Afferent and efferent projections of the anterior cortical amygdaloid nucleus in the mouse

Abstract

The anterior cortical amygdaloid nucleus (ACo) is a chemosensory area of the cortical amygdala that receives afferent projections from both the main and accessory olfactory bulbs. The role of this structure is unknown, partially due to a lack of knowledge of its connectivity. In this work, we describe the pattern of afferent and efferent projections of the ACo by using fluorogold and biotinylated dextranamines as retrograde and anterograde tracers, respectively. The results show that the ACo is reciprocally connected with the olfactory system and basal forebrain, as well as with the chemosensory and basomedial amygdala. In addition, it receives dense projections from the midline and posterior intralaminar thalamus, and moderate projections from the posterior bed nucleus of the stria terminalis, mesocortical structures and the hippocampal formation. Remarkably, the ACo projects moderately to the central nuclei of the amygdala and anterior bed nucleus of the stria terminalis, and densely to the lateral hypothalamus. Finally, minor connections are present with some midbrain and brainstem structures. The afferent projections of the ACo indicate that this nucleus might play a role in emotional learning involving chemosensory stimuli, such as olfactory fear conditioning. The efferent projections confirm this view and, given its direct output to the medial part of the central amygdala and the hypothalamic 'aggression area', suggest that the ACo can initiate defensive and aggressive responses elicited by olfactory or, to a lesser extent, vomeronasal stimuli.

Neurocircuitry of aggression and aggression seeking behavior: nose poking into brain circuitry controlling aggression

“…MeA neurons receive dense chemosensory cues from the vomeronasal organ [29] and relay signals to multiple regions including VMHvl. Furthermore, their activity increases during innate social behaviors such as fighting and mating [30].…”

Encoding of odor information and reward anticipation in anterior cortical amygdaloid nucleus

“…ACo sends the axons massively to the basolateral amygdala complex (BLA) 3 . The BLA plays a role in learning and storing CS-US associations 1819 .…”

“…5). Since the ACo receives direct inputs from the BLA 3 , it may also serve some function for the CS-US association by linking the olfactory information with the reward anticipation.…”

“…A study reported that the ACo receives dense projections from the main olfactory bulb (OB), moderate projections from the piriform cortex, lateral entorhinal cortex, basomedial amygdaloid nucleus (BMA), and medial amygdaloid nucleus (Me), and scarce projections from the ventral tegmental area (VTA) and the ventral tenia tecta (vTT) 3 . Moreover, the ACo projects densely to BMA 3 . These anatomical studies indicate that the ACo is closely related to the amygdala, and it is possible that the ACo is involved in odor-evoked motivational behaviors.…”

Corticotropin-Releasing Factor Receptor 1 in the Anterior Cingulate Cortex Mediates Maternal Absence-Induced Attenuation of Transport Response in Mouse Pups

“…LSI receives massive inputs from hippocampal formation, sends bidirectional projections with the preoptic and hypothalamic areas, and has been consistently found to be involved in stress responses ( Risold, 2004 ; Singewald et al, 2011 ; Nishi et al, 2013 ). Afferent and efferent connectivity of the ACo suggests that the ACo may initiate defensive and aggressive responses elicited by olfactory stimuli ( Cádiz-Moretti et al, 2017 ). The LPAG takes a major role in the flight response, receives inputs from the ACC and projects extensively to the rostral ventrolateral medulla that activates preganglionic sympathetic fibers ( Bandler and Keay, 1996 ; Kvetnansky et al, 2009 ).…”