ABSTRACT
Adenosine cyclic 3',5'-monophosphate and guanosine cyclic 3',5'-monophosphate have differential immunohistochemical distributions within retrogradely-labeled striatonigral neurons of the rat. Adenosine cyclic 3',5'-monophosphate is localized within more than half of the striatonigral projection neurons. It is also within the cytoplasm of other neurons and oligodendroglia. Guanosine cyclic 3'-5'-monophosphate is localized within 80% of the identified striatonigral neurons. These large percentages of cyclic nucleotide immunoreactivity within the striatonigral neurons suggest some of these efferent cells must contain both cyclic nucleotides. The immunofluorescent staining for guanosine cyclic 3',5'-monophosphate is almost identical to that reported for efferent neurotransmitter-containing neurons of the caudate nucleus. However, the large proportion of striatonigral neurons demonstrating guanosine cyclic 3',5'-monophosphate immunoreactivity precludes the association of the cyclic nucleotide with a selective neurotransmitter agent. Adenosine cyclic 3',5'-monophosphate-reactive elements are very different in staining appearance from guanosine cyclic 3',5'-monophosphate and neurotransmitter-identified somata. The number of striatonigral cells exhibiting reaction for this cyclic nucleotide does not eliminate the possibility that adenosine cyclic 3',5'-monophosphate might be preferentially co-localized with a specific neurotransmitter, such as gamma-aminobutyrate, as has been previously suggested through biochemical experimentation.
