Bidirectional connections of the medial amygdaloid nucleus in the Syrian hamster brain: Simultaneous anterograde and retrograde tract tracing

Abstract

In the male Syrian hamster, mating is dependent on chemosensory and hormonal stimuli, and interruption of either input prevents copulation. The medial amygdaloid nucleus (Me) is a key nodal point in the neural circuitry controlling male sexual behavior because it relays both odor and steroid cues. Me is comprised of two major subdivisions, anterior (MeA) and posterior (MeP), which have distinct, although overlapping efferent projections. The present study investigated the afferents and efferents of MeA and MeP by using combined anterograde and retrograde tract tracing. Phaseolus vulgaris-leucoagglutinin and cholera toxin B were injected by iontophoresis through a single glass micropipette and detected by immunohistochemistry. MeA has widespread connections with olfactory structures, whereas MeP is heavily interconnected with steroid-responsive brain regions. The efferent projections of MeA and MeP were similar to those reported previously for the rat and hamster. In particular, MeP projects to the posteromedial subdivision of the bed nucleus of the stria terminalis (BNST) and to the medial preoptic nucleus, whereas MeA projects to adjacent subnuclei in BNST and the preoptic area. MeA and MeP also have distinct patterns of afferent input. Furthermore, the combination of anterograde and retrograde tract tracers shows that MeA and MeP are each bidirectionally connected with each other and with limbic nuclei. These results demonstrate that subnuclei of Me are interconnected with limbic structures in hamster brain. These connections may contribute to chemosensory and hormonal integration to control male sexual behavior.

The paternally expressed gene Peg3 regulates sexual experience-dependent preferences for estrous odors.

“…It sends output to the cortical and medial amygdala (Coolen & Wood, 1998;Majak, Ronkko, Kemppainen, & Pitkanen, 2004), the latter being a key node in the control of male sexual behavior (Newman, 1999). Expression of androgen and estrogen receptors (Kritzer, 2004;Shughrue, Lane, & Merchenthaler, 1997;Simerly, Chang, Muramatsu, & The Paternally Expressed 23 Swanson, 1990) has been reported in the piriform cortex, suggesting it may be responsive to the key hormones that regulate male sexual behavior.…”

Obesity-inducing amygdala lesions: examination of anterograde degeneration and retrograde transport

“…Anatomically, and to some degree functionally, the various subdivisions in the area of the PDA appear to be interconnected and paired with similar subdivisions in the medial bed nucleus of the stria terminalis (1,19,24,110). The MePD appears to be homologous with the small-celled medial part of the posteromedial bed nucleus of the stria terminalis, whereas the homologous subdivision for the BSTIA is less clear.…”

The vertebrate social behavior network: Evolutionary themes and variations

“…These include aggression, appetitive and consummatory sexual behavior, various forms of communication, social recognition, affiliation, bonding, parental behavior and responses to social stressors (Kirkpatrick et al, 1994;Kollack-Walker and Newman, 1995;Bamshad and Albers, 1996;Coolen et al, 1997;Kollack-Walker et al, 1997;Wang et al, 1997;Lonstein et al, 1998;Morgan et al, 1999;Delville et al, 2000;Kalinichev et al, 2000;Gammie and Nelson, 2001;Heeb and Yahr, 2001;Sheehan et al, 2001;Ferguson et al, 2002;Cushing et al, 2003;Lim and Young, 2004). The nodes are also bidirectionally connected (Risold and Swanson, 1997b;Coolen and Wood, 1998;Dong and Swanson, 2004), and each area contains sex steroid receptors that are essential for the sexual differentiation and temporal coordination of social behavior (Morrell and Pfaff, 1978;Commins and Yahr, 1985;Simerly et al, 1990;Wood and Newman, 1995). The mammalian brain obviously contains a large number of other areas that are relevant for social behavior (e.g., other basal forebrain areas that regulate stress and reward processes, and cortical areas that serve executive functions); thus Newman's network should be regarded as the "core" of the social brain, not the social brain in toto.…”

“…These include a vocally-active tegmental field that lies lateral to the PAG and medial to the auditory torus/ inferior colliculus (Phillips et al, 1972;Kennedy, 1975;Jürgens, 1994;Goodson and Bass, 2002) in all classes except Amphibia, in which a comparable vocal site is located at isthmal levels (Wetzel et al, 1985). Other selected references : Northcutt, 1981;Bruce and Neary, 1995;Balthazart et al, 1996;Panzica et al, 1996;Wong, 1997;Coolen and Wood, 1998;Lanuza and Halpern, 1998;Nieuwenhuys et al, 1998;Cheng et al, 1999;Goodson and Bass, 2000c;Dong et al, 2001;Petrovich et al, 2001;Goodson et al, 2003;Moreno and Gonzalez, 2003;Dong and Swanson, 2004;Goodson et al, 2004a;Rink and Wullimann, 2004;…”