RESUMO
Taste memory depends on motivational and post-ingestional consequences after a single taste-illness pairing. During conditioned taste aversion (CTA), the taste and visceral pathways reach the nucleus of the solitary tract (NTS), which is the first relay in the CNS and has a vital function in receiving vagal chemical stimuli and humoral signals from the area postrema that receives peripheral inputs also via vagal afferent fibers. The specific aim of the present set of experiments was to determine if the NTS is involved in the noradrenergic and glutamatergic activation of the basolateral amygdala (BLA) during CTA. Using in vivo microdialysis, we examined whether chemical NTS stimulation induces norepinephrine (NE) and/or glutamate changes in the BLA during visceral stimulation with intraperitoneal (i.p.) injections of low (0.08 M) and high (0.3 M) concentrations of lithium chloride (LiCl) during CTA training. The results showed that strength of CTA can be elicited by chemical NTS stimulation (Ringer's high potassium solution; 110 mM KCl) and by intra-NTS microinjections of glutamate, immediately after, but not before, low LiCl i.p. injections that only induce a week aversive memory. However visceral stimulation (with low or high i.p. LiCl) did not induce significantly more NE release in the amygdala compared with the NE increment induced by NTS potassium depolarization. In contrast, high i.p. concentrations of LiCl and chemical NTS stimulation induced a modest glutamate sustained release, that it is not observed with low LiCl i.p. injections. These results indicate that the NTS mainly mediates the visceral stimulus processing by sustained releasing glutamate in the BLA, but not by directly modulating NE release in the BLA during CTA acquisition, providing new evidence that the NTS has an important function in the transmission of signals from the periphery to brain systems that process aversive memory formation.
Assuntos
Complexo Nuclear Basolateral da Amígdala/efeitos dos fármacos , Complexo Nuclear Basolateral da Amígdala/metabolismo , Memória/efeitos dos fármacos , Núcleo Solitário/metabolismo , Paladar/efeitos dos fármacos , Animais , Condicionamento Clássico/efeitos dos fármacos , Ácido Glutâmico/metabolismo , Injeções Intraperitoneais , Cloreto de Lítio/administração & dosagem , Cloreto de Lítio/farmacologia , Masculino , Microdiálise , Norepinefrina/metabolismo , Ratos , Ratos Sprague-Dawley , Núcleo Solitário/efeitos dos fármacos , Estimulação QuímicaRESUMO
The NTS catecholaminergic neurons, activated by a variety of afferent stimuli, are ideally situated to coordinate afferent signaling to multiple brain regions. In particular, there is evidence that systemic epinephrine injections induce a significant increase of norepinephrine (NE) in the amygdala during enhanced memory, which can be disrupted by NTS chemical blockade or interruption of vagal afferents. The present experiment was conducted to obtain information about the levels of NE release induced by activation of the whole NTS, which projects to the lateral and basolateral amygdala. Therefore, we compared NE levels before and after general stimulation of the NTS and the amygdala in anesthetized rats, without any behavioral or vagal stimulation, to find out the degree of noradrenergic activation modulated by the NTS through all its projections to the lateral and basolateral amygdala, as well as the degree of noradrenergic activation which may occur locally in the amygdala through rapid and general activation of this structure.