Regulation of 5-HT2A receptor mRNA levels and binding sites in rat frontal cortex by the agonist DOI and the antagonist mianserin
Introduction
Numerous subtypes of receptor for the neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) have been identified. Serotonin2A (5-HT2A) receptors in the central nervous system have been implicated in a variety of behaviors and have high affinity for psychoactive drugs such as hallucinogens (see Glennon, 1990), atypical antipsychotics (Meltzer et al., 1989; Leysen et al., 1993) and many antidepressants (see Frazer, 1997). The 5-HT2A receptor is enriched in many brain areas including the frontal cortex, claustrum, nucleus accumbens, and striatum (Pazos et al., 1985, Pazos et al., 1987). In the cortex, 5-HT2A receptors are thought to be located postsynaptically on intrinsic interneurons and pyramidal cells (Morilak et al., 1993; Willins et al., 1997). 5-HT2A receptors are coupled to the stimulation of phospholipase C and the hydrolysis of membrane phosphoinositides (see Sanders-Bush et al., 1990).
The regulation of the 5-HT2A receptor does not appear to follow the pattern established for many other G-protein-coupled receptors. Although repeated administration of 5-HT2 receptor agonists results in the expected desensitization and down-regulation of central 5-HT2A receptors (Buckholtz et al., 1988; McKenna et al., 1989), chronic administration of 5-HT2 receptor antagonists, including atypical neuroleptics, results in a paradoxical decrease in the density of 5-HT2A receptors (see Frazer et al., 1988; Kuoppamaki et al., 1995). Furthermore, the down-regulation of 5-HT2A receptors following chronic administration of many antidepressant drugs appears to be related to the potent 5-HT2A receptor antagonist properties of these drugs and not to the blockade of serotonin receptor reuptake or changes in serotonin neurotransmission (see Frazer et al., 1988; Eison et al., 1991; Frazer, 1997). The desensitization and the down-regulation of 5-HT2A receptors occur following chronic administration of a wide variety of antidepressants, as well as atypical neuroleptics, and may be important to the therapeutic action of these drugs. Interestingly, 5-HT2A receptors are down-regulated after a single systemic injection of the atypical antidepressant and 5-HT2 receptor antagonist mianserin (Sanders-Bush et al., 1987).
The study of drug-induced changes in 5-HT2A receptor mRNA, for which we have employed the ribonuclease protection assay, allows assessment of the potential contribution that changes in gene expression may make to drug-induced changes in receptor number. It has been previously demonstrated that chronic administration of the 5-HT2 receptor agonist (±)-2,5-dimethoxy-4-iodophenyl-2-aminopropane (DOI) results in down-regulation of 5-HT2A receptors (Buckholtz et al., 1988; Hensler and Truett, 1998). However, whether this agonist-induced decrease in 5-HT2A receptor number is accompanied by changes in 5-HT2A receptor mRNA levels has not been described previously. It has been demonstrated that a single injection of the 5-HT2 receptor antagonist mianserin results in down-regulation of cortical 5-HT2A receptors (Sanders-Bush et al., 1987; Hensler and Truett, 1998). However, whether changes in 5-HT2A receptor mRNA levels accompany this decrease in receptor number after acute mianserin administration has not been determined.
One of the goals of the present study was to characterize the time course of effect of chronic DOI administration on 5-HT2A receptor binding sites and mRNA levels in frontal cortex at 2, 4 and 8 days of treatment. Although acute treatment of rats with DOI does not alter the 5-HT2A receptor number (Buckholtz et al., 1988; McKenna et al., 1989), we also examined the effect of a single injection of DOI on 5-HT2A receptor mRNA levels at several time points post-injection. A second goal of the present study was to characterize the time course of effect of a single injection of mianserin on 5-HT2A receptor binding sites and mRNA in rat frontal cortex 1, 3, 6 and 24 h post-injection. Experiments were also performed to examine the effect of repeated mianserin administration for 4 days on cortical 5-HT2A receptors and mRNA levels. The combined use of radioligand binding and ribonuclease protection assay, performed with separate hemispheres of frontal cortex from each animal, allowed us to examine concomitant changes in 5-HT2A receptor binding sites and receptor mRNA levels in this brain region. Our data indicate that the decrease in cortical 5-HT2A receptor sites in response to chronic DOI administration is not accompanied by changes in 5-HT2A receptor mRNA. A reduction in cortical 5-HT2A receptor mRNA levels accompanies the down-regulation of 5-HT2A receptors following a single injection of mianserin. Sustained changes in 5-HT2A receptor mRNA, however, appear not to be involved in maintaining the down-regulation of 5-HT2A receptor number with chronic mianserin administration.
Section snippets
Animals
All experiments used male Sprague-Dawley rats (250–300 g). Animals were housed three per cage, with lighting on a 14:10 h day:night cycle and with constant access to food and water. These studies were carried out in accordance with the Guide for the Care and Use of Laboratory Animals as adopted and promulgated by the National Institutes of Health.
Drug treatments
In one experimental group, rats received a single injection of mianserin (5 mg/kg, s.c.) and were sacrificed 1, 3, 6 or 24 h after mianserin
Effect of DOI administration on cortical 5-HT2A receptor mRNA levels and 5-HT2A receptor binding sites
To characterize the time course of regulation of 5-HT2A receptor binding sites and mRNA levels in frontal cortex following repeated administration of the 5-HT2 receptor agonist DOI, rats were treated with DOI (1 mg/kg, s.c., once daily) for 2, 4 or 8 days. Animals were sacrificed 6 h after the last injection. Radioligand binding and ribonuclease protection assays were performed with separate hemispheres of frontal cortex from each animal to examine concomitant changes in 5-HT2A receptors and
Discussion
In the present study we have characterized the time course of effect of administration of the 5-HT2 receptor antagonist mianserin, or the 5-HT2 receptor agonist DOI, on 5-HT2A receptor binding sites and mRNA levels in rat frontal cortex. Radioligand binding and ribonuclease protection assays were performed with separate hemispheres of frontal cortex from each animal to examine concomitant changes in 5-HT2A receptor sites and mRNA levels. We found that although repeated administration of DOI for
Acknowledgements
The authors thank Hymavathi Durgam for excellent technical assistance. This work was supported by US PHS grant MH 52369.
References (32)
A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein–dye binding
Analytical Biochemistry
(1976)- et al.
Serotonin2 agonist administration down-regulates rat brain serotonin2 receptors
Life Sciences
(1988) - et al.
The effects of antipsychotic drugs on the mRNA levels of serotonin 5HT2A and 5HT2C receptors
Molecular Brain Research
(1997) - et al.
The effects of clozapine and haloperidol on serotonin-1A, -2A and -2C receptor gene expression and serotonin metabolism in the rat forebrain
Neuroscience
(1996) Serotonin receptors: clinical implications
Neuroscience and Biobehavioral Review
(1990)- et al.
Differential effects of N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) on various 5-HT receptor binding sites in the rat brain
Neuropharmacology
(1994) - et al.
Effect of chronic serotonin-2 receptor agonist or antagonist administration on serotonin-1A receptor sensitivity
Neurospychopharmacology
(1998) - et al.
Differential regulation of rat 5-HT2A and 5-HT2C receptors after chronic treatment with clozapine, chlorpromazine and three putative atypical antipsychotic drugs
Neuropsychopharmacology
(1995) - et al.
Immunocytochemical localization and description of neurons expressing serotonin2 receptors in the rat brain
Neuroscience
(1993) - et al.
Quantitative autoradiographic mapping of serotonin receptors in the rat brain. II. Serotonin-2 receptors
Brain Research
(1985)
Serotonin receptors in the human brain. IV. Autoradiographic mapping of serotonin-2 receptors
Neuroscience
Chronic mianserin treatment decreases 5HT2 binding without altering 5-HT2 receptor mRNA levels
European Journal of Pharmacology
5HT2 binding sites after mianserin: comparison of loss of sites and brain levels of drug
European Journal of Pharmacology
Clozapine and other 5-hydroxytryptamine-2A receptor antagonists alter the subcellular distribution of 5-hydroxytryptamine-2A receptors in vitro and in vivo
Neuroscience
Rapid agonist-induced internalization of the 5-hydroxytryptamine2A receptor occurs via the endosome pathway in vitro
Molecular Pharmacology
Serotonin receptor sensitivity after acute and chronic treatment with mianserin
Journal of Pharmacology and Experimental Therapeutics
Cited by (32)
Targeting 5-HT<inf>2A</inf> receptors and Kv7 channels in PFC to attenuate chronic neuropathic pain in rats using a spared nerve injury model
2022, Neuroscience LettersCitation Excerpt :Thus, SNI reduced the expression of two key proteins regulating PFC excitability in A32V. Chronic modulation negatively regulates 5-HT2AR receptor protein, without changes in 5-HT2AR mRNA [36–38]. To evaluate this in our chronic pain model, we determined whether uncannulated Sham (n = 4) and SNI (n = 3) rats expressed different levels of 5-HT2AR mRNA using in situ hybridization with RNAscope.
Effect of the dietary intake of fish oil on psycho-social behavioral disorder caused by social-defeat stress
2022, Physiology and BehaviorCitation Excerpt :SDS also increases the mRNA expression of 5-HT2A receptors in the basolateral amygdala [52]. In contrast, chronic treatment with antidepressants downregulated 5-HT2A receptor expression in the cerebral cortex of rodents [53]. Thus, it has been suggested that neural signaling via 5-HT1A and 5-HT2A receptors plays a key role in regulating depressive-like behavior.
5-Methoxy-α-methyltryptamine (5-MeO-AMT), a tryptamine derivative, induces head-twitch responses in mice through the activation of serotonin receptor 2a in the prefrontal cortex
2019, Behavioural Brain ResearchCitation Excerpt :On the other hand, it is surprising that DOI produced a downward trend in 5-HTR2a mRNA levels considering its ability to elicit the HTR in mice. A previous study showed that a single DOI treatment produced a transient reduction in cortical mRNA levels of 5-HTR2a; however, treatment did not change the density of 5-HTR2a or of the affinity for 5-HTR2a [48]. Based on this, we could hypothesize that, despite the downward trend of 5-HTR2a mRNA levels, the DOI-induced HTR in mice can be attributed to the likely unaffected 5-HTR2a density or affinity for the 5-HTR2a.
The neurobiology and control of anxious states
2003, Progress in NeurobiologyCitation Excerpt :Mianserin and mirtazapine also show pronounced anxiolytic actions in non-conflict paradigms sensitive to 5-HT2C antagonists and, in such models, their actions are generally more pronounced upon long-term application (Chopin and Briley, 1987; Bodnoff et al., 1989; Benjamin et al., 1992; Dazzi et al., 2001). The latter finding coincides with their ability (upon chronic treatment) to attenuate the response of FCX pools of NA to stress (Dazzi et al., 2002) and to down-regulate 5-HT2C and 5-HT2A sites, notably in the amygdala (Zohar et al., 1988; Sanders-Bush, 1990; Rocha et al., 1994; Anji et al., 2000; Van Oekelen et al., 2003). This desensitization of 5-HT2A or 5-HT2C receptors, an effect common to SSRIs (Sections 4.4.1 and 4.4.2), appears to be of key significance to the long-term control of anxious states and manifestly does not necessitate their direct activation (Van Oekelen et al., 2003).