Manuel Salas

Assessing pain threshold in the rat: Changes with estrus and time of day

Pain threshold was determined in female rats using the tail flick test. Latency to respond depended on the locus of the tail heated, with the most distal sites resulting in the shortest response times (Experiment 1). Tail flick latency also varied according to the time of day, with shorter response times recorded around the middle of the dark phase than near its beginning or after its end. This was the case for intact, for ovariectomized, and for ovariectomized, estradiol-treated rats (Experiment 2). However, response times also varied across the estrous cycle, with significantly shorter latencies recorded during estrus and metestrus. Ovariectomy abolished these fluctuations, and whereas administration of estradiol increased response times, progesterone had little effect (Experiment 3). These results suggest that site of tail heating, time of day, and presence of ovarian hormones can influence tail flick latency independently, thus demonstrating the complexity of the mechanisms that may contribute to pain threshold even within the same paradigm.

Effects of neonatal food deprivation on cortical spines and dendritic development of the rat

Abstract The large cortical pyramidal cells of layer V of the frontal and occipital areas have been examined with Golgi staining in normal and malnourished infant rats. The number of spines, the basilar dendritic density and the dendritic thickness were significantly reduced in the group of starved rats. The functional significance of these findings is discussed in relation to other morphological and electrophysiological changes in cortical structures, and their possible implications upon the physiological integrative processes of the CNS at later ages in life.

An ontogenetic study of olfactory bulb electrical activity in the rat

Abstract In studies designed to assess the role of olfaction in infant rat behavior, it was first found necessary to obtain normative data on the development of electrical activity of the olfactory bulb. This was compared with the development of the EEG in the visual cortex. Frequency distribution histograms were obtained for each age group by means of computer averaging of sampled sections from each record. In the visual cortex adult patterns are reached by about the 12th postnatal day, while adult olfactory bulb activity is not present until about day 24. At all developmental ages, olfactory bulb activity is faster than that observed for the visual cortex.

Neonatal Undernutrition and Amygdaloid Nuclear Complex Development: An Experimental Study in the Rat

This study describes the morphology of neurons from the basolateral (ABL), central (ACE), and medial (AM) nuclei of the amygdaloid complex in neonatally undernourished (U) and control (C) Wistar strain rats. The cells were impregnated with the Golgi-Cox technique and studied at the ages of 12, 20, and 40 days postnatally. In the U-pups the neurons of the three nuclei displayed a reduced somatic area compared to that of the C-group on Days 12 and 20. However, at 40 days, this difference diminished due to a reduction in the somatic area of the C-group. The dendritic area also appeared reduced on Days 12 and 20 in the U-group, but on Day 40 it reached control values. The neurons from ABL and ACE suffered a significant decrease in the number of dendritic branches due to undernutrition, but the AM nucleus did not show this change. The data suggest different vulnerability of these amygdaloid nuclei to neonatal undernutrition. The findings also suggest that the abnormal emotional response characteristic of perinatal undernourished rats could have a morphological cause.

Effects of early malnutrition on the development of swimming ability in the rat.

Abstract The ontogeny of swimming ability was studied in normally fed and in chronically starved rats to assess the effect of early malnutrition on CNS development. Swimming tests were performed on adult and infant rats from 4–30 days old in an aquarium. Scoring according to position of the nose and movement of front legs. Maturation of swimming performance was delayed 2–3 days in the chronically starved rats as compared to controls. The high sensitivity of nervous tissue during critical periods of maturation and the relationship between malnutrition and the development of some patterns of movement during swimming are considered.

Effect of estrogen on the responsivity of hypothalamic and mesencephalic neurons in the female cat

Summary The responsivity of hypothalamic and mesencephalic neurons to somatic, visual, acoustic and vaginal stimulation was studied in ovariectomized (anestrous) and estrogen-treated ovariectomized conscious cats (estrous) immobilized with Flaxedil. Comparison between the results obtained in the two groups revealed that in the anterior and medial hypothalamus estrogen facilitated the appearance of excitatory responses to all the types of stimulus used, whereas it reduced the number of inhibitory responses to vaginal stimulation. Excitatory responses to all sensory modalities clearly predominated over inhibitory ones in the mesencephalic reticular formation of anestrous cats. By contrast, a marked increased in the proportion of inhibitory responses, particularly to vaginal stimulation, was observed in estrous subjects. Our results suggest that estrogen affects differentially the responsivity of hypothalamic and mesencephalic neurons to peripheral stimulation.

Long-term alterations in the maternal behavior of neonatally undernourished rats.

The effect of early food and sensory deprivation on the maternal responsiveness of female rats was investigated. Animals that were neonatally undernourished by daily mother-litter separation (involving both food and sensory deprivation) showed significant deficits in maternal care, consisting of a reduction in nest rating, nursing time, and retrieving responses. Moreover, they exhibited exaggerated grooming and circling movements in comparison with the controls. Dams neonatally undernourished by the nipple-ligation of their mothers (a method that minimizes sensory deprivation) displayed less alterations in maternal behavior, and no significant differences in grooming and circling from the controls. The data suggest that nest rating, nursing time, and retrieving latency are closely related to food restriction, while the frequency of grooming and circling behavior are primarily associated with sensory deprivation. These results support the view that environmental influences related to food intake and sensory stimulation, interacting at critical stages of brain development, are essential for the maturation of adult behavioral patterns.

Nutritional influences upon somatosensory evoked responses during development in the rat.

Abstract Taking the evoked responses as indicators of CNS maturation, the effects of neonatal starvation on cortical evoked activity were studied in rats at different ages during development. Early malnutrition delayed the electrophysiological development of both primary and secondary responses, with the effects upon the secondary slow potentials being more severe than on the primary responses. These data suggest a differential effect of malnutrition upon the projecting system to the neocortex. The possible connection of these results with impaired nervous and mental processes following early malnutrition are discussed.

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

Abstract 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.

Retrieving of Pups by Neonatally Stressed Mothers

Abstract 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.