Effects of prenatal protein malnutrition on kindling-induced alterations in dentate granule cell excitability. II. Paired-pulse measures

Prenatal protein malnutrition decreases neuron numbers in the parahippocampal region but not prefrontal cortex in adult rats

OBJECTIVE

Prenatal protein malnutrition produces anatomical and functional changes in the developing brain that persist despite immediate postnatal nutritional rehabilitation. Brain networks of prenatally malnourished animals show diminished activation of prefrontal areas and an increased activation of hippocampal regions during an attentional task [1]. While a reduction in cell number has been documented in hippocampal subfield CA1, nothing is known about changes in neuron numbers in the prefrontal or parahippocampal cortices.

METHODS

In the present study, we used unbiased stereology to investigate the effect of prenatal protein malnutrition on the neuron numbers in the medial prefrontal cortex and the cortices of the parahippocampal region that comprise the larger functional network.

RESULTS

Results show that prenatal protein malnutrition does not cause changes in the neuronal population in the medial prefrontal cortex of adult rats, indicating that the decrease in functional activation during attentional tasks is not due to a reduction in the number of neurons. Results also show that prenatal protein malnutrition is associated with a reduction in neuron numbers in specific parahippocampal subregions: the medial entorhinal cortex and presubiculum.

DISCUSSION

The affected regions along with CA1 comprise a tightly interconnected circuit, suggesting that prenatal malnutrition confers a vulnerability to specific hippocampal circuits. These findings are consistent with the idea that prenatal protein malnutrition produces a reorganization of structural and functional networks, which may underlie observed alterations in attentional processes and capabilities.

The enduring effect of prenatal protein malnutrition on brain anatomy, physiology and behavior

There is increasing evidence that the maternal environment exerts enduring influences on the fetal brain. In response to certain environmental stimuli such as reduced protein content, the fetus changes the course of its brain development, which leads to specific and programed changes in brain anatomy and physiology. These alterations produce a brain with a fundamentally altered organization, which then translates to alterations in adult cognitive function. The effects on brain and behavior may be linked, such that a prenatal stimulus relays a signal to alter brain development and encourage the selection and development of brain circuits and behaviors that would be beneficial for the environment in which the animal was anticipated to emerge. At the same time, the signal would deselect behaviors unlikely to be adaptive. We draw on evidence from rodent models to suggest that the brain that develops after a reduction in protein during the prenatal phase is not uniformly dysfunctional, but simply different. This perspective has implications for the role of prenatal factors in the production and expression of behavior, and may account for the elevation of risk factors for neurological and psychiatric illnesses.

Facts and hypotheses about the programming of neuroplastic deficits by prenatal malnutrition

Studies in rats have shown that a decrease in either protein content or total dietary calories results in molecular, structural, and functional changes in the cerebral cortex and hippocampus, among other brain regions, which lead to behavioral disturbances, including learning and memory deficits. The neurobiological bases underlying those effects depend at least in part on fetal programming of the developing brain, which in turn relies on epigenetic regulation of specific genes via stable and heritable modifications of chromatin. Prenatal malnutrition also leads to epigenetic programming of obesity, and obesity on its own can lead to poor cognitive performance in humans and experimental animals, complicating understanding of the factors involved in the fetal programming of neuroplasticity deficits. This review focuses on the role of epigenetic mechanisms involved in prenatal malnutrition-induced brain disturbances, which are apparent at a later postnatal age, through either a direct effect of fetal programming on brain plasticity or an indirect effect on the brain mediated by the postnatal development of obesity.

Prenatal protein malnutrition decreases KCNJ3 and 2DG activity in rat prefrontal cortex

Prenatal protein malnutrition (PPM) in rats causes enduring changes in brain and behavior including increased cognitive rigidity and decreased inhibitory control. A preliminary gene microarray screen of PPM rat prefrontal cortex (PFC) identified alterations in KCNJ3 (GIRK1/Kir3.1), a gene important for regulating neuronal excitability. Follow-up with polymerase chain reaction and Western blot showed decreased KCNJ3 expression in the PFC, but not hippocampus or brainstem. To verify localization of the effect to the PFC, baseline regional brain activity was assessed with (14)C-2-deoxyglucose. Results showed decreased activation in the PFC but not hippocampus. Together these findings point to the unique vulnerability of the PFC to the nutritional insult during early brain development, with enduring effects in adulthood on KCNJ3 expression and baseline metabolic activity.

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.

Early protein malnutrition changes learning and memory in spaced but not in condensed trials in the Morris water-maze

Early protein malnutrition induces structural, neurochemical and functional changes in the central nervous system leading to alterations in cognitive and behavioral development of rats. The aim of the present study was to investigate the effects of protein malnutrition during lactation on acquisition and retention of spatial information using different training procedures (spaced x condensed trials). Rats treated with 16% (well-nourished) or 6% (malnourished) protein diets during the lactation phase and nutritionally recovered until 70 days of age were tested in the Morris water-maze in procedures of 1 trial/day (spaced trials), 4, 8, 12 trials/day (intermediate density) and 24 trials/day (condensed trials), completing 24 trials at the end of training. Seven and 28 days after the training the animals were tested again in just one trial to assess long-term memory. The results showed that protein malnutrition caused deficits on the spatial learning and memory in spaced but not in intermediate and condensed trials procedure. Seven and 28 days after the training there was an increase in the latency to find the platform but only malnourished animals submitted to 1 trial/day had significantly higher latency as compared with well-nourished controls. One of the possible hypotheses is that the effect protein malnutrition only in the procedure of spaced trials could be due to deficits in memory consolidation. It is suggested that these deficits can be the result of alterations produced by protein malnutrition in the hippocampal formation or in long-lasting emotional and/or motivational aspects of the rat's behavior.

Malnutrition and brain development: an analysis of the effects of inadequate diet during different stages of life in rat

Protein malnutrition or undernutrition can result in abnormal development of the brain. Depending on type, age at onset and duration, different structural and functional deficits can be observed. In the present review, we discuss the neuroanatomical, behavioral, neurochemical and oxidative status changes associated with protein malnutrition or undernutrition at different ages during prenatal and immediately postnatal periods as well as in adult rat. Analysis of all data suggests that protein malnutrition as well as undernutrition induced impaired learning and retention when imposed during the immediately postnatal period and in adulthood, whereas hyperactivity including increased impulsiveness and greater reactivity to aversive stimuli occurred when malnutrition or undernutrition was imposed either pre or postnatally. This general state of hyperreactivity may be linked essentially to an alteration in dopaminergic system. Hence, the present review shows that in spite of the attention devoted in the literature to prenatal effects, cognitive deficits are more serious following malnutrition or undernutrition after birth. We thus clearly establish a special vulnerability to malnutrition after weaning in rats.

Prenatal protein malnutrition alters the proportion but not numbers of parvalbumin-immunoreactive interneurons in the hippocampus of the adult Sprague-Dawley rat

Prenatal protein malnutrition alters the structure and function of the adult rat hippocampal formation. The current study examines the effect of prenatal protein malnutrition on numbers of parvalbumin-immunoreactive (PV-IR) GABAergic interneurons, which are important for perisomatic inhibition of hippocampal pyramidal neurons. Brain sections from prenatally protein malnourished and normally nourished rats were stained for parvalbumin and PV-IR neurons were quantified using stereology in the dentate gyrus, CA3/2 and CA1 subfields, and the subiculum for both cerebral hemispheres. Results demonstrated that prenatal malnutrition did not affect the number of PV-IR interneurons in the hippocampus. Since prenatal protein malnutrition reduces total neuron numbers in the CA1 subfield (1), this results in an altered ratio of PV-IR interneurons to total neuronal numbers (from 1:22.9 in controls to 1:20.5 in malnourished rats). Additionally, there was no hemispheric asymmetry of either PV-IR neuron numbers or ratio of PV-IR:total neuron numbers.

Regional changes in gene expression after limbic kindling

Repeated electrical stimulation results in development of seizures and a permanent increase in seizure susceptibility (kindling). The permanence of kindling suggests that chronic changes in gene expression are involved. Kindling at different sites produces specific effects on interictal behaviors such as spatial cognition and anxiety, suggesting that causal changes in gene expression might be restricted to the stimulated site. We employed focused microarray analysis to characterize changes in gene expression associated with amygdaloid and hippocampal kindling. Male Long-Evans rats received 1 s trains of electrical stimulation to either the amygdala or hippocampus once daily until five generalized seizures had been kindled. Yoked control rats carried electrodes but were not stimulated. Rats were euthanized 14 days after the last seizures, both amygdala and hippocampus dissected, and transcriptome profiles compared. Of the 1,200 rat brain-associated genes evaluated, 39 genes exhibited statistically significant expression differences between the kindled and non-kindled amygdala and 106 genes exhibited statistically significant differences between the kindled and non-kindled hippocampus. In the amygdala, subsequent ontological analyses using the GOMiner algorithm demonstrated significant enrichment in categories related to cytoskeletal reorganization and cation transport, as well as in gene families related to synaptic transmission and neurogenesis. In the hippocampus, significant enrichment in gene expression within categories related to cytoskeletal reorganization and cation transport was similarly observed. Furthermore, unique to the hippocampus, enrichment in transcription factor activity and GTPase-mediated signal transduction was identified. Overall, these data identify specific and unique neurochemical pathways chronically altered following kindling in the two sites, and provide a platform for defining the molecular basis for the differential behaviors observed in the interictal period.

Nutrition and neurodevelopment: mechanisms of developmental dysfunction and disease in later life

Nutrition plays a central role in linking the fields of developmental neurobiology and cognitive neuroscience. It has a profound impact on the development of brain structure and function and malnutrition can result in developmental dysfunction and disease in later life. A number of diseases, including schizophrenia, may be related to neurodevelopmental insults such as malnutrition, hypoxia, viruses or in utero drug exposure. Some of the most significant findings on nutrition and neurodevelopment during the last three decades, and especially during the last few years, are discussed in this review. Attention is focused on the underlying cellular and molecular mechanisms by which diet exerts its effects. Randomized intervention studies have revealed important effects of early nutrition on later cognitive development, and recent epidemiological findings show that both genetics and environment are risk factors for schizophrenia. Particularly important is the effect of early nutrition on development of the hippocampus, a brain structure important in establishing learning and memory, and hence for cognitive performance. A major aim of future research should be to elucidate the molecular mechanisms underlying nutritionally-induced impairment of neurodevelopment and specifically to determine the mechanisms by which early nutritional experience affects later cognitive performance. Key research objectives should include: (1) increased understanding of mechanisms underlying the normal processes of ageing and neurodegenerative disorders; (2) assessment of the role of susceptibility genes in modulating the effects of early nutrition on neurodevelopment; and (3) development of nutritional and pharmaceutical strategies for preventing and/or ameliorating the adverse effects of early malnutrition on long-term programming.

Prenatal malnutrition alters diazepam-mediated suppression of ultrasonic vocalizations in an age dependent manner

The sensitivity of prenatally malnourished rats to the ultrasonic vocalization (USV) suppressant effect of diazepam (a non-specific benzodiazepine (BZ) receptor agonist) was investigated. Male offspring of dams provided with a protein deficient diet (6% casein) for 5 weeks prior to mating and throughout pregnancy were compared to the offspring of mothers provided with a diet of adequate protein content (25% casein). At postnatal day 7 or 11, pups were injected with vehicle or one of five doses of DZ (0.03, 0.1, 0.3, 1 or 3mg/kg) 30 min after removal from their dam. Thirty minutes later they were subjected to 2 min of cooling on a 20 degrees C surface and their USVs were quantified. DZ dose-dependently suppressed USV at both ages. At P7, the USV suppressant effect of DZ was the same for both groups. However, by P11 the prenatally malnourished rats showed significantly greater suppression of USV by 0.03 and 0.1mg/kg DZ than well-nourished controls. These differences were not related to degree of temperature loss or body weight. Thus, differential sensitivity to BZ receptor agonists develops in the second postnatal week in prenatally malnourished rats. This reflects either an altered program of development of the GABAergic system, or adaptive, compensatory changes in the GABAergic system in response to more extensive functional disturbances in the developing brain.

A “deficient environment” in prenatal life may compromise systems important for cognitive function by affecting BDNF in the hippocampus

The intrauterine environment has the capacity to mold the prenatal nervous system. Particularly, recent findings show that an adverse prenatal environment produces structural defects of the hippocampus, a critical area sub-serving learning and memory functions. These structural changes are accompanied by a disruption in the normal expression pattern of brain-derived neurotrophic factor (BDNF) and its cognate tyrosine kinase B (TrkB) receptor. The important role that the BDNF system plays in neural modeling and learning and memory processes suggests that fetal exposure to unfavorable intrauterine conditions may compromise proper cognitive function in adult life. These findings have implications for disorders that involve a dysfunction in the BDNF system and are accompanied by cognitive deficits.

Frequency-dependent changes in the paired-pulse index in the hippocampus of the freely moving adult male rat

The paired-pulse index (PPI) has been widely used as a measure of modulation of cellular excitability in the hippocampal trisynaptic circuit. This paper presents a quantification of the changes in this measure of neuronal modulation as a result of the application of pulse trains having six different train frequencies (0.1, 1, 5, 8, 15, and 30 Hz) to one of the major efferent pathways to the dentate gyrus, the medial perforant path (MPP). Our findings indicate that the modulation of the first leg of the hippocampal trisynaptic circuit is dependent on the frequency of the "burst train" applied to the perforant pathway. This methodological finding is of importance to all investigators studying hippocampal plasticity via LTP or LTD approaches. The different synaptic mechanisms implicated in being responsible for the changes in the PPI are also discussed.

Long-term effects of early-life malnutrition and status epilepticus: assessment by spatial navigation and CREB(Serine-133) phosphorylation

Malnutrition and/or seizure in the developing brain cause hippocampal damages. However, underlying mechanisms remain unclear. The malnutrition group (MN) subjected with malnutrition alone was culled to 20-22 rats per dam on postnatal day 1 (P1). The rats subjected to lithium-pilocarpine (Li/PC)-induced status epilepticus at P21 were grouped as the SE group. The rats subjected to malnutrition and subsequent status epilepticus were grouped as the MS group. Visual-spatial memory test using the Morris water maze task was performed at P80. Following behavioral tests, the hippocampus was evaluated for histological lesions and phosphorylated cAMP-responsive, element-binding protein at serine-133 (pCREB(Ser-133)), an important transcription factor underlying learning and memory in the mammalian brain. Here, the MN group exhibited decreased body weight at P21. There was no significant difference in the seizure duration and mortality between the SE and MS groups. In adulthood (P80), both the SE and MS groups showed the spatial learning deficit, hippocampal cell loss and decreased pCREB(Ser133) level within hippocampal CA1 region. Although the MN group demonstrated a decreased level of pCREB(Ser133), no distinguishable changes in the cognitive deficit and hippocampal neuronal loss were detected. Collectively, the present results suggest that early-life malnutrition led to a reduced phosphorylation of CREB(Ser133) in hippocampal CA1 in the absence of the long-term spatial learning deficit. This decreased phosphorylation of CREB(Ser133) could suggest that cascades of signal transduction responsible for the phosphorylation of CREB(Ser133) might be disturbed by early-life malnutrition. In addition, malnutrition caused no discernible synergistic effects on Li/PC-induced status epilepticus.

Early postnatal protein malnutrition affects learning and memory in the distal but not in the proximal cue version of the Morris water maze

Learning and memory of early postnatal protein malnourished rats were investigated in the Morris water maze. During the lactation period (21 days) each litter (mother plus six male and two female pups) was provided with 16% (well-nourished) or 6% (malnourished) protein diets. After weaning, rats remained on the same diet until 49 days of age. From day 50 on all animals were fed a commercial lab chow. Experiments started on day 70. In experiment I (proximal cue version) the animals were trained to escape from water to a visible platform (3 cm above the water level) in six trials daily for four consecutive days, completing 24 trials. In experiment II (distal cue version) the animals were trained to escape from water to a submerged platform using the same procedure as in experiment II. After the 24th trial, the platform was removed and the animals were submitted to a 60-s trial (probe trial). Seven and twenty-eight days after training, the retention test was conducted in one 180-s trial. The results showed no impairment of the learning or memory of malnourished animals tested in the proximal cue version but an increased latency and distance traveled to find the submerged platform in the distal cue version of the procedure. In the distal cue version the malnourished animals also showed increased latency to find the platform 7 and 28 days after the test training. No difference due to diet was found in the probe trial test indicating that, once the task is acquired, malnourished rats can manage extra-maze cues as easily as well-nourished rats. It is suggested that the present results can be due to alterations produced by protein malnutrition in the hippocampal formation or also to reflect the higher emotionality of rats following early malnutrition, specially considering the fact that postnatally malnourished animals are more reactive to unpleasant or aversive stimuli as cold water.

Effects of prenatal protein malnutrition on the hippocampal formation

In this review we have assessed the effects of prenatal protein malnutrition on the hippocampal formation of the developing brain. In investigating this insult in the hippocampal neuronal model we have concentrated on aspects of enhanced inhibition we have shown in our earlier studies. Since this involves particular attention to the GABAergic interneurons we have examined the complex interneuronal networks of the hippocampal formation and their neurotransmitter afferent inputs, particularly the serotonergic system from the midbrain raphé nuclei. A variety of combinations of specialized interneurons are discussed in terms of how malnutrition insults perturb function in these inhibitory and disinhibitory networks. Pathological enhancement of inhibition manifests itself by diminished plasticity, alterations in theta activity and deficits in long-term learning behaviors. Long-term inhibition in select GABA interneuron systems may form a major derangement seen following prenatal protein malnutrition. The focus of this study is to relate enhanced inhibition to the several forms of inhibitory systems present in the hippocampal formation and develop hypotheses as to the primary derangements that may account for pathological inhibition in prenatal malnutrition.

Development and modulation of GABA(A) receptor-mediated neurotransmission in the CA1 region of prenatally protein malnourished rats

Prenatal protein malnutrition has been demonstrated to result in alterations in the serotonergic and GABAergic neurotransmitter systems in the rat hippocampus. In the present study, whole-cell patch clamp recordings of CA1 pyramidal cells were employed in an effort to gain insight into the specific cellular locus and functional consequences of the previously reported changes. Hippocampal slices were prepared from Sprague-Dawley rats whose dams were fed either a normal (25% casein) or low (6% casein) protein diet during pregnancy. The development of GABA(A) receptor-mediated miniature inhibitory postsynaptic currents (mIPSCs) and their modulation by the benzodiazipine agonist zolpidem were compared in cells from the two nutritional groups at postnatal days 7, 14, 21 and >90. The modulation of mIPSCs by serotonin was also examined in cells from 21 day old rats. No significant differences were observed in the characteristics of mIPSCs in cells from control vs. prenatally protein malnourished rats at any of the ages studied, although there was a trend for a higher frequency of mIPSCs in adult (>p90) prenatally protein malnourished rats. At all ages, zolpidem produced a significant increase in the mean decay time of mIPSCs that was not significantly different in cells from the two nutritional groups. Serotonin application resulted in a significant increase in the frequency of mIPSCs in CA1 pyramidal cells but there was no significant difference between cells from the two nutritional groups in the characteristics of this effect. These data demonstrate that the previously observed alterations in the serotonergic and GABAergic systems that result from prenatal protein malnutrition do not have significant functional consequences at a single cell level in the CA1 region of the rat hippocampus as measured in vitro.

Effects of prenatal protein malnutrition and neonatal stress on CNS responsiveness

Maturation of the nervous system and consequent behavior depends in part on prenatal nutritional factors and postnatal environmental stimulation. In particular, the hypothalamus and the hippocampus are two important CNS areas that are vulnerable to such pre- and postnatal manipulations. Therefore, the present study was undertaken to explore the effects of both prenatal protein malnutrition and neonatal isolation stress on hypothalamic and hippocampal functioning in infant rats. Specifically, we assessed the levels of plasma corticosterone, as well as dopamine, serotonin and their metabolites in both the hypothalamus and hippocampus in rat pups that had been prenatally malnourished (6% casein diet) and isolated from nest, dam, and siblings for 1 h daily during postnatal days (PND) 2 through 8. We found that on PND 9 malnourished pups weighed less, had smaller hypothalami and a suppressed corticosterone response to acute and chronic isolation stress. However, their dopamine metabolism in the hypothalamus was increased following acute isolation on PND 9 as seen in isolated controls. Prenatal protein malnutrition also resulted in a significant elevation in serotonin in both brain areas, increased 5HIAA in the hypothalamus, and decreased dopamine in the hippocampus. Repeated isolation caused a reduction in 5HIAA in both brain parts, but only in control pups. These pre- and postnatal challenges may each cause a specific pattern of modifications in the CNS and, in combination, may be additive, particularly in the hypothalamic-pituitary-adrenal (HPA) stress response and the serotonergic functioning in both the hypothalamus and hippocampus, a finding with important clinical implications.

Prenatally protein-malnourished rats are less sensitive to the amnestic effects of medial septal infusions of chlordiazepoxide

Evidence is mounting that prenatal protein malnutrition affects the physiological properties of the GABAergic neurotransmitter system in rats. To investigate the functional behavioral consequences of these changes, chlordiazepoxide (CDP, a positive modulator of the GABA(A) receptor) was applied directly to the medial septum and the amnestic response appraised. In adulthood, male offspring of rats provided with a protein-deficient diet (6% casein) for 5 weeks prior to mating and throughout pregnancy underwent stereotaxic surgery to implant steel cannulae aimed at the medial septum. After recovery, spatial learning performance in the submerged platform version of the Morris water maze task was assessed immediately following a 1 microl infusion of either artificial cerebrospinal fluid (aCSF), or one of three doses of CDP (15, 30 and 60 nmol). Well-nourished control rats demonstrated a robust amnestic response to intraseptal CDP. During task acquisition, well-nourished rats administered each of the doses exhibited significantly longer escape latencies than those given aCSF. On the probe trial (platform removed) a lower proportion of time was spent in the target quadrant (all three doses) at a greater average distance from the former platform location (30 and 60 nmol doses). In contrast, prenatally malnourished rats exhibited a muted sensitivity to CDP, most notable at the 30 nmol dose. These findings provide further support for functional changes within the GABAergic system consequent to malnutrition.

Prenatal protein malnutrition results in increased frequency of miniature inhibitory synaptic currents in rat CA1 pyramidal cells

There is growing evidence for an effect of prenatal protein malnutrition on the GABAergic neurotransmitter system in the rat hippocampus and associated structures. In the present study, we examined the functional electrophysiological consequences of observed alterations in GABA(A) and benzodiazepine receptor systems. Whole-cell patch clamp recordings of spontaneous and of miniature inhibitory postsynaptic currents (mIPSCs) generated by CA1 pyramidal cells were performed in in vitro hippocampal slices prepared from control and prenatally protein malnourished adult male rats. The characteristics of spontaneous synaptic currents were unaltered by the prenatal insult, as were the amplitudes and kinetics of GABA(A) receptor-mediated mIPSCs. The frequency of mIPSCs, however, was significantly increased in CA1 pyramidal cells in slices prepared from prenatally malnourished vs. control rats. The effect of the benzodiazepine receptor agonist chlordiazepoxide on the characteristics of mIPSCs was also examined and found to be the same in cells from both nutritional groups. The increased frequency of mIPSCs together with the lack of a change in amplitude, kinetics, or modulation by benzodiazepines of mIPSCs in response to prenatal protein malnutrition indicate a presynaptic locus of effect of this insult.

Modulation of paired-pulse responses in the dentate gyrus: effects of prenatal protein malnutrition

Since our major hypothesis is that prenatal protein malnutrition significantly affects hippocampal neuroplasticity, this study examined the effects of prenatal protein malnutrition on the modulation of dentate granule cell excitability in freely moving rats at 15, 30 and 90 days of age across the vigilance states of quiet waking (QW), slow-wave sleep (SWS) and rapid eye movement (REM) sleep. Using paired-pulse stimulation, the paired-pulse index (PPI), a measure of the type and degree of modulation of dentate granule cell excitability elicited by stimulation of the medial perforant path, was obtained for each vigilance state at each stage of development. Four specific measures of granule cell excitability were computed, namely, PPI using both population spike amplitude (PSA) and EPSP slope measures, absolute values of PSA(1) and EPSP(1) slope. PPI values obtained at 15, 30 and 90 days of age, however, were altered during normal ontogenetic development, but not by vigilance state. At 15 days of age, the malnourished group exhibits greater early inhibition of the PPI using the PSA measure at IPIs between 20 and 30 ms regardless of vigilance state, while at 30 days of age, the malnourished group exhibits greater facilitation at IPIs between 50 and 70 ms during QW and SWS, but not during REM sleep. In the control adult (PND90) and juvenile (PND30) animal, PSA(1) values are significantly higher during SWS than in QW or REM sleep. However, for the younger malnourished animals (PND15 and PND30), PSA(1) values were found to be significantly greater during REM sleep rather than SWS. Therefore, as the animal matures, there appears to be a shift in vigilance state dependent synaptic transmission through the hippocampal trisynaptic circuit from REM sleep to SWS in both control and malnourished animals, with the change occurring later in malnourished animals when compared to control ones. Furthermore, our findings suggests that prenatal protein malnutrition significantly alters modulation of dentate granule cell excitability (i.e., PPI values using the PSA measure) during the earlier stages of development but not in adulthood.

The effects of median raphé electrical stimulation on serotonin release in the dorsal hippocampal formation of prenatally protein malnourished rats

Our previous work had shown an enhanced inhibition in the hippocampal formation of prenatally protein malnourished rats. We have also found a diminishment in 5-hydroxytryptamine (5-HT) fibers in the hippocampal formation of malnourished rats as well as increased levels of 5-HT in the brain. The purpose of the present study was to determine 5-HT release in the dorsal hippocampal formation following electrical stimulation of the median raphé nucleus (MRN) in unanesthetized prenatally malnourished rats. Stimulation of this nucleus at 20 Hz in malnourished rats resulted in a significantly diminished release of 5-HT compared to well-nourished rats. The latter group showed a lesser, though still significant, decrease in 5-HT release following raphé stimulation. Basal release of 5-HT prior to stimulation was significantly higher in malnourished rats as compared to well-nourished controls. This may be the result of a decreased density of 5-HT neurons leading to a diminished control of release. Stimulation of the MRN in behaving malnourished animals may markedly affect the recurrent negative feedback collaterals onto somatodendritic 5-HT(1A) and 5-HT(1D) autoreceptors thus enhancing the inhibitory effects of stimulation of the median raphé on 5-HT release. Studies are underway to examine the sensitivity of both the somatodendritic and terminal 5-HT autoreceptors in malnourished animals, in order to understand possible mechanisms for our findings.

Dentate granule cell modulation in freely moving rats: vigilance state effects

Dentate granule cell population responses to paired-pulse stimulation applied to the perforant pathway across a range of interpulse intervals (IPIs) were examined during different vigilance states-quiet waking (QW), slow-wave sleep (SWS), and rapid-eye movement (REM) sleep-in freely moving rats at 15, 30 and 90 days of age. Using these evoked field potentials, the paired-pulse index (PPI), a measure of the type and degree of modulation of dentate granule cell excitability, was computed and shown to be altered as a function of age. Animals, 15 days old, showed significantly lower levels of early inhibition (20-40 ms IPIs), i.e., greater PPI values, during all three vigilance states when compared to both the 30- and 90-day old animals. Adult, i.e, 90-day old animals, on the other hand, showed significantly greater levels of late inhibition (300-1000 ms IPIs), i.e., lower PPI values, than the younger animals (15- and 30-day old) during QW and SWS. These results indicate that as the dentate field of the hippocampal formation matures there are significant alterations in the modulation of dentate granule cell activity.

Effects of prenatal protein malnutrition on hippocampal long-term potentiation in freely moving rats

It has been demonstrated that prenatal protein malnutrition significantly affects hippocampal plasticity, as measured by long-term potentiation, throughout development. This paper focuses on the hippocampal dentate granule cell population response to two separate paradigms of tetanization of the medial perforant pathway in prenatally protein-malnourished and normally nourished adult male rats. The 100-pulse paradigm consisted of the application of ten 25-ms-duration bursts of 400 Hz stimulation with an interburst interval of 10 s. The 1000-pulse paradigm consisted of the application of five 500-ms bursts of 400 Hz stimulation with an interburst interval of 5 s. No between-group differences were obtained for input/output response measures prior to tetanization. No between-group, nor between-paradigm, differences were obtained in the degree of population EPSP slope enhancement. However, in response to both paradigms, prenatally malnourished animals showed significantly less enhancement of the population spike amplitude (PSA) measure than normally nourished animals. Normally nourished animals showed a significantly greater level of PSA enhancement in response to the 100-pulse paradigm than the 1000-pulse paradigm. Prenatally malnourished animals showed no significant differences in the degree of PSA enhancement between the two paradigms. Results indicate that short duration bursts (< or = 25 ms) are more effective in inducing maximal PSA enhancement in normally nourished rats than longer duration stimulus bursts. The apparent inability of prenatally malnourished rats to transfer enhanced cellular activation (population EPSP slope enhancement) into enhanced cellular discharge (PSA enhancement) suggests that a preferential enhancement of GABAergic inhibitory modulation of granule cell excitability may result from the prenatal dietary insult. Such potentiation of inhibitory activity would significantly lower the probability of granule cell population discharge, resulting in the significantly lower level of PSA enhancement obtained from these animals.

The paired-pulse index: a measure of hippocampal dentate granule cell modulation

This study was undertaken to assess whether the paired-pulse index (PPI) is an effective measure of the modulation of dentate granule cell excitability during normal development. Paired-pulse stimulations of the perforant path were, therefore, used to construct a PPI for 15-, 30-, and 90-day old, freely moving male rats. Significant age-dependent differences in the PPI were obtained. Fifteen-day old rats showed significantly less inhibition at short interpulse intervals [interpulse interval (IPI): 20 to 30 msec), a lack of facilitation at intermediate IPIs (50 to 150 msec), and significantly less inhibition at longer IPIs (300 to 1,000 msec) than adults.

Postnatal changes of brain monoamine levels in prenatally malnourished and control rats

The effects of age and prenatal protein malnutrition (6% casein diet) on the concentration of monoamine neurotransmitters and their metabolites and precursors in the hippocampal formation, striatum, brain stem and cerebral cortex were investigated in 1-, 15-, 30-, 45-, 90- and 220-day-old rats. Concentrations of all neurotransmitters, i.e. dopamine, norepinephrine and serotonin changed significantly during the development. However, two main patterns were recognized. Serotonin in all areas, and dopamine in the striatum, increased from birth to day 45, and declined significantly in 90-day-old rats. In contrast, norepinephrine in all areas, and dopamine in areas other than the striatum, showed the lowest levels in 30-day-old rats, with levels increasing gradually after this age. Concentrations of metabolites paralleled changes in corresponding neurotransmitter levels. Prenatal protein malnutrition did not significantly affect any neurotransmitter concentrations with the exception of increased tryptophan levels (181%) in the hippocampal formation of newborn rats and decreased tyrosine levels (59%) in the striatum of day 30 rats. The results indicate that the monoamine transmitter content varied dynamically throughout postnatal life; however, they seem to counteract the insult from prenatal protein malnutrition after postnatal nutritional rehabilitation.

Response threshold to aversive stimuli in stimulated early protein-malnourished rats

Two animal models of pain were used to study the effects of short-term protein malnutrition and environmental stimulation on the response threshold to aversive stimuli. Eighty male Wistar rats were used. Half of the pups were submitted to malnutrition by feeding their mothers a 6% protein diet from 0 to 21 days of age while the mothers of the other half (controls) were well nourished, receiving 16% protein. From 22 to 70 days all rats were fed commercial lab chow. Half of the animals in the malnourished and control groups were maintained under stimulating conditions, including a 3-min daily handling from 0 to 70 days and an enriched living cage after weaning. The other half was reared in a standard living cage. At 70 days, independent groups of rats were exposed to the shock threshold or to the tail-flick test. The results showed lower body and brain weights in malnourished rats when compared with controls at weaning and testing. In the shock threshold test the malnourished animals were more sensitive to electric shock and environmental stimulation increased the shock threshold. No differences due to diet or environmental stimulation were found in the tail-flick procedure. These results demonstrate that protein malnutrition imposed only during the lactation period is efficient in inducing hyperreactivity to electric shock and that environmental stimulation attenuates the differences in shock threshold produced by protein malnutrition.

Effects of prenatal protein malnutrition on hippocampal CA1 pyramidal cells in rats of four age groups

The present study was undertaken to investigate the effect of prenatal protein deprivation on area CA1 hippocampal pyramidal cells on postnatal (P) days 15, 30, 90 and 220 using Golgi techniques. Age related changes in both groups and diet related changes between groups were assessed. There were significant diet effects at all four ages, with one of 12 different measurements showing a significant diet effect on P15, five on P30, one on P90, and seven on P220. The most marked effect of the diet was on pyramidal cell dendrite spine density in the stratum moleculare and stratum radiatum, with a different pattern of diet effects in the two strata. In pyramidal cell dendrites in the stratum moleculare, there was a deficit in spine density that was significant at three of the four ages and there were similar age-related changes in the two diet groups. Spines on pyramidal cell dendrites in the stratum radiatum showed a lack of synchrony of age-related changes in the two diet groups, with an increased spine density in the malnourished rats on P30 and a widening deficit in this parameter on P90 and P220. The bimodal distribution to these changes, with most marked deficits occurring on P30 and P220, with an intervening period of apparent "catch-up" on P90, is of interest and may be a significant brain adaptation to malnutrition. The present study is the final of three morphometric studies on the effect of prenatal protein restriction on three key neurons in the hippocampal trisynaptic circuit. When compared to our previous studies on the dentate granule cell and the CA3 pyramidal cell, it is noted that there is an effect of the low protein diet on all these neurons, with the most marked effect on the predominantly postnatally generated dentate granule cells.

Studies of dentate granule cell modulation: paired-pulse responses in freely moving rats at three ages

Dentate granule cell population responses to paired-pulse stimulations applied to the perforant pathway across a range of interpulse intervals (IPI) were examined in freely moving rats at 15, 30, and 90 days of age. The profile of the paired-pulse index (PPI), a measure of the type and degree of modulation of dentate granule cell excitability, was shown to change significantly as a function of age.

Prenatal protein malnutrition affects exploratory behavior of female rats in the elevated plus-maze test

To study the effects of prenatal protein deficiency in the exploration of the elevated plus-maze, an ethological procedure was used. Female rats were provided with 25% (control) or with 6% (low-protein) casein diets before and during pregnancy. After birth eight pups in each litter (six males and two females) were fostered to a control mother. After weaning (21 days of age) all animals received a lab chow diet until behavioral testing began at 70 days of age. Individual prenatally malnourished (n = 12) and well-nourished (n = 12) females were placed at the center of the elevated plus-maze and allowed to explore for a 5-min session. One session was given per day for 6 consecutive days. The following variables were recorded: percentage of open arm entries; percentage of time spent in open arms; total arm entries; time in the center platform; latency to first open arm entry; number of attempts to enter an open arm; number of rearings; number of head-dips. The results showed a significant effect of malnutrition on six behaviors (percent open arm entries, percent time spent in open arms, attempts to enter open arms, rearings, head-dips, and latency to first open arm entry) and a significant diet by session interaction on two behaviors (attempts to enter open arms and head-dips). These results indicate increased exploration of the open arms in prenatally malnourished as compared with well-nourished control rats, suggestive of lower anxiety and/or a higher impulsiveness in these animals.

Prenatal protein malnutrition affects avoidance but not escape behavior in the elevated T-maze test

An elevated T-maze was used to study the effects of prenatal protein deficiency on inhibitory avoidance and escape behaviors. Female rats were provided with a 25% (control) or a 6% (low protein) casein diets before and during pregnancy. After birth, eight pups in each litter (six males and two females) were fostered to a lactating well-nourished mother. After weaning (21 days of age) all animals received a lab chow diet. Behavioral testing of these offspring began at 70 days of age. To assess inhibitory avoidance, prenatally malnourished and control rats were placed individually at the end of an enclosed arm in an elevated T-maze (one enclosed and two open arms) and the time taken to emerge from this arm was recorded. The same procedure was repeated in 2 subsequent trials given at 30-s intervals. Thirty seconds after the last of these trials, the rat was placed at the end of one open arm and the time taken to withdraw from this arm was measured, thus estimating escape latency. To assess retention, inhibitory avoidance and escape were measured again 72 h later. Prenatally malnourished males and females did not significantly increase avoidance latency from trials 1-3, in contrast to male and female controls. Only control female rats significantly reduced their avoidance latency on the retention test. No significant differences in escape latency were found between diet groups. These results suggest that prenatal malnutrition results in a reduction of anxiety, and that there are gender-specific responses to this test.

Malnutrition and reactivity to drugs acting in the central nervous system

There is a well-established body of data demonstrating that protein or protein-calorie malnutrition experienced early in life is associated with neuroanatomical, neurochemical, as well as behavioral alterations in both animals and humans. A number of studies has focused on the following question: are the neuroanatomical and/or neurochemical changes produced by early malnutrition responsible for the altered behaviors reported in malnourished animals? A tool that has been used to help answer this question is the administration of drugs with specific actions in the various neurotransmitter systems in the central nervous system (CNS). This neuropharmacological approach has produced a considerable amount of data demonstrating that malnourished animals react to drugs differently from controls, suggesting that the altered behavioral expression of these animals could be partly explained by the alterations in the brain function following malnutrition. The present review will provide an overview of the literature investigating the reactivity of malnourished animals to psychoactive drugs acting through GABAergic, catecholaminergic, serotonergic, opioid and cholinergic neurotransmitter systems. Altered responsiveness to psychoactive drugs in malnourished animals may be especially relevant to understanding the consequences of malnutrition in human populations.

Effect of prenatal protein deprivation on postnatal granule cell generation in the hippocampal dentate gyrus

The effect of prenatal malnutrition, produced by protein deprivation, on postnatal neurogenesis of granule cells in the fascia dentata of the rat hippocampal formation was examined by injecting tritiated thymidine on P8 and P15 and sacrificing the pups on P30, or by injecting on P30 and sacrificing on P90. The number of labeled granule cells was significantly decreased in prenatally malnourished rats injected on P8, and unaffected in those injected on P15. In contrast, the number of labeled granule cells in prenatally malnourished rats was significantly increased in animals injected in P30. The study shows that prenatal malnutrition significantly alters the postnatal pattern of granule cell neurogenesis in rat hippocampal formation and that the effect persists despite nutritional rehabilitation at birth.

Diet-induced alterations in the ontogeny of long-term potentiation

The ability of prenatally malnourished rats to establish and maintain long-term potentiation (LTP) of the perforant path/dentate granule cell synapse was examined in freely moving rats at 15, 30, and 90 days of age. Measures of the population EPSP slope and population spike amplitude (PSA) were calculated from dentate field potential recordings obtained prior to and at various times following tetanization of the perforant pathway. Significant enhancement of both population EPSP slope and PSA measures was obtained from all animals of both malnourished and well-nourished diet groups at 15 days of age. However, the magnitude of enhancement obtained from 15-day-old prenatally malnourished animals was significantly less than that of age-matched, well-nourished controls. At 30 days of age, PSA measures obtained from approximately 50% of prenatally malnourished 30-day-old rats showed no significant effect of tetanization, while measures obtained from the remaining 50% of these animals did not differ significantly from controls. EPSP slope measures for this age group followed much the same pattern, i.e., malnourished animals showing no significant enhancement of PSA measures exhibited only slight increases in EPSP slope beginning 1 h after tetanization and returned to baseline by 18 h post-tetanization. EPSP slope measures obtained from PSA-enhanced malnourished animals did not differ significantly from controls. At 90 days of age, PSA measures obtained from 50% of malnourished animals declined from pretetanization levels immediately following tetanization. Three hours after tetanization, however, this measure had increased to a level which did not differ significantly from that of the control group. PSA measures obtained from the remaining 50% of 90-day-old malnourished animals showed initial and sustained enhancement which did not differ significantly from those obtained from well-nourished age-matched controls. These results indicate that gestational protein malnutrition significantly affects the magnitude of tetanization-induced enhancement of dentate granule cell response in preweanling rats (15-day-old animals) and significantly alters the time-course and magnitude of potentiation in approximately half of prenatally malnourished animals tested at 30 and 90 days of age. Given the primarily postnatal development of the dentate granule cells, these results may reflect malnutrition-induced delays in the neurogenesis and functional development of granule cells previously reported by our group. Most striking is the fact that significant impairments in LTP establishment were obtained from prenatally malnourished animals at 90 days of age, implying that dietary rehabilitation commencing at birth is an intervention strategy incapable of ameliorating the effects of the gestational insult.

Effect of prenatal malnutrition on release of monoamines from hippocampal slices

The effect of prenatal protein malnutrition on release of monoamine neurotransmitters, their precursors and metabolites, from hippocampal slices was investigated in 15, 30, 90 and 220 days old male rats. The release of dopamine and its metabolites, tryptophan, and 5-hydroxyindoleacetic acid from hippocampal slices of malnourished rats was greater than release from control slices at all ages studied. Malnutrition also significantly increased the release of normetanephrine but only in the 220 day age group. Potassium-induced depolarization increased release of tyrosine, normetanephrine and 5-hydroxyindoleacetic acid less from slices of malnourished than from control rats. The release of norepinephrine, normetanephrine, serotonin and 5-hydroxyindoleacetic acid increased significantly with age while the release of tyrosine, 3,4-dihydroxyphenylacetic acid and homovanillic acid decreased significantly with age. Age was also significantly associated with the effectiveness of potassium-induced depolarization in increasing release of tyrosine, norepinephrine, normetanephrine, tryptophan, serotonin and 5-hydroxyindoleacetic acid.

Effects of an every other day rapid kindling procedure in prenatally protein malnourished rats

Prenatally protein (6/25) rats have been reported to require significantly more stimulations to attain a stage 5 seizure than well-nourished controls (25/25) when using either a traditional or rapid every day, kindling procedure. In the present study, a rapid kindling procedure was utilized where both prenatally malnourished and control rats received every other day perforant path kindling (50 Hz, 10 s train) 12 times a day at 5-min intervals. Using this procedure, stage 5 seizures and a fully state were attained in both nutritional groups at approximately the same rate. It is postulated that it is the every other day component of the present procedure which overcomes seizure-induced inhibition in the 6/25 subjects, thereby allowing them to attain stage 5 seizures at the same rate as controls.

Quantitative analysis of long-term potentiation in the hippocampal dentate gyrus of the freely-moving 15-day-old rat

The magnitude and duration of long-term potentiation (LTP) of perforant path/dentate granule cell synapses was examined in freely moving rats beginning at 15 days of age. Measures of dentate granule cell population EPSP slope and population spike amplitude (PSA) obtained before and after tetanization were used to evaluate the level of LTP. Tetanization resulted in significant enhancement of both the population EPSP slope (approximately +75%) and PSA (approximately +40%) measures. This enhancement was maintained without significant change for 18 h, after which both measures began a steady and continuous rise. Daily input/output response measures from age-matched nontetanized animals were used to factor out enhancement related to normal development. Under this schema, tetanization-induced enhancement of both EPSP slope and PSA measures decayed slowly, beginning 18-24 h after tetanization, returning to baseline 5 days after tetanization. Enhancement obtained from 90-day-old animals decayed to baseline 24 h after tetanization. The longer duration of LTP obtained from preweanlings is discussed with regard to the development of inhibitory systems modulating granule cell excitability.

Effects of prenatal malnutrition and postnatal nutritional rehabilitation on CA3 hippocampal pyramidal cells in rats of four ages

The effects of prenatal protein malnutrition and postnatal nutritional rehabilitation on CA3 hippocampal pyramidal cells were investigated in rats of 15, 30, 90 and 220 days of age. Female rats were fed either 6% or 25% casein diet 5 weeks before conception. Following delivery, litters born the same day to 6% and 25% casein diet rats were randomly cross-fostered to 25% casein diet dams and maintained on that diet until sacrificed. In 288 rapid-Golgi impregnated cells, we measured somal size, length of the longest apical dendrite, number of apical and basal dendrites intersecting 10 concentric rings 38 microns apart, synaptic spine density in three 50 microns segments of the largest apical dendrite and the thorny excrescence area. Prenatal protein malnutrition produced differential morphological changes on CA3 pyramidal cells. We observed significant decreases of somal size (at 90 and 220 days of age), of length of apical dendrites (at 15 days old), of apical (in 15 day animals) and basal (in 15, 90 and 220 day animals) dendritic branching and of spine density (in 30, 90 and 220 day animals). We also found significant increases of apical dendritic branching in 90 and 220 day old rats. These results indicate that prenatal protein malnutrition affects normal development and produces long-term effects on CA3 pyramidal cells.

Effects of early protein malnutrition and environmental stimulation upon the reactivity to diazepam in two animal models of anxiety

In order to investigate the effects of early protein malnutrition and environmental stimulation upon the response to the anxiolytic properties of diazepam, two animal models of anxiety (elevated plus-maze and light-dark transition tests) were used. Rats were malnourished by feeding their dams a 6% protein diet during the lactation period (0-21 days of age) while well-nourished controls received a 16% protein diet. From 21 to 70 days of age all rats received a balanced lab chow diet. Environmental stimulation consisted of 3-min daily handling from birth to 70 days of age. Additional stimulation was provided from 21 to 70 days of age by rearing the rats in an enriched living cage. Eight groups of rats were studied in a 2 (malnourished or well-nourished) x 2 (stimulated or nonstimulated) x 2 (diazepam or vehicle) design. At 70 days of age, independent groups of rats treated with diazepam (2.5 mg/kg, IP) or vehicle were submitted to testing in the elevated plus-maze or light-dark transition procedures. The results showed that both diazepam and environmental stimulation reduced anxiety in the elevated plus-maze; stimulation changed the anxiolytic response to diazepam and the two diet conditions altered differentially the response to both pharmacological and stimulation procedures. These results suggest that environmental stimulation can affect differentially the behavioral response of malnourished and well-nourished rats treated with diazepam.

An analysis of spatial navigation in prenatally protein malnourished rats

Developing rats were either malnourished or adequately nourished during the prenatal period by feeding their dams diets of low (6% casein) or adequate (25% casein) protein content 5 weeks prior to mating and throughout pregnancy. All pups received adequate nutrition from the day of birth onwards. Male offspring were tested in one of two spatial navigation tests in the Morris water tank. In proximal-cue tests (postnatal days 16-20), the position of a platform, which provided a means to escape from swimming, was denoted by an obvious visual cue located directly on the platform. In distal-cue tests (postnatal days 20-27 and adult ages, days 70-71 and days 220-221), the escape platform was submerged below the surface of the water so that the rats were required to use extramaze visual cues to guide them to the platform. Neither proximal-cue nor distal-cue navigation was significantly impaired in the prenatally malnourished rats relative to controls, at any of the ages tested.

Prenatal malnutrition effect on pyramidal and granule cell generation in the hippocampal formation

The effects of prenatal malnutrition produced by protein deprivation on the neurogenesis of granule and pyramidal cells in the rat hippocampal formation was investigated by injecting pregnant rats with tritiated thymidine on E12, E16, or E20 and sacrificing the pups on P30. Granule cell neurogenesis was significantly decreased in the pups injected on E20, but not in E12 or E16 groups. There was no effect on the generation of pyramidal cells at the times noted, indicating a differential effect of prenatal malnutrition on the generation of these two different neuronal types in the hippocampal formation.

Prenatal protein malnutrition effects on the serotonergic system in the hippocampal formation: an immunocytochemical, ligand binding, and neurochemical study

Prenatally protein malnourished rats born to dams maintained on a 6% casein diet during pregnancy and then fostered at birth to females on a 25% casein diet show adult alterations in hippocampal kindling and long-term potentiation and behavioral changes that all suggest dysfunction of hippocampal formation (HF). In the present investigation, compared to well-nourished controls, 220 day malnourished rats exhibited a decrease in the 5-HT fiber density in the dentate gyrus (DG) and CA3 subfield and, a 15-25% decrease 5-HT uptake sites assayed with [3H]-citalopram in CA3 and CA1. In malnourished rats, 5-HT1A receptors assayed with [3H]8-OH-DPAT were decreased by 20% in CA3. Because most hippocampal subfields showed no 5-HT changes, hippocampal 5-HT levels determined via HPLC methods were similar in adult malnourished and control rats. These results suggest that there are localized changes in the 5-HT afferent system in the hippocampal formation of the 220 day prenatally protein malnourished rat. Considering the 5-HT afferent input to inhibitory intrahippocampal neurons, the decreased 5-HT plexus may result in increased inhibition within specific hippocampal subfields despite overall normal levels of 5-HT in the total HF.

Prenatal malnutrition and development of the brain

In this review, we have summarized various aspects as to how prenatal protein malnutrition affects development of the brain and have attempted to integrate several broad principles, concepts, and trends in this field in relation to our findings and other studies of malnutrition insults. Nutrition is probably the single greatest environmental influence both on the fetus and neonate, and plays a necessary role in the maturation and functional development of the central nervous system. Prenatal protein malnutrition adversely affects the developing brain in numerous ways, depending largely on its timing in relation to various developmental events in the brain and, to a lesser extent, on the type and severity of the deprivation. Many of the effects of prenatal malnutrition are permanent, though some degree of amelioration may be produced by exposure to stimulating and enriched environments. Malnutrition exerts its effects during development, not only during the so-called brain growth spurt period, but also during early organizational processes such as neurogenesis, cell migration, and differentiation. Malnutrition results in a variety of minimal brain dysfunction-type syndromes and ultimately affects attentional processes and interactions of the organism with the environment, in particular producing functional isolation from the environment, often leading to various types of learning disabilities. In malnutrition insult, we are dealing with a distributed, not focal, brain pathology and various developmental failures. Quantitative assessments show distorted relations between neurons and glia, poor formation of neuronal circuits and alterations of normal regressive events, including cell death and axonal and dendritic pruning, resulting in modified patterns of brain organization. Malnutrition insult results in deviations in normal age-related sequences of brain maturation, particularly affecting coordinated development of various cell types and, ultimately, affecting the formation of neuronal circuits and the commencing of activity of neurotransmitter cell types and, ultimately, affecting the formation of neuronal circuits and the commencing of activity of neurotransmitter systems. It is obvious that such diffuse type "lesions" can be adequately assessed only by interdisciplinary studies across a broad range of approaches, including morphological, biochemical, neurophysiological, and behavioral analyses.

Protein energy malnutrition and the nervous system

Protein-energy malnutrition (PEM), a natural ramification of poverty, continues to be a perennial source of concern to a large segment of the world population. The developing nervous system of a child is specially vulnerable to deprivations in nurture. Peripheral nerve and muscle derangements are clinically evident by weakness, hypotonia and hyporeflexia in accordance with severity and duration of PEM. Motor and sensory nerve conduction studies exhibit significant abnormalities and often furnish useful and ominous correlation with grades of PEM. The human sural nerve histology in cases of severe PEM is characterized by persistence of small myelinated fibres, striking failure of internodal elongation and significant segmental demyelination. Young rhesus monkeys are ideal experimental PEM models and they show myopathic EMG changes amenable to rehabilitation. Muscle pathology comprises obliteration of cross-striations, streaming of Z bands, increased interfibrillary spaces, mitochondriomegaly and small-for-age fibres. Radioisotope assays reveal anomalous incorporation into various nerve and muscle constituents. Central nervous system, specially the neuropsychological functions are affected in a lasting manner. Learning deficits, behavioural problems and manual indexterity are most obtrusive features.

Prenatal protein malnutrition alters behavioral state modulation of inhibition and facilitation in the dentate gyrus

We have examined the effects of prenatal protein malnutrition on interneuronally mediated inhibition and facilitation in the dentate gyrus of the rat using the paired-pulse technique. Field potentials were recorded in the dentate gyrus in response to paired stimuli delivered to the perforant path. The paired-pulse index (PPI) was used as a measure of the net short-term facilitation or interneuronally mediated inhibition effective at the time of the paired-pulse test and was computed by dividing the amplitude of the second population spike (p2) by the amplitude of the first population spike (p1). PPIs were classified according to p1 in order to compare PPIs between behavioral states and dietary treatments since population spike amplitudes in the dentate gyrus vary in relation to behavioral state. Testing was performed during 4 behavioral states: slow-wave sleep (SWS), paradoxical sleep (REM), immobile waking (IW) and exploratory locomotion (AW) using interpulse intervals (IPI) from 20 to 400 ms. The magnitude and duration of interneuronally mediated inhibition was significantly increased in prenatal protein malnourished animals when compared with controls. Paired-pulse tests performed using an IPI of 20 ms under the high p1 (p1 greater than median) condition showed significantly smaller PPIs in prenatal protein malnourished rats regardless of behavioral state. For IPIs greater than 20 ms PPIs were consistently smaller in prenatal protein malnourished rats during SWS and IW. These data indicate that both the magnitude and duration of interneuronally mediated inhibition are increased in prenatally malnourished rats. No consistent diet-related differences were found during AW and REM using IPIs greater than 20 ms because interneuronally mediated inhibition was relatively suppressed during these behavioral states for both dietary groups. There was no consistent behavioral state modulation of paired-pulse facilitation (IPI = 40 to 80 ms) or late inhibition (IPI = 400 ms) in either diet group. In addition, a new relation between PPI and IPI was found under the low p1 (p1 greater than median) condition. During AW the PPIs observed using IPIs of 40 and 50 ms were smaller than those observed using IPIs of 30 and 60 ms. This depression interrupts what is generally considered the "facilitatory" phase of paired-pulse response and may indicate an interaction between perforant path stimulation and hippocampal theta rhythm which is masked when p1 amplitude is high.(ABSTRACT TRUNCATED AT 400 WORDS)

Prenatal protein malnutrition and hippocampal function: rapid kindling

A stimulation paradigm evoking rapidly recurring seizure activity from the hippocampal dentate gyrus was used to examine perforant path kindling in prenatally protein malnourished adult rats. Biphasic electrical stimulations (50 Hz) of five s duration were applied to the perforant path every five min for one hour over five consecutive days. Behavioral manifestations of seizure activity were assessed using the standard 0-5 scale. Prenatally malnourished rats exhibited significantly fewer convulsive seizures (stage 5) and required significantly more stimulations to attain the first stage 5 seizure than controls. Animals of the malnourished group also exhibited significantly more stage 1 seizures than control animals, indicating a significant retardation in the kindling rate of these animals. Additionally, 3 of the 11 malnourished animals failed to exhibit a single stage 5 seizure during the 60 stimulation test period. These findings parallel previous results reported for prenatally protein malnourished rats using the traditional one stimulation-per-day kindling paradigm and indicate that this rapid kindling paradigm can be effectively used to study the impact of various insults on seizure susceptibility and development in a shortened time frame.