Submitted on May 28, 2008
Revised on August 13, 2008
Accepted on August 13, 2008
Local Circuit Input to the Medullary Reticular Formation from the Rostral Nucleus of the Solitary Tract
Jason Nasse1, David Terman2, Sharmila Venugopal1, Gerlinda Hermann3, Richard C Rogers3, and Joseph B. Travers1*
1 Ohio State University
2 Ohio State Univ.
3 Pennington Biomedical Research Center
* To whom correspondence should be addressed. E-mail: travers.1{at}osu.edu.
The intermediate reticular formation (IRt) subjacent to the rostral (gustatory) nucleus of the solitary tract (rNST) receives projections from the rNST and appears essential to the expression of taste elicited ingestion and rejection responses. We used whole-cell patch clamp recording and calcium imaging to characterize responses from an identified population of pre-hypoglossal neurons in the IRt in response to electrical stimulation of the rNST in a neonatal rat pup slice preparation. The calcium imaging studies indicated that IRt neurons could be activated from rNST stimulation and that many neurons were under tonic inhibition. Whole cell patch clamp recording revealed both mono- and polysynaptic projections from the rNST to identified pre-hypoglossal neurons. The projection was primarily excitatory and glutamatergic, however there were some inhibitory GABAergic projections and many neurons received both excitatory and inhibitory inputs. There was also evidence for disinhibition. Overall, bath application of GABAA antagonists increased the amplitude of excitatory currents by 110%.and there were several neurons in which stimulation of the rNST systematically decreased inhibitory currents. We have hypothesized that the transition from licks to gapes by natural stimuli such as QHCl could occur via such disinhibition. We present an updated dynamic model that both summarizes the complex synaptic interface between the rNST and the IRt and demonstrates how disinhibition could contribute to the transition from an ingestion to a rejection response.
