1. 1. Neuronal responses to noxious stimulations and innocuous scrotal thermal stimulations were studied in the preoptic area, anterior hypothalamus (POAH) and the ventrobasal complex (VB) of the thalamus in rats. 2. 2. In both sites, neurons excited and inhibited by noxious stimulations were excited and inhibited by scrotal warming, respectively. 3. 3. Microinjection of morphine in the midbrain periaqueductal grey region of the mesencephalon suppressed the neuronal responses of POAH and VB neurons to both scrotal warming and noxious stimulations, while the sensitivity of the same POAH neurons to local brain temperature remained unchanged.
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