Cannabinoid CB1 receptor immunoreactivity in the prefrontal cortex: Comparison of schizophrenia and major depressive disorder

Abstract

We recently showed that measures of cannabinoid 1 receptor (CB1R) mRNA and protein were significantly reduced in dorsolateral prefrontal cortex (DLPFC) area 9 in schizophrenia subjects relative to matched normal comparison subjects. However, other studies have reported unaltered or higher measures of CB1R levels in schizophrenia. To determine whether these discrepancies reflect differences across brain regions or across subject groups (eg, presence of depression, cannabis exposure, etc), we used immunocytochemical techniques to determine whether lower levels of CB1R immunoreactivity are (1) present in another DLPFC region, area 46, in the same subjects with schizophrenia, (2) present in area 46 in a new cohort of schizophrenia subjects, (3) present in major depressive disorder (MDD) subjects, or (4) attributable to factors other than a diagnosis of schizophrenia, including prior cannabis use. CB1R immunoreactivity levels in area 46 were significantly 19% lower in schizophrenia subjects relative to matched normal comparison subjects, a deficit similar to that observed in area 9 in the same subjects. In a new cohort of subjects, CB1R immunoreactivity levels were significantly 20 and 23% lower in schizophrenia subjects relative to matched comparison and MDD subjects, respectively. The lower levels of CB1R immunoreactivity in schizophrenia subjects were not explained by other factors such as cannabis use, suicide, or pharmacological treatment. In addition, CB1R immunoreactivity levels were not altered in monkeys chronically exposed to haloperidol. Thus, the lower levels of CB1R immunoreactivity may be common in schizophrenia, conserved across DLPFC regions, not present in MDD, and not attributable to other factors, and thus a reflection of the underlying disease process.

Figure 1

Brightfield photomicrographs demonstrating the density and laminar pattern of CB1R immunoreactivity in DLPFC area 46 of a representative triad of matched normal comparison (a), schizophrenia (b), and major depressive disorder (MDD) subjects (c) (triad 3; Supplementary Table S2). Intense CB1R immunoreactivity was localized to axons and varicosities in all three subjects; however, note the lower density of CB1R-IR axons in the subject with schizophrenia (b). Numbers and hash marks to the left indicate the relative positions of the cortical layers, and the dashed lines denote the layer 6-white matter (WM) border. Scale bar in (c)=300 μm and applies to all panels.

Figure 2

Lower CB1R immunoreactivity in DLPFC area 46 of subjects with schizophrenia from cohort 1. (a) Unpaired analysis of mean cortical ROD levels of CB1R immunoreactivity in normal comparison subjects (C; filled circles) and matched subjects with schizophrenia (S; open circles) or schizoaffective disorder (open triangles). Mean values for each subject group are indicated by horizontal bars. The ROD levels of CB1R immunoreactivity (b) and within-pair percent change in CB1R immunoreactivity levels (c) measured in area 46 correlated with those previously reported in area 9 (Eggan et al, 2008) of the same subjects with schizophrenia. (b) Closed circles denote normal comparison subjects and open circles or triangles denote schizophrenia or schizoaffective disorder subjects, respectively. (c) Closed squares denote matched normal comparison and schizophrenia subject pairs and closed diamonds denote normal comparison and schizoaffective disorder subject pairs.

Figure 3

Lower CB1R immunoreactivity in DLPFC area 46 of subjects with schizophrenia from cohort 2. Unpaired analysis of cortical ROD levels of CB1R immunoreactivity in matched normal comparison subjects (C; closed circles), subjects with schizophrenia (S; open circles) or schizoaffective disorder (open triangles), and subjects with major depressive disorder (M; gray circles). Mean values for each subject group are indicated by horizontal bars.

Figure 4

Lower CB1R immunoreactivity levels across cortical layers in DLPFC area 46 of subjects from cohort 2. The distinctive laminar pattern of CB1R immunoreactivity was conserved across subject groups; however, the levels of CB1R immunoreactivity for the schizophrenia group were reduced across all layers relative to the normal comparison and MDD groups. Comparison of mean (±SD) ROD levels of CB1R immunoreactivity in each cortical layer revealed that CB1R immunoreactivity levels were significantly (p<0.05) lower in schizophrenia subjects in layers 1–4 relative to both normal comparison and MDD subjects (^*), and in layer 6 relative to MDD subjects (†). 3s indicates superficial layer 3; 3d indicates deep layer 3.

Figure 5

The effects of confounding factors on CB1R immunoreactivity levels in schizophrenia. Mean (bar) and individual subject (circles) ROD levels of CB1R immunoreactivity in the subjects with schizophrenia grouped by potential confounding factors. Neither sex, diagnosis of schizoaffective disorder, suicide, antidepressant medication use at the time of death, benzodiazepine use at the time of death, antipsychotic medication use at the time of death, diagnosis of substance abuse/dependence at the time of death, nor history of cannabis use/abuse significantly affected levels of CB1R immunoreactivity. Numbers in bars indicate the number of subjects with schizophrenia in each category. A history of cannabis use was unknown for five of the schizophrenia subjects in cohort 2; thus those subjects were not included in the analysis.

Figure 6

Higher CB1R immunoreactivity in DLPFC area 46 of monkeys chronically exposed to the antipsychotic haloperidol. Paired analysis of mean cortical ROD levels of CB1R immunoreactivity in sham-exposed monkeys (filled circles) and matched monkeys chronically exposed to haloperidol (open circles). Mean values for each subject group are indicated by horizontal bars.