Compared to males, aggression is less frequently noticed in females. Fierce maternal-aggression to thwart the attack/threat of a male conspecific/intruder is transiently expressed as she defends her pups. The odor cues emanated by the intruder provoke aggressive behavior by robustly activating the ventral-premammillary nucleus (PMv) in the hypothalamic-attack area (HAA). But, how PMv activation triggers aggression is unclear. In view of neuropeptide cocaine- and amphetamine-regulated transcript (CART)'s potential to reconfigure neural circuits for behavioral demands, occurrence throughout aggression circuitry, and abundance particularly in PMv, we test the role of PMv
CART
in maternal and inter-male aggression in rats. Males/dams actively attacked the intruder; virgin females did not. The dams/males without intruder showed isolated c-Fos cells in PMv, but the intruder's presence triggered c-Fos-activation in different PMv-subdivisions in dams/males. Compared to dams without intruder, confrontation with intruder robustly activated PMv
CART
-neurons and augmented CART-ir in ventral-PMv and
cart
-mRNA in PMv-containing tissues in dams. Conversely, in males, the intruder's presence activated lateral-PMv
CART
neurons, but CART-levels remained unaltered. Intra-PMv CART-siRNA administration suppressed maternal-aggression, but male aggression was unaffected. Since PMv is strongly connected with the ventrolateral–ventromedial hypothalamus (VMHvl) and medial preoptic nucleus (MPN), we test whether CART signaling to these nuclei triggers maternal aggression. While VMHvl showed stronger CARTergic-axonal input than MPN, immunoneutralization of CART in VMHvl, but not MPN, blocked maternal-aggression. CART may drive the circuit beyond HAA since VMHvl neurons contacted by CART-axons project to periaqueductal gray. We identify the engagement of vPMv and lPMv during maternal and inter-male aggression, respectively, and CART as a key mediator in the PMv–VMHvl pathway to express maternal-aggression in rats.