Licking and gaping elicited by microstimulation of the nucleus of the solitary tract

Abstract

Intraoral infusions of bitter tastants activate expression of the immediate-early gene c-Fos in neurons located in the medial third of the rostral nucleus of the solitary tract (rNST). The distribution of these neurons is distinct from that activated by sour or sweet stimuli. Bitter stimuli are also distinctive because of their potency for eliciting gaping, an oral reflex that functions to actively reject potentially toxic substances. Glossopharyngeal nerve transection profoundly reduces, whereas decerebration spares, the bitter-evoked Fos-like immunoreactivity (FLI) pattern and gaping, implicating the medial rNST as a substrate for the sensory limb of oral rejection. The present experiment tested this hypothesis using microstimulation (100 Hz, 0.2 ms, 5-40 microA) to activate the rNST in awake rats. NST microstimulation elicited licking and gaping, and gaping was evoked from a restricted rNST region. The results indicated some topographic organization in sites effective for evoking gaping, but, in direct conflict with the hypothesis, lateral sites farther from bitter-evoked FLI were more effective than medial sites centered closer to FLI-expressing neurons. The gape-effective sites resemble locations of bitter-responsive neurons recently observed in neurophysiological recordings. These results indicate that bitter-responsive rNST neurons critical for triggering gaping may not express FLI and imply an alternate function for bitter-responsive neurons that do.

Speed and accuracy of taste identification and palatability: impact of learning, reward expectancy, and consummatory licking

“…The fact that sucrose and quinine elicited opposite effects on consummatory reflex (ALs), suggests a fine-grain sensorimotor integration of taste with a specific oromotor response. This sensorimotor integration is present from the nucleus of the solitary tract (NTS), since both taste-and licking-related activity are found in the NTS, and its projections to preoromotor neurons of the medullary reticular formation modulate licking and gaping behaviors (22,37,55). Our results indicate that a liquid introduced on the tongue can directly modulate the oromotor output of consummatory licking in a context-dependent manner, indicating that taste and oromotor responses are tightly coupled.…”

Local circuit input to the medullary reticular formation from the rostral nucleus of the solitary tract

“…Because neurons in both compartments project to the subjacent RF (39), stimulation at this location likely activated some neurons with projections to the RF. In the awake adult rat, similar placements are effective in producing licking and gaping in response to electrical stimulation (48). Although the ventral subdivision of the rNST has the greatest number of direct projections to the ventral RF (39), we deliberately avoided a more ventral placement to minimize direct activation of RF neurons that have dendrites extending in that direction.…”

Statistical Analysis and Decoding of Neural Activity in the Rodent Geniculate Ganglion Using a Metric-Based Inference System

“…Prior studies using electrical brain stimulation mimicking the rate and temporal patterns of sweet sucrose and bitter quinine have obtained mixed success in eliciting specific taste-mediated behaviors. For example, electrical stimulation of the nucleus of the solitary tract (NST) with a spike pattern indicative of quinine stimulation terminated the licking behavior of thirsty rats drinking water [59], [60], and stimulation of the NST in an area associated with quinine taste processing can elicit the aversive reaction of gaping [61]. Additionally, when conditioned to avoid sucrose, some thirsty rats stopped drinking water while receiving brain stimulation that mimicked the pattern for sucrose [62].…”