[Centrifugal influence from the cortical taste area on neural activity of the parabrachial nucleus in rats].

Abstract

To reveal the functional significance of fiber connections from the cortical taste area (CTA) to the parabrachial nucleus (PBN), a combined study with neuroanatomical and electrophysiological techniques were performed on male Wistar rats anesthetized with urethane. The results were as follows: 1. Tracing of WGA-HRP showed that the fibers connecting the CTA and PBN passed through the central tegmental field (CTF). 2. Injection of glutamate into the PBN and electrical stimulation of the PBN elicited copious salivary secretion. Electrolytic lesion of the CTF and ibotenic acid lesion of PBN neurons diminished salivary secretion induced by electrical stimulation of the CTA. These results suggest that some PBN neurons receive inputs from the CTA and send axons to the lower brain stem for salivary secretion. 3. Electrical stimulation of the CTA induced both salivary secretion and jaw movements. Lesions of the CTF at the inferior colliculus level inhibited the cortically induced salivary secretion, but did not affect the jaw movements. On the contrary, lesions of the pyramidal tract (PT) at the same level inhibited jaw movements, but did not affect salivary secretion. These results suggest that corticofugal fibers concerned with salivary secretion pass through the CTF and those concerned with jaw movements pass through the PT. 4. Of 61 PBN neurons that responded to taste stimuli, 14 (23%) showed facilitatory (F), 11 (18%) facilitatory-inhibitory (F-I), 1 (2%) inhibitory-facilitatory (I-F), and 2 (3%) inhibitory (I) responses to single pulse stimulation of the ipsilateral CTA. Repetitive CTA stimulation induced F responses in 16 (33%) and I responses in 6 (12%). This proportion of F and I responses was essentially the same in any groups of neurons classified by responsiveness to taste stimuli.