Proinflammatory activity and the sensitization of depressive-like behavior during maternal separation.

When guinea pig pups are isolated for a few hours in a novel environment, they exhibit a distinctive passive behavioral response that appears to be mediated by proinflammatory activity. Recently, we observed that pups separated on two consecutive days show an enhanced (sensitized) passive response on the second day. In Experiment 1, pups receiving intracerebroventricular infusion of 50 ng of the anti-inflammatory cytokine interleukin-10 prior to a first separation failed to show a sensitized behavioral response to separation the next day. In Experiment 2, pups separated on Days 1 and 2, or just 2, showed an increase in passive responding during separation on Day 5. Pups injected with the bacterial antigen lipopolysacchride (LPS; 75 μg/kg body weight, intraperitoneal) prior to separation on Day 1 showed an increase in passive behavior several days later not shown by pups injected with saline prior to Day 1 separation. However, injection of LPS without separation on the first day did not enhance responding during an initial separation on the second day. These results suggest that immune activation is necessary, but not sufficient, to account for the sensitization of passive behavior of isolated guinea pig pups the following day, that boosting proinflammatory activity during an initial separation may promote sensitization several days later, and that the sensitized response persists for at least several days. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Light-dark variation and changes across the lactational period in the behaviors of undisturbed mother and infant guinea pigs (Cavia porcellus).

Lactating guinea pigs (Cavia porcellus) and their litters were observed by videophotography across the light/dark cycle at 1, 11, 21, and 31 days postpartum. The highest level of behavioral activity was seen in the dark, particularly in the hour after light offset. This circadian pattern was evident from Day 1 in mothers and from Day 11 in pups. Contact between mothers and pups was inversely related to activity, occurring more frequently during light. Maternal grooming of pups occurred on Day 1 and then declined; self-grooming by pups increased across days. Intake of solid food and water by pups occurred on Day 1 and increased thereafter. A nearly complete transition from nursing to independent ingestion was observed between 21–31 days of age. Overall, we document several ontogenetic changes in young guinea pigs and demonstrate that under laboratory conditions mother and infant guinea pigs exhibit a nocturnal activity pattern. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cortisol facilitates induction of sexual behavior in the female musk shrew (Suncus murinus).

The role of cortisol in sexual behavior in the female musk shrew (Suncus murinus) was examined. High levels of cortisol were associated with sexual receptivity, as indicated by species-typical tail-wagging behavior, during brief (15-min) mating tests. When cortisol production was blocked by metyrapone, an 11-β-hydroxylase inhibitor, females exhibited reduced sexual behavior relative to controls, an effect that was reversed with acute cortisol replacement. These results indicate that cortisol facilitates, rather than inhibits, sexual behavior in this species and expands the comparative understanding of hypothalamic–pituitary–adrenal (HPA) effects on reproduction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temporal aspects of female musk shrew (Suncus murinus) sexual behavior.

The effects of testing condition on sexual behavior were examined in female musk shrews (Suncus murinus). Females were tested in 2 conditions, a pair test and a paced test. The pair test was similar to traditional sex test conditions in which the female and male are placed into the same chamber together until mating occurs. The paced condition allowed the female to leave the male's chamber and revisit him at will, thus "pacing" the interaction. Females displayed receptivity continuously for 14 days in both conditions. In the paced condition, females were less likely to become receptive within 30 min and mate to ejaculation. However, few additional differences were found between test conditions. Because this is the 1st experiment to use a pacing test paradigm in a species with induced ovulation, the authors speculate that the absence of pacing behavior during mating may be shown by other species that have induced ovulation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)