Synapses and malnutrition: quantitative ultrastructural study of rat cerebral cortex

Nutritional effects on neuron numbers

Undernutrition during early life is known to cause deficits and distortions of brain structure although it has remained uncertain whether or not this includes a diminution of the total numbers of neurons. Estimates of numerical density (e.g. number of cells per microscopic field, or number of cells per unit area of section, or number of cells per unit volume of tissue) are extremely difficult to interpret and do not provide estimates of total numbers of cells. However, advances in stereological techniques have made it possible to obtain unbiased estimates of total numbers of cells in well defined biological structures. These methods have been utilised in studies to determine the effects of varying periods of undernutrition during early life on the numbers of neurons in various regions of the rat brain. The regions examined so far have included the cerebellum, the dentate gyrus, the olfactory bulbs and the cerebral cortex. The only region to show, unequivocally, that a period of undernutrition during early life causes a deficit in the number of neurons was the dentate gyrus. These findings are discussed in the context of other morphological and functional deficits present in undernourished animals.

Dendritic spine pathology in infants with severe protein-calorie malnutrition

BACKGROUND

Experimental undernutrition in animals, during the critical brain development period, produces retardation of brain growth as well as a number of different morphologic and functional abnormalities in neurons, mainly in the dendritic synaptic apparatus. These alterations are the cause of the poor neurointegrative development that occurs in experimental malnutrition. Severe malnutrition during early postnatal life in humans is known to produce similar neurointegrative disorders as well as mental retardation, but there are very few studies describing the morphology of the dendritic apparatus in infants suffering from this condition.

OBJECTIVE

To study the dendritic spine density and morphology in dendrites from cortical neurons in infants dying from severe malnutrition.

METHODOLOGY

Brain sections from the somestesic, motor, and occipital cortical areas of 13 infants who died of severe malnutrition and 7 eutrophic infants who died of other causes were studied by means of the rapid Golgi method. Apical dendritic spines from neurons of the fifth cortical layer were studied and counted in all sections.

RESULTS

Apical dendrites were significantly shorter in malnourished infants than in the control group (581.54 +/- 54.32 microm in severe malnutrition vs 846.3 microm in normal infants). The number of dendritic spines per dendrite was also significantly diminished (185.3 +/- 36.1 in malnourished vs 374.3 +/- 41.6 in eutrophic infants). There were marked morphologic abnormalities in the dendritic spines of infants dying of severe malnutrition that were classified as dysplastic.

CONCLUSIONS

Short apical dendrites, fewer spines, and dendritic spine abnormalities occur in severe infant malnutrition. These anatomic anomalies might be related to the neuropsychological deficits that occur in these children.

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.

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.

Functional development of the visual system in normal and protein-deprived rats. VII. Lamination of oxidative enzyme activity in the visual cortex during post-natal development

Lamination of activity of two mitochondrial enzymes-succinate dehydrogenase (SDH) and menadione-dependent alpha-glycerophosphate dehydrogenase (M-GPDH) - was examined in the visual cortex of control (C) and protein-deprived (PD) rats from 10 days old to adult. In C rats, lamination of enzyme activity was evident from 10 days by a band of higher activity in lamina IV. A band of higher SDH activity was seen in superficial lamina VI from 15 days. Lamination of M-GPDH activity became less pronounced with increasing age, whereas distinct bands of high SDH activity in lamina IV and VI remained also in adult rats. PD rats showed a developmental delay of approximately 5 days with regard to the general increase in neuropile activity. A band of higher enzyme activity in lamina IV was present from 10 days, but it was markedly less distinct in the PD rats compared to the C rats between 15 and 25 days. A band of higher SDH activity in superficial lamina VI was not seen until 25 days in PD rats. No apparent differences were seen between adult C and PD rats. The observed developmental alterations are discussed in relation to other delays, distortions and deficits found in the visual system of PD rats.

Estimation of the numerical density of synapses in rat neocortex. Comparison of the 'disector' with an 'unfolding' method

The numerical density of synapses in the molecular layer of the parietal cortex of normal 28-day-old rats has been estimated by using two stereological methods, namely an unfolding technique and the disector method. For the unfolding technique it was assumed that the synapses formed a polydispersed population of disc-shaped particles. The technique also relies upon various assumptions regarding the size, shape and projection of synapses in the plane of section, these assumptions producing a result that is biased to an unknown extent. Such simplifying assumptions are unnecessary for the disector method. The mean +/- S.E.M. numerical density of synapses was found to be 2.16 +/- 0.14 x 10(9)/mm3 using the disector method. This was not significantly different (paired t-test; P less than 0.05) from the value of 2.41 +/- 0.22 x 10(9)/mm3 obtained using the unfolding technique with correction for truncation ('lost caps'). When the unfolding method was used without a correction for lost caps the numerical density was 1.98 +/- 0.10 x 10(9)/mm3, a value also not significantly different from that obtained using the disector method. The mean projected height (Hs) of the synaptic particles was also determined using both procedures; the results were not significantly different. When the variances of the final estimates and the time taken to carry out the procedures described were taken into account, it was estimated that the disector method was about 86% more efficient than the unfolding method with capping correction. Although the unfolding method can give essentially similar values for the numerical density of synapses to those obtained by the disector method, it is biased and much less efficient. It is concluded, therefore, that the disector method is the superior method for the estimation of the number and size of particles such as synapses, particularly when they have complex spatial configurations.

Functional development of the visual system in normal and protein-deprived rats. VI. Evoked responses in adult rats, protein deprived in early life and nutritionally rehabilitated from weaning

Previous studies have shown an increase in latency of the visual evoked response (VER) recorded from the cortical surface of adult rats subjected to protein deprivation (PD) during pre- and postnatal development. This alteration has been shown to originate mainly from the cortex itself. In the present study the possibility of normalizing such VER alterations by nutritional rehabilitation after early protein deprivation (R-PD) was investigated. Male rats were subjected to pre- and early postnatal protein deprivation through their mothers. Nutritional rehabilitation was started from weaning. The rats gained weight rapidly compared with rats subjected to protein deprivation throughout postnatal development but never reached the weight of controls (C) of the same age. Food consumption in relation to body weight was similar to that of controls. Rehabilitation continued until adult age when neurophysiological experiments were performed. The VER recordings from the dorsal lateral geniculate nucleus (dLGN) showed latencies similar to those reported previously for adult C and PD rats. The latencies of onset and first peaks of the cortical response recorded from the surface were increased by 5-6 ms in R-PD compared with C rats and hence similar to the latencies of adult PD rats. Intracortical responses to electrical stimulation in the dLGN were also similar to those of adult PD rats showing an normal onset latency but an increased latency of the peaks of the monosynaptic and late responses compared with C rats. The present results imply that the increased VER latencies noted in adult PD and R-PD rats are due to changes installed by protein deprivation during early development since they can not be reversed by nutritional rehabilitation starting at weaning.

Effects of pre-weaning undernutrition and post-weaning rehabilitation on polyphosphoinositide pools in rat brain regions

In order to assess the effects of undernutrition during the pre-weaning period on polyphosphoinositide (PolyPI) pools in rat cerebral cortex, brain stem, and cerebellum, dams were fed 5% (L-) or 22% (L+) protein diets from birth to weaning and the pups were used at this age for analyses. To examine rehabilitation post-weaning, L- and L+ pups were fed 22% protein diets (P+) for an additional six week period. Rats were decapitated and the dissection begun either immediately ("0 min" samples) or 10 min later (10 min samples). Body and tissue weights, and cerebroside levels were determined in addition ot PolyPI concentrations. In brain the extent of disappearance of PolyPI during the 10 min post-mortem period paralleled the content of gray matter: cerebral cortex greater than cerebellum greater than brain stem in all groups regardless of diet. Levels of PtdIns4P and PtdIns4,5P2 were decreased by 40% and 70% respectively in cerebral cortex of L- "0 min" samples. Deficits of both lipids in brain stem and cerebellum were 40-50%. In the L- 10 min samples, deficits were 20-30% in all three regions as compared with L+ 10 min levels, indicating the presence of a portion of both lipids affected only moderately by nutritional insufficiency. The effects on this relatively inert pool, much of it localized in myelin, were reversed on nutritional rehabilitation. The PolyPI pool lost post-mortem in L+ brain regions was practically absent in L- brain regions and was not restored in L-P+ animals. Thus, this study indicates that a metabolically labile pool, primarily located in gray matter structures, is more sensitive to nutritional deprivation during the pre-weaning period than the more stable pool. The precise role and function of these pools remain to be determined.

Prefrontal cortex excitability in early postnatally malnourished rats

The effect of early postnatal malnutrition on the responsiveness of the rat prefrontal cortex was studied by determining excitability thresholds and fatigability to direct cortical stimulation. Malnutrition imposed during the period of rapid brain growth caused a significant increase of cortical chronaxie values as well as increased fatigability of direct cortical responses, indicating a detrimental effect on the axodendritic synapses. Since the prefrontal cortex plays an important role in the temporal organization of behavior, a dysfunction of this cortical area could be a causal link between nutritional and behavioral deficits.

Early undernutrition and [3H]gamma-aminobutyric acid binding in rat brain

The effect of early undernutrition and dietary rehabilitation on [3H]gamma-aminobutyric acid ([3H]GABA) binding in rat brain cerebral cortex and hippocampus was examined. Undernourished animals were obtained by exposing their mothers to a protein-deficient diet during both gestation and lactation. Saturation analysis of [3H]GABA binding in the cerebral cortex and hippocampus revealed high- and low-affinity components in the undernourished group, whereas control animals possessed only a low-affinity site. The concentration of low-affinity binding sites was greater in the undernourished animals. Rehabilitation of undernourished animals completely abolished the binding site differences. Treatment of brain membranes with Triton X-100 yielded two binding components in both the undernourished and control animals, although the concentration of lower affinity sites was still greater in the undernourished group. Neither the efficacy nor the potency of GABA to activate benzodiazepine binding in cerebral cortex was modified by undernutrition. These data suggest that early undernourishment modifies the characteristics of [3H]GABA binding, perhaps by reducing the brain content of endogenous inhibitors of the higher affinity binding site. The lack of effect on GABA-activated benzodiazepine binding suggests the possibility that neither the high- nor the low-affinity GABA binding sites are coupled to this receptor component.

Developmental protein malnutrition in the rat: effects on single-unit activity in the frontal cortex

This study evaluated the effects of developmental protein malnutrition on the spontaneous electrical activity of frontal cortex neurons in the anesthetized rat. Rats were raised prenatally and postnatally on either an 8% or 6% casein diet until adulthood. Compared to the 25% casein controls, both malnourished groups showed a 30-36% decrease in mean discharge rates and a 100-200% increase in the percentage of cells with very slow (less than 1/s) discharge rates. Most of the diet-related changes were confined to a zone 600-1200 micron below the brain surface, approximately cortical layers III, IV and V. A second set of studies in which diet reversals were introduced at birth or in adulthood found that: (a) restoration of a normal 25% casein diet at birth did not appreciably attenuate the effect of prenatal administration of an 8% casein diet; (b) introduction in adulthood of the 8% casein diet to a normally fed rat had no effect; (c) introduction of the 8% diet at birth, however, produced effects in adulthood comparable to those seen when the protein malnutrition was introduced in the prenatal period. Thus, the rat brain is sensitive to both prenatal and postnatal protein malnutrition (starting at birth). Most importantly, the effects of prenatal protein malnutrition on the activity of frontal cortex neurons do not appear to be reversible by restoration of a normal diet in adulthood or at birth.

Synaptic density in chronic animals with experimental neurofibrillary changes

Synaptic density was quantitated in the cerebral cortex and subiculum of rabbits with experimental neurofibrillary changes. Animals were subjected to subcutaneous injection of aluminum tartrate for 90 days, and synapses stained with ethanolic phosphotungstic acid were analyzed in animals killed 100, 200, or 300 days postinjection with aluminum tartrate. A significant difference was found in synaptic density between animals injected with aluminum tartrate and their age-matched controls. This difference was a result of a low synaptic density present in animals killed 200 or 300 days postinjection of aluminum tartrate. In contrast, animals killed 100 days postinjection revealed the same synaptic density as their control. The data suggest that the synaptic depopulation associated with experimental neurofibrillary changes is a gradual process, and such changes are demonstrable only long after the initial appearance of neurofibrillary changes.

The effects of protein deprivation on the nucleus locus coeruleus: a morphometric Golgi study in rats of three age groups

In a previous morphometric Golgi study of the nucleus locus coeruleus we identified in rats fed a 25% casein diet 3 cell types, fusiform, multipolar and ovoid, and compared their age-related changes from 30 to 90 days and 90 to 220 days. In the present study we investigated the effects of an 8% casein diet, initiated prenatally and continued postnatally in the pups, using the same morphometric parameters at the same 3 ages. In these rats the majority of significant age-related changes were in primary and secondary dendritic spine density. On all 3 cell types between 30 and 90 days there was a decreased spine density followed by an increase between 90 and 220 days. These age-related changes closely followed those in controls and, as a result, when the two diet groups were compared at each age they showed only 4 significant differences out of 18 comparisons. In control rats these age-related changes in dendritic spine density in the nucleus locus coeruleus were diametrically out-of-phase with those found in the nucleus raphe dorsalis in a previous study. This is consistent with the postulated mutual inhibitory relationship between the nucleus locus coeruleus and nucleus raphe dorsalis. Comparison of these same events in the nucleus locus coeruleus and nucleus raphe dorsalis in the 8% casein diet rats show no evidence of an out-of-phase relationship. Thus, the relationship between these two closely related nuclei appears to be fundamentally altered by the 8% casein diet. In these comparisons of dendrite spine density and other parameters the 8% casein diet rats have shown in both the nucleus locus coeruleus and nucleus raphe dorsalis deficits and increases as compared to controls. In contrast, in morphometric Golgi studies of pyramidal and Purkinje cells undernutrition generally results in deficits or little change in the various parameters. This suggests that the adaptation of the non-pyramidal neurons in the present study is different from that shown by pyramidal and Purkinje cells.

Functional development of the visual system in normal and protein deprived rats. I. Persistent changes in light-induced cortical evoked response

During an investigation focused on development of visual evoked responses (VER) in normal and protein deprived rats indications of persisting latency differences were found. Since such differences are in variance with previous reports special attention was paid to compare control and protein deprived adult rats. Protein deprivation was induced by feeding rats a diet with 50% reduction in protein content compared with control rat diet from two weeks before onset of gestation until examination. Dependence on experimental variables of latencies and complexity of the VER illustrated the need of a well defined experimental situation. Adult protein deprived rats showed significantly longer latencies to onset and to the first three peaks of the VER and an altered complexity of the response. It is suggested that the observed alterations result from effects of the protein deprivation on early brain development since this and previous studies have shown similar alterations in developing young rats. The divergence in findings between the present and previous reports may be explained by differences in degree of malnutrition and in other experimental conditions.

Reciprocal relationship between size of postsynaptic densities and their number: constancy in contact area

Plasticity in the size of postsynaptic membrane specializations (postsynaptic densities) was analyzed by quantitation following lesioning of parallel fiber afferent axons to Purkinje cells in the cerebellum. Double sectioning of parallel fibers in the same folium as well as longitudinal undercutting of the molecular layer to destroy granule cells and their parallel fibers were used to produce various levels of afferent reduction to Purkinje cells. The length of profiles of membrane densities was measured utilizing semi-automated, computer-electron microscopy and the number of synapses was determined from their volume density and changes in volume estimated from cortical thickness. Correlation between the number of synapses on Purkinje cells and their average contacts area revealed a reciprocal relationship throughout a range of 0-67% reductions in parallel fiber synapses. Larger reduction levels had a progressive decrease in average size of contacted postsynaptic densities and an accompanying increase in the number of vacant postsynaptic specializations. Total absence of parallel fibers resulted in nearly all vacant sites on spines (except for a few connections with boutons having irregular shaped vesicles). These vacant sites were, on the average, only half the size of controls but their number was approximately double the control amount. This study confirms that location and size of synapses are not permanent and that plasticity in size of contacts allows reorganization in circuitry to compensate alterations in the number of inputs following a number of perturbations. The finding of a reciprocal relationship indicates that total contact area on Purkinje cells remained relatively constant throughout the entire range of reductions in the number of afferents. A 'constancy principle for total postsynaptic contact area' is envisioned to stabilize functional aspects of circuitry during developmental organization and to direct compensation following reduction in pre- or postsynaptic neurons from environmental effects or attrition in aging. Constancy in target area provides a realm under which the size of individual synapses can be modified as functional adaptations in circuitry even without changes in the number of connections.

Effect of early undernutrition on reactivity of the rat parietal association area

Cortical reactivity of parietal association area was studied in normal and undernourished rats. (i) The normal group was from mothers which were fed a 21.5% protein diet during lactation. (ii) The undernourished group was from mothers which were fed a 6.5% protein diet during the same period. At 21 days of age (weaning age) all animals received the same diet as that fed to the normal group. At 45 days of age, cortical chronaxie and fatigability of direct cortical responses were evaluated. The results showed that postnatal malnutrition induced alterations on cortical reactivity of that area.

Effects of preweaning undernutrition and continued postweaning protein deficiency or nutritional rehabilitation on polyphosphoinositides in rat brain

Metabolically inert polyphosphoinositides seem to play an important role in the structural development of neurons, glia, and myelin. The metabolically active pool of PhIpp appears to be important for the functional development of glia and myelin during the postweaning period, whereas PhIp seems to be more important for the functional development of neurons during the preweaning period. Neonatal undernutrition reduces the concentrations of structural polyphosphoinositides and metabolic PhIp while metabolic PhIpp remains unaltered. These effects can be reversed by postweaning nutritional rehabilitation. A continued postweaning protein deficiency of neonatally undernourished rats affects structural PhIpp more than PhIp. Metabolically active PhIpp is drastically reduced.

Effects of nutritional rehabilitation on the content and lipid composition of brain gray and white matter of neonatally undernourished rats

Neonatal undernutrition affects the content and lipid concentrations of gray and white matter. Nutritional rehabilitation reverses the deficit observed in gray matter. In the case of white matter the lipid concentration but not the content comes back to normal.

Synapse-to-neuron ratios in the visual cortex of adult rats undernourished from about birth until 100 days of age

Male rats undernourished from the 18th day of gestation until 100 days of age were nutritionally rehabilitated until 200 days of age. Six control and six experimental rats at each of 100 and 200 days of age were killed by perfusion with buffered 2.5% glutaraldehyde. Pieces of visual cortex from each rat were postfixed in osmium tetroxide and embedded in resin. Stereological procedures at the light and electron microscopy levels were used to estimate the synapse-to-neuron ratios in cortical layers II to IV. Rats undernourished until 100 days of age had a mean +/- S.E. of 10,350 +/- 470 synapses associated with each neuron. This represented a 13% deficit (P less than 0.05) when compared to the control value of 11,950 +/- 530. Following nutritional rehabilitation till 200 days of age it was found that the previously undernourished rats had about 23% more (P less than 0.05) synapses-per-neuron than their age-matched controls. This was due almost entirely to a substantial increase in the ratio in the previously undernourished animals; the value of controls did not alter significantly between the two age groups. It appears that the deficit in the synapse-to-neuron ratio seen after a lengthy period of undernutrition is not permanent, at least in rats subsequently allowed nutritional rehabilitation. In fact, such animals seem to be capable of not only "catching-up" but "overshooting" the values found in age-matched controls.

Gangliosides associated with microsomal subfractions of brain: comparison with synaptic plasma membranes

To study ganglioside distribution within subcellular components and test the hypothesis that they are localized at the nerve ending, microsomes and synaptic plasma membranes were isolated from young adult rat brains and compared with respect to ganglioside composition. These were shown to be heterogeneous preparations by fractionation on a discontinuous sucrose gradient into subfractions which had differing ganglioside concentrations. The highest ganglioside concentrations occurred in membranes banding at the 0.8M/1.0M and 1.0M/1.3M interfaces for both microsomes and synaptic plasma membranes. These subfractions had closely similar ganglioside concentrations and pattern distributions. In addition, the kinetics of ganglioside labeling following administration of [3H]-glucosamine were similar for the two preparations. The fact that microsomal subfractions representing heterogeneous mixtures of brain cell membranes showed close similarity to synaptosomal plasma membranes argues against localization of gangliosides at the nerve ending. These results, together with other lines of evidence, support the concept that gangliosides are distributed over large portions of the neuron (and perhaps other brain cells). Data concerning the labeling of gangliosides in different microsomal subfractions indicated a movement of label over time from the more dense to the less dense membranes, as was also noted for the glycoproteins in the same subfractions. Specific radioactivity of the gangliosides increased relative to that of the glycoproteins with time.

Effects of neonatal undernutrition on the lipid composition of gray matter and white matter in rat brain

Separate analyses were made of gray matter and white matter from rat brain after neonatal undernutrition. Newborn rats were redistributed into control, large-litter, and protein-deficient groups. Large litters had 16 rather than 8 pups with a dam. Protein-deficient dams were fed a 4%, instead of a 24%, casein diet. For controls at 21 days of age, the 2',3'-cyclic nucleotide-3'-phosphohydrolase activity was more than fivefold greater in white matter than in gray matter. Severe undernutrition (protein-deficient) gave 2',3'-cyclic nucleotide-3'-phosphohydrolase activities that were 36% lower in gray matter and 56% lower in white matter. Lipid galactose concentrations were 17% less than control in both gray matter and white matter. In protein-deficient white matter, phospholipid concentrations were 15% lower than control. Ethanolamine plasmalogens and phosphatidyl serine were affected most. Moderate nutrition (large litter) had no effect on 2',3'-cyclic nucleotide-3'-phosphohydrolase activity. A 14% deficit of galactolipids was the only difference from controls in large-litter white matter. In large-litter gray matter, phospholipid concentrations were 16% higher than controls. Nearly all glycerophospholipids, including plasmalogens, were affected. With the exception of the myelination markers, 2'3',-cyclic nucleotide-3'-phosphohydrolase and lipid galactose, the development of lipids in gray matter is almost completely spared from the effects of undernutrition. The primary effect of undernutrition is on myelination, especially in white matter.

The effects of protein deprivation on the nucleus raphe dorsalis: a morphometric Golgi study in rats of three age groups

In a previous study we identified 3 cell types in the nucleus raphe dorsalis (NRD): fusiform, multipolar and ovoid. In the present study, we have investigated the effect of an 8% casein diet on these 3 cell types using quantitative techniques on rapid Golgi-impregnated neurons from rats of 3 different ages: 30, 90 and 220 days. Major and minor axes of the cell body and dendritic diameter were unaffected and primary dendritic linear extent was only slightly affected by the diet. All 3 cell types in control rats showed an increase in synaptic spines on both primary and secondary dendrites between 30 and 90 days followed by a decrease for all 3 of the cell types at 220 days. Protein-deprived rats failed to show these age-related changes. Other parameters of comparison showed clear differences between the 3 cell types. These differences could be readily seen when total synaptic spine input to the primary and secondary dendrites was calculated from the data on dendritic number, linear extent and spine density. When viewed in this way the fusiform and ovoid cells show either little change or a decreased synaptic input at all ages, while the presumed serotonergic multipolar cells showed an increase. This is in agreement with neurochemical studies in these rats showing increased levels of this biogenic amine in protein malnourished rats.

Some effects of protein-calorie undernutrition on the developing central nervous system of the rat

Some effects of undernutrition were noted in the brains of 21-day-old pups undernourished from birth by being reared by nursing dams fed on a low protein diet. As compared to the normally fed control pups, the body weight, brain weight, and thickness of the parietal neocortex and paravermal cerebellar cortex were significantly lower in the undernourished pups (p less than 0.001), while the thickness of the cortices of the dentate gyrus and hippocampus CA3 only reached significance at the 5% level. Again, as compared to the control pups, the number of spines per unit length on the distal dendritic segments of the pyramidal cells of lamina III of the parietal neocortex and of the hippocampus CA3 reached significance at the 5% level whereas that of the granule cells of dentate gyrus and Purkinje cells of the paravermis did not reach significance at the 5% level. The myelination of the pyramidal tract and spinal trigeminal tract in the lower medulla was less advanced in the undernourished pups. To date, the demonstration of precise functional correlates for the observed changes of morphological and physiological parameters in animals subjected to undernutrition has been elusive. An approach that may lead to unraveling this problem is suggested in a discussion of relating sources of input to the specific dendritic segments where the spine counts were made.

The influence of protein restriction, rehabilitation and changing nutritional status on synaptic development: a quantitative study in rat brain

Quantitative ultrastructural technique were employed to compare the development and maturation of cortical synapses in rats subjected to protein deprivation, control diet, nutritional rehabilitation and a normal-low crossover diet. Osmicated preparations of the molecular layer of occipital cortex were prepared at 15, 20, 28, 75 and 224 days postnatal in male rats. At 15 and 30 days the values for mitochondrial and synaptic densities, vesicle number and packing per terminal, synaptic length, terminal area and brain weight were lower in the protein-deprived than in the control animals. These initial deficits were progressively transformed to excesses, with the most marked crossover period occurring between 20 and 28 days. By 224 days only brain weight and presynaptic terminal area were lower in the protein-deprived material. A further parameter, synaptic curvature, showed a decrease in negativity in protein-deficient junctions between 15 days (64%) and 224 days (41%). Well-nourished tissue had fewer negatively-curved synapses during early development. These data suggest that the morphological development of the presynaptic terminals is not simply delayed, but is ultimately different in the protein-deprived animals. The nature of these changes may facilitate an adaptation to provide more efficient functioning in the adverse condition. Nutritionally rehabilitated tissue ultimately approaches the control, although significant differences occur in synaptic and mitochondrial densities and in brain weight. The normal--low crossover procedure intensities the differences noted in animals subjected to continuous deprivation.

Effect of prenatal malnutrition on cortical reactivity of the rat parietal association area

The influence of prenatal malnutrition on the reactivity of the rat parietal association cortex was studied by testing thresholds of direct cortical responses. Chronic and acute prenatal starvation caused a significant increase of cortical chronaxy values, indicating a detrimental effect on the axodendritic synapses. Since these synapses subserve cortico-cortical influxes underlying association processes, this detrimental effect could be correlated with behavioral and learning deficits found in malnutrition.

Cerebrovascular integrity in protein-deprived rats

Protein-deprivation does not increase the permeability of the blood-brain barrier in rats aged 3.5--12 months. PA, the product of cerebrovascular permeability (P) to 14C-sucrose and of cerebral capillary surface area (A), is very low in mature rats that have been maintained either on an 8% or 25% casein diet, and equals about 8 X 10(-6) sec-1 in both groups. There is a tendency for the calculated distribution volume of 14C-sucrose within the brain to decline in protein-deprived rats. Conscious, partially immobilized, protein-deprived rats have the same mean blood pressure, heart rate, arterial plasma pH and adreno-sympathetic response to stress (as measured by plasma norepinephrine and epinephrine concentrations) as do normally fed animals.

Long-term effects of postnatal undernutrition and maternal malnutrition on mouse cerebral cortex. I. Cellular densities, cortical volume and total numbers of cells

Quantitative analysis of cellular densities as well as an estimate of the cortical volume and of its total cell population were performed on the cortex of postnatally undernourished mice (2--21 days) and on that of pups from malnourished mothers (gestation and lactation). Animals were followed until 180 days of age after more than 5 months of nutritional rehabilitation, and data were obtained at 10, 30, 60, and 180 days of age. The neuronal density was much higher in all cortical layers of the two experimental series, suggesting a delay in cortical maturation. Moreover, layers II, III, and IV were more delayed than layers I, V, and VI. Postnatal undernutrition had more severe effects than maternal malnutrition and the degree of recovery after a long rehabilitation was much less. The increase of the cortical volume was greatly reduced in postnatal undernutrition and to a lesser degree in maternal malnutrition. The total number of glial cells was also reduced more in postnatal undernutrition than in maternal malnutrition, but the total number of neurons was never smaller than in the controls.

Long-term effects of postnatal undernutrition and maternal malnutrition on mouse cerebral cortex. II. Evolution of dendritic branchings and spines in the visual region

Quantitative analysis of the dendritic branchings of pyramidal cells from layers V and III, as well as of the number of spines on their apical dendrites, were performed on the visual cortex of postnatally undernourished mice (2nd--21st day) and on that of pups from malnourished mothers (gestation and lactation). Animals were followed till 180 days of age after more than 5 months of nutritional rehabilitation, and data were obtained at 10, 15, 21, 30, 60, and 180 days of age. The increase and maturation of dendritic branchings and spines were much more reduced in postnatal undernutrition than in maternal malnutrition. Furthermore, permanent damage still remained at 180 days in postnatal undernutrition while almost no damage was statistically detectable after maternal malnutrition.

Postnatal vascular growth in the neocortex of normal and protein-deprived rats. Morphometric studies

The postnatal vascular growth in the neocortical area 18 of normal and pre- and postnatally protein-deprived rats was examined. For control rats the specific length, the specific surface and the volume fraction of vessels increased rapidly between 7 and 20 days of age. Thereafter, only a minor increase was seen. In protein-deprived rats there was no increase in the specific length of vessels between 7 and 10 days of age and this variable was still reduced at 30 days of age compared to controls. This reduction was due to a decrease in the specific length of thin vessels (luminal diameter less than 8.25 mu) whereas the specific length of wider vessels was not affected by the protein deprivation. There were no significant differences in the specific surface or volume fraction of vessels between control and protein-deprived rats. These findings indicate an adaptive increase in luminal diameter of vessels in the protein deprived rats during postnatal development. At 90 days of age no significant differences between vascular variables of control and protein-deprived rats were seen.

A stereological analysis of the neuronal and synaptic content of the frontal and cerebellar cortex of weanling rats undernourished from birth

The frontal cortex and granular layer of the cerebellum have been examined in 30-day-old rats undernourished from birth. Quantitative stereological procedures at the light microscopical level have been used to estimate the volume proportion and numerical densities of neuronal nuclei. Similar methods at the electron microscopical level were employed to calculate the numerical densities of synapses. Hence, synapse-to-neuron ratios have been calculated in these brain regions. In the frontal cortex, the undernourished group of rats showed a 37% deficit (P less than 0.05) in the synapse-to-neuron ratio. This was due to a combination of an increase in the numberical density of neurons and a decrease in the numerical density of synapses, although, individually, neither of these reached statistical significance at the 5% level. In the granular layer of the cerebellum there was a 31% (P less than 0.01) deficit in the synapse-to-neuron ratio. This was a function of the reduced numerical density of synapses, with no difference in the numerical density of granule cells between groups. For the frontal cortex, the volume proportion of neuronal nuclei was significantly greater in the undernourished group of rats. There were no significant differences between control and undernourished rats in the volume of the 'forebrain' occupied by cortex. The mean diameters of neuronal nuclei and synaptic discs did not differ in any given region between treatment groups. These observations are discussed in context with the previously published results on synapses and neurons in undernourished animals.

Rehabilitation following early malnutrition in the rat: body weight, brain size, and cerebral cortex development

Sprague-Dawley rats were malnourished by giving their mothers an 8% casein diet starting at day 10 of gestation, while controls were fed a 24% casein diet. Starting at postnatal day 20 (P20), rehabilitation of the malnourished animals was attempted by: (1) feeding both mother and young a 24% casein diet, (2) leaving the pups with their mothers until they were 40 days old, and (3) reducing the litter size from 8 to 4 pups. Observations were made on aldehyde-perfused tissue from animals 20, 40 and 70 days old. The somatosensory cortex from one hemisphere was embedded in Araldite, and that from the other side was processed fro Golgi staining. At 20 days of age the body weight of the malnourished animals was 21% that of the controls, but at 70 days it was no longer different. The anterior-posterior length, the width, and the height of the cerebral hemispheres were also significantly reduced at P20, but the differences had disappeared by P70. The thickness of area 3 of the cerebral cortex was measured in 1 micron sections. It was significantly reduced in the malnourished animals at P20, but at P40, following rehabilitation, the difference was no longer statistically significant. In tangential 1 micron sections the fraction of the volume of tissue occupied by neuropil was measured in layers II through IV. At P20 it was significantly reduced only in the upper half of layers II/III of the malnourished animals; at P40 this difference was no longer present. The mean volume of upper layer II/III cell bodies was estimated and found to be significantly reduced in the experimental animals at P20 but not at P40. In the Golgi preparations, pyramidal cells in upper layer II/III were studied. Their estimated volume, as well as the thickness of their basal dendrites, was significantly reduced in the 20 day malnourished animals, but not in the rehabilitated animals. These results show that animals severely malnourished until 20 days of age can reach normal body weight and attain cerebral hemispheres of normal size when proper nutrition is provided. The effects of malnutrition on the cerebral cortex of these animals are most apparent in upper layer II/III which, during the time of nutritional restriction, is the least developed of the cortical layers. However, when proper nutrition is provided, the cerebral cortex may attain normal morphology.

Studies on neurotransmitter-stimulated phospholipid metabolism with cerebral tissue suspensions: a possible biochemical correlate of synaptogenesis in normal and undernourished rats

The phenomenon of neurotransmitter-stimulated incorporation of 32Pi into phosphatidic acid and inositol phosphatides (neurotransmitter effect) in developing brain was studied in vitro as a possible measure of synaptogenesis. While the neurotransmitter effect was not observed with brain homogenates, highly consistent and significant effects were noted with brain tissue suspensions obtained by passing the tissue through nylon bolting cloth. The magnitude of the effect decreased with the increase in mesh number. Maximum stimulations obtained with the 33 mesh adult brain cortex preparations (mean +/- S.E.M. of 6 experiments) were 203 +/- 8%, 316 +/- 17% and 150 +/- 8% with 10(-3) M acetylcholine (ACh) + 10(-3) M eserine; 10(-2) M norepinephrine (NE) and 10(-2) M serotonin (5-HT), respectively. Experiments with developing rat brain at 7, 14 and 21 days of age showed that the neurotransmitter effects due to ACh, NE and 5-HT increase progressively in different regions of the brain but that there are marked regional differences. It is suggested that the neurotransmitter effect is a valid biochemical correlate of synaptogenesis. In rats undernourished from birth to 21 days of age, by increasing the litter size, the neurotransmitter effect with ACh, NE or 5-HT was not altered in the cortex but was significantly reduced in the brain stem. In cerebellum the effects due to ACh and NE were significantly altered, while that with 5-HT was unaffected. It is concluded that cholinergic, adrenergic and serotonergic synapses are relatively unaffected in the cortex but are significantly affected in the brain stem by undernutrition. In the cerebellum of undernourished rats the adrenergic and cholinergic, but not serotonergic systems, are altered.

Effect of a low protein diet on the anatomical development of subcortical formations

The effects of a low protein diet during gestation, lactation, and after weaning on the anatomical development of a subcortical nucleate formation, the neostriatum, and a reticulate formation, the diagonal band of Broca, were studied. At 10, 30, and 90 days the volume of the neostriatum was decreased in the experimental rats. However, the percent of the brain volume that was neostriatum was unaffected at each of these ages. In a rapid Golgi study of individual neurons at 90 days of age there was no significant effect of the low protein diet on the dendritic length of three different types of neurons within the neostriatum. However, its heavily spined dominant neuron showed a significant decrease in synaptic spine density. In the reticular formation, there was also no significant effect on dendritic length. A minute, apparently axonless cell corresponding to the neurogliaform cell of Ramón y Cajal, showed a decrease in extent of its cell processes only in the neostriatum. When compared to cortical formations, these phylogenetically more conservative neuronal substrates appear to be more resistant to the effects of undernutrition.

Tissue culture analysis of neurogenesis: myelination and synapse formation are retarded by serum deprivation

Explants from newborn mouse cerebellum were cultured in nutrient media containing either adequate (30%) or low (15% or 7.5%) serum content. By light microscopic observation, delayed and inhibited myelination was detected in cultures fed with low serum media (experimental cultures). Specific activities of two enzymes related to myelin synthesis, 2',3'-cyclic nucleotide-3'-phosphohydrolase and 3-hydroxy-3-methylglutaryl coenzyme A reductase, were also reduced in experimental cultures. Morphometric analysis of electron micrographs showed that the size of presynaptic endings and total area occupied by synapses in experimental cultures were substantially reduced, while synaptic density per unit area increased. Reflecting the results of synaptic underdevelopment, the levels of two neurotransmitter enzymes, choline acetyltransferase and glutamic acid decarboxylase, were also decreased in experimental cultures.

The effect of refeeding after neonatal starvation on Purkinje cell dendritic growth in the rat

Male rats, undernourished from birth until 30 days by restricting access to the lactating dam, were given ad libitum food supplies unitl 80 days. Body weight, whole brain weight and cerebellar remained significantly lower in these animals than in normally fed controls. Significant deficits in the area of the molecular and granular layers persisted at 80 days, although there was some recovery during the refeeding period. At the same time granule and Purkinje cell density declined, suggesting that the areal recovery was due to the expansion of the interneuronal matrix. Granule cell numbers remained unchanged between 30 and 80 days. Network analysis of Golgi-Cox preparations indicated a 28% decrease in overall size of the Purkinje cell dendritic networks, due primarily to a deficit in segment frequency which remained unchanged throughout the rehabilitation period. Segment length did, however, show some recovery; distal segments from 80-day experimental networks were significantly longer than those of 30-day undernourished animals. The results of the topological analysis suggested that dendritic remodelling had taken place during the rehabilitation period. The failure to observe a complete recovery in the size and morphology of the dendritic network may be explained in terms of recent suggestions that dendritic development is influenced both by the metabolism of the neurons themselves, and by the number and density of adjacent afferent axons. It is suggested that refeeding from 30 days leads to the recovery of Purkinje cell metabolism, but is unable to restore the parallel fiber deficit.

Synaptic vesicles and other organelles of human mossy fibre endings. A morphometric study

The mossy fibre ending organelles of 6 men were studied, using morphometric methods. The numerical densities of agranular, coated and dense core vesicles, as well as the number of agranular vesicles per micrometer2 of the synaptic surface and per synapse were calculated.

The effects of undernutrition on Purkinje cell dendritic growth in the rat

The effects of undernutrition on the developing cerebellum were studied in 30-day-old rats undernourished from birth by restricting access to the lactating mother. These animals showed a significant reduction in cerebellar weight when compared with well-nourished controls. Quantitative studies of the cerebellar vermis revealed a 34.2% reduction in total area, with the density of both granule cells and Purkinje cells increased. Network analysis of Golgi-Cox preparations indicated a significant increase in the density of dendritic fields of Purkinje cells, although there was a 37% decrease in overall network size, due to reduction in the total number of dendritic segments, and a reduction in the length of distal segments. Topological analysis indicated that the network had developed by terminal branching, as in normal animals, but with some deviation from the usual purely random branching pattern. All the observed modifications may be accounted for in terms of alterations in protein synthesis and DNA synthesis occurring in undernourished animals. This leads to alterations in the extent of the interneuronal matrix, a reduction in the number of granule cells and direct effects on Purkinje cell metabolism, all of which influence dendritic development, although the relative importance of each of these factors awaits precise definition.

Some effects of undernutrition on synaptic development -- a quantitative ultrastructural study

The development of synaptic junctions in rat occipital cortex has been studied at 7 and 20 days postnatal in control and undernourished animals. In addition, adult control cortex has been compared with cortex derived from animals undernourished until 35 days postnatal and then nutritionally rehabilitated. Emphasis has been placed on material stained with phosphotungstic acid (E-PTA technique) although osmicated material has been examined. The body weights of the undernourished animals were lower than those of their age-matched controls, the deficit at 20 days being 55%. The number of synaptic junctions per unit area of the molecular layer was lower in the undernourished animals at 7 and 20 days, the most prominent deficit being at 20 days. In an attempt to detect ultrastructural correlates of undernutrition, E-PTA stained synaptic junctions were divided into 5 types (A-E), based upon their presynaptic characteristics are reflecting varying degrees of maturity. During normal development the immature synaptic types, particularly type E, are predominant, giving way to the more mature types (A-C) as development proceeds. Undernutrition however, appears to disrupt this developmental sequence, with a higher than normal percentage of immature synaptic types present at the age studied. Nutritional rehabilitation rectifies the imbalance to a degree, the adult rehabilitated pattern resembling the 20-day control pattern. Preliminary examination of the 20-day osmicated material confirmed the deficit of synapses per area of tissue in the undernourished cortex. It also revealed decreases in the number of vesicles per terminal unit area and in the internal area of the synaptic vesicles in the undernourished tissue.