Effects of peripheral stimulation on the activity of neurons in the ventral tegmental area, substantia nigra and midbrain reticular formation of rats.

Extracellular recordings were obtained from neurons in the ventral tegmental area (VTA), the substantia nigra, including the zona compacta (SNC) and the zona reticulata (SNR), and the midbrain reticular formation (FOR) of adult female albino rats anesthetized with urethane and chloral hydrate. Based on electrophysiological characteristics the neurons were divided into two types. Type I neurons, with relatively long spike durations and slow discharge rates, were confined to the VTA and SNC. Type II neurons, with shorter spike durations and faster discharge rates, were observed in the SNR and FOR as well as the VTA and SNC. The effects of foot pinch (FP), tail pinch (TP) and stimulation of the vaginal cervix (VC) on the activity of the two types of neurons were investigated. Previously it was demonstrated that FP was aversive, TP elicited locomotion, sniffing and gnawing responses and VC lordosis response, vocalization and immobility. For approximately two-thirds of the neurons the effects of the three peripheral stimuli were similar; either they were activated or suppressed. Approximately 8 percent of the neurons were suppressed by FP and TP and activated by VC whereas a similar number were activated by FP and TP and suppressed by VC. Type 1 and Type II neurons in the VTA and SN were activated and suppressed by the peripheral stimuli with suppression being the most common response to FP and TP. The results are consistent with the view that VTA and SN neurons integrate a number of central and peripheral inputs.