STEERING THE MICROBIOTA-GUT-BRAIN AXIS BY ANTIBIOTICS TO MODEL NEURO-IMMUNE-ENDOCRINE DISORDERS

BACKGROUND

Over the last century, animal models have been employed to study the gut-brain axis and its relationship with physiological processes, including those necessary for survival, such as food intake regulation and thermoregulation; those involved in diseases, ranging from inflammation to obesity; and those concerned to the development of neurodegenerative diseases and neuropsychiatric disorders, such as Alzheimer's disease and autism spectrum disorder, respectively.

SUMMARY

The gut microbiota has been recognized in the last decade as an essential functional component of this axis. Many reports demonstrate that the gut microbiota influences the development of a vast array of physiological processes. Experiments that use animal models to assess the effect of the gut microbiota on the brain and behavior may involve the acute or chronic administration of wide-spectrum antibiotics.

KEY MESSAGES

This narrative review summarizes the beneficial or detrimental effects of antibiotics administered prenatally or postnatally to rodents during acute or chronic periods in a wide range of protocols. These include animal models of disease and behavioral paradigms of learning and memory, anxiety, obsessive-compulsive disorder, and autism spectrum disorder. Biomarkers and behavioral assays associated with antibiotic exposure are also included in this review.

Advancing Alzheimer's Therapeutics: Exploring the Impact of Physical Exercise in Animal Models and Patients

Alzheimer's disease (AD) is the main neurodegenerative disorder characterized by several pathophysiological features, including the misfolding of the tau protein and the amyloid beta (Aβ) peptide, neuroinflammation, oxidative stress, synaptic dysfunction, metabolic alterations, and cognitive impairment. These mechanisms collectively contribute to neurodegeneration, necessitating the exploration of therapeutic approaches with multiple targets. Physical exercise has emerged as a promising non-pharmacological intervention for AD, with demonstrated effects on promoting neurogenesis, activating neurotrophic factors, reducing Aβ aggregates, minimizing the formation of neurofibrillary tangles (NFTs), dampening inflammatory processes, mitigating oxidative stress, and improving the functionality of the neurovascular unit (NVU). Overall, the neuroprotective effects of exercise are not singular, but are multi-targets. Numerous studies have investigated physical exercise's potential in both AD patients and animal models, employing various exercise protocols to elucidate the underlying neurobiological mechanisms and effects. The objective of this review is to analyze the neurological therapeutic effects of these exercise protocols in animal models and compare them with studies conducted in AD patients. By translating findings from different approaches, this review aims to identify opportune, specific, and personalized therapeutic windows, thus advancing research on the use of physical exercise with AD patients.

Oxidative stress, the immune response, synaptic plasticity, and cognition in transgenic models of Alzheimer disease

INTRODUCTION

Worldwide, approximately 50 million people have dementia, with Alzheimer disease (AD) being the most common type, accounting for 60%-70% of cases. Given its high incidence, it is imperative to design studies to expand our knowledge about its onset and development, and to develop early diagnosis strategies and/or possible treatments. One methodological strategy is the use of transgenic mouse models for the study of the factors involved in AD aetiology, which include oxidative stress and the immune response.

DEVELOPMENT

We searched the PubMed, Scopus, and Google Scholar databases for original articles and reviews published between 2013 and 2019. In this review, we address two factors that have been studied independently, oxidative stress and the immune response, in transgenic models of AD, and discuss the relationship between these factors and their impact on the loss of synaptic and structural plasticity, resulting in cognitive impairment.

CONCLUSION

This review describes possible mechanisms by which oxidative stress and the immune response participate in the molecular, cellular, and behavioural effects of AD, observing a close relationship between these factors, which lead to cognitive impairment.

Chronic-Antibiotics Induced Gut Microbiota Dysbiosis Rescues Memory Impairment and Reduces β-Amyloid Aggregation in a Preclinical Alzheimer's Disease Model

Alzheimer's disease (AD) is a multifactorial pathology characterized by β-amyloid (Aβ) deposits, Tau hyperphosphorylation, neuroinflammatory response, and cognitive deficit. Changes in the bacterial gut microbiota (BGM) have been reported as a possible etiological factor of AD. We assessed in offspring (F1) 3xTg, the effect of BGM dysbiosisdysbiosis in mothers (F0) at gestation and F1 from lactation up to the age of 5 months on Aβ and Tau levels in the hippocampus, as well as on spatial memory at the early symptomatic stage of AD. We found that BGM dysbiosisdysbiosis with antibiotics (Abx) treatment in F0 was vertically transferred to their F1 3xTg mice, as observed on postnatal day (PD) 30 and 150. On PD150, we observed a delay in spatial memory impairment and Aβ deposits, but not in Tau and pTau protein in the hippocampus at the early symptomatic stage of AD. These effects are correlated with relative abundance of bacteria and alpha diversity, and are specific to bacterial consortia. Our results suggest that this specific BGM could reduce neuroinflammatory responses related to cerebral amyloidosis and cognitive deficit and activate metabolic pathways associated with the biosynthesis of triggering or protective molecules for AD.

High-fat and combined high-fat-high-fructose diets impair episodic-like memory and decrease glutamate and glutamine in the hippocampus of adult mice

BACKGROUND

Diet-induced obesity is associated with premature cognitive decline. Elevated consumption of fats and sugars in humans and rodents has been associated with deficits in recognition memory, which is modulated by the hippocampus. Alterations in excitatory and inhibitory neurotransmitters in this area have been observed after hypercaloric diets, but the effects on episodic-like memory are not conclusive.

OBJECTIVE

To investigate the effects of hypercaloric diets on memory and their relationship with γ-aminobutyric acid (GABA), glutamate and glutamine and their genetic expression in the hippocampus.

DESIGN

A control diet (CD), a high-fat diet (HFD) and a combined high-fat-high-fructose diet (HFFrD) were administered to 30 C57BL/6 adult mice for 10 weeks. The discrimination indexes and exploration time of the novel object recognition (NOR) and novel object location (NOL) tasks were evaluated and GABA, glutamate and glutamine concentrations and their genetic expression were obtained from the hippocampus.

RESULTS

The HFFrD induced lower discrimination indexes, decreased exploration time in the recognition memory tasks, and lowered the concentrations of glutamate and glutamine, and HFD increased their expression in the hippocampus.

CONCLUSIONS

These findings suggest that a possible adaptative long-term mechanism in the hippocampal neurotransmitters, and this possibility may underlie the episodic-like memory deficits in mice fed HFD and HFFrD.

Cortical Synaptic Reorganization Under Chronic Arsenic Exposure

There is solid epidemiological evidence that arsenic exposure leads to cognitive impairment, while experimental work supports the hypothesis that it also contributes to neurodegeneration. Energy deficit, oxidative stress, demyelination, and defective neurotransmission are demonstrated arsenic effects, but it remains unclear whether synaptic structure is also affected. Employing both a triple-transgenic Alzheimer's disease model and Wistar rats, the cortical microstructure and synapses were analyzed under chronic arsenic exposure. Male animals were studied at 2 and 4 months of age, after exposure to 3 ppm sodium arsenite in drinking water during gestation, lactation, and postnatal development. Through nuclear magnetic resonance, diffusion-weighted images were acquired and anisotropy (integrity; FA) and apparent diffusion coefficient (dispersion degree; ADC) metrics were derived. Postsynaptic density protein and synaptophysin were analyzed by means of immunoblot and immunohistochemistry, while dendritic spine density and morphology of cortical pyramidal neurons were quantified after Golgi staining. A structural reorganization of the cortex was evidenced through high-ADC and low-FA values in the exposed group. Similar changes in synaptic protein levels in the 2 models suggest a decreased synaptic connectivity at 4 months of age. An abnormal dendritic arborization was observed at 4 months of age, after increased spine density at 2 months. These findings demonstrate alterations of cortical synaptic connectivity and microstructure associated to arsenic exposure appearing in young rodents and adults, and these subtle and non-adaptive plastic changes in dendritic spines and in synaptic markers may further progress to the degeneration observed at older ages.

Oxidative stress, the immune response, synaptic plasticity, and cognition in transgenic models of Alzheimer disease

INTRODUCTION

Worldwide, approximately 50 million people have dementia, with Alzheimer disease (AD) being the most common type, accounting for 60%-70% of cases. Given its high incidence, it is imperative to design studies to expand our knowledge about its onset and development, and to develop early diagnosis strategies and/or possible treatments. One methodological strategy is the use of transgenic mouse models for the study of the factors involved in AD aetiology, which include oxidative stress and the immune response.

DEVELOPMENT

We searched the PubMed, Scopus, and Google Scholar databases for original articles and reviews published between 2013 and 2019. In this review, we address 2 factors that have been studied independently, oxidative stress and the immune response, in transgenic models of AD, and discuss the relationship between these factors and their impact on the loss of synaptic and structural plasticity, resulting in cognitive impairment.

CONCLUSION

This review describes possible mechanisms by which oxidative stress and the immune response participate in the molecular, cellular, and behavioural effects of AD, observing a close relationship between these factors, which lead to cognitive impairment.

Spatial Memory and Gut Microbiota Alterations Are Already Present in Early Adulthood in a Pre-clinical Transgenic Model of Alzheimer's Disease

The irreversible and progressive neurodegenerative Alzheimer’s disease (AD) is characterized by cognitive decline, extracellular β-amyloid peptide accumulation, and tau neurofibrillary tangles in the cortex and hippocampus. The triple-transgenic (3xTg) mouse model of AD presents memory impairment in several behavioral paradigms and histopathological alterations from 6 to 16 months old. Additionally, it seems that dysbiotic gut microbiota is present in both mouse models and patients of AD at the cognitive symptomatic stage. The present study aimed to assess spatial learning, memory retention, and gut microbiota alterations in an early adult stage of the 3xTg-AD mice as well as to explore its sexual dimorphism. We evaluated motor activity, novel-object localization training, and retention test as well as collected fecal samples to characterize relative abundance, alpha- and beta-diversity, and linear discriminant analysis (LDA) effect size (LEfSe) analysis in gut microbiota in both female and male 3xTg-AD mice, and controls [non-transgenic mice (NoTg)], at 3 and 5 months old. We found spatial memory deficits in female and male 3xTg-AD but no alteration neither during training nor in motor activity. Importantly, already at 3 months old, we observed decreased relative abundances of Actinobacteria and TM7 in 3xTg-AD compared to NoTg mice, while the beta diversity of gut microbiota was different in female and male 3xTg-AD mice in comparison to NoTg. Our results suggest that gut microbiota modifications in 3xTg-AD mice anticipate and thus could be causally related to cognitive decline already at the early adult age of AD. We propose that microbiota alterations may be used as an early and non-invasive diagnostic biomarker of AD.

Protective effects of intracerebroventricular adiponectin against olfactory impairments in an amyloid β1-42 rat model

BACKGROUND

Alzheimer's disease (AD) is characterized by cognitive impairment that eventually develops into dementia. Amyloid-beta (Aβ) accumulation is a widely described hallmark in AD, and has been reported to cause olfactory dysfunction, a condition considered an early marker of the disease associated with injuries in the olfactory bulb (OB), the hippocampus (HIPP) and other odor-related cortexes. Adiponectin (APN) is an adipokine with neuroprotective effects. Studies have demonstrated that APN administration decreases Aβ neurotoxicity and Tau hyperphosphorylation in the HIPP, reducing cognitive impairment. However, there are no studies regarding the neuroprotective effects of APN in the olfactory dysfunction observed in the Aβ rat model. The aim of the present study is to determine whether the intracerebroventricular (i.c.v) administration of APN prevents the early olfactory dysfunction in an i.c.v Amyloid-beta1-42 (Aβ1-42) rat model. Hence, we evaluated olfactory function by using a battery of olfactory tests aimed to assess olfactory memory, discrimination and detection in the Aβ rat model treated with APN. In addition, we determined the number of cells expressing the neuronal nuclei (NeuN), as well as the number of microglial cells by using the ionized calcium-binding adapter molecule 1 (Iba-1) marker in the OB and, CA1, CA3, hilus and dentate gyrus (DG) in the HIPP. Finally, we determined Arginase-1 expression in both nuclei through Western blot.

RESULTS

We observed that the i.c.v injection of Aβ decreased olfactory function, which was prevented by the i.c.v administration of APN. In accordance with the olfactory impairment observed in i.c.v Aβ-treated rats, we observed a decrease in NeuN expressing cells in the glomerular layer of the OB, which was also prevented with the i.c.v APN. Furthermore, we observed an increase of Iba-1 cells in CA1, and DG in the HIPP of the Aβ rats, which was prevented by the APN treatment.

CONCLUSION

The present study describes the olfactory impairment of Aβ treated rats and evidences the protective role that APN plays in the brain, by preventing the olfactory impairment induced by Aβ1-42. These results may lead to APN-based pharmacological therapies aimed to ameliorate AD neurotoxic effects.

Arsenic Exposure Contributes to the Bioenergetic Damage in an Alzheimer's Disease Model

Worldwide, every year there is an increase in the number of people exposed to inorganic arsenic (iAs) via drinking water. Human populations present impaired cognitive function as a result of prenatal and childhood iAs exposure, while studies in animal models demonstrate neurobehavioral deficits accompanied by neurotransmitter, protein, and enzyme alterations. Similar impairments have been observed in close association with Alzheimer's disease (AD). In order to determine whether iAs promotes the pathophysiological progress of AD, we used the 3xTgAD mouse model. Mice were exposed to iAs in drinking water from gestation until 6 months (As-3xTgAD group) and compared with control animals without arsenic (3xTgAD group). We investigated the behavior phenotype on a test battery (circadian rhythm, locomotor behavior, Morris water maze, and contextual fear conditioning). Adenosine triphosphate (ATP), reactive oxygen species, lipid peroxidation, and respiration rates of mitochondria were evaluated, antioxidant components were detected by immunoblots, and immunohistochemical studies were performed to reveal AD markers. As-3xTgAD displayed alterations in their circadian rhythm and exhibited longer freezing time and escape latencies compared to the control group. The bioenergetic profile revealed decreased ATP levels accompanied by the decline of complex I, and an oxidant state in the hippocampus. On the other hand, the cortex showed no changes of oxidant stress and complex I; however, the antioxidant response was increased. Higher immunopositivity to amyloid isoforms and to phosphorylated tau was observed in frontal cortex and hippocampus of exposed animals. In conclusion, mitochondrial dysfunction may be one of the triggering factors through which chronic iAs exposure exacerbates brain AD-like pathology.

Phosphorylation of Tau protein correlates with changes in hippocampal theta oscillations and reduces hippocampal excitability in Alzheimer's model

Tau hyperphosphorylation at several sites, including those close to the microtubule domain region (MDr), is considered a key pathological event in the development of Alzheimer's disease (AD). Recent studies indicate that at the very early stage of this disease, increased phosphorylation in Tau's MDr domain correlates with reduced levels of neuronal excitability. Mechanistically, we show that pyramidal neurons and some parvalbumin-positive interneurons in 1-month-old triple-transgenic AD mice accumulate hyperphosphorylated Tau protein and that this accumulation correlates with changes in theta oscillations in hippocampal neurons. Pyramidal neurons from young triple-transgenic AD mice exhibited less spike accommodation and power increase in subthreshold membrane oscillations. Furthermore, triple-transgenic AD mice challenged with the potassium channel blocker 4-aminopyridine had reduced theta amplitude compared with 4-aminopyridine-treated control mice and, unlike these controls, displayed no seizure-like activity after this challenge. Collectively, our results provide new insights into AD pathogenesis and suggest that increases in Tau phosphorylation at the initial stages of the disease represent neuronal responses that compensate for brain circuit overexcitation.

Hippocampal mechanisms in impaired spatial learning and memory in male offspring of rats fed a low-protein isocaloric diet in pregnancy and/or lactation

Maternal nutritional challenges during fetal and neonatal development result in developmental programming of multiple offspring organ systems including brain maturation and function. A maternal low-protein diet during pregnancy and lactation impairs associative learning and motivation. We evaluated effects of a maternal low-protein diet during gestation and/or lactation on male offspring spatial learning and hippocampal neural structure. Control mothers (C) ate 20% casein and restricted mothers (R) 10% casein, providing four groups: CC, RR, CR, and RC (first letter pregnancy, second lactation diet). We evaluated the behavior of young adult male offspring around postnatal day 110. Corticosterone and ACTH were measured. Males were tested for 2 days in the Morris water maze (MWM). Stratum lucidum mossy fiber (MF) area, total and spine type in basal dendrites of stratum oriens in the hippocampal CA3 field were measured. Corticosterone and ACTH were higher in RR vs. CC. In the MWM acquisition test CC offspring required two, RC three, and CR seven sessions to learn the maze. RR did not learn in eight trials. In a retention test 24 h later, RR, CR, and RC spent more time locating the platform and performed fewer target zone entries than CC. RR and RC offspring spent less time in the target zone than CC. MF area, total, and thin spines were lower in RR, CR, and RC than CC. Mushroom spines were lower in RR and RC than CC. Stubby spines were higher in RR, CR, and RC than CC. We conclude that maternal low-protein diet impairs spatial acquisition and memory retention in male offspring, and that alterations in hippocampal presynaptic (MF), postsynaptic (spines) elements and higher glucocorticoid levels are potential mechanisms to explain these learning and memory deficits.

Fibrillar Amyloid-β Accumulation Triggers an Inflammatory Mechanism Leading to Hyperphosphorylation of the Carboxyl-Terminal End of Tau Polypeptide in the Hippocampal Formation of the 3×Tg-AD Transgenic Mouse

Alzheimer's disease (AD) is a degenerative and irreversible disorder whose progressiveness is dependent on age. It is histopathologically characterized by the massive accumulation of insoluble forms of tau and amyloid-β (Aβ) asneurofibrillary tangles and neuritic plaques, respectively. Many studies have documented that these two polypeptides suffer several posttranslational modifications employing postmortem tissue sections from brains of patients with AD. In order to elucidate the molecular mechanisms underlying the posttranslational modifications of key players in this disease, including Aβ and tau, several transgenic mouse models have been developed. One of these models is the 3×Tg-AD transgenic mouse, carrying three transgenes encoding APPSWE, S1M146V, and TauP301L proteins. To further characterize this transgenicmouse, we determined the accumulation of fibrillar Aβ as a function of age in relation to the hyperphosphorylation patterns of TauP301L at both its N- and C-terminus in the hippocampal formation by immunofluorescence and confocal microscopy. Moreover, we searched for the expression of activated protein kinases and mediators of inflammation by western blot of wholeprotein extracts from hippocampal tissue sections since 3 to 28 months as well. Our results indicate that the presence of fibrillar Aβ deposits correlates with a significant activation of astrocytes and microglia in subiculum and CA1 regions of hippocampus. Accordingly, we also observed a significant increase in the expression of TNF-α associated to neuritic plaques and glial cells. Importantly, there is an overexpression of the stress activated protein kinases SAPK/JNK and Cdk-5 in pyramidal neurons, which might phosphorylate several residues at the C-terminus of TauP301L. Therefore, the accumulation of Aβ oligomers results in an inflammatory environment that upregulates kinases involved in hyperphosphorylation of TauP301L polypeptide.

Tibolone modulates neuronal plasticity through regulating Tau, GSK3β/Akt/PI3K pathway and CDK5 p35/p25 complexes in the hippocampus of aged male mice

Aging is a key risk factor for cognitive decline and age-related neurodegenerative disorders. Also, an age-related decrease in sex steroid hormones may have a negative impact on the formation of neurofibrillary tangles (NFTs); these hormones can regulate Tau phosphorylation and the principal kinase GSK3β involved in this process. Hormone replacement therapy decreases NFTs, but it increases the risk of some types of cancer. However, other synthetic hormones such as tibolone (TIB) have been used for hormone replacement therapy. The aim of this work was to evaluate the long-term effects of TIB (0.01 mg/kg and 1 mg/kg, intragastrically for 12 weeks) on the content of total and hyperphosphorylated Tau (PHF-1) proteins and the regulation of GSK3β/Akt/PI3K pathway and CDK5/p35/p25 complexes in the hippocampus of aged male mice. We observed that the content of PHF-1 decreased with TIB administration. In contrast, no changes were observed in the active form of GSK3β or PI3K. TIB decreased the expression of the total and phosphorylated form of Akt while increased that of p110 and p85. The content of CDK5 was differentially modified with TIB: it was increased at low doses and decreased at high doses. When we analyzed the content of CDK5 activators, an increase was found on p35; however, the content of p25 decreased with administration of low dose of TIB. Our results suggest a possible mechanism of action of TIB in the hippocampus of aged male mice. Through the regulation of Tau and GSK3β/Akt/PI3K pathway, and CDK5/p35/p25 complexes, TIB may modulate neuronal plasticity and regulate learning and memory processes.

Spatial Memory Impairment is Associated with Intraneural Amyloid-β Immunoreactivity and Dysfunctional Arc Expression in the Hippocampal-CA3 Region of a Transgenic Mouse Model of Alzheimer's Disease

Dysfunction of synaptic communication in cortical and hippocampal networks has been suggested as one of the neuropathological hallmarks of the early stages of Alzheimer's disease (AD). Also, several lines of evidence have linked disrupted levels of activity-regulated cytoskeletal associated protein (Arc), an immediate early gene product that plays a central role in synaptic plasticity, with AD "synaptopathy". The mapping of Arc expression patterns in brain networks has been extensively used as a marker of memory-relevant neuronal activity history. Here we evaluated basal and behavior-induced Arc expression in hippocampal networks of the 3xTg-AD mouse model of AD. The basal percentage of Arc-expressing cells in 10-month-old 3xTg-AD mice was higher than wild type in CA3 (4.88% versus 1.77% , respectively) but similar in CA1 (1.75% versus 2.75% ). Noteworthy, this difference was not observed at 3 months of age. Furthermore, although a Morris water maze test probe induced a steep (∼4-fold) increment in the percentage of Arc+ cells in the CA3 region of the 10-month-old wild-type group, no such increment was observed in age-matched 3xTg-AD, whereas the amount of Arc+ cells in CA1 increased in both groups. Further, we detected that CA3 neurons with amyloid-β were much more likely to express Arc protein under basal conditions. We propose that in 3xTg-AD mice, intraneuronal amyloid-β expression in CA3 could increase unspecific neuronal activation and subsequent Arc protein expression, which might impair further memory-stabilizing processes.

Decreased levels of NMDA but not AMPA receptors in the lipid-raft fraction of 3xTg-AD model of Alzheimer's disease: Relation to Arc/Arg3.1 protein expression

It was recently suggested that alteration in lipid raft composition in Alzheimer's disease may lead to perturbations in neurons signalosome, which may help explain the deficits observed in synaptic plasticity mechanisms and long-term memory impairments in AD models. As a first effort to address this issue, we evaluated lipid-raft contents of distinct NMDA and AMPA receptor subunits in the hippocampus of the 3xTg-AD model of Alzheimer's disease. Our results show that compared to controls, 10 months-old 3xTg-AD mice have diminished levels of NMDA receptors in rafts but not in post-synaptic density or total fractions. Additionally, the levels of GluR1 were unaltered in all the analyzed fractions. Finally, we went on to show that the diminished levels of NMDA receptors in rafts correlated with diminished global levels of Arc/Arg3.1, a synaptic protein with a central role in long-term memory formation. This study adds to our current understanding of the signaling pathways disruptions observed in current Alzheimer's disease models.

REST/NRSF-induced changes of ChAT protein expression in the neocortex and hippocampus of the 3xTg-AD mouse model for Alzheimer's disease

AIMS

The cholinergic system is one of the neurotransmitter systems altered in Alzheimer's disease (AD), the most common form of human dementia. The objective of this work was to determine the REST/NRSF involvement in altered ChAT expression in the neocortex and hippocampus of an AD transgenic mouse (homozygous 3xTg-AD) that over-expresses 3 proteins, amyloid-β precursor protein, presenilin-1, and tau, all of which are associated with AD and cause cellular degeneration.

MAIN METHODS

Two groups (WT and 3xTg-AD) of 11-month-old female mice were analyzed and compared. Half of the brains of each group were used for ChAT immunohistochemistry, and Western Blot analyses of ChAT and REST/NRSF were performed on the other half.

KEY FINDINGS

We observed significant decreases in the number of ChAT-immunoreactive cells in the Meynert nucleus and of fibers in the frontal motor cortex and hippocampal CA1 area in transgenic mice compared with control mice. An increased level of REST/NRSF protein and a reduction of ChAT protein expression in the 3xTg-AD mice compared with their controls were also found in both in the latter two cerebral regions.

SIGNIFICANCE

The increased REST/NRSF expression reported here and its effect on the regulatory region for ChAT transcription could explain the decreased expression of ChAT in the 3xTg-AD mouse; these findings may be associated with the degeneration observed in AD.

Cholinergic markers in the cortex and hippocampus of some animal species and their correlation to Alzheimer's disease

INTRODUCTION

The cholinergic system includes neurons located in the basal forebrain and their long axons that reach the cerebral cortex and the hippocampus. This system modulates cognitive function. In Alzheimer's disease (AD) and ageing, cognitive impairment is associated with progressive damage to cholinergic fibres, which leads us to the cholinergic hypothesis for AD.

DEVELOPMENT

The AD produces alterations in the expression and activity of acetyltransferase (ChAT) and acetyl cholinesterase (AChE), enzymes specifically related to cholinergic system function. Both proteins play a role in cholinergic transmission, which is altered in both the cerebral cortex and the hippocampus due to ageing and AD. Dementia disorders are associated with the severe destruction and disorganisation of the cholinergic projections extending to both structures. Specific markers, such as anti-ChAT and anti-AChE antibodies, have been used in light immunohistochemistry and electron microscopy assays to study this system in adult members of certain animal species.

CONCLUSIONS

This paper reviews the main immunomorphological studies of the cerebral cortex and hippocampus in some animal species with particular emphasis on the cholinergic system and its relationship with the AD.

Extinction procedure induces pruning of dendritic spines in CA1 hippocampal field depending on strength of training in rats

Numerous reports indicate that learning and memory of conditioned responses are accompanied by genesis of dendritic spines in the hippocampus, although there is a conspicuous lack of information regarding spine modifications after behavioral extinction. There is ample evidence that treatments that typically produce amnesia become innocuous when animals are submitted to a procedure of enhanced training. We now report that extinction of inhibitory avoidance (IA), trained with relatively low foot-shock intensities, induces pruning of dendritic spines along the length of the apical dendrites of hippocampal CA1 neurons. When animals are trained with a relatively high foot-shock there is a high resistance to extinction, and pruning in the proximal and medial segments of the apical dendrite are seen, while spine count in the distal dendrite remains normal. These results indicate that pruning is involved in behavioral extinction, while maintenance of spines is a probable mechanism that mediates the protecting effect against amnesic treatments produced by enhanced training.

Effects of postnatal malnutrition and senescence on learning, long-term memory, and extinction in the rat

There is a wealth of information indicating that the hippocampal formation is important for learning and memory consolidation. The hippocampus is very sensitive to ageing and developmentally stressful factors such as prenatal malnutrition, which produces anatomical alterations of hippocampal pyramidal cells as well as impaired spatial learning. On the other hand, there are no reports about differential effects of postnatal malnutrition, installed at birth and maintained all through life in young and aged rats, on learning and memory of active avoidance, a task with an important procedural component. We now report that learning and long-term retention of this task were impaired in young malnourished animals, but not in young control, senile control, and senile malnourished Sprague-Dawley rats; young and senile rats were 90 and 660 days of age, respectively. Extinction tests showed, however, that long-term memory of the malnourished groups and senile control animals is impaired as compared with the young control animals. These data strongly suggest that the learning and long-term retention impairments seen in the young animals were due to postnatal malnutrition; in the senile groups, this cognitive alteration did not occur, probably because ageing itself is an important factor that enables the brain to engage in compensatory mechanisms that reduce the effects of malnutrition. Nonetheless, ageing and malnutrition, conditions known to produce anatomic and functional hippocampal alterations, impede the maintenance of long-term memory, as seen during the extinction test.

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.

The mossy fiber system of the hippocampal formation is decreased by chronic and postnatal but not by prenatal protein malnutrition in rats

We tested in 70-day-old Sprague-Dawley rats, whether malnutrition imposed during different periods of hippocampal development produced deleterious effects on the total reference volume of the mossy fiber system. Animals were treated under four nutritional conditions: (a) well nourished; (b) prenatal protein malnourished; (c) chronic protein malnourished and (d) postnatal protein malnourished. Timm's stained material was used in coronal hippocampal sections (40 microm) to estimate--using the Principle of Cavalieri--the total reference volume of the mossy fiber system in each experimental group. Our results show that chronic and postnatal protein malnourished, but not prenatal malnourished rats, decrease the mossy fiber system and the total reference volume of the mossy fiber system are selectively vulnerable to the type of dietary restriction. Thus, chronic and posnatal protein malnutrition produce deleterious effects, but only rats under prenatal protein malnutrition were able to reorganize synapses in this plexus. These findings raise the possibility that chronic malnutrition, as a long-term stressful factor, might be an important paradigm to test structural hippocampal changes that produce physiological and pathophysiological effects, or the possibility to recover its function for nutritional rehabilitation.

Enhanced inhibitory avoidance learning prevents the memory-impairing effects of post-training hippocampal inactivation

Rats were trained on an inhibitory avoidance task to study the effects of post-training administration of tetrodotoxin (TTX, which temporarily inactivates neural activity) on memory consolidation. During training, independent groups of rats received either a mild foot shock (0.8 mA) or a stronger (1.0 mA) foot shock. TTX was administered bilaterally into the dorsal hippocampus immediately after training, and memory of the task was measured 48 h later. We corroborated the typical amnesic effect of intrahippocampal infusions of TTX in those rats trained with the mild-intensity foot shock. More importantly, with the stronger foot shock, the same treatment was ineffective in producing amnesia. These results suggest that, after an enhanced learning experience, other brain regions are also activated, which may compensate for the amnesic effect of TTX infusions into the hippocampus.

Effects of lesions of hippocampal fields CA1 and CA3 on acquisition of inhibitory avoidance

Performance decrements of inhibitory avoidance (IA) induced by lesions in either the dorsal or ventral hippocampus have been interpreted as a deficiency in acquisition. Alternative interpretations are that short-term learning occurs despite the lesions and the long-term performance decrements reflect a failure of consolidation or retrieval. To assess the alternative explanations of the performance decrements, rats received lesions in either CA1 or CA3 fields of dorsal and ventral hippocampus, respectively, 8 days before IA training. Retention was tested at 30 min or 24 h after training. Kainic acid lesions were also produced in either hippocampal field 1 day after training and retention measured 8 days later. The group assessed 30 min after IA training showed little or no performance decrements, whereas the remaining groups did show marked performance decrements. These results do not support the conclusion that the hippocampus is essential for acquisition and support the idea that the hippocampus is highly involved in the consolidation or retrieval of information germane to these procedures.

Prenatal protein malnutrition decreases mossy fibers-CA3 thorny excrescences asymmetrical synapses in adult rats

Prenatal protein malnutrition has deleterious effects on hippocampal structure and function that likely result from decreased synapse number. We thus evaluated long-term effects of prenatal protein malnutrition on the mossy fibers-CA3 thorny excrescences asymmetrical synapses in 220-day-old rats. Protein malnourished rats born from pregnant dams fed with 6% casein diet were cross-fostered to lactating control rats at birth. Control animals were fed with a 25% casein diet. Timm's stained material was used to estimate the total reference volume of the mossy fiber system suprapyramidal bundle by means of stereology. The mossy fiber-CA3 asymmetrical synapse numerical density was obtained by electron microscopy, using the physical disector method. The total number of mossy fiber-CA3 asymmetrical synapses was determined on the basis of the total reference volume of the mossy fiber system suprapyramidal bundle and the mossy fiber-CA3 asymmetrical synapse numerical density. Prenatal protein malnutrition produced long-lasting, significant decreases in the volume of the mossy fiber system suprapyramidal bundle and in the numerical density of mossy fiber-CA3 asymmetrical synapse, suggesting a reduction in the total number of this synapse type. Hence, prenatal protein malnutrition induces long lasting deleterious effects on the progression of developmental programs controlling synaptogenesis and/or synaptic consolidation, likely by affecting a myriad of cellular processes.

Acetylcholinesterase-positive innervation is present at undifferentiated stages of the sea turtle Lepidochelis olivacea embryo gonads: implications for temperature-dependent sex determination

In embryos of different reptile species, incubation temperature triggers a cascade of endocrine events that lead to gonad sex differentiation. The cellular and molecular mechanisms by which temperature sets in motion this process are still controversial. Here, we begin evaluating the possible participation of the nervous system in temperature-dependent sex determination by showing the existence and origin of acetylcholinesterase (AchE)-positive nerve fibers in undifferentiated gonads of the Lepidochelys olivacea (L. olivacea) sea turtle putative male and female embryos, along the thermosensitive period for sex determination (TPSD; stages 20-27). AChE-positive nerve bundles and fibers were readily visualized until developmental stage 24 and thereafter. DiI injections and confocal imaging showed that some of these gonadal nerves arise from the lower thoracic and upper lumbar spinal cord levels, and might thus be sensory in nature. Because the vertebrate spinal cord is capable of integrating by itself thermoregulatory responses with no intervention of uppermost levels of the central nervous system, we also evaluated spinal cord maturation during the TPSD. The maturation of the spinal cord was more advanced in putative female than in male embryos, when sex determination is taking place for each sex; this process starts and ends earlier in male than in female embryos. Together these observations open the possibility that the spinal cord and the innervation derived from it could play a direct role in driving or modulating the process of temperature-dependent gonad sex determination and/or differentiation, particularly in female L. olivacea embryos.

Comparable activity levels in developmentally deprived and non-deprived layer IV cortical columns of the adult rat primary somatosensory cortex

It has been suggested that evoked neural activity levels promote the selective construction of the primary somatosensory cortex (S1) neuropil. Sensory deprivation after S1 formation has, however, no effects on its postnatal growth. This indicates that S1 neuropil elaboration is independent from the ongoing levels of evoked cortical activity, and/or that sensory deprivation does not reduce overall levels of S1 evoked activity. We thus indirectly evaluated chronic and acute levels of neural activity in the developmentally, sensory deprived adult S1. Relative succinic dehydrogenase activity and 3H2-deoxyglucose uptake were comparable in control and deprived barrels. Our observations support the idea that normal levels of evoked neural activity prevent atrophic changes in the developmentally deprived adult S1. They can not rule out, however, that early selective S1 neuropil construction occurs independent from evoked neural activity levels.

Increased neural activity in transgenic mice with brain IGF-I overexpression: a [3H]2DG study

To evaluate whether insulin-like growth factor-I (IGF-I) modulates neural activity in vivo, relative levels of brain [3H]2-deoxyglucose (2DG) uptake were compared in adult behaving and anesthetized wild type (wt) mice, and transgenic (Tg) mice with either brain IGF-I overexpression or ectopic brain expression of IGF binding protein-1 (IGFBP-1). Overall, awake behaving IGF-I Tg mice showed significant increases in brain 2DG uptake compared with wt and IGFBP-1 Tg mice. These differences were eliminated after anesthesia. 2DG uptake was similar in awake behaving, and anesthetized wt and IGFBP-1 Tg mice. Our observations thus suggest that IGF-I increases neural activity levels in vivo, and that it is not involved in regulating glucose consumption in the adult brain.

Effects of acute prenatal ethanol exposure on Bergmann glia cells early postnatal development

The effects of acute ethanol exposure during the prenatal phase of Bergmann glia cell (Bgc) generation were evaluated in three postnatal days. Ethanol exposed rats showed Bgc with reduced soma size, decreased number and width of their fibers, and increased fiber length, when compared with control animals. These differences, however, were significant at postnatal day 12. Our results demonstrate that acute, prenatal exposure to ethanol during critical stages of brain development disrupts Bgc early postnatal development.

Effects of prenatal protein malnutrition on mossy fibers of the hippocampal formation in rats of four age groups

The present study was undertaken to investigate the effect of prenatal protein deprivation on the postnatal development of the mossy fiber plexus of the hippocampal formation on postnatal (P) days 15, 30, 90, and 220. Although there is extensive information about the effects of malnutrition on cell body and dendrite morphology, little attention has been paid to axons or axon plexuses. The mossy fiber plexus represents the dentate gyrus granule cell axonal projection to areas CA4 and CA3 of the hippocampal formation and is readily demonstrated with Timm's heavy metal stain. With the use of this stain, the plexus was measured at 13 levels throughout the hippocampal complex. There was no effect of the diet on the anatomical distribution of the plexus. The current study, however, does show significant effects of prenatal protein malnutrition on postnatal development of the mossy fiber plexus that are age dependent. The prenatally malnourished rats show significant deficits in the total rostro-caudal extent and volume of the plexus on P15, P90, and P220, with the most marked dietary effect on P220. There was no significant diet effect on P30 in either extent or volume.

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.

Morphometric Study of Fetal Brain Transplants in the Insular Cortex and NGF Effects on Neuronal and Glial Development

Homotopic grafts supplemented with nerve growth factor (NGF) speed the recovery from learning deficits observed following electrolytic lesions of the insular cortex in rats. NGF also reduces the time in which the activity of choline acetyltransferase (ChAT) is first detected inside the graft by histochemical techniques. It is not known whether this behavioral and biochemical recovery correlates with an advanced maturation of the cellular elements within the graft, presumably induced by NGF. To investigate the degree of maturation of neurons, glial cells and blood vessels in NGF-supplemented grafts, adult rats were lesioned electrolytically in the insular cortex, and homotopic embryonic grafts (E16) with or without NGF supplementation were transplanted into the lesion. Fifteen days post grafting, the rats were perfused and the brains stained using silver impregnation techniques. Our results showed that neuronal maturation, as evaluated through several morphometric parameters, was advanced in NGF-supplemented grafts when compared with other experimental groups. Furthermore, grafts supplemented with NGF also showed significant increases in the number of neurons, oligodendrocytes, astrocytes and blood vessels. These observations indicated that the addition of NGF to insular cortex grafts promoted the maturation of neuronal and glial elements within the graft. They also support the possibility that the advanced morphological maturation of insular cortex grafts supplemented with NGF underlies the accelerated functional and biochemical recovery of animals with lesions of the insular cortex.

Neuronal regeneration and estrous cycle restoration after locus coeruleus-periventricular gray substance section

The locus coeruleus (LC) was anatomically separated from the periventricular gray substance (PVG) by means of knife cuts in the adult female rat presenting regular estrous cycling. This resulted in a transient suppression of the estrous cycling that lasted 10-13 days after surgery. After this period, irregular or regular cycling activity was observed. The regular cycling was restored 30-45 days after the knife cuts. Golgi impregnation of some of the brains of these rats revealed regenerative elements in the knife-cut-insulted area. Thus, blood vessels, macrophagic-like elements, and glial-like elements were observed in close relation with the knife-cut pathway. Additionally, well-defined stained neurons typical of the LC and PVG were observed in close proximity to the knife-cut pathway. Dendritic and axon projections towards the insulted area were observed. Well defined axons were seen across the knife-cut pathway. These data support, first, that the LC-PVG communication is part of a circuitry for the modulation of gonadotropic activity, and second, that in the restoration of the estrous cyclicity after the knife cut, regenerative processes leading to a LC-PVG functional reconnection occurred after the knife cut.

Mossy fibers of the hippocampal formation in prenatal malnourished rats

Timm's impregnated mossy fiber plexus, in five coronal levels throughout the hippocampal complex, of normal and prenatally protein deprived rats at 15, 30, 90 and 220 days of age were analyzed. Morphometric computer assisted image analysis, showed significant decrease in total extent of the mossy fibers area in the prenatally malnourished rats on postnatal day 15 at levels 2, 3, and 4; on day 90 at level 1, and on day 220 at all five levels. This pattern of diet effect is similar to that noted at the same ages in the prior studies of the granule cell dendrites (Brain, Res., 1990; 532:271-277, J. Comp. Neurol, 1991; 310:356-364). This similarity of effects at these loci suggests that the diet effects on the hippocampal trisynaptic circuit are closely linked to each other. In all loci the effect of the diet was most marked on P220, indicating the late appearance of dietary deprivation effects in the hippocampal formation.

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.

Cartographic system for spatial distribution analysis of corneal endothelial cells

A combined cartographic and morphometric endothelium analyser has been developed by integrating the HISTO 2000 histological imaging and analysis system with a prototype human corneal endothelium analyser. The complete system allows the elaboration and analysis of cartographies of corneal endothelial tissue, and hence the in vitro study of the spatial distribution of corneal endothelial cells, according to their regional morphometric characteristics (cell size and polygonality). The global cartographic reconstruction is obtained by sequential integration of the data analysed for each microscopic field. Subsequently, the location of each microscopically analysed field is referred to its real position on the histologic preparation by means of X-Y co-ordinates; both are provided by micrometric optoelectronic sensors installed on the optical microscope stage. Some cartographies of an excised human corneal keratoconus button in vitro are also presented. These cartographic images allow a macroscopic view of endothelial cells analysed microscopically. Parametric colour images show the spatial distribution of endothelial cells, according to their specific morphometric parameters, and exhibit the variability in size and cellular shape which depend on the analysed area.

Protein malnutrition on suprachiasmatic nucleus cells in rats of three ages

The effects of prenatal and postnatal protein malnutrition on the major and minor somatic axes of the suprachiasmatic nucleus (SCN) cells of the rat were investigated. Female rats were fed either 6%, 8% or 25% casein diet 5 weeks before mating, during gestation and lactation. After weaning the pups were maintained on the same diet until sacrifice at 30, 90 or 220 days of age. The major and minor axes in fusiform, multipolar and ovoid cells were measured in Nissl-stained SCN slices. Although the 8% diet group displayed significant reductions in fusiform and ovoid cells, the 6% diet group showed the most intense reductions in cell size of the three cell types. In the 6% diet group, cell size was significantly lower at 30 days but the difference with the other nutritional groups ameliorated at 90 days and almost reached control values at 220 days. These data suggest that malnutrition maintained during gestation and postnatal life reduces the somatic size of SCN cells. This alteration may be a morphological substrate underlying sleep and behavioral circadian alterations observed in malnourished rats.

Effect of protein malnutrition on CA3 hippocampal pyramidal cells in rats of three ages

Prenatal and postnatal protein deprivation effects on CA3-hippocampal pyramidal cells were investigated in 30-, 90- and 220-day-old rats. Female rats were fed either a 6% or a 25% casein diet 5 wk before conception and the litters were maintained on their respective diet until sacrificed. In 216 rapid Golgi-impregnated cells, we measured somal size, length and diameter of apical dendrite, number of apical dendrites intersecting 10 concentric rings 38 microns apart, thorny excrescence area and length, head diameter and density of synaptic spines on 50-microns segments of apical dendrite. The present experiments showed that malnutrition produced significant reductions of somal size in animals at 220 days of age. There were significant reductions of apical dendrite diameters in animals of 30 and 90 days, and of density and head diameter of synaptic spines at the three ages studied, and significant decrease of the thorny excrescence area at 220 days of age. At this latter age, dendritic branching was significantly decreased in the last four rings representing the area into which the perforant pathway projects. In 30-day malnourished rats, dendritic branching showed a significant increase in rings 4-6 representing the area in which the Schaffer collaterals synapse. The location of the deficit in dendritic spines corresponds to the sites where mossy fibers synapse on the apical dendrites of CA3 neurons. Age-related changes normally observed in control rats (e.g., the 30-day-old control group showed the smallest somal size and 220-day-old controls the largest size) failed to occur in the malnourished rats. The deficits in spine density and dendritic branching (in animals of 220 days old) were similar to those found in our previous studies on fascia dentata.

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.

Effects of protein undernutrition on the dentate gyrus in rats of three age groups

The effect of an 8% casein and a control 25% casein diet on the granule cells in the dorsal blade of the dentate gyrus of the rat hippocampal formation was studied at 30, 90 and 220 days of age. Female rats were fed either an 8% or 25% casein diet 5 weeks prior to conception and the litters were maintained on these respective diets until killed. In rapid-Golgi-impregnated cells, we measured major and minor axes of the soma of the dentate granule neurons, the number of spines on 50-microns segments of proximal, middle and terminal regions of the largest dendrite per granule cell and the number of dendrites intersecting 8 concentric rings 38 microns apart. At all 3 ages studied undernourished rats showed, when compared to controls, significant reductions of the major and minor axes of the somata and significant reductions in the number of spines on dendrites in the middle and terminal dendritic segments. Dendritic branching was significantly reduced in undernourished rats compared to controls in all but the 4th concentric rings, with the greatest effect being seen on the outer 3 concentric rings at 90 and 220 days of age. The location of the deficit in dendritic synaptic spines and the greatest deficit in dendritic branching correspond to the sites of termination of the lateral and medial perforant pathway projection to the dentate gyrus on the terminal and middle dendritic segments of the granule cells. The deficits noted in the granule cells of the dentate gyrus in this study were more severe than those found in our previous studies on the effect of the low protein diet in these same rats on visual cortical pyramidal cells and on the 3 cell types in the nucleus raphe dorsalis and nucleus locus coeruleus.

Effects of protein deprivation on pyramidal cells of the visual cortex in rats of three age groups

The effect of protein deprivation on rapid Golgi impregnated pyramidal neurons in layers II/III and V of the rat visual cortex was studied at 30, 90, and 220 days of age using morphometric methods. In order to mimic human under-nutrition female rats were adapted to either an 8% or control 25% casein diet 5 weeks prior to conception and maintained on these diets during gestation and lactation. The pups were then weaned and maintained on their respective diets. The undernourished rats showed a significant decrease in brain weight only at 90 days, indicating that the protein deprivation had a mild effect on brain development. Correspondingly, the number of significant histological differences between the two diet groups were least at 30 and 220 days of age. The effect of the diet was greater on layer V than on layer II/III pyramids. At 30 days of age the effect of the diet was different on the pyramids of these two cell layers, at 90 days there was a mixture of similar and dissimilar effects, and at 220 days the pyramids of these two cell layers showed only minor differences between the two diet groups. Analysis of age-related changes indicated that the effect of the diet was different on layer II/III pyramids compared to layer V pyramidal cells. These different effects apparently accounted for the progression from a dissimilar effect of the diet at 30 days on the pyramids of the two cell layers to only minor differences between them at 220 days. Further analysis of these age-related changes shows that two prominent effects of protein deprivation are for age-related changes to occur in undernourished rats but not in controls and for age-related changes to be out-of-phase with each other in the two diet groups. From these findings, and a review of similar studies in the literature, we propose that these mechanisms are a prominent effect of undernutrition in the post-weaning period and help account for the unexpected increases in morphometric measurements noted in undernourished rats in this and other studies.

Nucleus locus coeruleus: a morphometric Golgi study in rats of three age groups

Using Rapid Golgi and Nissl techniques, 3 major cell types: fusiform, multipolar and ovoid shaped cells were identified in the nucleus locus coeruleus of male rats. Each cell type was described and quantitated as to age-related changes between 30 and 90 and between 90 and 220 days of age. The orientation and dendritic architecture of each type of cell in the locus coeruleus and relationship of these cells to blood vessels in the locus coeruleus and to surrounding structures is also described. One hundred neurons per age group were measured as to their maximal linear extent and the number of spines on the somal surfaces were counted. Dendritic number, linear extent, diameter and number of spines along a 50 microns segment near the mid-point of dendritic extensions in an equal number of primary and secondary dendrites were quantified for each age group and comparisons of these parameters between each cell group were made. Axons of each cell type were defined as to their origin and general orientation and trajectory. Axon collaterals of multipolar cells were shown to be recurrent in type projecting back onto the dendrites and soma of multipolar cells. One of the most striking findings was that between 30 and 90 days there were significant decreases in spine density on both primary and secondary dendrites in all three cell types in the locus coeruleus. This was followed by significant increases in spine density on both primary and secondary dendrites between 90 and 220 days in each of the 3 cell types. It is of interest that these age-related cell changes in spine density in the nucleus locus coeruleus are exactly out-of-phase with those of the nucleus raphe dorsalis.