Sensory stimuli differentially affect in vivo nigral and striatal [H]serotonin release in the cat

The effect of auditory, visual and peripheral nerve stimulation on in vivo [³H]serotonin release in both caudate nuclei and substantiae nigrae was studied in either awake ‘encéphale isolé’ or halothane-anesthetized cats. Release of endogenously synthesized [³H]serotonin was estimated in each brain structure, using push-pull cannulae, continuously superfused with [³H]tryptophan. Bilateral and simultaneous application of click noises and light flashes to awake ‘encéphale isolé’ cats enhanced [³H]serotonin release in both substantiae nigrae but was without effect on striatal [³H]serotonin release. Unilateral, low intensity electrical stimulation of the forepaw of halothane-anesthetized cats diminished [³H]serotonin release in both caudate nuclei and the ipsilateral substantia nigra. No effect was observed in the contralateral substantia nigra. In contrast, high-intensity electrical stimulation of one forepaw increased [³H]serotonin release in the ipsilateral substantia nigra but was without significant effect on release in the other brain areas examined. The results are discussed in light of previously known anatomical data concerning serotoninergic pathways and electrophysiological evidence of the effect of sensory stimuli on serotoninergic neurons. Our findings suggest that serotonin neurons may serve an important function in the integration of sensory information.