Recovery of long-term maternal behavioral deficiencies of neonatally underfed rats by early sensory stimulation: effects of successive parturitions

Early undernourishment interferes with the maternal aggressive response triggered by an intruder entering the homing cage

The maternal aggressive response (MAR) against intruders is temporarily expressed during lactation in association with the rearing and protection of offspring to promote their survival and growth in the nest. This normal component of maternal behaviour requires both the hormonal changes occurring at the end of pregnancy and the presence of pups for its establishment. Because early food restriction in the rat results in long-term maternal deficiencies, we analysed in Wistar rats the effects of perinatal undernutrition on the MAR to an intruder at days 1, 4, and 8 postpartum. The data showed that undernourished dams exhibited significant reductions of sniffing frequency on days 4 and 8 and significant increases of biting on day 4 and of lateral attacks on postpartum days 4 and 8. The finding of an altered MAR during the lactating period may be relevant for the survival and long-term behavioural development of the progeny.

Alterations in the Solitary Tract Nucleus of the Rat Following Perinatal Food Restriction and Subsequent Nutritional Rehabilitation

Newborn of altricial species maintain functional gustatory communication with the mother because the neural substrate and the capacity to discriminate and promote gustofacial responses are already operating. Because little is known about the effects of perinatal food restriction upon gustatory neuronal brain stem structures, we characterized neuronal Golgi-Cox alterations of the solitary tract rostral portion (NSTr) where gustatory information is known to convey in neonatal Wistar rats. Pre-and neonatally undernourished rats exhibited a general reduction in the number and extension of distal dendrites particularly in small neurons but little effect upon perikarya measurements of the NSTr neuronal population. By contrast, in nutritional and sensory rehabilitated rats the number of distal dendrites increased, although the dendritic extensions were less affected compared to perinatally underfed and control subjects. The data indicate that perinatal food restriction interferes with the NSTr dendritic arbor organization, while nutritional and sensorial rehabilitation given by normally lactating dams induced plastic changes presumably modifying the integrative processes underlying early taste discriminative capabilities. Moreover, since perinatal food restriction is a powerful stressor influence and the NST forms a part of a complex system underlying adaptive stress responses, the neuronal alterations observed here may be partly due to this noxious perinatal influence.

Contributions of undernutrition and handling to huddling development of rats

When newborn rats are separated from the mother, they consistently exhibit the huddling response to maintain body temperature and physical contact. Therefore, we investigated if preweaning handling/sensory stimulation may overcome the huddling deficiencies associated to neonatal undernourishment/maternal deprivation of Wistar rats maintained at constant temperature (30 degrees C). The data indicated that initial and final temperatures in the pile of undernourished (U) and undernourished stimulated (Us) pups was reduced compared to their controls (C and Cs, respectively). Huddling latency was prolonged at 5 days of age in the Us group and at 20 days of age in the U pups. On postpartum day 5, U and Us subjects were similar in battery and pile-huddling performance compared to their controls; thereafter, the frequency of battery type was low and pile type was high (in frequency) in all experimental treatments. The frequency of recycling from the pile in the Us pups in most of the ages was significantly reduced compared to U and C subjects, suggesting that early sensory stimulation possibly accelerates the maturation of thermoregulatory brain structures underlying the huddling response and causing increased physical contacts. The data provide evidence that both neonatal undernutrition/maternal deprivation and early sensory stimulation may modify the huddling response by reducing or increasing, respectively, brain mechanisms underlying huddling. The amount of physical contact the newborns receive from their littermates and the mother may be a fundamental source of sensory cues for neuronal maturation and brain functioning.

Movements restriction and alterations of the number of spines distributed along the apical shafts of layer V pyramids in motor and primary sensory cortices of the peripubertal and adult rat

The number and distribution of spines along apical shafts of rapid-Golgi-stained layer V pyramidal cells from visual, motor and somatosensory cortical areas were analyzed in control and movement-restricted (beginning at 20 days old) Wistar rats killed at 30, 40, 80 and 120 days of age (experiment A). In other group of rats, spine density was analyzed when restriction initiates on day 40 and the animals were killed at 50, 60 and 80 days postpartum, or after restriction starting on day 80 and killed at 120 days of age (experiment B). It has been found that the restriction of movements significantly reduces the total number of spines on apical shafts in the three cortical areas, when this condition starts at 20, 40 or 80 days without changing the overall distribution of spines. Also present findings indicate that the effects of movements restriction are attenuated when they were concurrent with maturational brain processes (20-40 days) than when they occurred later in life. The question remains open of which part of the measured reduction on the number of spines is due to the immobilization and which to the stress associated with this maneuver.

Retrieving of pups by neonatally stressed mothers

In the rat, perinatal food and maternal deprivation provoke long-lasting effects upon the retrieving responses of dams to displaced pups. In the current study, the retrieving latency and the disruption in the body area of pups chosen by the mother to transport them to a new location was investigated on days 4, 8 and 12 postpartum in lactating Wistar rats. Rats, neonatally underfed by daily (12 h) mother-litter separation in an incubator from days 1 to 23 postpartum, exhibited prolonged retrieving latencies and disruption in the body area of young ones chosen by the dam to transport them to the nest. Furthermore, neonatally underfed dams frequently transported pups in a rude manner eliciting sonic distress cries from them compared to control mothers. These findings are possibly relevant to understand the impact of epigenetic influences on offspring brain and physiological maturation partly mediated through maternal care.