Youichi Ishikawa

Ultrastructure of ascending cholinergic terminals in the anteroventral thalamic nucleus of the rat: A comparison with the mammillothalamic terminals

In this study, to identify the ultrastructure and distribution of ascending cholinergic afferent terminals in the anteroventral thalamic nucleus, we used an anti-vesicular acetylcholine transporter antibody as marker of cholinergic afferents, and characterized the immunoreactive terminals at the ultrastructural level. We then compared the distribution pattern of the cholinergic terminals and that of the mammillothalamic terminals identified by anterograde transport of a tracer injected into the mammillary body. The cholinergic terminals were small, and formed both symmetrical and asymmetrical synaptic contacts throughout the dendritic arborizations, particularly in the distal region. This distribution pattern differed from that of mammillothalamic terminals, that were of LR (large terminal containing round synaptic vesicles) type and were preferentially distributed in the proximal region of dendrites. We also found relatively numerous cholinergic terminals making contact directly with immunonegative excitatory terminals, both LR and SR (small terminal containing round vesicles) terminals, without clear postsynaptic specialization. A few cholinergic terminals even seemed to form a synaptic complex with the LR or SR terminals. These findings suggest that the ascending cholinergic afferents in the anteroventral thalamic nucleus can effectively modulate excitatory inputs from both the mammillothalamic and corticothalamic terminals, in close vicinity to a synaptic site.

Localization of α7 nicotinic acetylcholine receptor immunoreactivity on GABAergic interneurons in layers I–III of the rat retrosplenial granular cortex

The rat retrosplenial granular cortex (RSG) receives cholinergic input from the medial septum-diagonal band (MS-DB) of the cholinergic basal forebrain (CBF), with projections terminating in layers I-III of RSG. The modulatory effects of acetylcholine (ACh) on cortical GABAergic interneurons in these layers are mediated by α7 nicotinic acetylcholine receptors (α7nAChRs). α7nAChRs are most abundant in the cerebral cortex and are largely localized to GABAergic interneurons. However, the CBF projection to the RSG has not been studied in detail, and the cellular or subcellular distribution of α7nAChRs in the rat RSG remains unclear. The main objective of this study was to test that α7nAChRs reside on GABAergic interneurons in CBF terminal fields of the rat RSG. First, we set out to define the characteristics of CBF projections from the MS-DB to layers of the RSG using anterograde neural tracing and immunohistochemical labeling with cholinergic markers. These results revealed that the pattern of axon terminal labeling in layer Ia, as well as layer II/III of the RSG is remarkably similar to the pattern of cholinergic axons in the RSG. Next, we investigated the relationship between α7nAChRs, labeled using either α-bungarotoxin or α7nAChR antibody, and the local neurochemical environment by labeling surrounding cells with antibodies against glutamic acid decarboxylase (GAD), parvalbumin (PV) and reelin (a marker of the ionotropic serotonin receptor-expressing GABAergic interneurons). α7nAChRs were found to be localized on both somatodendritic and neuronal elements within subpopulations of GABAergic PV-, reelin-stained and non PV-stained neurons in layers I-III of the RSG. Finally, electron microscopy revealed that α7nAChRs are GAD- and PV-positive cytoplasmic and neuronal elements. These results strongly suggest that ACh released from CBF afferents is transmitted via α7nAChR to GAD-, PV-, and reelin-positive GABAergic interneurons in layers I-III of the RSG.

Molecular orbital approach to odor molecules: Normal fatty acids and cyclamenaldehydes

Eight normal fatty acids and 24 cyclamenaldehydes were analyzed based on the molecular orbital theory using Computer-Aided Chemistry Programs (CAChe Programs) with PM3 parameters. We found reactive sites with high values of electrophilic frontier densities (EFDs) at appointed positions in both molecules. EFD is a theoretical index that predicts reactive sites acting as electron donors. A change in the values of EFDs in normal fatty acids would account for the selectivity in the response of a single olfactory receptor cell to the fatty acids. Changes in the values of EFDs at appointed positions of cyclamenaldehydes also correlated with their odor characteristics and intensities. This fact indicates that cyclamenaldehydes have common reactive sites that play a critical role in interactions with a receptor. Changes in their reactivities alter the odor characteristics and intensities of the molecules judged by perfumers, indicating that human discrimination of cyclamenaldehyde odor is determined at the stage of interaction between cyclamenaldehydes and an odor receptor.

Quantitative analysis of development and aging of genital corpuscles in glans penis of the rat

The aim of the present postnatal developmental study was to determine densities of unique genital corpuscles (GCs) in glans penis of developing and aged rats. GCs were identified as corpuscular endings consisting of highly branched and coiled axons with many varicosities, which were immunoreactive for protein gene product 9.5. In addition, GCs were immunoreactive for calcitonin gene-related peptide and substance P, but not for vasoactive intestinal polypeptide and neuropeptide Y. GCs were not found in the glans penis of 1 week old rats. Densities of GCs were low at 3 weeks, significantly increased at 5 and 10 weeks, reached the peak of density at 40 weeks, and tended to decrease at 70 and 100 weeks. Sizes of GCs were small in 3 weeks old rats, increased at 5 and 10 weeks, reached the peak-size at 40 weeks and reduced in size at 70 and 100 weeks. Considering sexual maturation of the rat, the results reveal that GCs of the rat begins to develop postnatal and reaches to the peak of their development after puberty and continues to exist until old age, in contrast to prenatal and early postnatal development of other sensory receptors of glabrous skin.