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In situ hybridization histochemistry was performed to analyse the distribution of the messenger RNA (mRNA) of three putative somatostatin (SRIF) receptors in rat brain, using oligonucleotide probes derived from the cDNA coding for SSTR-1, SSTR-2, and SSTR-3 receptors. SSTR-1 signals were found in layers V-VI of the cerebral cortex, in primary olfactory cortex, taenia tecta, subiculum, entorhinal cortex, granular layer of the dentate gyrus, amygdala and cerebellar nuclei. Signals for SSTR-2 were found in the frontal cerebral cortex (layers IV, V and VI), taenia tecta, claustrum, endopiriform nucleus, locus coeruleus, medial habenula, subiculum, granular cell layer of the dentate gyrus and amygdala. High levels of SSTR-3 hybridization were found in the olfactory bulb, primary olfactory cortex, islands of Calleja, medial habenula, amygdala, granular layer of the dentate gyrus, various thalamic and pontine nuclei and in the granular and Purkinje cell layers of the cerebellum. The distribution of the hybridization signals of the oligoprobes is consistent with the labelling of specific SRIF binding sites in rat brain. Especially, SSTR-2 and SSTR-1 oligos seem to label regions in which SS-1 and SS-2 receptors, respectively, have been previously characterized in autoradiographical studies. The situation is less clear with SSTR-3 mRNA, since SRIF binding in adult rats is usually low or absent in cerebellum, although some cerebellar nuclei appear to be labelled in the adult. The localization of SSTR-1, SSTR-2 and SSTR-3 mRNAs suggests that SRIF receptor subtypes in rat brain show profound differences in their distribution and are involved in a variety of central, in addition to neuroendocrine, functions.

The density of [125I]iodo-cyanopindolol binding to beta-1 and beta-2 adrenergic receptors was studied in post mortem basal ganglia samples of Huntington's chorea and Parkinson's disease patients using autoradiography. Whereas no significant changes were observed in sections from Parkinson's and Huntington's chorea grade 2 patients, a nearly complete loss of beta-1 binding sites was observed in the basal ganglia of Huntington patients at later stages of the disease. The concentration of beta-2 receptors was increased by a factor 2 in the posterior putamen of all choreic cases. These results are consistent with the view that beta-1 receptors are predominantly located on a subpopulation of neurons which degenerate at late stages of Huntington's chorea, while beta-2 receptors are present mainly on glial elements.

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The regional distribution of mRNA coding for the neuropeptide somatostatin has been studied in the human brain by in situ hybridization histochemistry using 32P-labeled oligonucleotides. We show that somatostatin mRNA-containing neurons are widely distributed in a number of nuclei and grey areas of the human brain, including neocortex, putamen, nucleus caudatus, nucleus accumbens, amygdala, midbrain, medulla oblongata, hippocampal formation, reticular nucleus of the thalamus, and posterior nucleus of the hypothalamus. No significant hybridization signal was observed in the substantia nigra, claustrum, globus pallidus, thalamus, and cerebellum. The topographic localization of neurons containing SOM mRNA in the human brain is in agreement with previous studies using immunocytochemical or radioimmunoassay techniques. These results show that in situ hybridization histochemistry with oligonucleotide probes can be used to map the distribution of neurons expressing SOM mRNA in human postmortem materials.

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Autoradiographic techniques were used to examine the distribution and levels of neurotensin receptor binding sites in the basal ganglia and related regions of the human brain. Monoiodo ([125I]-Tyr3)neurotensin was used as a ligand. High amounts of neurotensin receptor binding sites were found in the substantia nigra pars compacta. Lower but significant quantities of neurotensin receptor binding sites characterized the caudate, putamen, and nucleus accumbens, while very low quantities were seen in both medial and lateral segments of the globus pallidus. In Huntington's chorea, the levels of neurotensin receptor binding sites were found to be comparable to those of control cases. Only slight but not statistically significant decreases in amounts of receptor binding sites were detected in the dorsal part of the head and in the body of caudate nucleus. No alterations in the levels of neurotensin receptor binding sites were observed in the substantia nigra pars compacta and reticulata. These results suggest that a large proportion of neurotensin receptor binding sites in the basal ganglia are located on intrinsic neurons and on extrinsic afferent fibers that do not degenerate in Huntington's disease.