ソマトスタチン神経系の免疫細胞化学的検討

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The neuroanatomical distribution of the somatostatinergic system in mice and human brains was studied by immunocytochemistry. The co-localization of choline acetyltransferase and somatostatin, and the pathological changes of the somatostatinergic system in dementia of Alzheimer type (DAT) were also examined. Cryostat sections were stained by the avidin-biotin complex method (ABC) and the double immunoenzymatic staining method combining the peroxidase-anti-peroxidase method (PAP) and the avidin-biotin-alkaline phosphatase complex method (ABC-AP). Periodic acid Schiff staining (PAS), periodic acid-methenamine-silver staining (PAM), Hirano staining and β-protein immunostaining were also used in order to localize senile plaque amyloids.
Somatostatin-like immunoreactive (SSI) neurons were widely distributed in various regions of the central nervous system of mice. The cells had small-or medium-sized cell bodies and some processes. SSI neurons were found in the following regions : the olfactory tubercle, piriform cortex, basal ganglia, substantia innominata, cerebral neocortex, amygdaloid complex, hippocampus, zona innertia, bed nucleus of the stria terminalis, periventricular gray of the third ventricle, nucleus arcuatus, some areas of the thalamic nuclei, and the hypothalamus. Varicose or dot-like SSI fibers formed dense networks in the neocortex, olfactory tubercle, nucleus accumbens, basal ganglia, substantia innominata, amygdaloid complex, some thalamic nuclei, median eminence, lateral geniculate body, area postrema, nucleus of solitary tract, spinal trigeminal nucleus, and dorsal horn of the spinal cord.
Choline acetyltransferase-like immunoreactive (ChATI) cell bodies were found in the following regions : the olfactory tubercle, nucleus accumbens, lateral preoptic region, basal ganglia (caudate, putamen, globus pallidus), basal forebrain (medial septal nucleus, diagonal band of Broca, substantia innominata (basal nucleus of Meynert)), medial habenular nuclei, pedunculopontine tegmental nucleus, somatic and viceral motor nuclei in the brainstem and spinal cord. In the neocortex, there were a few small weakly-staining neurons. The localizations of ChATI neurons were classified into four major groups : 1) basal ganglia, 2) basal forebrain, 3) pontine tegmentum, and 4) spinal and cranial nerve motor nuclei. ChATI neurons were medium-or large-sized multipolar cells. The cell bodies were divided into a deeply-staining group (basal ganglia, basal forebrain, pontine tegmentum), and a weakly-staining group which had ChATI nerve terminals (spinal and cranial nerve motor nuclei). Areas with dense networks of ChATI nerve fibers included the olfactory tubercle, basal ganglia, neocortex, hippocampus, amygdaloid complex, interpeduncular nucleus, and superior colliculus.
Double immunoenzymatic staining demonstrated the clear separation of both immunoreactivities in the central nervous system. ChATI neurons were stained blue and SSI neurons were stained brown. Black-stained cell bodies suggesting the co-localization of both immunoreactivities were not seen in the four major cell groups of the ChATI neurons, or in the other regions.
In human brains, SSI neurons were found in the cerebral cortex (IInd to VIth layers), basal ganglia, hippocampus, and substantia innominata. These SSI cells were small and medium-sized. The large neurons in the nucleus basalis of Meynert (nbM) were not stained. However, these neurons had many SSI nerve terminals. Anti-choline acetyltransferase antibody only stained the large neurons in the nbM. It is speculated that cholinergic fibers project from the ribM in human brains.