Micturition-related electrophysiological properties in the substantia nigra pars compacta and the ventral tegmental area in cats.

Parkinson's disease patients are known to have not only motor but also urinary autonomic disorders, suggesting central dopaminergic pathways being involved in the micturition function. However, there is little evidence that the substantia nigra pars compacta (SNC) and the ventral tegmental area (VTA), the major dopamine-containing nuclei in the midbrain, should participate in regulating micturition. We investigated micturition-related electrophysiological properties in the SNC and VTA. In 20 male cats under ketamine anaesthesia, in which spontaneous isovolumetric micturition reflex was generated, we performed electrical stimulation and extracellular single-unit recording in the SNC and the VTA, and correlation analysis of the neuronal firings and antidromic stimulation between the SNC/VTA and the pontine storage centre (PSC). Electrical stimulations in the SNC elicited termination of the micturition reflex, whereas those in the VTA elicited both termination and facilitation of the reflex. Forty-nine neurons in the SNC/VTA showed firing in response to the bladder storage/micturition cycles. The major neurons were tonic storage (55%) and phasic storage neurons (22%), which were found diffusely in th e SNC/VTA. The rest were tonic micturition (16%) and phasic micturition neurons (6%), which were concentrated in the caudal part (A2-4 in the Horsley-Clarke coordinates). These neuronal types were further subclassified into augmenting, constant, binary and decrementing neurons according to their temporal discharge rate change. The decrementing neurons were concentrated in the caudal part (A2-4), whereas the augmenting neurons in the rostral part (A4-6). Some of the recorded neurons had preceding firing pattern, which was more frequently found in the tonic type than in the phasic-type neurons. Twenty-four of the neuronal firings in the SNC/VTA were recorded simultaneously with those in the PSC. However, there was no apparent time-correlation between both sets of neuronal firings. In 15 of the simultaneous recording sites, electrical stimulation was applied to one site to see if antidromic response might be evoked in another site. However, there was no orthodromic or antidromic response in either SNC/VTA or PSC. In conclusion, the present study indicates that neurons in the SNC and the VTA are involved in supra-pontine control of micturition, particularly of urinary storage phase. It is also likely that the major role of the SNC is inhibition of the micturiton reflex, whereas that of the VTA is both facilitation and inhibition of the micturition reflex.