Substantia nigra GABA neurons

Striatum Normally, the striatum is connected to the substantia nigra by neurons that secrete the inhibitory transmitter GABA at their termini in the substantia nigra. In turn, cells of the substantia... 

Paladini CA, Tepper JM (1999) GABA(A) and GABA(B) antagonists differentially affect the firing pattern of substantia nigra dopaminergic neurons in vivo. Synapse 32 165-176. 

Of course, while the identification of these distinct systems may be useful there are many neural pathways that would not fit easily into one of them. Thus some inhibitory pathways, such as that from the caudate nucleus to substantia nigra, utilising GABA, are not intrinsic neurons. The dopamine pathway from the substantia nigra to striatum may start from a small nucleus but unlike other monoamine pathways it shows little ramification beyond its influence on the striatum. The object of the above classification is not to fit all neural pathways and mechanisms into a restricted number of functional categories but again to demonstrate that there are different forms of neurotransmission. 

Both the histamine neuron innervation and the density of H3 receptors are increased in the substantia nigra of Parkinsonian patients (Anichtchik et al. 2000 2001). The receptors probably are the H3 heteroreceptors on striato-nigral GABA terminals, and their increase may contribute to the depression of GABA release in the substantia nigra in Parkinson s disease (Garcia-Ramirez et al. 2004). 

Stanford IM, Lacey MG. Differential actions of serotonin, mediated by 5-HT1B and 5-HT2C receptors, on GABA-mediated synaptic input to rat substantia nigra pars reticulata neurons in vitro. J Neurosci 1996 16 7566-7573. 

Levey et al. (1993) found that axon terminals immunoreactive for D1 and D2 receptor proteins formed symmetrical synapses exclusively, and primarily with unlabeled dendritic shafts. In cultures, D1 and D2 receptors have been colocalized to terminals of intrinsic neurons (Wong et al., 1999). Functional D1 receptors have also been demonstrated on the terminals of striatal cells in the substantia nigra (Fiorillo and Williams, 1998). Collectively, the results for D1 and D2 receptors suggest their presence on the terminals of intrinsic GABA neurons. 

Oertel WH, Tappaz ML, Berod A, Mugnaini E (1982) Two-color immunohistochemistry for dopamine and GABA neurons in rat substantia nigra and zona incerta. Brain Res Bull 9 463-474. 

Immunohistochemical analyses have provided evidence of D4 receptors in mediumsized spiny neurons in the human striatum (Khan et al., 1998). Using immunohistochem-istry, D4 dopamine receptors were also localized within the GABA-containing cells of the striatum as well as GABAergic cells in the cerebral cortex, hippocampus, globus pallidus, substantia nigra and thalamic reticular nucleus of the nonhuman primate (Mrzljak et al., 1996). Thus, dopaminergic transmission via the D4 dopamine receptor appears to be predominantly inhibitory, so that blockade of D4 dopamine receptors may result in disinhibition of excitatory transmission in intrinsic cortical, thalamocortical and extrapyramidal pathways. 

Hamano, H., Nabekura, J., Nishikawa, M., and Ogawa, T. (1996). DcKohcxaenolc add reduces GABA response in substantia nigra neuron of rat. /. Nenrophyshl. 75,1264-1270-... 

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