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.

Kinzeler NR, Travers SP. -Opioid modulation in the rostral solitary nucleus and reticular formation alters taste reactivity: evidence for a suppressive effect on consummatory behavior. Am J Physiol Regul Integr Comp Physiol 301: R690 -R700, 2011. First published June 22, 2011; doi:10.1152/ajpregu.00142.2011.-The neural control of feeding involves many neuromodulators, including the endogenous opioids that bind -opioid receptors (MORs). Injections of the MOR agonist, Damgo, into limbic and hypothalamic forebrain sites increase intake, particularly of palatable foods. Indeed, forebrain Damgo injections increase sucrose-elicited licking but reduce aversive responding (gaping) to quinine, suggesting that MOR activation may enhance taste palatability. A -opioid influence on taste reactivity has not been assessed in the brain stem. However, MORs are present in the first-order taste relay, the rostral nucleus of the solitary tract (rNST), and in the immediately subjacent reticular formation (RF), a region known to be essential for consummatory responses. Thus, to evaluate the consequences of rNST/dorsal RF Damgo in this region, we implanted rats with intraoral cannulas, electromyographic electrodes, and brain cannulas aimed at the ventral border of the rNST. Licking and gaping elicited with sucrose, water, and quinine were assessed before and after intramedullary Damgo and saline infusions. Damgo slowed the rate, increased the amplitude, and decreased the size of fluid-induced lick and gape bouts. In addition, the neutral stimulus water, which typically elicits licks, began to evoke gapes. Thus, the current results demonstrate that -opioid activation in the rNST/dorsal RF exerts complex effects on oromotor responding that contrast with forebrain effects and are more indicative of a suppressive, rather than a facilitatory effect on ingestion.licking; gaping; feeding; nucleus of the solitary tract CONSIDERABLE EVIDENCE SUGGESTS that the endogenous opioid system modulates feeding and ingestive behavior. Until recently, the focus had been primarily on opioid effects at forebrain sites or after systemic injections. Systemic injections of morphine increase feeding, whereas the general opioid antagonist, naltrexone, attenuates intake (38, 39, 43). These effects are greatest when the animals are presented with a diet high in sugar or fat, suggesting that opioids can facilitate feeding by enhancing palatability. Experiments using the taste reactivity test support this conclusion. Morphine lengthens (11), and naltrexone shortens (52), the length of licking bouts elicited by sucrose, a measure positively correlated with stimulus palatability (15, 68), whereas systemic morphine reduces the number of aversive reactions (i.e., gapes) to the bitter stimulus, quinine (52).Experiments conducted using central injections have begun to establish which brain sites underlie these effects. Similar to systemic administration, infusions of the -opioid receptor (MOR) agonist D-Ala 2 , N-Me-Phe 4 , and Gly-ol 5 -enkephalin (Damgo) into various h...

A unique Alcohol, Tobacco, and Other Drug (ATOD) prevention program called PALS (Prevention through Alternative Learning Styles) was implemented with middle school students with the goal of enhancing student knowledge of the harmful effects of ATOD, promoting the use of refusal skills and reducing intentions to use ATOD in the future. Intentions to use were measured at four points: pre-PALS, post-PALS, and at 1-year and 2-year follow-ups. Student survey responses were then matched and compared across the four time periods. This article reports on the long-term effectiveness of PALS on student intentions to use ATOD in high school. When follow-up surveys of PALS students were compared to students not exposed to PALS (comparison group), the PALS students had significantly lower intentions to use alcohol and tobacco, providing evidence that the PALS intervention did have a long-term impact on intentions to use these substances.

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