Postsynaptic potentials and axonal projections of tegmental neurons responding to electrical stimulation of the toad striatum.

The amphibian telencephalic striatum as a major component of the basal ganglia receives multisensory information and projects to the tegmentum and other structures. However, how striatal neurons modulate tegmental activity remains unknown. Here, we show by using intracellular recording and staining in toads that electrical stimulation of the ipsilateral striatum evoked an inhibitory postsynaptic potential (IPSP) in presumably binocular tegmental neurons. Seventy-one neurons were intracellularly stained with Lucifer yellow or horseradish peroxidase. They were located in the anterodorsal tegmental nucleus, anteroventral tegmental nucleus, nucleus profundus mesencephali, and superficial isthmal reticular nucleus, with axons projecting to the tectum, nucleus isthmi, and spinal cord. It appears that the striatum can control visually guided behaviors through the striato-tegmento-spinal pathway and the tegmento-spinal pathway mediated by the tectum and nucleus isthmi.