Dendritic morphology and orientation of pyramidal cells of the neocortex in two groups of early postnatal undernourished-rehabilitated rats

Late-emerging effects of perinatal undernutrition in neuronal limbic structures underlying the maternal response in the rat

Maternal care in the rat is an ancient behavioral response to specific multisensory inputs widely integrated in a complex forebrain, limbic and brain stem network to meet the basic needs of the young. Early undernutrition interferes with the morphofunctional organization of the brain, including maternal circuitry. The late-emerging effects of pre- and neonatal undernutrition on nest building and pup retrieval by lactating Wistar rats were correlated with dendritic arbor and perikaryon measurements (Golgi-Cox) in layer II pyramidal neurons of the anterior cingulate cortex, layer III pyramidal neurons of the medial prefrontal cortex and multipolar basolateral amygdala neurons examined on lactation days 4 and 12. In the underfed group, pregnant F0 dams received different percentages of a balanced diet. After birth, prenatally underfed (F1) pups continued the undernutrition by remaining with a nipple-ligated mother for 12 h. Weaning occurred at 25 days of age, and pups were subsequently provided an ad libitum diet. At 90 days of age, F1 dams were maternally tested. Early underfed dams showed significant reductions in nest building and prolonged retrieval latencies for grasping pups by inappropriate body areas. The behavioral alterations were concurrent with highly significant reductions in the somatic cross-sectional area and perimeter, spine density and dendritic crossings of cingulate cells and medial prefrontal cortical pyramids, as well as smaller effects on amygdala neurons. The anatomical findings suggest different postsynaptic organizations that may affect the neuronal excitability stages for the integration and encoding of cues triggering the altered maternal response components of early underfed dams.

The implication of protein malnutrition on cardiovascular control systems in rats

The malnutrition in early life is associated with metabolic changes and cardiovascular impairment in adulthood. Deficient protein intake-mediated hypertension has been observed in clinical and experimental studies. In rats, protein malnutrition also increases the blood pressure and enhances heart rate and sympathetic activity. In this review, we discuss the effects of post-weaning protein malnutrition on the resting mean arterial pressure and heart rate and their variabilities, cardiovascular reflexes sensitivity, cardiac autonomic balance, sympathetic and renin-angiotensin activities and neural plasticity during adult life. These insights reveal an interesting prospect on the autonomic modulation underlying the cardiovascular imbalance and provide relevant information on preventing cardiovascular diseases.

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.

Physiological slowing and upregulation of inhibition in cortex are correlated with behavioral deficits in protein malnourished rats

Protein malnutrition during early development has been correlated with cognitive and learning disabilities in children, but the neuronal deficits caused by long-term protein deficiency are not well understood. We exposed rats from gestation up to adulthood to a protein-deficient (PD) diet, to emulate chronic protein malnutrition in humans. The offspring exhibited significantly impaired performance on the 'Gap-crossing' (GC) task after reaching maturity, a behavior that has been shown to depend on normal functioning of the somatosensory cortex. The physiological state of the somatosensory cortex was examined to determine neuronal correlates of the deficits in behavior. Extracellular multi-unit recording from layer 4 (L4) neurons that receive direct thalamocortical inputs and layers 2/3 (L2/3) neurons that are dominated by intracortical connections in the whisker-barrel cortex of PD rats exhibited significantly low spontaneous activity and depressed responses to whisker stimulation. L4 neurons were more severely affected than L2/3 neurons. The response onset was significantly delayed in L4 cells. The peak response latency of L4 and L2/3 neurons was delayed significantly. In L2/3 and L4 of the barrel cortex there was a substantial increase in GAD65 (112% over controls) and much smaller increase in NMDAR1 (12-20%), suggesting enhanced inhibition in the PD cortex. These results show that chronic protein deficiency negatively affects both thalamo-cortical and cortico-cortical transmission during somatosensory information processing. The findings support the interpretation that sustained protein deficiency interferes with features of cortical sensory processing that are likely to underlie the cognitive impairments reported in humans who have suffered from prolonged protein deficiency.

Differential effects of undernourishment on the differentiation and maturation of rat enteric neurons

The colocalization, number, and size of various classes of enteric neurons immunoreactive (IR) for the purinergic P2X2 and P2X7 receptors (P2X2R, P2X7R) were analyzed in the myenteric and submucosal plexuses of control, undernourished, and re-fed rats. Pregnant rats were exposed to undernourishment (protein-deprivation) or fed a control diet, and their offspring comprised the following experimental groups: rats exposed to a normal diet throughout gestation until postnatal day (P)42, rats protein-deprived throughout gestation and until P42, and rats protein-deprived throughout gestation until P21 and then given a normal diet until P42. Immunohistochemistry was performed on the myenteric and submucosal plexuses to evaluate immunoreactivity for P2X2R, P2X7R, nitric oxide synthase (NOS), choline acetyltransferase (ChAT), calbindin, and calretinin. Double-immunohistochemistry of the myenteric and submucosal plexuses demonstrated that 100% of NOS-IR, calbindin-IR, calretinin-IR, and ChAT-IR neurons in all groups also expressed P2X2R and P2X7R. Neuronal density increased in the myenteric and submucosal plexuses of undernourished rats compared with controls. The average size (profile area) of some types of neurons in the myenteric and submucosal plexuses was smaller in the undernourished than in the control animals. These changes appeared to be reversible, as animals initially undernourished but then fed a normal diet at P21 (re-feeding) were similar to controls. Thus, P2X2R and P2X7R are present in NOS-positive inhibitory neurons, calbindin- and calretinin-positive intrinsic primary afferent neurons, cholinergic secretomotor neurons, and vasomotor neurons in rats. Alterations in these neurons during undernourishment are reversible following re-feeding.

Malnutrition during central nervous system growth and development impairs permanently the subcortical auditory pathway

The brain that grows and develops under the continued influence of malnutrition presents permanent impairment on functioning and neurotransmitter release. The aim of this study was to investigate the chronic effects of neonatal food restriction on neurochemical and neurodynamical aspects within the primary auditory sensory pathway. Our working hypothesis is that neonatal malnutrition may affect the flow of primary sensory information both at a neurochemical and neurodynamical level. To test this hypothesis, three groups of rats were assigned, from birth to 370 days of life, to the following dietary scheme: a well-nourished (WN) group fed ad libitum lab chow diet; an undernourished (UN) group fed 60% of diet consumed by WN group; and a rehabilitated group, undergoing same dietary restriction as undernourished until 42 days of age and thereafter fed ad libitum until the end of the experiment. At 370 days of age, the animals were submitted to brainstem auditory-evoked potentials (BAEPs) recordings and sacrificed for neurochemical evaluation of glutamate release. Undernutrition decreased glutamate release in the cortex, hippocampus, midbrain and brainstem, and significantly increased the latency of BAEP wave V. In addition; the re-establishment of the dietary conditions was not sufficient to reverse the neurochemical and electrophysiological alterations observed in the UN group. Taken altogether, our results suggest that malnutrition imposed at a critical development period caused an irreversible effect within the auditory primary sensory pathway.

Effects of prenatal protein malnutrition on the electrical cerebral activity during development

Early protein restriction during the prenatal period has significant repercussions on the ontogeny and development of the central nervous system. The present study investigates whether early prenatal protein malnutrition could alter the electrical cerebral activity of the progeny. We used Sprague-Dawley female rats of 200 g randomly divided into three groups: a control group that received a diet with 25% of the protein content (lactalbumin), the experimental group, that received a diet with 6% of the protein content and the rehabilitated group that initially received a diet with 6% of the protein content, then switched to a diet with 25% of the protein content after the weaning period (P20D) up to 60 days of life (P60D). Reduction of the protein content from 25% to 6% of lactalbumin in the diet of pregnant rats produces impairment in the electrical cerebral activity in the progeny at P20D and at P60D. The power spectral analysis for each one of the electroencephalograms revealed that prenatal protein malnutrition in rats produced a significant reduction of the alpha (8-13 Hz) and the beta bands (13-30 Hz) and a significant increase of the theta (4-8 Hz), and delta bands (1-4 Hz), at two different stages of life (P20D and P60D). Similar results were obtained for the rehabilitated group. These results indicate that early malnutrition in life affects the ontogeny of the electrical cerebral activity. This insult probably disrupts the establishment of cortical neural circuits during the critical period of brain development. The rehabilitation period did not revert the impairment in the electrical cerebral activity produced by malnutrition. We used one-way ANOVA analysis, followed by Tukey test (*p<0.001).

Effects of perinatal protein deprivation and recovery on esophageal myenteric plexus

AIM: To evaluate effects of pre- and postnatal protein deprivation and postnatal recovery on the myenteric plexus of the rat esophagus.

METHODS: Three groups of young Wistar rats (aged 42 d) were studied: normal-fed (N42), protein-deprived (D42), and protein-recovered (R42). The myenteric neurons of their esophagi were evaluated by histochemical reactions for nicotinamide adenine dinucleotide (NADH), nitrergic neurons (NADPH)-diaphorase and acetylcholinesterase (AChE), immunohistochemical reaction for vasoactive intestinal polypeptide (VIP), and ultrastructural analysis by transmission electron microscopy.

RESULTS: The cytoplasms of large and medium neurons from the N42 and R42 groups were intensely reactive for NADH. Only a few large neurons from the D42 group exhibited this aspect. NADPH detected in the D42 group exhibited low reactivity. The AChE reactivity was diffuse in neurons from the D42 and R42 groups. The density of large and small varicosities detected by immunohistochemical staining of VIP was low in ganglia from the D42 group. In many neurons from the D42 group, the double membrane of the nuclear envelope and the perinuclear cisterna were not detectable. NADH and NADPH histochemistry revealed no group differences in the profile of nerve cell perikarya (ranging from 200 to 400 μm²).

CONCLUSION: Protein deprivation causes a delay in neuronal maturation but postnatal recovery can almost completely restore the normal morphology of myenteric neurons.

The effects of dietary protein restriction on chorda tympani nerve taste responses and terminal field organization

Prenatal dietary sodium restriction produces profound developmental effects on rat functional taste responses and formation of neural circuits in the brainstem. Converging evidence indicates that the underlying mechanisms for these effects are related to a compromised nutritional state and not to direct stimulus-receptor interactions. We explored whether early malnourishment produces similar functional and structural effects to those seen following dietary sodium restriction by using a protein deficient, sodium replete diet. To determine if early dietary protein-restriction affects the development of the peripheral gustatory system, multi-fiber neurophysiological recordings were made from the chorda tympani nerve and anterograde track tracing of the chorda tympani nerve into the nucleus of the solitary tract (NTS) was accomplished in rats fed a protein-restricted or a control diet (6% and 20%, respectively). The dietary regimens began on embryonic day 7 and continued until rats were used for neurophysiological recordings (postnatal days (P) 35-50) or for chorda tympani terminal field labeling (P40-50). Responses to a concentration series of NaCl, sodium acetate, KCl, and to 0.50 M sucrose, 0.03 M quinine-HCl, and 0.01 N HCl revealed attenuated responses (30-60%) to sodium-specific stimuli in rats fed the 6% protein diet compared with those fed the 20% protein diet. Responses to all other stimuli were similar between groups. Terminal field volumes were nearly twofold larger in protein-restricted rats compared with controls, with the differences located primarily in the dorsal-caudal zone of the terminal field. These results are similar to the results seen previously in rats fed a sodium-restricted diet throughout pre- and postnatal development, suggesting that dietary sodium- and protein-restriction share similar mechanisms in altering gustatory development.

Protein malnutrition differentially alters the number of glutamic acid decarboxylase-67 interneurons in dentate gyrus and CA1–3 subfields of the dorsal hippocampus

In 30- and 90-day-old rats, using immunohistochemistry for glutamic acid decarboxylase 67 (GAD-67), we have tested whether malnutrition during different periods of hippocampal development produces deleterious effects on the population of GABA neurons in the dentate gyrus (DG) and cornu Ammonis (CA1-3) of the dorsal hippocampus. Animals were under one of four nutritional conditions: well-nourished controls (Con), prenatal protein malnourished (PreM), postnatal protein malnourished (PostM), and chronic protein malnourished (ChroM). We found that the number of GAD-67-positive (GAD-67+) interneurons was higher in the DG than in the CA1-3 areas of both Con and malnourished groups. Regarding the DG, the number of GAD-67+ interneurons was increased in PreM and PostM and decreased in ChroM at 30 days. At 90 days of age the number of GAD-67+ interneurons was increased in PostM and ChroM and remained unchanged in PreM. With respect to CA1-3, the number of labeled interneurons was decreased in PostM and ChroM at 30 days of age, but no change was found in PreM. At 90 days no changes in the number of these interneurons were found in any of the groups. These observations suggest that 1) the cell death program starting point is delayed in DG GAD-67+ interneurons, and 2) protein malnutrition differentially affects GAD-67+ interneuron development throughout the dorsal hippocampus. Thus, these changes in the number of GAD-67+ interneurons may partly explain the alterations in modulation of dentate granule cell excitability, as well as in the emotional, motivational, and memory disturbances commonly observed in malnourished rats.

Effects of pre- and postnatal protein deprivation and postnatal refeeding on myenteric neurons of the rat small intestine: a quantitative morphological study

We investigated weight gain, the size of the small intestine and numbers and sizes of enteric neurons in rats whose mothers had been deprived of protein during pregnancy and who themselves were deprived postpartum. Postnatally, protein deprivation was for 42 days, or for 21 days with refeeding for a further 21 days. Control animals received normal nourishment. Neurons were located by nicotinamide adenine dinucleotide (NADH) diaphorase staining, by acetylcholinesterase (AChE) activity and immunoreactivity for choline acetyltransferase (ChAT). The collagen and elastic fibers in the myenteric ganglia were evaluated histologically. The myenteric ganglia were regular and uniform in the nourished and refed groups. In the undernourished group, the myenteric ganglia were irregularly arranged and the cytoplasm of most of the neurons showed less intense staining for NADH diaphorase, AChE and ChAT. AChE activity and ChAT immunoreactivity showed that most ganglionic neurons were stained in nourished and refed groups, but the neurons of undernourished rats were unstained or moderately stained. The distribution of the connective tissue of the ganglionic capsule was similar in the three groups. There was a decrease in weight of undernourished rats, which was restored in refed rats. The size of the small intestine of the undernourished group was smaller than in the normally fed group, by about 45%, but it was similar in nourished and refed rats. After 42 days of protein deprivation the numbers of neurons that were revealed by NADH diaphorase were fewer than in well nourished rats, but numbers were not different between nourished and refed rats. These observations indicate that protein deprivation alters histological features and acetylcholinesterase activity of neurons and also reduces body weight but these were restored by refeeding.

Undernutrition and food rehabilitation effects on the locus coeruleus in the rat

Perinatal nutrition plays a fundamental role on the morphological organization and function of a number of brain stem structures. Because little is known of the effects of perinatal undernutrition upon sexually dimorphic structures underlying reproductive behavior, the locus coeruleus morphology of 60-day-old male and female Wistar rats was analyzed. Perinatal food deprivation until weaning significantly decreased the volume and neuronal number of locus coerulus in male and female rats, while nutritional rehabilitation ameliorated these alterations in males but not in females. Data suggest that perinatal undernutrition interferes with the neuroendocrine mechanisms underlying the establishment of sex differences of the locus coeruleus.

Perinatal iron deficiency alters apical dendritic growth in hippocampal CA1 pyramidal neurons

Iron deficiency early in life is associated with cognitive disturbances that persist beyond the period of iron deficiency. Within cognitive processing circuitry, the hippocampus is particularly susceptible to insults during the perinatal period. During the hippocampal growth spurt, which is predominantly postnatal in rodents, iron transport proteins and their messenger RNA stabilizing proteins are upregulated, suggesting an increased demand for iron import during this developmental period. Rat pups deprived of iron during the perinatal period show a 30-40% decrease in hippocampal metabolic activity during postnatal hippocampal development. We hypothesized that this reduced hippocampal neuronal metabolism impedes developmental processes such as neurite outgrowth. The goals of the current study were to investigate the effects of perinatal iron deficiency on apical dendritic segment growth in the postnatal day (P) 15 hippocampus and to determine if structural abnormalities persist into adulthood (P65) following iron treatment. Qualitative and quantitative immunohistochemical analyses of dendritic structure and growth using microtubule-associated protein-2 as an index showed that iron-deficient P15 pups have truncated apical dendritic morphology in CA1 and a persistence of an immature apical dendritic pattern at P65. These results demonstrate that perinatal iron deficiency disrupts developmental processes in the hippocampal subarea CA1 and that these changes persist despite iron repletion. These structural abnormalities may contribute to the learning and memory deficits that occur during and following early iron deficiency.