Single-cell RT-PCR, in situ hybridization histochemical, and immunohistochemical studies of substance P and enkephalin co-occurrence in striatal projection neurons in rats.

Single-cell RT-PCR studies in 3-4-week-old rats have raised the possibility that as many as 20% of striatal projection neurons may be a unique type that contains both substance P (SP) and enkephalin (ENK). We used single-cell RT-PCR, retrograde labeling, in situ hybridization histochemistry, and immunolabeling to characterize the abundance of this cell type, its projection target(s), and any developmental changes in its frequency. We found by RT-PCR that 11% of neurons containing either SP or ENK contained both in 4-week-old rats, while in 4-month-old rats SP/ENK colocalization was only 3%. SP-only neurons tended to co-contain dynorphin and ENK-only neurons neurotensin, while SP/ENK neurons tended to contain dynorphin. Single-cell RT-PCR showed SP/ENK co-occurrence in 4-week-old rats to be no more common among striatal neurons retrogradely labeled from the substantia nigra than among those retrogradely labeled from globus pallidus. Double-label in situ hybridization showed SP/ENK perikarya to be scattered throughout striatum, making up 8% of neurons containing either SP or ENK at 4 weeks, but only 4% at 4 months. Immunolabeling showed that presumptive striatal terminals in globus pallidus externus, globus pallidus internus and substantia nigra pars reticulata that colocalized SP and ENK were scarce. Terminals colocalizing SP and ENK were, however, abundant in the substantia nigra pars compacta. Thus, SP-only and ENK-only neurons make up the vast majority of striatal projection neurons in rats, the frequency of SP/ENK colocalizing striatal neurons is low in adult rats (3-4%), and SP/ENK colocalizing neurons primarily project to SNc but do not appear to be confined to striosomes.

Visual discrimination in the pigeon (Columba livia): effects of selective lesions of the nucleus rotundus.

The nucleus rotundus is a large thalamic nucleus in birds and plays a critical role in many visual discrimination tasks. In order to test the hypothesis that there are functionally distinct subdivisions in the nucleus rotundus, effects of selective lesions of the nucleus were studied in pigeons. The birds were trained to discriminate between different types of stationary objects and between different directions of moving objects. Multiple regression analyses revealed that lesions in the anterior, but not posterior, division caused deficits in discrimination of small stationary stimuli. Lesions in neither the anterior nor posterior divisions predicted effects in discrimination of moving stimuli. These results are consistent with a prediction led from the hypothesis that the nucleus is composed of functional subdivisions.