Volume 17, Number 9,
Issue of May 1, 1997
pp. 3364-3378
Copyright ©1997 Society for Neuroscience
Role of the Midbrain Periaqueductal Gray in Maternal Nurturance
and Aggression: c-fos and Electrolytic Lesion Studies
in Lactating Rats
Received Jan. 3, 1997; accepted Jan. 27, 1997.
Joseph S. Lonstein and
Judith M. Stern
Department of Psychology, Rutgers, The State University of New
Jersey, New Brunswick, New Jersey 08903
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
(cPAGl,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
cPAGl,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.
Key words:
nursing behavior;
maternal aggression;
c-fos;
suckling;
lactation;
rostral PAG;
caudal PAG