Katerina Zavitsanou

Selective antagonist [3H]SR141716A binding to cannabinoid CB1 receptors is increased in the anterior cingulate cortex in schizophrenia

Previous studies suggest that long-term cannabis use causes cognitive impairment, including lack of motivation and impaired attention, conditions that also resemble core negative symptoms of schizophrenia. The anterior cingulate cortex (ACC) plays an important role in normal cognition, particularly in relation to motivation and attention. This could suggest that changes in the cannabinoid (CB) system might be present in the ACC of patients suffering schizophrenia. The present study examined the distribution and density of CB1 cannabinoid receptors in the left ACC taken postmortem from patients with schizophrenia (n=10) and matched control subjects (n=9). Radioligand binding of [3H]SR141716A, an antagonist that specifically targets CB1 receptors of the endogenous cannabinoid system, was examined on ACC sections using quantitative autoradiography. CB1 receptors had a homogeneous distribution among the layers of ACC. A significant 64% increase in [3H]SR141716A specific binding to CB1 receptors was found in the schizophrenia group as compared to the control group (mean+/-S.E.M.: 46.15+/-6.22 versus 28.02+/-4.20 fmol/mg estimated tissue equivalents; p=0.03). The present results support the suggestion that changes in the endogenous cannabinoid system in the ACC may be involved in the pathology of schizophrenia particularly in relation to negative symptoms.

Investigation of M1/M4 Muscarinic Receptors in the Anterior Cingulate Cortex in Schizophrenia, Bipolar Disorder, and Major Depression Disorder

Abnormal cholinergic neurotransmission has been suggested to occur in psychiatric illness. Therefore, this study investigated cholinergic muscarinic receptors in the anterior cingulate cortex (ACC) of schizophrenia, bipolar disorder and major depression disorder (n=15 per group). We used quantitative autoradiography to measure [3H]pirenzepine binding to M1 and M4 receptors. Brain tissue was obtained from the Stanley Foundation Neuropathology Consortium. [3H]pirenzepine binding was higher in superficial laminae (I–II) than in deep laminae (III–VI) of the ACC. There was a significant 24% reduction in the density of [3H]pirenzepine in the deep laminae and a significant 19% reduction in the upper laminae of the ACC in the schizophrenia group compared to the control group. There were no differences in [3H]pirenzepine binding in any laminae of the ACC in the bipolar or major depression groups compared with the control group, except for a trend towards decreased [3H]pirenzepine binding in subjects with major depression relative to control subjects. We also detected a significant effect of suicide on [3H]pirenzepine binding in the ACC in subjects who died as a result of suicide relative to those who did not, which was more evident in patients with schizophrenia. A significant effect of the onset of the disease was also observed that was more evident in patients with bipolar disorder. The study provides evidence of decreased muscarinic receptor density in the ACC in schizophrenia but no evidence for significant changes in these receptors in the bipolar and major depression groups. The changes observed in schizophrenia may contribute to dysfunctional ACC neural circuits.

Dopamine transporter and D2 receptor binding densities in mice prone or resistant to chronic high fat diet-induced obesity

This study examined the density of dopamine transporter (DAT) and D2 receptors in the brains of chronic high-fat diet-induced obese (cDIO), obese-resistant (cDR) and low-fat-fed (LF) control mice. Significantly decreased DAT densities were observed in cDR mice compared to cDIO and LF mice, primarily in the nucleus accumbens, striatal and hypothalamic regions. D2 receptor density was significantly lower in the rostral part of caudate putamen in cDIO mice compared to cDR and LF mice.

Alterations of muscarinic and GABA receptor binding in the posterior cingulate cortex in schizophrenia

The posterior cingulate cortex (PCC), a key component of the limbic system, has been implicated in the pathology of schizophrenia because of its sensitivity to NMDA receptor antagonists. Recent studies have shown that the PCC is dysfunctional in schizophrenia, and it is now suspected to be critically involved in the pathogenesis of schizophrenia. Studies also suggest that there are abnormalities in muscarinic and GABAergic neurotransmission in schizophrenia. Therefore, in the present study we used quantitative autoradiography to investigate the binding of [(3)H]pirenzepine, [(3)H]AF-DX 384 and [(3)H]muscimol, which respectively label M1/4 and M2/4 muscarinic and GABA(A) receptors, in the PCC of schizophrenia and control subjects matched for age and post-mortem interval. The present study found that [(3)H]pirenzepine binding was significantly decreased in the superficial (-24%, p=0.002) and deep (-35%, p<0.001) layers of the PCC in the schizophrenia group as compared with the control group. In contrast, a dramatic increase in [(3)H]muscimol binding was observed in the superficial (+112%, p=0.001) and deep layers (+100%, p=0.017) of the PCC in the schizophrenia group. No difference was observed for [(3)H]AF-DX 384 binding between the schizophrenia and control groups. The authors found a significant inverse correlation between [(3)H]pirenzepine binding in the deep cortical layers and [(3)H]muscimol binding in the superficial layers (rho=-0.732, p=0.003). In addition, negative correlations were also found between age and [(3)H]pirenzepine binding in both superficial and deep cortical layers (rho=-0.669 p=0.049 and rho=-0.778, p=0.014), and between age of schizophrenia onset and [(3)H]AF-DX 384 binding (rho=-0.798, p=0.018). These results for the first time demonstrated the status of M1/M4, M2/M4 and GABA(A) receptors in the PCC in schizophrenia. Whilst the exact mechanism causing these alterations is not yet known, a possible increased acetylcholine and down regulated GABA stimulation in the PCC of schizophrenia is suggested.

Olanzapine differentially affects 5-HT2A and 2C receptor mRNA expression in the rat brain

This study examined regional changes in rat brain mRNA levels encoding 5-HT(2A) and 5-HT(2C) receptors following chronic olanzapine treatment. The immediate effect (2h after the last treatment) was a down-regulation of 5-HT(2A) receptor mRNA expression, predominantly in the hypothalamus, limbic system and striatum, while a rebound effect was observed 48 h later. 5-HT(2C) receptor mRNA expressions were decreased in the substantia nigra. Correlations between 5-HT(2A) receptor mRNA expression and total food intake, weight gain and energy efficiency were observed.

Neuropeptide Y mRNA expression levels following chronic olanzapine, clozapine and haloperidol administration in rats

Using quantitative in situ hybridization, this study examined regional changes in rat brain mRNA levels encoding neuropeptide Y (NPY) following olanzapine, clozapine and haloperidol administration (1.2, 1.5 and 2.0 mg/kg, oral) for 36 days. The NPY mRNA expression levels and patterns were examined after the last drug administration at both time points enabling the measurement of immediate effect at 2h and the effects after 48 h of drug administration. It was found that all these drugs had an immediate effect on NPY mRNA expression, while virtually all these changes normalized 48 h after the drug treatments. A similarity in altered NPY mRNA expression patterns was seen between the olanzapine and clozapine groups; however, haloperidol was very different. Olanzapine and clozapine administration decreased NPY mRNA levels in the nucleus accumbens, striatum and anterior cingulate cortex (from -60% to -77%, p<0.05). Haloperidol decreased NPY mRNA expression in the amygdala and hippocampus (-69%, -64%, p<0.05). In the lateral septal nucleus, NPY mRNA levels significantly decreased in the olanzapine group (-66%, p<0.05), a trend toward a decrease was observed in the clozapine group, and no change was found in the haloperidol treated group. These results suggest that the different effects of atypical and typical antipsychotics on NPY systems may reflect the neural chemical mechanisms responsible for the differences between these drugs in their effects in treating positive and negative symptoms of schizophrenia. The immediate decrease of NPY mRNA levels suggests an immediate reduction of NPY biosynthesis in response to these drugs.

M2/M4 muscarinic receptor binding in the anterior cingulate cortex in schizophrenia and mood disorders.

We have previously shown a decrease in [(3)H]pirenzepine binding to M1/M4 muscarinic receptors in the anterior cingulate cortex in schizophrenia but not in major depression or bipolar disorder. The present study aimed to extend these findings by examining the binding of [(3)H]AF-DX 384 to M2/M4 receptors in the same cohort of subjects. Using quantitative autoradiography we measured [(3)H]AF-DX 384 binding in the anterior cingulate cortex of 15 schizophrenia, 15 bipolar, 15 major depression and 15 control cases. Post-mortem tissue was obtained from the Stanley Foundation Brain Bank. [(3)H]AF-DX 384 binding had a homogenous distribution amongst the layers of the anterior cingulate cortex, was higher in males than in females and declined with prolonged storage of tissue. An inverse correlation between [(3)H]AF-DX384 binding and age of onset of the disease was observed in the schizophrenia group suggesting that the earlier the age at onset the higher the binding was. In the depression group, there was a significant effect of gender on [(3)H]AF-DX 384 binding with females having lower binding in comparison to males. In the bipolar group, there was a significant inverse correlation between antipsychotic medication and [(3)H]AF-DX 384 binding, suggesting that the higher the dose of medication the lower the binding was. No differences in [(3)H]AF-DX 384 binding were seen between the four groups. The present results provide no evidence of M2/M4 receptor alterations in the anterior cingulate cortex in schizophrenia and affective disorders and extend the body of evidence implicating cortical M1 but not M2 involvement in the pathology and pharmacotherapy of schizophrenia.

Short and long term changes in NMDA receptor binding in mouse brain following chronic phencyclidine treatment

SummaryPhencyclidine (PCP) is an antagonist of the NMDA subtype of glutamate receptor. PCP treatment induces psychosis in normal humans, which provides a valuable model of schizophrenia. PCP administration also models some of the symptoms of schizophrenia in experimental animals. NMDA hypofunction has been hypothesized to explain these schizophrenia-like symptoms. Acute or chronic administration of the NMDA receptor antagonist PCP has been shown to induce several short or long-term effects in both humans and experimental animals. In an attempt to clarify the neurochemical substrates of these effects in the present study, we used quantitative autoradiography to examine the effects of chronic (14 days) PCP treatment on NMDA receptor binding in mouse brain following both a short- (1 and 24 h) and long-term (14 days) delay after the last PCP treatment. NMDA receptors were targeted using [3H]MK801. Chronic PCP treatment increased [3H]MK801 binding consistently in the hippocampus in the short-term (p < 0.01). Conversely in the long-term, there were widespread reductions in NMDA receptor binding and this effect was most evident in the hippocampus where a 35% reduction of binding was found (p < 0.001). These results suggest that the hippocampus has a strong involvement in both the short and long-term effects of PCP treatment and that reduced NMDA receptor function might be one of the neurochemical substrates of the long lasting actions of PCP or PCP-induced psychosis. Importantly, this study shows that the long-term delay following chronic PCP treatment more accurately represents a state of NMDA hypofunction than the short-term PCP model.

Cannabinoid effects on CB1 receptor density in the adolescent brain: An autoradiographic study using the synthetic cannabinoid HU210

The short‐ and long‐term behavioral effects of cannabinoids differ in adolescent and adult rodents. Few studies though have examined the underlying neurochemical changes that occur in the brain following adolescent cannabinoid exposure. In this study, we examined the effect of treatment with the synthetic cannabinoid, HU210, on CB1 receptor density in the brain and on body weight in adolescent male rats. Rats were treated daily with 25, 50, or 100 μg/kg HU210 for 4 or 14 days, or received a single dose of 100 μg/kg HU210 and sacrificed 24 h later. Receptor density was investigated using in vitro autoradiography with the CB1 receptor ligand [3H] CP55,940. In contrast to adult animals treated under the same paradigm in a previous study, adolescents continued on average, to gain weight over the course of the study. Weight gain was slowest in the 100 μg/kg group and improved dose dependently with controls gaining the most weight. Following the acute dose of HU210, a trend for a reduction in [3H] CP55,940 binding and a significant effect of treatment was observed. Statistically significant, dose‐dependent, region‐specific decreases in binding were observed in all brain regions examined following 4 and 14 days treatment. The pattern of CB1 receptor downregulation was similar to that observed in adults treated with cannabinoids in previous studies; however, its magnitude was smaller in adolescents. This reduced compensatory response may contribute to some acute behavioral effects, the pharmacological cross‐tolerance and the long‐lasting, adverse psychological consequences of cannabinoid exposure during adolescence. Synapse 64:845–854, 2010.

CANNABINOID ADMINISTRATION INCREASES 5HT1A RECEPTOR BINDING AND mRNA EXPRESSION IN THE HIPPOCAMPUS OF ADULT BUT NOT ADOLESCENT RATS

The endocannabinoid and serotonin systems share a high level of overlap in terms of the physiological processes that they regulate, however, little is known about their functional interactions particularly during adolescence, a vulnerable period for both the development of psychosis and for initiation to substance use. In the present study, the effects of cannabinoid treatment on serotonin 5HT1A receptor density and mRNA expression were investigated in two age groups: Adolescent (postnatal day 35) and adult (postnatal day 70) rats were injected with the synthetic cannabinoid HU210 (25, 50 or 100 microg/kg) or vehicle for 1, 4 or 14 days and sacrificed 24 h after the last injection. 5HT1A receptor density was measured in different brain regions using [(3)H]8-OH-DPAT quantitative autoradiography whereas mRNA expression was measured in adjacent brain sections. Higher levels of both serotonin 5HT1A receptor binding and mRNA expression were observed in limbic regions in adolescent control animals compared to adults. 5HT1A receptor density was increased by 23% in the CA1 region of the hippocampus of adult rats treated with 100 microg/kg HU210 for 4 days compared to vehicle treated controls. The same treatment increased mRNA expression by 27% and by 14% in the CA1 region and dentate gyrus of the hippocampus respectively. 5HT1A receptor density was increased by 22% in the CA1 of adult animals treated with 50 microg HU210, by 26% in the dentate gurus of adult rats treated with 100 microg for 14 days. By contrast, 5HT1A receptor density or mRNA expression was not affected in the brain of adolescent animals in any of the brain regions examined. These results suggest that cannabinoid treatment has differential effects on serotonin-related neurochemistry in adolescent compared to adult rats. The effects in the adult brain may compromise hippocampal function and could account for the cognitive deficits seen in habitual heavy cannabis users.