The effects of clozapine and haloperidol on serotonin-1A, -2A and -2C receptor gene expression and serotonin metabolism in the rat forebrain

Decreased serotonin2A receptors in Brodmann's area 9 from schizophrenic subjects. A pathological or pharmacological phenomenon?

There have been repeated reports of a decrease in serotonin2A receptors in the frontal cortex from subjects with schizophrenia. Similarly, in rats treated with antipsychotic drugs, it has been shown that many antipsychotic drugs decrease cortical serotonin2A receptors, an affect not seen with the antipsychotic drug haloperidol. We therefore compared the density of serotonin2A receptors in frontal cortex from schizophrenic subjects treated with haloperidol, schizophrenic subjects treated with other antipsychotic drugs, and nonschizophrenic subjects. Independent of antipsychotic drug treatment, serotonin2A receptors were decreased in the frontal cortex from schizophrenic subjects. Importantly, the density of serotonin2A receptors was not different in schizophrenic subjects whether or not they had been treated with haloperidol. This study suggests that data obtained from treating rats with antipsychotic drugs cannot be simplistically extrapolated to studies on tissue obtained postmortem from schizophrenic subjects treated with the same drugs.

Gonadal hormones modulate 5-hydroxytryptamine2A receptors: emphasis on the rat frontal cortex

The effect of short-term (Sprague-Dawley rats, two weeks) and long-term ovariectomy (Sprague-Dawley and Fischer rats, three months) on serotonin 5-hydroxytryptamine2A receptors in different regions of the brain and its possible correction with an 17 beta-estradiol treatment (10 micrograms, b.i.d., two weeks) were studied in comparison to intact rats. Saturation binding assays were performed using [3H]ketanserin to estimate 5-hydroxytryptamine2A receptor density and affinity in tissue homogenates of frontal cortex of Fischer rats and quantitative autoradiography was performed to evaluate receptor specific binding in frontoparietal cortex, nucleus accumbens, striatum and dorsal raphe nucleus of Fischer rats, and in frontal cortex of the two strains of rats. Messenger RNA levels of 5-hydroxytryptamine2A receptors were measured by in situ hybridization in frontal cortex of the two strains of rats. An overall decrease of 5-hydroxytryptamine2A receptor densities was found in all the brain regions of ovariectomized Fischer rats assayed, and this could be restored towards control levels by estradiol treatment. No change in the 5-hydroxytryptamine2A receptor affinity was measured in the frontal cortex. A similar pattern of changes was observed for the messenger RNA levels encoding the 5-hydroxytryptamine2A receptors and receptor density, suggesting the implication of a genomic mechanism. Experiments in Sprague-Dawley rats confirmed and extended the results obtained with Fischer rats. By analogy, in humans, this 5-hydroxytryptamine2A receptor modulation may underlie the mood and movement disorders associated with menopause.

5-Hydroxytryptamine2A serotonin receptors in the primate cerebral cortex: possible site of action of hallucinogenic and antipsychotic drugs in pyramidal cell apical dendrites

To identify the cortical sites where 5-hydroxytryptamine2A (5-HT2A) serotonin receptors respond to the action of hallucinogens and atypical antipsychotic drugs, we have examined the cellular and subcellular distribution of these receptors in the cerebral cortex of macaque monkeys (with a focus on prefrontal areas) by using light and electron microscopic immunocytochemical techniques. 5-HT2A receptor immunoreactivity was detected in all cortical layers, among which layers II and III and layers V and VI were intensely stained, and layer IV was weakly labeled. The majority of the receptor-labeled cells were pyramidal neurons and the most intense immunolabeling was consistently confined to their parallelly aligned proximal apical dendrites that formed two intensely stained bands above and below layer IV. In double-label experiments, 5-HT2A label was found in calbindin D28k-positive, nonphosphorylated-neurofilament-positive, and immuno-negative pyramidal cells, suggesting that probably all pyramidal cells express 5-HT2A receptors. 5-HT2A label was also found in large- and medium-size interneurons, some of which were immuno-positive for calbindin. 5-HT2A receptor label was also associated with axon terminals. These findings reconcile the data on the receptor's cortical physiology and localization by (i) establishing that 5-HT2A receptors are located postsynaptically and presynaptically, (ii) demonstrating that pyramidal neurons constitute the major 5-HT2A-receptor-expressing cells in the cortex, and (iii) supporting the view that the apical dendritic field proximal to the pyramidal cell soma is the "hot spot" for 5-HT2A-receptor-mediated physiological actions relevant to normal and "psychotic" functional states of the cerebral cortex.

The effects of antipsychotic drugs on the mRNA levels of serotonin 5HT2A and 5HT2C receptors

We have looked for both global and regional changes in rat brain mRNA levels encoding serotonin 5HT2A and 5HT2C receptors following acute and chronic administration of antipsychotic drugs. In whole brain clozapine (30 mg/kg/day) elicited a transient rise in 5HT2C mRNA levels after 4 days and chlorpromazine (15 mg/kg/day) elicited a decrease of 20% in 5HT2A mRNA levels after 32 days. Regionally, 32 days treatment with haloperidol (3 mg/kg/day), sulpiride (100 mg/kg/day) or clozapine (10 mg/kg/day) resulted in a drop of approximately 30-40% in 5HT2C mRNA levels in both cortex and cerebellum, and decreases (or non-significant trends) of 15-40% in 5HT2A mRNA levels in hippocampus, brainstem and mid brain. 4 days treatment with clozapine resulted in a 40% rise of 5HT2C mRNA in the mid brain and a 24% rise of 5HT2A mRNA in the nucleus accumbens which were not found after 32 days of treatment. These results demonstrate common chronic effects of typical and atypical drugs but unique short term effects of clozapine.