The effect of aging and suicide on m opioid receptors was studied in the human brain postmortem. Quantitative autoradiography with [³H]DAGO revealed region specific increases in m receptor density with age. Suicide was accompanied by a significant increase, up to 9-fold, in m receptor density in the young, but not the old, subjects as compared to age-matched controls. This effect was evident in the frontal and temporal cortical gyri. Saturation binding studies with the same ligand show that the increased binding in the elderly and in the young suicides is due to an increase in receptor density (B_max) rather than affinity (K_d).

Brains were removed from the cranium, cut into approx. 2.5 cm-thick blocks which were immediately frozen over dry ice, and kept at - 70°C. Coronal sections, 40 m m thick, cut on a Bright whole body cryotome at -15°C, were thaw-mounted onto gelatin-coated glass slides and kept overnight at -20°C. Slides were incubated for 60 min, at 25°C, with 1 nM [³H]DAGO (N.E.N., 58 Ci/mmol) in 50 mM Tris-HCl buffer, pH 7.4²³. Non-specific binding was determined in the presence of 1 m M etorphine. A 9-min wash in the same ice-cold buffer followed the incubation. Slides were then dipped in ice-cold water to remove buffer salts, dried on a 50°C hot plate and apposed to tritium-sensitive film (Amersham [³H]Hyperfilm) for 12 weeks. The film was coexposed to commercial (Amersham) tritiated standards. It was then manually developed and fixed with Kodak developer and fixer. Sections were stained with Cresyl violet for anatomical reverence and several neuroanatomical texts were used for identification of structures^6,22. All sections were obtained from the right cerebral hemisphere, at the level of the amygdala or hippocampus and at the level of prefrontal cortex. Since preliminary results showed that under these conditions non-specific binding was at the level of film background, two consecutive sections from each brain and each anatomical level were run to obtain total binding, which in this case equalled specific binding. Experiments were run in a matched pair design so that each one included sections from a suicide brain and its matched control. Autradiograms were analyzed with the aid of an IBM-PC based computerized image analysis system with a PC-vision digitizing board (Imaging Technology Inc.) and customized software. Standardization curves derived from the tritiated standards were used to convert gray level readings of the autoradiograms into equivalents of fmol [³H]DAGO/mg protein. All measurements were done in dupicate for each brain and each region.

As expected, we found a highly heterogeneous distribution of m receptors in the human brain. Thus, high density of binding appeared over the frontal cortex and caudate, while parietal and especially occipital cortex and hippocampus were characterized by low density in binding (Fig. 1). (***A note from typist: in the photocopy of this article that I am working from the picture in fig 1 is so bad that I haven’t bothered to scan it in. You just can’t see anything. The caption from fig 1 is: "Distribution of m receptors in suicide and control brains. Figure presents autoradiograms of [³H]DAGO binding in coronal sections at the level of the hippocampus taken from a control brain, age 40 years (top left) and a suicide brain, age 38 years (top right). Bottom presents a Cresyl violet stained section adjacent to the one that created the autoradiogram at the right top. hp, hippocampus; c, tail of caudate nucleus; I, insular cortex; t, thalamus."***)Initial analysis has shown highly significant positive correlation between age and m binding in most brain regions (Table I). In addition, some biochemical correlates of suicide appear to be age-specific¹³. We therefore divided the sample into young and aged subgroups at the median age of 41 years, and performed two-way analyses of variance (group^* age) corrected for unbalanced designs. Significant group effects were found in the medial frontal gyrus, superior temporal gyrus and medial temporal gyrus (Table I). Several trends were also present (Table I). Individual comparisons of the young suicides to their age-matched controls revealed significant increases in m receptor binding in the precentral, postcentral, superior temporal and cingulate cortical tyri of the suicides. A similar trend (0.05 < P < 0.10) was apparent also in the frontal superior, medial temporal, lateral occipitotemporal and parahippocampal gyri. In the aged subgroup, where age alone was correlated with increased binding, there was no further increase in the suicides in most regions, with the exception of the medial frontal gyrus (Table I). Much smaller differences were found in the prefrontal cortex (Table I).

TABLE I

Mean + S.E.M. [³H]DAGO bound

Results represent means + S.E.M. of specific [³H]DAGO binding in n brains, expressed as fmol/mg protein.

r, Pearson coefficient of correlation between specific binding and age.

P, probability of r.

Table presents meant + S.D. of n subjects/group.

#, P < 0.05, group effect in a two-way ANOVA for unbalanced designs.

*, P< 0.01. t₁₀ = 3.26, Student’s t-test, two-tailed, compared to young controls.