Role of the Midbrain Periaqueductal Gray in Maternal Nurturance and Aggression:c-fosand Electrolytic Lesion Studies in Lactating Rats

Abstract

The upright crouched, or kyphotic, nursing posture of lactating rats is dependent on suckling stimulation from pups. Because of the neuroanatomical connections of the periaqueductal gray (PAG) and its sensorimotor integration of the analogous lordosis posture displayed by sexually receptive female rats, the possible role of the PAG in kyphosis was investigated using c-fos immunocytochemistry and electrolytic lesions. Lactating rats interacting with and nursing a litter of suckling pups showed greater Fos-immunoreactive nuclei in the lateral and ventrolateral caudal PAG (cPAG l,vl ) compared with dams receiving nonsuckling somatosensory, distal, or no stimulation from pups. In contrast, this pattern was not evident in the rostral PAG, where the highest Fos levels occurred in nonsuckled dams, or in five other brainstem sites with either no group differences (peripeduncular, dorsal raphe, and pontine nuclei) or negligible Fos (ventral tegmental area, spinal trigeminal nuclei). After bilateral electrolytic lesions of the cPAG l,vl during gestation or on day 7 postpartum, active maternal behaviors, such as retrieval and licking of pups, and total nursing time were essentially normal. Kyphotic nursing, however, was reduced by 85%, nursing in prone and supine postures increased substantially, and 24 hr litter weight gains were reduced, particularly early in lactation (by 26%). Furthermore, lesioned rats attacked a strange male twice as often as controls did, which is suggestive of reduced fearfulness. These results extend the known roles of the PAG in reproductive and defensive behaviors to the postural control of suckling-induced kyphotic nursing and the modulation of maternal aggression.

Morphine infusions into the rostrolateral periaqueductal gray affect maternal behaviors

“…Our results were consistent with the reports that nursing kyphosis is related to the ventrolateral PAG (2,21,22). There is no role for this parameter in the rostral PAG (22).…”

“…There is no role for this parameter in the rostral PAG (22). Lesions in the ventrolateral PAG reduce kyphosis by 85% (2,22), whereas lesions in the rostral PAG do not inhibit kyphosis (22).…”

Comparison of the “Nursing” and Other Parental Behaviors of Nulliparous and Lactating Female Rats

“…In the absence of suckling-induced quiescence, nonsuckled dams actively hover over pups more and display increased pup licking, self-grooming, and exploration (Lonstein and Stern, 1997a,b;Lonstein, Simmons, Swann, and Stern, 1998;Stern and Johnson, 1990;Stern and Lonstein, 1996;Stern, Dix, Bellomo, and Thramann, 1992). Kyphosis can also be disrupted by destruction of neural sites that transmit (dorsolateral funiculus of spinal cord; Stern, Yu, and Crockett, 1993) or receive (lateral and ventrolateral regions of the caudal midbrain periaqueductal gray (cPAG l,vl ); Lonstein and Stern, 1997a;1998;Lonstein, Simmons, and Stern, 1998) suckling inputs necessary for the mediation of this posture. In the absence of kyphosis, lesioned dams remain highly motivated to remain with the pups and nurse them, but do so in more atypical postures.…”

Modularity and Specialized Learning: Mapping between Agent Architectures and Brain Organization

“…Further, animals that have had their forebrains surgically removed have been shown capable of conducting complex species-typical behaviors -they are simply unable to apply these behaviors in appropriate contexts. In particular, the periaqueductal grey matter has been implicated in complex species-typical behaviors such as mating rituals and predatory, defensive and maternal maneuvers [39]. However, there appears to be little literature as to exactly how such skills are coordinated.…”