Abstract
It is well known that striatonigral neurons produce substance P (SP); however, no SP receptor (SPR) has so far been found in the substantia nigra. On the other hand, a previous study in the rat striatum indicated that SPR was expressed only in cholinergic or somatostatinergic intrinsic neurons (Kaneko et al. [1993] Brain Res. 631:297-303). Thus, it was assumed that SP produced by striatonigral neurons might be released through their intrastriatal axon collaterals to act upon intrinsic neurons in the striatum. To confirm this assumption, the distribution of axon collaterals of striatonigral neurons was examined in the striatum of the rat. The experiments were performed on brain slices by combining retrograde labeling with tetramethylrhodamine-dextran amine, electrophysiological recording, intracellular staining with biocytin, and immunocytochemistry for SPR. The distribution of axons of cholinergic striatal neurons (a group of SP-negative intrinsic striatal neurons) was also examined. It was observed that 16% of varicosities of intrastriatal axon collaterals of striatonigral neurons, as well as 6% of axonal varicosities of cholinergic neurons, were in close apposition to dendrites and cell bodies of SPR-immunoreactive striatal neurons. Since SPR-immunoreactive striatal neurons constituted only 2.7% of the total population of striatal neurons (Kaneko et al. [1993] Brain Res. 631:297-303), it appeared that axonal varicosities of striatonigral neurons were preferentially apposed to SPR-immunoreactive striatal neurons and that the varicosities in close apposition to SPR-immunoreactive neurons were derived more frequently from striatonigral neurons than from cholinergic interneurons. Confocal laser scanning microscopy indicated that axonal varicosities in close apposition to SPR-immunoreactive cells showed synaptophysin immunoreactivity, a marker of synaptic vesicles. In intrastriatal axons of striatonigral neurons, it was further revealed from electron microscopy that axonal varicosities in close apposition to SPR-immunoreactive dendrites, at least a part of them, made synapses of the symmetric type. Striatonigral neurons might release SP preferentially around cholinergic or somatostatinergic intrinsic neurons to regulate them through SP-SPR interactions.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.