Differential efferent projections of the anterior, posteroventral, and posterodorsal subdivisions of the medial amygdala in mice

Abstract

The medial amygdaloid nucleus (Me) is a key structure in the control of sociosexual behavior in mice. It receives direct projections from the main and accessory olfactory bulbs (AOB), as well as an important hormonal input. To better understand its behavioral role, in this work we investigate the structures receiving information from the Me, by analysing the efferent projections from its anterior (MeA), posterodorsal (MePD) and posteroventral (MePV) subdivisions, using anterograde neuronal tracing with biotinylated and tetrametylrhodamine-conjugated dextranamines. The Me is strongly interconnected with the rest of the chemosensory amygdala, but shows only moderate projections to the central nucleus and light projections to the associative nuclei of the basolateral amygdaloid complex. In addition, the MeA originates a strong feedback projection to the deep mitral cell layer of the AOB, whereas the MePV projects to its granule cell layer. The Me (especially the MeA) has also moderate projections to different olfactory structures, including the piriform cortex (Pir). The densest outputs of the Me target the bed nucleus of the stria terminalis (BST) and the hypothalamus. The MeA and MePV project to key structures of the circuit involved in the defensive response against predators (medial posterointermediate BST, anterior hypothalamic area, dorsomedial aspect of the ventromedial hypothalamic nucleus), although less dense projections also innervate reproductive-related nuclei. In contrast, the MePD projects mainly to structures that control reproductive behaviors [medial posteromedial BST, medial preoptic nucleus, and ventrolateral aspect of the ventromedial hypothalamic nucleus], although less dense projections to defensive-related nuclei also exist. These results confirm and extend previous results in other rodents and suggest that the medial amygdala is anatomically and functionally compartmentalized.

Dorsomedial hypothalamus CRF type 1 receptors selectively modulate inhibitory avoidance responses in the elevated T-maze

“…Concerning the relationship of the medial amygdala with ETM avoidance, previous evidence by our research group [49] has shown that avoidance performance significantly increased FOS immunoreactivity in the region and that the pharmacological inhibition of the medial amygdala by midazolam administration impairs avoidance responses [50], an anxiolytic effect. Therefore, it is not a surprise that the results obtained with the DMH in the present study are similar to the ones previously observed [47] for this amygdaloid nucleus, that is, anxiety-related.…”

“…In fact, using anterograde neuronal tracing with biotinylated and tetrametylrhodamine-conjugated dextran amines to analyze efferent projections from the anterior, posterodorsal and posteroventral subdivisions of the medial amygdala, it was shown that the densest outputs of the region targeted the bed nucleus of the stria terminalis and the hypothalamus [47]. Through its projections to the hypothalamus the medial amygdala regulates the activation of the HPA axis in response to emotional stressors [48].…”

Amygdala Kisspeptin Neurons: Putative Mediators of Olfactory Control of the Gonadotropic Axis

“…In this study, we found that the amygdala kisspeptin neurons project via the stria terminalis ( fig. 5 ), the major pathway from the amygdala region [29] to reach GnRH neurons in the POA. Taken together, the three kisspeptin populations projecting to the POA [68] form a complex network to control GnRH neurons.…”

“…Vomeronasal cells project to the AOB, where they make contact with mitral cells [26] . Mitral cells in the AOB project to the amygdala [27] , and cells in the amygdala send projections back to the AOB [28,29] , suggesting a feedback control of olfaction by the amygdala.…”

Focal lesions within the ventral striato-pallidum abolish attraction for male chemosignals in female mice

“…215 The cortical division of the amygdala, including both olfactory and 216 vomeronasal nuclei, sends important projections to the Tu and 217 ICj [4-6]. Also, scarce input from the medial amygdala reaches 218 the medial region of the Tu [27]. We have hypothesised that this 219 amygdalo-striatal pathway might underlie the rewarding proper concentrations of cocaine in the medial Tu, whereas higher con-228 centrations are needed to achieve self-administration in adjoining 229 structures (medial shell of the Acb and posterolateral Tu [1]).…”