Effects of undernutrition during suckling on novelty-induced analgesia in young and adult rats

The effects of undernutrition on novelty-induced analgesia were investigated in young and adult rats. Rats were undernourished by feeding their dams an 8% casein diet from birth until weaning (21 days of age). Rats were exposed to an open field (novelty) for 2 min and the nociception was measured by the tail-flick method. At adult age, only well-nourished rats presented novelty-induced analgesia, suggesting that early undernutrition abolishes this response. At 21 days of age, the exposure to the open field had no effect on nociception of both nutritional groups, suggesting that some developmental factor is necessary for the emergence of novelty-induced analgesia.     

The compensatory role of food-motivation in the maze learning performance of lactationally undernourished rats.

To test the hypothesis that the motivational effects of neonatal undernutrition might conceal the detrimental effects on learning, we tested previously undernourished and normally nourished Sprague-Dawley rats on learning of a novel maze pattern under either latent learning (nonappetitive) or food-motivated conditions. Under the nonappetitive conditions, the previously undernourished rats learned significantly less than the normal controls, but when motivated for food, the undernourished rats performed as well as the controls. When learning performance measures are sensitive to motivation, differential motivation between undernourished and normal subjects must be controlled or eliminated.     

Deficits in spatial memory performance induced by early undernutrition

Recent studies have shown that rats have a remarkable ability to keep track of their spatial location. Explanations stress the involvement of a form of short-term (working) memory in which the hippocampus appears to play a major role. The hippocampus appears to be vulnerable to early undernutrition and preliminary investigations indicate that Areas CA3 and CA4 suffer the most. Ninety-day-old rats, previously undernourished prenatally and throughout lactation, were tested in an 8- and, then, a 16-arm radial maze. Significant differences were observed between the experimental and control groups on both tests, especially in the 16-arm maze. Error distributions were also significantly different with experimental animals tending to perseverate in 1 area of the maze. Differences were also observed in the time taken to make the choices and in exploratory behavior. We conclude that early undernutrition affected the spatial learning ability of the animals and that this may be due to the distortions observed in the normal growth pattern of the hippocampus.     

Postpubertal feeding experience affects sex-specific spatial ability in rats

We previously reported that feeding with powdered diet after weaning (3 weeks of age) enhanced spatial ability, and increased the amount of acetylcholine (ACh) released in the dorsal hippocampus in female rats. In the present study, to specify the time when feeding conditions caused these effects, a radial 8-arm maze task and an in vivo microdialysis study were performed in both sexes of rats. In rats fed standard laboratory diet (i.e., pelleted diet), males learned the radial 8-arm maze faster than females. Moreover, the ACh release showed a distinct diurnal rhythm which was high during the dark phase and low during the light phase, but males showed a greater amount of ACh released in the dorsal hippocampus than females. However, in rats fed powdered diet after 6 weeks of age, no significant sex differences were observed in the radial 8-arm maze task or in the amount of ACh released, since feeding with powdered diet enhanced spatial ability, and increased the amount of ACh released only in females. These results suggest that feeding conditions after 6 weeks of age may contribute to the sex difference in the spatial ability associated with the changes in the amount of ACh released in the dorsal hippocampus in rats.     

Behavioral effects of severe and moderate early malnutrition

Rats with a history of prenatal and early postnatal undernutrition (6 or 8% casein diets) were "nutritionally rehabilitated" at weaning, and were compared to well-fed animals (25% casein) at maturity. The severely-malnourished (6%) animals were hyperactive in the open field and when tested in a stabilimeter. They also appeared to be highly active during the early trials in 8-arm radial maze testing where they made more arm entries and re-entry errors than the well-fed rats. In terms of trials to criterion, however, their scores on the radial maze and on a spatial alternation task fell within normal limits. The moderately-malnourished (8%) rats tended to perform at control levels on the learning measures, but these rats were not as active as the 6% rats on the measures of activity. Brain size and weight differences among the three groups of rats also are presented and discussed.     

Fetal undernutrition induces overexpression of CRH mRNA and CRH protein in hypothalamus and increases CRH and corticosterone in plasma during postnatal life in the rat

Prenatal undernutrition induces a variety of cardiovascular alterations in mammals when adults, including hypertension and hypercortisolism, which are thought to be caused by decreased glucocorticoid feedback control of the hypothalamus–pituitary–adrenal (HPA) axis programmed during fetal life. Hypothalamic CRH seems to be involved in blood pressure elevation of spontaneously hypertensive rats and in primary hypertension of humans, but the influence of prenatal undernutrition on CRH expression has deserved little attention. Here, we studied the expression of both CRH mRNA and CRH protein in the hypothalamus of neonatal and juvenile offspring of rats undernourished during fetal life, as well as the plasma levels of CRH and corticosterone. Prenatal undernutrition of pups was induced by submitting pregnant rats to diet restriction (10 g daily of 21% protein standard laboratory diet). Pups born from dams with free access to the standard laboratory diet served as controls. At day 2 of postnatal age, undernourished pups showed lower body and brain weights, but higher plasma CRH and corticosterone than normal pups. At day 40 of age, brain weight was significantly decreased in the undernourished rats, while plasma corticosterone, plasma CRH and systolic pressure were significantly increased in these animals. At days 2 and 40 of postnatal age, increased CRH mRNA expression and CRH concentration were found in the hypothalamus of undernourished rats. Results indicate that, in the rat, prenatal undernutrition led to fetal programming of CRH overexpression, a neuropeptide serving as activating signal to the HPA axis and/or to extrahypothalamic brain regions concerned with cardiovascular regulation.     

Emotional, cognitive and neurochemical alterations in a premotor stage model of Parkinson's disease

In addition to classic motor symptoms, Parkinson's disease (PD) is characterized by cognitive and emotional deficits, which have been demonstrated to precede motor impairments. The present study addresses the question of whether a partial degeneration of dopaminergic neurons using 6-hydroxydopamine (6-OHDA) in rats is able to induce premotor behavioral signs. The time-course of nigrostriatal damage was evaluated by tyrosine hydroxylase immunohistochemistry and the levels of dopamine, noradrenaline, and 5-HT in various brain regions were analyzed by high performance liquid chromatography (HPLC). Behavioral tests that assessed a variety of psychological functions, including locomotor activity, emotional reactivity and depression, anxiety and memory were conducted on 6-OHDA lesioned rats. Bilateral infusion of 6-OHDA in the striatum of rats caused early (1 week) damage of dopaminergic terminals in striatum and in cell bodies in substantia nigra pars compacta. The nigrostriatal lesion was accompanied by early loss of dopamine in the striatum, which remained stable through a 3-week period of observation. In addition, a late (3 weeks) loss of dopamine in the prefrontal cortex, but not in the hippocampus, was seen. Additional noradrenergic and serotonergic alterations were observed after 6-OHDA administration. The results indicated that 6-OHDA lesioned rats show decreased sucrose consumption and an increased immobility time in the forced swimming test, an anhedonic-depressive-like effect. In addition, an anxiogenic-like activity in the elevated plus maze test and cognitive impairments were observed on the cued version of the Morris water maze and social recognition tests. These findings suggest that partial striatal dopaminergic degeneration and parallel dopaminergic, noradrenergic and serotonergic alterations in striatum and prefrontal cortex may have caused the emotional and cognitive deficits observed in this rat model of early phase PD.     

Parietal and frontal object areas underlie perception of object orientation in depth

Attention deficit/hyperactivity disorder (ADHD) is a developmental disorder of cognition. Behavioral symptoms of ADHD are inattention, hyperactivity, and impulsivity. We investigated the effects of treadmill exercise and methylphenidate (MPH) on activity and spatial learning memory in relation to dopamine synthesis and brain-derived neurotrophic factor (BDNF) expression using spontaneously hypertensive adult male rats. The rats in the MPH-treated group received 1 mg/kg MPH orally once a day for 28 days. The rats in the treadmill exercise group were made to run on a treadmill for 30 min once a day, five times a week, for 28 days. Activity was determined by an open-field test and spatial learning memory was evaluated by an 8-arm maze test. Immunohistochemistry and Western blotting were conducted to examine the levels of tyrosine hydroxylase (TH), the rate-limiting enzyme in the synthesis of dopamine, and BDNF. The rats in the ADHD group showed hyperactivity and spatial learning memory deficit. Reduction of TH in the striatum and substantia nigra and BDNF in the hippocampus was observed of the rats in the ADHD group. Treadmill exercise and MPH alleviated the ADHD-induced hyperactivity and spatial learning memory impairment. Expressions of TH and BDNF in the ADHD rats were also increased by both treadmill exercise and MPH. These findings provide a possibility that exercise may be used as an effective therapeutic intervention for ADHD patients as MPH treatment.     

Social behaviour of rats following pre- and early postnatal undernutrition

The social behaviour of adult male rats which had been undernourished at some stage before weaning was investigated. Litters were cross-fostered at birth between well fed and underfed dams. Thus, some were undernourished only during gestation, others only during the suckling period and others throughout both periods. After weaning all animals had free access to food and were grouped with two or three littermates. Each adult previously undernourished rat was allocated its own control partner which had been well fed throughout life. Four measures of social interaction were recorded during five 10 min tests. Postnatal undernutrition increased the frequency of allogroom and walk over and pre with postnatal undernutrition had a similar effect. Rearing and mount were unaffected by either treatment. Prenatally growth restricted rats did not differ from controls on any measure. Thus, adult social behaviour was more affected by the postnatal than by the prenatal experience. In another experiment smaller control rats were found not to differ in their social behaviour from larger control rats, indicating that size is not an important factor in these studies.     

Spatial learning ability of rats undernourished during early postnatal life.

Experiments to determine whether undernutrition during early life results in deficits in spatial learning behavior has produced conflicting results. It was hypothesized that this may be due to the differing degrees of undernutrition used in the various studies, and/or to the timing of the testing procedures with respect to the period of food deprivation. These possibilities were tested by undernourishing rats between birth and 30 days of age to two different levels (i.e., level-1 and level-2). The degree of undernutrition was greater at level-2 than level-1. Behavioral testing of these rats and well-fed controls was carried out in the Morris water maze when they were between either 35 and 65 or 170 and 200 days of age. Statistical analyses of the escape latency data from these experiments revealed that rats tested almost immediately after the period of undernutrition have alterations in their spatial learning behavior compared with controls. However, even a short period of nutritional rehabilitation removed any differences between control and previously undernourished groups, irrespective of the level of undernutrition.     

The effects of early stress and undernutrition on the behavior of young adult rats and the correlations between behavioral and brain parameters.

Control and chronic undernourished newborn rat pups were exposed to cold stress for 3 min daily or left undisturbed on Days 2–11. On Days 25–29 (preweaning) and at 90 days of age, stressed and non-stressed pups in each group were tested in a cross-maze and a T-maze, and their preference for novel and social stimulation and activity levels were measured. At 90 days only, another group of such pups was trained to learn an active avoidance response to electric shock. The results on maze performance show that prior to weaning, stressed controls (SC) and nonstressed undernourished (NSU) pups exhibited shorter response latencies, and a greater preference for social stimulation than the non-stressed controls (NSC). At 90 days, SC and NSU again exhibited shorter latencies, and higher activity levels, and also a greater preference for novel stimulation than the NSC animals. In these parameters, there were no significant differences between stressed undernourished (SU) and NSU animals. In original avoidance learning, undernourished animals exhibited a slower rate of acquisition learning than controls. However, in reversal learning, NSU animals made significantly more errors than the SU animals. There were no significant differences between the two control groups and the SU group. These results show that early cold stress alone can have the same behavioral effects as early undernutrition alone and that early stress can have a significant reversing effect on the learning performance of previously undernourished adult animals. Statistical correlations between behavioral parameters (X- and T-maze behavior and active avoidance learning) and crude brain parameters (weight, cell number (DNA), cell density and protein) were investigated in the above animals. It was found that, in general, behavioral parameters whose high values appear to be of advantage for the animal (e.g. number of entries or social time in mazes and percent correct moves in the original and reversal learning) had significant positive correlations with weight, cell number (DNA), and protein content, at least in cerebral cortex and cerebellum, and negative correlations with cortical cell density. Conversely, parameters whose high values are of disadvantage (latency in mazes, or total trials to criterion and total errors in learning) generally had significant negative correlations with brain weight, cell number, and protein content, and positive with cortical cell density. Age, stress or undernutrition had no effect on these results. It is concluded that, statistically, even these crude brain parameters may be significantly correlated with behavior. That is, animals tend to perform better if their cortical cells are further apart and if their brain weight, cell number (DNA), and protein content are higher.     

Behavioral correlates of vitamin D deficiency

Rats deprived of vitamin D at weaning were compared to control rats on open field, stabilimeter, radial arm maze and spatial reversal tasks in order to test the hypothesis that vitamin D deficiency alters behavior and learning. The deficient animals engaged in statistically less open field rearing activity and spent more time each day negotiating the radial maze than did the control rats. These findings are consistent with the known influence of vitamin D on the musculoskeletal system. The deprived rats did not differ from the control animals on the learning measures. This would indicate that vitamin D deficiency may not significantly impair cognitive functions in young adult rats.     

Incidental learning is impaired during early-life undernutrition

Rats were either well-nourished (control) or undernourished (PU) during the suckling and early post-weaning periods (birth to 45 days), after which all animals were fed ad libitum. From 25 to 45 days half of the rats in each group were exposed continuously in their home cases to shape stimuli (triangles and circles). Half of each of these 4 groups were given "reminders" of the stimuli through exposure for 2 h every 10-12 days from 55 to 131 days. Beginning on day 132, ability to discriminate these same visual stimuli was tested using a nonappetitively motivated version of the Lashley jumping stand technique. Discrimination learning per se was unimpaired by previous undernutrition (control and PU rats not viewing the stimuli prior to training performed equally well). However, early-life exposure led to improved learning performance only in control rats; it had no effect on the performance of PU rats (significant exposure X nutrition interaction). These findings indicate that undernutrition interfered with early "incidental learning", that is, learning about features of the environment which are not, at the time, biologically relevant. Finally, retention of the discrimination was assessed 9 weeks after the rats had attained criterion performance. There were no effects of nutrition or prior exposure on long-term memory.     

Learning and memory impairment in adult rats due to severe zinc deficiency during lactation

In a series of three experiments, adult rats who suffered severe zinc deficiency and/or undernutrition during lactation were tested in a 17-arm radial maze for working memory, reference memory, forgetting and learning. In Experiment 1, eight out of 17 arms were baited. The zinc deficient (ZD) and undernourished (PF) rats revealed a learning deficit when compared to adequately nourished rats (AL). ZD rats also appeared to display a loss of working memory. No evidence of loss of reference memory was observed among any of the groups. A reverse learning procedure was used in Experiment 2 to test the same rats used in Experiment 1. ZD rats were significantly inferior in performance of the reverse learning task compared to the AL and PF rats. No significant differences in performance were noted between the AL and PF rats. Although all groups displayed forgetfulness from Experiment 1 to Experiment 2, no significant differences in forgetfulness were evidenced among the groups. In Experiment 3, all 17 arms were baited. The ZD rats displayed a significant working memory deficit as compared to the AL and PF rats. No significant differences in working memory between the AL and PF rats occurred. The possibility that the differences in performance were due to differences in food motivation or attention was considered and rejected. It was concluded that ZD rats experienced a severe learning deficit and some working memory deficit while the PF rats experienced a mild learning deficit as compared to the AL rats.     

Prenatal undernutrition decreases the sensitivity of the hypothalamo-pituitary-adrenal axis in rat, as revealed by subcutaneous and intra-paraventricular dexamethasone challenges

Prenatal undernutrition is known to disturb the hypothalamo-pituitary-adrenal (HPA) axis, possibly through the programming of decreased expression of hypothalamic and pituitary glucocorticoid receptors. To test this hypothesis, we examined the corticosterone response to moderate subcutaneous (100 microg/kg) and intra-paraventricular (50 pmol, bilaterally) dexamethasone (DEX) challenges in normal eutrophic and prenatally undernourished young rats. Undernutrition was induced during fetal life by restricting the diet of pregnant mothers to 10 g daily, while mothers of eutrophic rats received the same diet ad libitum. At day 40 of postnatal life (i) undernourished rats showed increased plasma corticosterone concentration compared to normals; and (ii) subcutaneous and intra-paraventricular administrations of DEX led to reduced corticosterone levels in normal and undernourished animals, the effect of DEX (administered either peripherally or centrally) being significantly lower in the latter group. Results suggest that the low sensitivity of the HPA axis to DEX as well as the increased plasma corticosterone observed in prenatally undernourished rats could be due to the already reported glucocorticoid receptor underexpression found in the hypothalamus and pituitary of in utero undernourished animals, but alternative explanations involving central noradrenergic adaptive changes could also be possible.     

Perinatal decortication impairs performance on an 8-arm radial maze task

Two experiments evaluate the role of the neocortex in rodent spatial learning. In Experiment 1, perinatally decorticated rats and sham-operated controls began ten training sessions at day 200 on an 8-arm radial maze. Decorticated rats made more errors than controls, but showed improvement by the tenth session. In the second experiment, training was extended to determine whether decorticates could eventually match control performance levels if given sufficient training. Spontaneous activity levels were also recorded and compared to maze performance to investigate the relationship between poor performance on the radial maze and activity. More than half of the decorticates reached criterion performance. Decorticates had significantly elevated spontaneous activity levels when compared to controls, and the magnitude of this hyperactivity was related to performance deficits on the radial maze. These results suggest that with extended training decorticates can learn a spatial task. Performance deficits may reflect the hyperactive tendency of decorticates rather than a specific impairment of spatial learning abilities.     

Effects of undernutrition and handling during suckling on shuttle avoidance and footshock escape behavior and on plasma glucose levels of young rats

The present report examined the effects of undernutrition and handling on shuttle and footshock escape avoidance behavior of female rats. Rats were undernourished by feeding their dams a 7% casein diet from birth until 23 days of life. During this period rats were separated from their dams for 4 to 10 min. On days 23 and 24 after delivery, young rats were subjected to sessions in a two-way shuttle avoidance task. The results demonstrated that nonstimulated and stimulated undernourished and stimulated well-nourished rats escape faster than nonstimulated well-nourished animals from footshock during the first session of shuttle avoidance. Further, undernutrition interacted with early stimulation, disrupting the shuttle avoidance behavior of female rats. These results suggest that both undernutrition and early handling can change the footshock behavior of young rats. Undernourished rats presented lower basal glucose levels than well-nourished animals, but responded to shuttle avoidance testing in the same way as do normal rats, increasing the glucose levels.     

Lipid peroxidation in developing rat brain during undernutrition

The effect of undernutrition has been studied in relation to lipid peroxidation, both in vitro and in vivo, in the brain of developing rats. Lipid peroxidation in brain homogenates as well as in the mitochondrial fraction of brain was significantly higher in undernourished groups than in controls. This difference was maximal at the 12th postnatal day. Following rehabilitation for two weeks, this increased lipid peroxidation in brains of undernourished rats could no longer be observed. Determination of malonaldehyde levels in vivo did not show an appreciable difference between control and undernourished animals.     

Maternal isobutyl-paraben exposure alters anxiety and passive avoidance test performance in adult male rats

Isobutyl-paraben (IBP), one of the most widely used preservatives, exhibits estrogenic activity. In this study, we analyzed the effects of maternal IBP treatment on the emotional behavior and learning performance in mature offspring. Pregnant female Sprague–Dawley rats were treated with IBP via a subcutaneous Silastic capsule. Consequently, the offspring were exposed to IBP during gestation through the placentae, and before weaning through the milk. Male and female offspring were tested for emotional behavior in an open field and in an elevated plus maze at five and six weeks old, respectively. IBP-exposed male (but not female) rats spent less time in the open arms of the elevated plus maze. At 11 weeks old, all females were gonadectomized and treated chronically with 17β-estradiol or cholesterol by Silastic capsules; all males were kept intact. They were tested for learning performance in a passive avoidance test and a Morris water maze. IBP exposure impaired the performance of males in the passive avoidance test. These findings suggest that male rats are more affected by early exposure to IBP than female rats. IBP affects their adult behavior including anxiety and learning abilities.     

Evidence of reorganization in the hippocampal mossy fiber synapses of adult rats rehabilitated after prolonged undernutrition

We have previously demonstrated that prolonged low-protein diet leads to irreversible cell loss in the hippocampal formation of the adult rat. Because the extent of the resulting hippocampal synaptic alterations is not well characterized, we studied the contacts between mossy fibers and the dendritic excrescences of CA3 pyramidal cells (MF-CA3 synapses) using quantitative methods. Moreover, we investigated whether rehabilitation from undernutrition would influence the morphology of hippocampal synapses. To address these issues, three groups of adult rats were compared: (a) rats fed with a normal diet for 12 months (control rats); (b) rats treated during the same period with low-protein diet (undernourished rats); and (c) rats undernourished for 6 months and then switched to normal diet for 6 months (recovery rats). Timm staining and electron microscopy were employed to estimate the volume of the mossy fiber system and the number and related quantitative features of MF-CA3 synapses. The volume of the suprapyramidal bundle of the mossy fiber system and its total number of synapses were smaller in undernourished rats than in control and recovery animals. These parameters did not differ between the latter two groups. The size of mossy fiber terminals and dendritic excrescences and the surface area of synapses were smaller in undernourished than in control and recovery groups. Conversely, in recovery animals, the volume of the suprapyramidal bundle of the mossy fiber system, the size of mossy fiber terminals and dendritic excrescences, and the total number and surface area of synapses were similar to those of controls. These findings indicate that, following rehabilitation, the pre- and postsynaptic compartments of MF-CA3 synapses undergo structural alterations which compensate for the neuronal loss induced by undernutrition.