SOMATOSENSORY CONTRIBUTIONS TO C-FOS ACTIVATION WITHIN THE CAUDAL PERIAQUEDUCTAL GRAY OF LACTATING RATS - EFFECTS OF PERIORAL, ROOTING, ANDSUCKLING STIMULI FROM PUPS

In lactating rats, the immediate-early gene c-fos was previously shown to be highly activated in several brain sites by physical interaction with either suckling or nonsuckling pups but not by distal stimuli fr om pups, a non-pup stimulus, or no stimulation. Further, even greater levels of Fos-immunoreactivity (ir) occurred following suckling versus nonsuckling contact with pups in only 1 of over 25 sites-the caudal p eriaqueductal gray (cPAG) at an intercollicular level, lesions of whic h severely reduced the typical suckling-induced kyphotic nursing postu re. Herein we further evaluated the effects and site-specificity of va rious somatosensory cues received from pups during 60 min on Fos-ir in the FAG of day 7 postpartum rats after a 48-h dam-litter separation. Darns interacting with suckling versus nonsuckling pups showed relativ ely high numbers of Fos-ir cells in the intercollicular cPAG site iden tified earlier, but not in three other rostrocaudal planes of the FAG. Elimination of rooting on the dam's ventrum by use of fully anestheti zed pups did not further diminish Fos-ir in maternally behaving, nonsu ckled dams. Perioral anesthesia of dams prior to reunion with the litt er prevented retrieval and licking of pups but not pup-initiated nursi ng behavior, the duration of which was positively correlated with Fos- ir levels within the intercollicular cPAG. Thus, various somatosensory stimuli from pups activate c-fos in a discrete region of the cPAG but only interactions that include suckling and its behavioral consequenc es elicit maximal expression, consistent with a role for this midbrain site in the sensorimotor control of kyphotic nursing in rats. (C) 199 7 Academic Press.