Location and taste responses of parabrachio-thalamic relay neurons in rats.

Thirty of the 55 taste units in the parabrachial nucleus were activated antidromically by stimulation of either or both of the ipsi- or contralateral thalamic taste areas. Such parabrachio-thalamic taste relay neurons produced bilateral thalamic afferent fibers (B type, N = 14), exclusively ipsilateral thalamic afferent fibers (I type, N = 12), or exclusively contralateral thalamic afferent fibers (C type, N = 4). Most of the B-type neurons were excited best by NaCl among the four basic taste stimuli; approximately one-half the I-type neurons by HCl. Most of the NaCl-best neurons were located in the medial part of the parabrachial nucleus but most of the HCl-best neurons were in the lateral part. In addition, NaCl-best neurons had shorter ipsilateral latencies (modal value = 1.0 to 3.0 ms) from the ipsilateral thalamic taste area, whereas HCl-best neurons had longer latencies (modal value = 4.0 to 6.0 ms).