Amygdalar noradrenergic and dopaminergic mechanisms in the regulation of hunger and thirst-motivated behavior

The feeding behavior of rats was studied after neurochemical damage of the amygdalar terminal fields of mesolimbic dopaminergic (DA) and coerular noradrenergic (NA) pathways. 6-Hydroxydopamine (6-OHDA) or 6-hydroxydopa (6-OHDOPA) were injected bilaterally into the central part of amygdala. 6-OHDA was also injected after desmethylimipramine (DMI) pretreatment in order to study the selective destruction of DA terminals. The body weight increased after 6-OHDA injection and a mild hyperphagia and hyperdipsia developed. The 6-OHDA plus DMI treatment resulted in body weight decrease, hypophagia and hypodipsia. These effects were dose-dependent. While a high dose of 6-OHDOPA (15 mug/mul) decreased the body weight, an increase of weight was observed after a low dose (4 mug/0.5 mul). After 6-OHDA, 6-OHDA plus DMI or the high dose of 6-OHDOPA the DA concentration dropped significantly in the amygdala while low-dose 6-OHDOPA resulted in DA increase. In every case there was a parallel change in striatal DA content. The amygdalar NA concentration decreased after both 6-OHDA and the high dose of 6-OHDOPA. There was no change in NA levels after 6-OHDA plus DMI treatment and the NA concentration increased after the injection of a low dose of 6-OHDOPA. When DA/NA ratio was calculated the results showed that body weight increases were accompanied by a relative deficit in NA while a relative deficit of DA was present if body weight decreased. Our results suggest that the amygdalar balance of these transmitters may play an important role in the regulation of body weight and the contradictions of results with electrolytic lesions in the amygdala can be resolved at transmitter level.     

Selective participation of the bed nucleus of the stria terminalis and CRF in sustained anxiety-like versus phasic fear-like responses

The medial division of the central nucleus of the amygdala (CeA_M) and the lateral division of the bed nucleus of the stria terminalis (BNST_L) are closely related. Both receive projections from the basolateral amygdala (BLA) and both project to brain areas that mediate fear-influenced behaviors. In contrast to CeA_M however, initial attempts to implicate the BNST in conditioned fear responses were largely unsuccessful. More recent studies have shown that the BNST does participate in some types of anxiety and stress responses. Here, we review evidence suggesting that the CeA_M and BNST_L are functionally complementary, with CeA_M mediating short- but not long-duration threat responses (i.e., phasic fear) and BNST_L mediating long- but not short-duration responses (sustained fear or ‘anxiety’). We also review findings implicating the stress-related peptide corticotropin-releasing factor (CRF) in sustained but not phasic threat responses, and attempt to integrate these findings into a neural circuit model which accounts for these and related observations.