Effects of Neonatal Undernutrition on Development of the Dorsolateral Prefrontal Cortex Pyramidal Cells in the Rat

The dorsolateral prefrontal cortex (dlPFC) of the rat plays a role in the encoding of neuronal signals involved in conflict-induced behavioral adjustment, working memory, planning and executive abilities, attentional control and other cognitive responses. In altricial species, early perinatal undernutrition interferes with the morphofunctional organization of a number of central nervous system (CNS) structures including the prefrontal cortex. The effects of neonatal undernutrition on dendritic arbor density, perikaryon measurements, and the number of spines (detected by rapid-Golgi) of basilar dendritic segments in layer III pyramidal neurons of the dlPFC were examined in male Wistar rats on postnatal (PDs) 12, 20, and 30. In the underfed (U) subjects the distal portions of the dendritic arbors had a consistent hipoplasia, mainly on PD 30, with reduced cross sectional area, perimeter, and spine densities on the basilar dendrites on all days studied. Thus, the alterations of the dlPFC pyramidal neurons may interfere with the plastic synaptic activity and cognitive performance of rats subjected to the stress of early underfeeding. Characterizing these anatomical alterations may help to understand the disrupted cognitive processes associated with neonatal undernutrition.

Maternal Response of Perinatally Underfed Wistar Virgin Females Exposed to Newborn Rats

Nutrition plays a major role in the survival of the progeny, and its perinatal deficiencies delay physical development and interfere with social and cognitive performance later in life. The effects of early undernutrition on maternal social performance of sensitized adult virgin rats were evaluated. Several maternal and non-maternal responses were measured in virgin female Wistar rats randomly divided into two groups, control and early undernourished, during 19 days of chronic daily exposure to fresh foster pups in home-cage conditions. Underfed females (F0) received different percentages of a balanced diet during gestation. After birth, pups were underfed (F1) by alternating every 12 h between litters two lactating dams, one with ligated nipples. Weaning was at 25 days of age followed by an ad lib diet until postpartum day 90, when sensitized virgins were maternally tested daily for seven successive sessions. Significantly (p < 0.05) low body weight scores in UG F1 virgins of five different ages were observed. The UG F1 females expressed significantly (p < 0.05) lower frequency values in sniffing, licking, retrieving, crouching, and handling shavings, with clear prolonged sniffing, retrieving and handling shaving latencies towards the foster pups compared with CG F1 sensitized females. Self-grooming was not affected, whereas exploration was significantly reduced. Current findings suggest that perinatal undernutrition interfered the organization of a core neuronal circuitry underlying the mother-litter interactions involved in social and cognitive performance of sensitized adult virgins. Furthermore, the behavioral maternal alterations in F1 virgins may possibly generate a risky negative social environment to induce cognitive and/or brain disorders in later generations.

Development of the Gusto Facial Reflex in Perinatally Undernourished Rats

In the rat, the taste system plays a critical role in motivating the animal to consume nutrients and avoid toxic substances. In neonatal rat the orofacial movements can be modified by the application of sucrose and quinine in the mouth, producing ingestion or rejection responses, respectively, but there is no information available on the gusto facial reflexes (GFR) under perinatal fasting. The aim of the present study was to determine how undernutrition can affect the development of orofacial responses to sucrose, quinine, and NaCl during early development. Pregnant dams were undernourished by being given 50% of a balanced diet from G6 to G12, 60% from G13-G18, and 100% from G19-G21. On postpartum days 0 - 9, prenatally underfed (UG) pups continued the undernourishment by remaining for 12 h with a foster dam and 12 h with a nipple-ligated mother. Stimuli were presented as a single droplet of sucrose (S), sodium chloride (NaCl), quinine hydrochloride (Q), and water (W) onto the lips at 1, 3, 5, 7, and 9 days of age, and mouth-opening frequency (MO) and lip-licking frequency (LL) were analyzed. The results show consistent effects associated with age, but not with diet, except in the cases of 0.01 M Q, which provoked in the UG subjects increased MO and the reduction of LL, and 0.1 M Q, which consistently reduced both responses. Moreover, S provoked increases in both MO and LL at 0.1 M while NaCl and water elicited minimal effects on GFR. These data suggest that perinatal undernutrition affects the basic components of the gustatory system necessary to produce GFR in the first postnatal days by possibly interfering with the integration of taste input for food learning and the hedonic aspects of gustatory cues.

Olfactory Discrimination in Adult Male Rats Undernourished during the Pre- and Neonatal Period

In the neonatal rat, the olfactory system is a fundamental channel to locate and recognize the mother, to survive and develop early social behavior, and to distinguish related or unrelated members of a litter. Perinatal undernutrition in rats alters the neuronal organization and functioning of the olfactory system and its ascending relays, possibly affecting odor discrimination. In this study we compared the frequency and time spent visiting the source of urine obtained from unrelated female subjects and amyl acetate odors vs water in adult perinatally underfed rats. Each test initiated with one daily presentation during three consecutive aliquots of deionized water (10 μl) placed on a filter paper for 2 min, separated by 1-min intervals for habituation. The water presentations were followed by three exposures to an odor, all at the same dilution (either 1:1 or 1:80) for dishabituation. Control (C) and undernourished (U) subjects display similar, significant habituation/dishabituation responses, except that the U subjects showed greater increases in the frequency and duration of visits to undiluted and diluted urine and amyl acetate cues compared to the controls. These findings are similar to previous studies showing that adult rats investigate novel odors longer than the familiar ones. Thus, perinatal undernutrition appears to interfere with the foundation of the olfactory development causing long-term olfactory discrimination deficits as revealed by the increased frequency and duration of visits to the source of odors that may be relevant for social behavior.

Parabrachial neuron development: Effects of pre- and neonatal undernutrition in the rat

Pre-and neonatal fasting in the rat has been used as an experimental model to obtain information on how the newborn gustatory system can be damaged, in- terfering with the basic sensory and hedonic proc- esses to different tastants. Fasting during the prenatal period and for 24 days postnatally results in signifi- cant reductions of body and brain weight, number of branches, dendritic density, and cross-sectional area of the PBN multipolar neurons in the central lateral and central medial subnucleus particularly at post- natal days 20 and 30. Furthermore, the underfeeding paradigm affected more the middle portions of the dendritic tree than other parts of the neurons possibly disturbing the afferent characteristics of neuronal acti- vity propagation that may partly disrupt the elabora- tion of synaptic plasticity at later ages. These findings may play a role in the development of complex physio- logical phenomena such as food intake, taste discrimi- nation, learning taste aversion, and appetitive beha- vior.