Distinctive Responses in the Medial Amygdala to Same-Species and Different-Species Pheromones

Abstract

Chemosignals related to reproductive and social status (pheromones) carry messages between opposite-sex and same-sex individuals in many species. Each individual must distinguish signals relevant to its own social behavior with conspecifics from signals used by other (heterospecific) species relevant to their social behavior. In male hamsters, the medial amygdala responded in a categorically different way to conspecific stimuli (socially relevant) and heterospecific stimuli (not socially relevant but serving similar purposes for other species), and may play an important role in this decision. Immediate-early gene responses to conspecific chemosignals and heterospecific chemosignals were characteristically different. The categorical responses, generated by chemosensory input from the vomeronasal organ and (probably) GABA inhibition within the amygdala, were not apparent at more peripheral sensory levels. This is the first evidence for an important role of the amygdala, a limbic structure known to be involved in social and emotional behavior, in discrimination of species specificity in chemosignals.

In vivo electrophysiological recordings in amygdala subnuclei reveal selective and distinct responses to a behaviorally identified predator odor

“…B: scatterplot depicting the timing of the peak response to cat urine of all recorded units and the mean Ϯ SE timing of the response peak to cat urine in the MeAV (n ϭ 7), MePV (n ϭ 21), MeAD (n ϭ 16), MePD (n ϭ 28), CoA (n ϭ 7), BLa and BLv (n ϭ 4 each), BMa (n ϭ 6), BMp (n ϭ 10), AHi (n ϭ 13), CeM (n ϭ 3), and BSTIA (n ϭ 8 1995) and is the first site of olfactory convergence (Meredith 1998), it is in an excellent position to integrate olfactory cues signaling predators and engage excitatory or inhibitory events in downstream targets that regulate defensive responses. These findings are consonant with gene activation studies Meredith and Westberry 2004) and converge with lesion studies (Li et al 2004;Masini et al 2009) to highlight the critical involvement of the MeA in predator odor-generated fear.…”

“…The activity observed in the MePV and anterior MeA reinforces the well-established involvement of these nuclei in predator odor-induced defensive behavior Meredith and Westberry 2004). As these nuclei share projection pathways similar to the major components of the defensive circuit (Pardo-Bellver et al 2012), increased activation likely reflects a functional role concerned with generating defensive responses.…”

“…Consequently, it is plausible that increased ventral MeA activity to predator odor additionally stimulates GABAergic cells in the BNST that in turn decrease MeA output, thereby providing the necessary regulatory mechanism required to dampen the largely excitatory ventral MeA. Given that the MeAV and MeAD are thought to serve as filters and evaluators of chemosensory information (Meredith and Westberry 2004), the suppression observed in the MeAV may be relatively brief compared with the MePV to specifically enable the MeAV to be more receptive to any additional chemosensory information related to the initial threat and adjust behavioral responses accordingly.…”

Pubertal activation of estrogen receptor α in the medial amygdala is essential for the full expression of male social behavior in mice

“…The importance of the MeA in the regulation of male-type social behaviors has been demonstrated in numerous studies (13)(14)(15)(16)(17)(18). Particularly, the MeA plays a significant role in chemosensory information processing (15,16,33,34) as part of the social behavior network in the CNS (35). It relays socially meaningful signals to activate or inhibit various downstream brain sites, such as the MPOA, anterior hypothalamic area (AHA), and VMN, that are more directly involved in the execution of male sexual and aggressive behaviors (14,(36)(37)(38)(39)(40).…”

Proliferation, Migration, and Survival of Cells in the Telencephalon of the Ball Python, Python Regius

“…However, the amygdala itself is not a memory storage site (Malin and McGaugh, 2006). It is also important in processing information about pheromones and other olfactory or vomeronasal input, causing it to directly influence the endocrine system (Halpern and Martínez-Marcos, 2003) and behavior during confrontations with conspecifics (agonistic behavior) (Meredith and Westberry, 2004). Support for mammalian amygdalar neurogenesis has been limited to studies indicating proliferation, cell genesis, and specification in Orictolagus cuniculus (New Zealand white rabbits) (Luzzati et al, 2006), Mus musculus (laboratory mice) (Shapiro et al, 2009), and Saimiri sciureus (common squirrel monkeys) and Macaca fascicularis (crab-eating macaques) (Bernier et al, 2002).…”