The co-occurrence of substance P-like immunoreactivity and dynorphin-like immunoreactivity in striatopallidal and striatonigral projection neurons in birds and reptiles.

Using an immunofluorescence procedure that allows the simultaneous labeling of tissue for two different antigens, substance P-like immunoreactivity (SPLI) and dynorphin-like immunoreactivity (DLI) were observed to co-occur extensively in striatal neurons of the avian and reptilian basal ganglia and in fibers and terminals in the projection targets of the avian and reptilian striata. Thus, SPLI and DLI apparently co-occur extensively in striatopallidal and striatonigral projection neurons of the avian and reptilian basal ganglia. Since basal ganglia organization is fundamentally similar among amniotes, the present results suggest that SPLI and DLI may also co-occur extensively in striatal neurons in mammals.