Organization of projections from the medial nucleus of the amygdala: A PHAL study in the rat

Abstract

The organization of axonal projections from the four recognized parts of the medial amygdalar nucleus (MEA) were characterized with the Phaesolus vulgaris leucoagglutinin (PHAL) method in male rats. The results indicate that the MEA consists of two major divisions, ventral and dorsal, and that the former may also consist of rostral and caudal regions. As a whole, the MEA generates centrifugal projections to several parts of the accessory and main olfactory sensory pathways, and projections to a) several parts of the intrahippocampal circuit (ventrally); b) the ventral striatum, ventral pallidum, and bed nuclei of the stria terminalis (BST) in the basal telencephaon; c) many parts of the hypothalamus; d) midline and medial parts of the thalamus; and e) the periaqueductal gray, ventral tegmental area, and midbrain raphé. The dorsal division of the MEA (the posterodorsal part) is characterized by projections to the principal nucleus of the BST, and to the anteroventral periventricular, medial, and central parts of the medial preoptic, and ventral premammillary hypothalamic nuclei. These hypothalamic nuclei project heavily to neuroendocrine and autonomic-related parts of the hypothalamic periventricular zone. The ventral division of the MEA (the anterodorsal, anteroventral, and posteroventral parts) is characterized by dense projections to the transverse and interfascicular nuclei of the BST, and to the lateral part of the medial preoptic, anterior hypothalamic, and ventromedial hypothalamic nuclei. However, dorsal regions of the ventral division provide rather dense inputs to the medial preoptic region and capsule of the ventromedial nucleus, whereas ventral regions of the ventral division preferentially innervate the anterior hypothalamic, dorsomedial, and ventral parts of the ventromedial nuclei. Functional evidence suggests that circuits associated with dorsal regions of the ventral division may deal with reproductive behavior, whereas circuits associated with ventral regions of the ventral division may deal preferentially with agonistic behavior.

Acute and chronic effects of ferret odor exposure in Sprague–Dawley rats

“…Our results, and those of others using cat odor, are consistent with the hypothesis that one of the major recipients of accessory olfactory projections, the "vomeronasal" medial amygdala, is also necessary for the behavioral and neuroendocrine responses induced by predator odor exposures. Although the medial amygdala is not reported to project directly to many, if any, of the effector/motor centers controlling behavioral, autonomic, and neuroendocrine responses (Canteras et al, 1995), it nevertheless projects to many regions such as the anterior bed nucleus of the stria terminalis, medial preoptic region, and a number of hypothalamic nuclei (dorsomedial, ventromedial, and premammillary divisions), that have those characteristics. Current anatomico-functional studies are under way to precisely define the input-output relationships of the medial amygdala with a specific focus on the vomeronasal subdivisions.…”

“…A number of studies have also associated relatively specifically the medial amygdaloid nucleus in defensive behavioral responses induced by cat or cat odor, or TMT exposures Li et al, 2004;Muller and Fendt, 2006). Given the emerging circuits controlling a variety of predator-induced defensive responses, we targeted the medial amygdaloid nucleus in our studies of the effects of ferret odors due to its well-known reception of odor information from a number of main and accessory olfactory regions, and its putative position to relay this information to regions controlling different effector response systems (Canteras et al, 1995). …”

Effects of Substance P in the Amygdala, Ventromedial Hypothalamus, and Periaqueductal Gray on Fear-Potentiated Startle

“…In addition, we recently reported that fear-potentiated startle is also blocked by infusion of the AMPA receptor antagonist NBQX into the MeA (Walker et al, 2005). It is unclear how the MeA influences fear-potentiated startle as it does not project directly to the startle reflex circuit, the dSC/DpMe, or the CeA (Canteras et al, 1995). However, the MeA does have heavy projections to the ventromedial nucleus of the hypothalamus (VMH), and this pathway was found to contain SP (Canteras et al, 1994(Canteras et al, , 1995Han et al, 1996;Shaikh et al, 1993).…”

“…It is unclear how the MeA influences fear-potentiated startle as it does not project directly to the startle reflex circuit, the dSC/DpMe, or the CeA (Canteras et al, 1995). However, the MeA does have heavy projections to the ventromedial nucleus of the hypothalamus (VMH), and this pathway was found to contain SP (Canteras et al, 1994(Canteras et al, , 1995Han et al, 1996;Shaikh et al, 1993). Lesions of the VMH have been shown to disrupt other affective behaviors (Colpaert and Wiepkema, 1976;de Oliveira et al, 1997;Dielenberg et al, 2001;Han et al, 1996;Sudakov, 1987).…”

CRF type 1 receptors in the dorsal periaqueductal gray modulate anxiety-induced defensive behaviors

“…Canteras (2002) proposed that a medial hypothalamic defensive system (MHZ) mediates stimulus activation of the defense response elicited by a psychological threat stimulus, a predator. The MHZ initially integrates information relayed from the septohippocampal system with projections from several amygdala sites that receive or integrate information about threat stimuli (Canteras, et al, 1995). In turn, the MHZ relays the information upstream, via the thalamus, to the cortex , and downstream, through descending projections to brain stem regions, particularly the PAG (Canteras, et al, 1997;Canteras and Goto, 1999;.…”