Keith D. Anderson

The patterns of neurotransmitter and neuropeptide co-occurrence among striatal projection neurons: conclusions based on recent findings

The neurotransmitter organization of striatal projection neurons appears to be less complex than once thought. Only 4 major evolutionarily conserved populations appear to be present. The neurons of two of these populations contain SP, DYN and GABA, with one of these two populations consisting of striatonigral projection neurons and the other of striatopallidal projection neurons. The two additional major populations of striatal projection neurons consist of striatopallidal and striato-nigral neurons that both contain both ENK and GABA. Although these conclusions greatly simplify the understanding of the organization of striatal projection neurons by suggesting that only a few major populations are present, these conclusions complicate understanding of neurotransmission between these neurons and their target areas by suggesting that each neuron utilizes multiple neuroactive substances to influence target neurons. Further studies will therefore be required to explore the mechanisms of neurotransmission by which striatal neurons communicate with their target areas.

Immunohistochemical localization of DARPP-32 in striatal projection neurons and striatal interneurons: implications for the localization of D1-like dopamine receptors on different types of striatal neurons

Immunohistochemical double-label techniques were used to study the localization of DARPP-32, a phosphoprotein that is enriched in neurons possessing members of the D1 subfamily of dopamine receptors, in several different types of striatal neurons in the rat basal ganglia. The vast majority (94.1%) of striatonigral projection neurons (the vast majority of which contain substance P), identified by retrograde labeling with fluorogold, were observed to contain DARPP-32. Similarly, the vast majority of striatopallidal projection neurons (87.7%), identified by immunofluorescence labeling for enkephalin (ENK), were found to label for DARPP-32. In contrast, cholinergic and neuropeptide Y-containing striatal interneurons were never observed to contain DARPP-32. These results suggest that essentially all major types of striatal medium spiny projection neurons may possess members of the D1 subfamily of dopamine receptors, but that striatal local circuit neurons do not possess members of the D1 subfamily of receptors.

Co-occurrence of γ-aminobutyric acid, parvalbumin and the neurotensin-related neuropeptide LANT6 in pallidal, nigral and striatal neurons in pigeons and monkeys

Immunohistochemical double-labeling techniques were used to examine the co-localization of the neurotransmitter gamma-aminobutyric acid (GABA), the calcium-binding protein parvalbumin and the neurotensin-related hexapeptide LANT6 in neurons of the striatum and its target areas in pigeons and monkeys. The studies revealed the existence of a population of striatal interneurons apparently containing all three of these substances in both monkeys and pigeons. The results also revealed that GABA and LANT6 were co-localized in numerous pallidal and nigral reticulata neurons that also contained parvalbumin in both species. Examination of diverse other cell groups in avian forebrain and midbrain revealed that parvalbumin and LANT6 were typically co-localized to GABAergic neurons. In light of the presence of pallidal, reticulata and striatal neurons containing these three substances in two widely divergent amniote groups such as pigeons and monkeys, it seems likely that: (1) comparable neuronal populations are present in other avian and mammalian species; and (2) these neuronal populations play a fundamental role in basal ganglia functions that requires these three substances.

Dopaminergic terminals form synaptic contacts with enkephalinergic striatal neurons in pigeons : an electron microscopic study

Medium spiny projection neurons of the striatum consist of two major neuropeptide-specific types, one type containing substance P and another type containing enkephalin. Both of these types have been shown to receive dopaminergic input onto their perikarya and proximal dendrites. However, whether each of these types receives direct dopaminergic input onto distal dendritic shafts and onto dendritic spines has not been explored in depth. In the present study, we used electron microscopic immunohistochemical double-label techniques to examine the synaptic organization of dopaminergic input onto enkephalin-positive (ENK+) striatal neurons in pigeons, in whom ENK+ striatal perikarya, dendritic shafts and spines can be readily labeled. Antibodies against tyrosine hydroxylase were used to label dopaminergic terminals using a silver-intensified immunogold method. ENK+ neurons were labeled using diaminobenzidine. We found that dopaminergic terminals make appositions and form symmetric synapses with the perikarya, dendritic shafts, and dendritic spine necks of ENK+ striatal neurons. Thus, nigral dopaminergic neurons provide a monosynaptic input onto ENK+ striatal neurons in a manner similar to that described previously by us for substance P-positive striatal medium spiny neurons.