Electrophysiological evidence of collateral projections of parabrachio-thalamic relay neurons

We studied axonal branching of 14 parabrachial nucleus neurons, activated antidromically from 2 of the 3 stimulation sites, i.e. the ipsi- and contralateral thalamic taste area (TTAs) and the ipsilateral central nucleus of the amygdala (CA). Making use of antidromic latencies, collision times and refractory periods at the 2 sites of stimulation, the conduction times were calculated for the distance between the branching point of the axon and the stimulation sites or the recording site at the soma. Nine of these 14 neurons had a significant length of axon branches terminating at 2 of the 3 sites of stimulation. Five neurons sent axon branches to the bilateral TTAs, 3 to both the CA and the ipsilateral TTA and the remaining one to both the CA and the contralateral TTA. Four of these 9 neurons with collateral branches responded to taste stimulation.