Identification of synapse pairs between neurons in the basal forebrain nuclei

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Brain slices containing basal forebrain nuclei (BF) obtained from 10-14 day-old rats were used. Paired whole-cell recordings were made from visually identified large (>25 μm) and small (<15 μm) neurons within the BF.Large neurons were identified as cholinergic since their electrophysiological properties conformed to the reported ones. When a depolarizing pulse was applied to the small neuron through the recording pipette, a synaptic current was evoked in the large neurone in 10 % of the recorded pairs. The evoked synaptic currents were blocked by bicuculline (10 μM), suggesting that the small neurons are GABAergic. The separate series of morphological studies have clarified that somatostatin-containing GABAergic neurons make synaptic contacts with cholinergic neurons, indicating the existence of functional interactions between these two types of neurons.Neuronal activities of ventral tegmental dopaminergic neurons which project to the BF are regulated by glutamatergic inputs fro cortex or brain stem. Dopamine-induced modulation of non-NMDA glutamatergic synaptic transmission onto dopaminergic neurons was elucidated using slice patch-clamp technique. The findings suggest that afferent glutamatergic fibers terminating dopaminergic neurons possess presynaptic D_2-like dopamine receptors, activation of which inhibits glutamate release by reducing Ca^<2+> influx (Koga ＆ Momiyama, 2000).BF is often compared with striatum in both morphological and functional aspects. GABAergic synaptic transmission and its modulation by dopamine in striatal cholinergic interneurons were also investigated. The results suggest that activation of D_2-like receptors in the GABAergic terminals selectively block N-type to reduce GABA release. Thus is the first report that identified the Ca^<2+> channel subtype unvolved in presynaptic dopamine receptor-mediated modulation of synaptic transmission (Momiyama ＆ Koga, 2001).