivo voltammetry

Brain Research

(1979)

PeiQ. et al.

Measurement of extracellular 5-HT and 5-HIAA in hippocampus of freely-moving rats using microdialysis: long-term applications

Neurochem. Int.

(1989)

SarkissianC.F. et al.

Effects of fluoxetine ord-fenfluramine on serotonin release from, and levels in rat frontal cortex

Brain Research

(1990)

SterankaL.R. et al.

Long-term effects of fenfluramine on central serotoninergic mechanisms

Neuropharmacology

(1979)

WesterinkB.H.C. et al.

Scope and limitations of in vivo brain dialysis: a comparison of its application to various neurotransmitter systems

Life Sci.

(1987)

BenvenisteH. et al.

Determination of brain interstitial concentrations by microdialysis

J. Neurochem.

(1989)

BorroniE. et al.

Differences betweend-fenfluramine andd-norfenfluramine in serotonin presynaptic mechanisms

J. Neurochem.

(1983)

Cited by (19)

Rapid analysis of glutamate, glutamine and GABA in mice frontal cortex microdialysis samples using HPLC coupled to electrospray tandem mass spectrometry
2018, Journal of Pharmaceutical and Biomedical Analysis
Citation Excerpt :
As a proof of concept, we chose as mood relevant brain area, the mPFC, which is mainly involved in the antidepressant-like activity of selective serotonin reuptake inhibitors (SSRI). Moreover, neuronal depolarization with a high potassium concentration (120 mM) was performed to induce neurotransmitters’ release [23]. KCl-evoked neurotransmitter release is one of the tests used to verify the neuronal origin of extracellular neurotransmitter levels measured in dialysate samples.
In vivo measurement of multiple neurotransmitters is highly interesting but remains challenging in the field of neuroscience. GABA and l-glutamic acid are the major inhibitory and excitatory neurotransmitters, respectively, in the central nervous system, and their changes are related to a variety of diseases such as anxiety and major depressive disorder. This study described a simple method allowing the simultaneous LC–MS/MS quantification of l-glutamic acid, glutamine and GABA. Analytes were acquired from samples of the prefrontal cortex by microdialysis technique in freely moving mice. The chromatographic separation was performed by hydrophilic interaction liquid chromatography (HILIC) with a core-shell ammonium-sulfonic acid modified silica column using a gradient elution with mobile phases consisting of a 25 mM pH 3.5 ammonium formate buffer and acetonitrile. The detection of l-glutamic acid, glutamine and GABA, as well as the internal standards [d6]-GABA and [d5]-glutamate was performed on a triple quadrupole mass spectrometer in positive electrospray ionization and multiple reaction monitoring mode. The limit of quantification was 0.63 ng/ml for GABA, 1.25 ng/ml for l-glutamic acid and 3.15 ng/ml for glutamine, and the intra-day and inter-day accuracy and precision have been assessed for the three analytes. Therefore, the physiological relevance of the method was successfully applied for the determination of basal extracellular levels and potassium-evoked release of these neuroactive substances in the prefrontal cortex in adult awake C57BL/6 mice.
Pre- and postsynaptic responses to 1-(1-naphthylpiperazine) following adaptation to stress in rats
2002, Progress in Neuro-Psychopharmacology and Biological Psychiatry
In view of a role of pre- and postsynaptic serotonin (5-hydroxytryptamine; 5-HT) receptors in adaptation to stress, effects of 1-(1-naphthylpiperazine) (1-NP) were compared in unrestrained and repeatedly restrained adapted rats. In the first part of the study, effects of various doses (1.0–15 mg/kg ip) of 1-NP were monitored on brain 5-HT metabolism (presynaptic response) and on the activity (postsynaptic response) of rats in an activity cage to which the rats were habituated before the drug administration. The drug injected at doses of 2.5–15.0 mg/kg increased motor activity and decreased brain 5-hydroxyindoleacetic acid (5-HIAA) concentration in a dose-dependent manner. In the second part of the study, rats were restrained on wire grids 2 h/day for 5 days. First-day episode of 2-h restraint decreased 24-h cumulative food intake, water intake and growth rate. The decreases attenuated following second-, third- and fourth-day episodes of 2-h restraint were not observed following fifth-day episode of 2-h restraint stress, suggesting adaptation to the stress schedule has occurred. Serotonergic and motor responses to 1-NP in unrestrained and repeatedly restrained adapted rats were compared by injecting the drug at a dose of 5 mg/kg, a dose that above results suggested would not produce maximal effects on 5-HT metabolism or motor activity. Administration of 1-NP at a dose of 5 mg/kg increased motor activity and decreased brain 5-HIAA concentration in unrestrained and repeatedly restrained adapted rats. Increases of motor activity were much greater in repeatedly restrained adapted than unrestrained rats. Decreases of 5-HIAA concentration were comparable in the two groups. The results are discussed in the context of an increase in the effectiveness of postsynaptic 5-HT-1A and 5-HT-1B receptors and a decrease in the effectiveness of presynaptic 5-HT-1A (somatodendritic) and 5-HT-1B (terminal) receptors following adaptation to stress. It is suggested that these changes of receptor responsiveness might help coping with stress demand to produce adaptation to stress.
Role of 5-HT<inf>1A</inf> receptors in the effects of acute and chronic fluoxetine on extracellular serotonin in the frontal cortex
1996, Pharmacology Biochemistry and Behavior
Fluoxetine 10 mg/kg IP significantly increased the extracellular concentrations of serotonin (5-HT) in the frontal cortex as assessed by in vivo microdialysis. This effect was significantly potentiated when 0.3 mg/kg SC WAY-100635, a 5-HT_1A receptor antagonist, was administered 30 min before. WAY-100635 by itself had no effect on extracellular 5-HT. Twenty-four hours after chronic fluoxetine schedule (10 mg/kg/day IP × 14 days), basal extracellular 5-HT concentrations in the frontal cortex were higher than those of animals that had received the vehicle chronically. At 24 h after the last dose, a challenge dose of fluoxetine (10 mg/kg IP) raised extracellular 5-HT similarly in chronically vehicle or fluoxetine treated rats. At this same interval 25 μg/kg SC 8-OH-DPAT, a 5-HT_1A receptor agonist, significantly reduced extracellular 5-HT only in the frontal cortex of rats treated chronically with the vehicle. Examining basal extracellular 5-HT, the effect of a challenge dose of fluoxetine and the effect of 25 μg/kg 8-OH-DPAT after 96 h washout, no differences were found between chronically fluoxetine and vehicle-treated rats. The results confirm that the ability of fluoxetine to stimulate 5-HT_1A autoreceptors through an increase of endogenous 5-HT attenuates its effect on cortical dialysate 5-HT. Chronic fluoxetine increased the basal concentrations of extracellular 5-HT only when a substantial amount of its metabolite was present in the brain and during the desensitization of presynaptic 5-HT_1A autoreceptors (24 h after the last dose). These effects, in fact, disappeared after 96 h washout. The continuous presence of the drug may, therefore, be necessary to maintain extracellular 5-HT at concentrations high enough to produce a therapeutic effect.
Development of an animal model of fluoxetine akathisia
1995, Progress in Neuropsychopharmacology and Biological Psychiatry
- 1.
  1. Akathisia describes the pattern of intense inner restlessness often associated with neuroleptic and antidepressant treatment.
- 2.
  2. The authors postulated that drug-induced akathisia would be characterized by more position changes and less time spent immobile, in the absence of significant increase in ambulation. In contrast, a psychomotor stimulant would produce both activation and ambulation.
- 3.
  3. Procedures and instruments were developed to test this hypothesis. Adult rats were habituated for 72 hours to the testing environment, and their precise pattern of movements was tracked and recorded (10 reading per second; resolution 0.04 mm) by an infrared motion analysis system. Activity was recorded for a 90 min period after a single injection of sub-stereotypic doses of d-amphetamine (0, 0.3, 1.0 mg/kg) or racemic fluoxetine (0, 3.0, 10.0, 20.0, or 30.0 mg/kg, s.c.).
- 4.
  4. Amphetamine produced both activation and ambulation. Activation was indicated by a decrease in time spent immobile, and an increase in the temporal scaling exponent, which reflects the degree the animal is “acting” in its environment, and the number of position changes. Enhanced locomotion was inferred from marked increases in both the total distance traversed and the ratio of forward movements-to-reversals and a decrease in the spatial scaling exponent, indicative of a less complex and more linear movement pattern.
- 5.
  5. Fluoxetine caused animals to spend more time active, but exerted little effect on locomotion. Activation was indicated by a decrease in time spent immobile and an increase in the temporal scaling exponent and number of position changes. Fluoxetine failed to significantly effect either the ratio of forward movements-to-reversals or the spatial scaling exponent.
- 6.
  6. These findings provide an operational definition and methodology that can be used to differentiate between psychostimulant effects and akathisic effects. This approach may have utility for screening drugs for akathisic potential, for exploring underlying mechanisms, and for developing novel treatments.
Effects of fluoxetine on basal and K<sup>+</sup>-induced tritium release from synaptosomes preloaded with [<sup>3</sup>H]serotonin
1995, Life Sciences
Synaptosomes from rat brain cortex and spinal cord were preloaded with [³H]serotonin (³H]5-HT), super/fused and exposed to fluoxetine and/or 15 mM K⁺. In both regions 10 μM, but not 1 μM fluoxetine evoked a marked tritium overflow, about 2 min later than the immediate [³H]5-HT release induced by K⁺, and mainly (73%) due to the efflux of a tritiated metabolite of 5-HT, possibly [³H]5-hydroxy-indoleacetic acid. These findings confirm previous data in the rat hippocampus and are probably due to fluoxetine interacting with the 5-HT storage vesicles. One μM fluoxetine significantly reduced the d-fenfluramine-induced [³H]5-HT overflow, in accordance with its action as 5-HT uptake blocker, but did not affect the K⁺-induced [³H]5-HT overflow. This latter finding does not confirm that fluoxetine inhibits the depolarization-induced Ca²⁺-influx, suggested to involve a drug interaction with the L-type Ca²⁺-channels. Thus, the overflow induced by 10 μM fluoxetine was additive with the depolarization-induced overflow, when the two stimuli were applied together. When 10 μM fluoxetine was added 7 min before 15 mM K⁺, there was no depolarization-induced overflow. Such inhibition might be only apparent and due either to the fluoxetine-induced loss of vesicular 5-HT or to a fluoxetine-induced alteration of synaptic vesicles. The in vivo relevance of the fluoxetine releasing effect remains to be assessed.
Potentiation by choline of basal and electrically evoked acetylcholine release, as studied using a novel device which both stimulates and perfuses rat corpus striatum
1993, Brain Research
We examined the release of acetylcholine (ACh) and dopamine (DA) using a novel probe through which striatal neurons could be both superfused and stimulated electrically in both anesthetized and freely moving awake animals. Optimal stimulation parameters for eliciting ACh release from cholinergic neurons differed from those required for eliciting DA release from dopaminergic terminals: at 0.6 ms pulse duration, 20 Hz and 200 μA, ACh release increased to357±30% (P < 0.01) of baseline and was blocked by the addition of tetrodotoxin (TTX). Pulse durations of 2.0 ms or greater were required to increase DA release. Unlike ACh release, DA release showed no frequency dependence above 5 Hz. The mmximal evoked releases of ACh and DA were556±94% (P < 0.01)and254 ±38% (P < 0.05) of baseline, respectively. Peripheral administration of choline (Ch) chloride (30–120 mg/kg) to anesthetized animals caused dose-related (r = 0.994, P < 0.01) increases in ACh release; basal release rose from117±7%to141±5% of initial baseline levels (P < 0.05) and electrically evoked ACh release rose from386±38%to600±34% (P < 0.01) in rats given 120 mg/kg. However, Ch failed to affect basal or evoked DA release although neostigmine (10 μM) significantly elevated basal DA release (from 36.7 fmol/10 min to 71.5 fmol/10 min;P < 0.05). In Awake animals, Ch (120 mg/kg) also elevated both basal (from106±7%to154±17%; P < 0.05) and electrically evoked (from146±13to262±19%; P< 0.01) ACh release. These experiments demonsrates that ACh and DA release can both be reliably evoked from rat striatum and that an intraperitoneal (i.p.) injection of Ch can increase both basal and evoked striatal ACh release.

View all citing articles on Scopus

: These studies were supported in part by a grant from The Center For Brain Sciences and Metabolism Charitable Trust.

View full text

Persistent blockade of potassium-evoked serotonin release from rat frontocortical terminals after fluoxetine administration

Abstract

Brain Research

Neuroscience

Life Sci.

Eur. J. Pharmacol.

Eur. J. Pharmacol.

Pharmacol. Biochem. Behav.

Brain Res. Bull.

Eur. J. Pharmacol.

Brain Research

Brain Research

Brain Research

Brain Research

Neurochem. Int.

Brain Research

Neuropharmacology

Life Sci.

Determination of brain interstitial concentrations by microdialysis

J. Neurochem.

Differences betweend-fenfluramine andd-norfenfluramine in serotonin presynaptic mechanisms

J. Neurochem.