Corticofugal input to taste-responsive units in the parabrachial pons

Taste responses in units in the parabrachial nucleus of the pons (PbN) that receive direct projections from the gustatory neocortex (GN) were examined in the rat. Electrical stimulation was applied to the GN with bipolar stimulating electrodes. Time-locked responses to GN stimulation were observed in 19 of 62 (31%) taste-responsive units identified in the PbN. Of these, 17 units produced excitatory responses following GN stimulation and 2 units showed evidence of inhibition. No evidence of antidromic activation of PbN units was apparent. These results are consistent with descriptions of the anatomical projections from the GN to the PbN and demonstrate that some portion of taste-responsive neural elements within the PbN receive direct cortical input. PbN units that followed GN stimulation could not be distinguished from those that did not follow either by their spontaneous rates or their response profiles. These results suggest that axons from the GN do not select targets within the PbN based on the particular response properties.