CYTOCHEMICAL CHARACTERISTICS OF CAT SPINAL NEURONS ACTIVATED DURING FICTIVE LOCOMOTION

Using standard immunohistochemical and histochemical techniques, we ha ve examined the neurochemical characteristics of a subpopulation of lo comotor-related neurons as labeled by the activity-dependent marker c- fos. Results were compared to those obtained from a small sample of in tracellularly labeled locomotor-related neurons. In the paralyzed, dec erebrate cat, fictive locomotion was evoked by electrical stimulation of the mesencephalic locomotor region. Most c-fos-immunoreactive neuro ns were distributed in medial lamina VI and VII and in lamina VIII and X. Double labeling of c-fos with various cytochemical markers reveale d that about one-third of the c-fos-immunoreactive neurons were cholin e acetyltransferase immunoreactive, about one-third were glutamate imm unoreactive, and about one-third were aspartate immunoreactive. in add ition, approximately 15% of the c-fos-labeled neurons contained NADPH- diaphorase reaction product, while almost 40% appeared to receive clos e contacts from calcitonin gene-related peptide-immunoreactive fibers and boutons. Choline acetyltransferase- or aspartate immunoreactivity was observed in some intracellularly labeled neurons. These findings h ave implications regarding the putative neurotransmitters utilized by subpopulations of locomotor-related neurons in the cat spinal cord.