Activation of Organum Vasculosum of Lamina Terminalis, Median Preoptic Nucleus, and Medial Preoptic Area in Anticipation of Nursing in Rabbit Pups

Abstract

Rhythmic feeding in rabbit pups is a natural model to study food entrainment because, similar to rodents under a schedule of food restriction, these animals show food-anticipatory activity (FAA) prior to daily nursing. In rodents, several brain systems, including the orexinergic system, shift their activity to the restricted feeding schedule, and remain active when subjects are hungry. As the lamina terminalis and regions of the preoptic area participate in the control of behavioral arousal, it was hypothesized that these brain regions are also activated during FAA. Thus, the effects of daily milk ingestion on FOS protein expression in the organum vasculosum of lamina terminalis (OVLT), median preoptic nucleus (MnPO), and medial preoptic area (MPOA) were examined using immunohistochemistry before and after scheduled time of nursing in nursed and fasted subjects. Additionally, FOS expression was explored in orexin (ORX) cells in the lateral hypothalamic area and in the supraoptic nucleus (SON) because of their involvement in arousal and fluid ingestion, respectively. Pups were entrained by daily nursing, as indicated by a significant increase in locomotor behavior before scheduled time of nursing in both nursed and fasted subjects. FOS was significantly higher in the OVLT, MnPO, and MPOA at the time of nursing, and decreased 8 h later in nursed pups. In fasted subjects, this effect persisted in the OVLT, whereas in the MnPO and MPOA, values did not drop at 8 h later, but remained at the same level or higher than those at the time of scheduled nursing. In addition, FOS was significantly higher in ORX cells during FAA in nursed pups in comparison with 8 h later, but in fasted subjects it remained high during most fasting time points. Additionally, OVLT, SON, and ORX cells were activated 1.5 h after nursing. We conclude that the OVLT, MnPO, and MPOA, but not SON, may participate in FAA, as they show activation before suckling of periodic milk ingestion, and that sustained activation of the OVLT, MnPO, and MPOA by fasting may contribute to the high arousal state associated with food deprivation. In agreement with this, ORX cells also remain active after expected nursing, which is consistent with reports in other species.

The median preoptic nucleus exhibits circadian regulation and is involved in food anticipatory activity in rabbit pups

“…These areas are involved in motivation, reward and the homeostatic regulation of food ingestion. Alternatively, some brain areas do not shift in relation to the food timing, such as the SCN in both rodents (Mistlberger, 2011) and in the rabbit pup (Caba et al, 2008;Moreno et al, 2013;present results). However, as shown in Results, lack of food induces a decrease of PER1 in this nucleus in agreement with a previous publication (Caba et al, 2008).…”

“…On the day of parturition, litters were adjusted to six pups and remained undisturbed in the maternal nest in constant darkness for the entire experiment. To determine that pups were synchronized to daily food intake, their locomotor behavior was monitored in the nest with a detector sensitive to the pups' movements through the infrared radiations emitted by their body (Moreno et al, 2013;Morgado et al, 2010). For the present experiment, we used the same brains of pups where we demonstrated synchronization of locomotor behavior and high FOS expression at the time of FAA in the same brain regions (Moreno et al, 2013), and additional brains were processed to complement additional time points.…”

“…To determine that pups were synchronized to daily food intake, their locomotor behavior was monitored in the nest with a detector sensitive to the pups' movements through the infrared radiations emitted by their body (Moreno et al, 2013;Morgado et al, 2010). For the present experiment, we used the same brains of pups where we demonstrated synchronization of locomotor behavior and high FOS expression at the time of FAA in the same brain regions (Moreno et al, 2013), and additional brains were processed to complement additional time points. All experimental procedures were approved by the Ethics Committee of Universidad Veracruzana, in accordance with the procedures of the National Guide for the Production, Care and Use of Laboratory Animals (Norma Oficial Mexicana NOM-062- ZOO-1999), which complies with iInternational Guidelines laid down by the Society for Neuroscience and international ethical standards for chronobiological experimentation (Portaluppi et al, 2010).…”

“…In order to quantify PER1 immunoreactive (-ir) positive cells, we analyzed one representative section, at the levels indicated for each structure (Moreno et al, 2013). Images of selected sections were digitized at 20 Â magnification using a computerized image system (Image Pro Plus v. 5; Media Cybernetics, Silver Spring, MD) attached to a light microscope (Olympus BX41, Tokyo, Japan).…”

“…We recently identified that three structures in the forebrain -median preoptic nucleus (MnPO), organum vasculosum of lamina terminalis (OVLT) and medial preoptic area (MPOA), but not the supraoptic nucleusdisplay high levels of FOS at the time of FAA, then significantly decrease 8 h later (Moreno et al, 2013). This effect is interesting considering that cells in these three areas change their FOS expression and discharge profile according to the sleep-wake state of subjects (Sakai, 2011;Uschakov et al, 2006), and cells in these regions are related to the control of core body temperature, which is entrained in subjects during conditions of food restriction (Jilge et al, 2000;Krieger, 1974;Nakamura, 2011).…”