Brief daily suckling shifts locomotor behavior and induces PER1 protein in paraventricular and supraoptic nuclei, but not in the suprachiasmatic nucleus, of rabbit does

Abstract

Nursing in the rabbit is a circadian event during which mother and pups interact for a period of < 5 min every day. Here we explored behavioral and neuronal changes in the mother by analyzing the suprachiasmatic nucleus (SCN), and oxytocinergic (OT) neurons in the paraventricular nucleus (PVN) and the supraoptic nucleus (SON). We maintained lactating does in a light-dark cycle (lights on at 07 : 00 hours; ZT0); they were scheduled to nurse during either the day (ZT03) or the night (ZT19). Groups of intact and nursing females was perfused, one at each 4-h point through a 24-h cycle. We explored, by immunohistochemistry, the PER1 expression and double-labeling, with OT antibody, of neurons in the PVN and SON at lactation on day 7. In the SCN, intact and lactating groups had peak PER1 expression at ZT11; however, there was a reduction in PER1 at peak time in the nursing groups. There was a locomotor activity rhythm with increased activity around the time of lights-on in intact subjects and around the time of suckling in lactating does. There was an induction of PER1 in OT cells in the PVN and SON that shifted in phase with timing of nursing. We further explored the maintenance of the PER1 expression in OT cells in nursing-deprived does and found a significant decrease at 24 and 48 h after the last nursing. We conclude that suckling induced PER1 in the PVN and SON, but not in the SCN, in nursing does, and also shifted their locomotor behavior.

Behavioral, Physiological, and Neuroendocrine Circadian Rhythms During Lactation

“…Whether nursing was scheduled in the day or in the night, this rhythm shifted and PER1 peaked 4-8 h after suckling by pups. This effect was specifi c to these nuclei as PER1 rhythm in the SCN did not shift in any condition (Meza et al 2008 ; Fig. 10.2 ).…”

“…Indeed, as shown in Fig. 10.2 , in intact control females, PER1 in SCN has a rhythm that reaches a peak at ZT11 (ZT0 = 7 a.m., lights on), but timing of nursing decreases PER1 at times of their maximal expression when compared to intact does (Meza et al 2008 ).…”

“…This circadian fl exibility was explored in relationship to locomotor behavior in lactating does. Intact female rabbits in non-sound-isolated conditions exhibit a circadian rhythm (periodogram, X 2 P < 0.001) with increased activity around the fi rst hours of light and lower activity during the evening and most of the night (Meza et al 2008 ). However, this activity pattern is not maintained during lactation.…”

“…Whether nursing is scheduled in the day or the night, locomotor behavior is maximal at around the same hours and consequently the does behave mostly as diurnal or as nocturnal, depending on the time at which nursing is imposed (Meza et al 2008 ). This shift in locomotor behavior suggests an alteration in the circadian oscillations of the SCN.…”

“…Black and white bar at bottom of c and e represents L/D condition. Bar = 100 μm; ZT zeitgeber time, ZT0 = light on at 07:00 (Meza et al 2008 ) cycle of females. For instance, PER1 protein was not detected in the mammary glands of virgin mice but was robustly expressed in ductal epithelial cells during lactation (Metz et al 2006 ).…”