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

Effects of pre- and neonatal undernutrition on the kyphotic response and c-Fos activity in the caudal periaqueductal gray of primiparous lactating Wistar rats

In rodents, the most representative component of maternal behavior that meets the purpose of newborn nutrition is the kyphotic posture. During this posture, the mother maintains a unique environment for the protection, thermal regulation and breast-feeding of the progeny. The aim of this study was to investigate possible deficiencies in the kyphotic posture of adult lactating dams with pre- and neonatal undernutrition evoked by their own pups suckling in a home-cage situation. Wistar dams that had been previously exposed to perinatal undernutrition were mated at 90days of age, and pregnancy was confirmed by vaginal smears. Before testing if the perinatal underfed dam affected behavior, pups were removed (4h), and both the maternal response and the kyphotic posture were video-recorded (1h) and analyzed at 4 and 12days of lactation. Pre- and post-test litter weight gain was obtained. To immunostain the caudal periaqueductal gray, the litter was separated from their dams 24h before suckling stimulation. The results showed that underfed dams significantly reduced the duration of high kyphosis by choosing unconventional postures (prone and partial kyphosis). The body weight of the F1 offspring was significantly reduced, and the underfed F0 dams showed reduced c-Fos immunostaining at the caudal periaqueductal gray. The findings showed that early underfed dams have deficiencies in the mechanisms underlying the kyphosis, possibly because the pups' cues to evoke this posture were suboptimal and/or because the dam expressed deficient nursing. The results suggest that the abnormal kyphotic posture may affect the mother-litter bonds and have long-term effects on neonatal brain functions.

Interaction between pre-weaning undernutrition and post-weaning environmental enrichment on somatic development and behaviour in male and female rats

Male and female rats were undernourished from birth to 30 days by restricting access to the lactating mother, and then fed ad libitum. At weaning, underfed and normally suckled controls were permanently housed either in pairs in standard cages or in groups of 10 in 1 m(3) cages containing ladders, ropes etc. Severe undernutrition during suckling followed by 4 months of refeeding, produced some changes in sexual behaviour in adult males (increased ejaculation frequency) but had no effect on behaviour in open field, dark preference or passive avoidance. Differential post-weaning environment produced significant differences in behaviour, irrespective of previous feeding conditions. Enriched animals were more active and exploratory. Females differed from males in the same direction as enriched from standard, and were more responsive to social and housing conditions.

Critical periods in brain development

The growth of the brain after organogenesis can be described as occurring in two somewhat overlapping phases: a phase of neuronal multiplication followed by one of glial proliferation, during and after which occur myelination and dendritic and axonal arborization. Within this gross chronology is a finer-grained chronology, with, for instance, different neuronal populations dividing at different times. The course of brain development can be affected by a variety of factors, the nature and extent of the perturbation dependent on the timing of the treatment with respect to stage of brain development. Growth processes completed before treatment are unaffected. Only those processes occurring at the time of the treatment are affected, plus some later-occurring processes, as a result of a cascade of effects. These concepts are examined briefly with reference to ionizing radiation, hormones and environmental stimulation and more fully with respect to nutrition. Undernutrition appears to depress the rate of all brain growth processes contemporaneous with it to the same extent. Whether the effects produced are likely to be permanent is discussed, together with the possibility that there may be mechanisms that attenuate or compensate for adverse effects.

Regulation of cyclin dependent kinase inhibitor proteins during neonatal cerebella development

The cyclin dependent kinase holoenzymes (CDKs), composed of catalytic (cdk) and regulatory (cyclin) subunits, promote cellular proliferation and are inhibited by cyclin dependent kinase inhibitor proteins (CDKIs). The CDKIs include the Ink4 family (p15Ink4b, p16Ink4a, p18Ink4c, p19Ink4d) and the KIP family (p21Cip1 and p27Kip1). The sustained induction of p21 and p18 during myogenesis implicates these CDKI in maintaining cellular differentiation. Herein we examined the CDK (cyclin D1, cdk5) and CDKI expression profiles during the first 24 days of postnatal rat cerebella development. Cdk5 abundance increased and cyclin D1 decreased from day 9 through to adulthood. The CDKIs increased transiently during differentiation. p27 increased 20-fold between days 4 and 24, whereas p21 rose twofold between 6 to 11 days. p19, p18 and p16 increased approximately two- to threefold, falling to low levels in the adult. Immunostaining of cyclin D1 was localized in the external granular cells, whereas p27, was found primarily in the Purkinje cells. The period of maximal differentiation between days 9 to 13 was associated with a change in p21 and p16 staining from the external granular and Purkinje cells to a primarily Purkinje cell distribution. Protein-calorie malnutrition, which was previously shown to arrest rat cerebella development, reduced cyclin D1 kinase activity and p27 levels. However, p16 and p21 levels were unchanged. We conclude that the CDKIs are induced with distinct kinetics in specific cell types and respond differentially to growth factors during cerebella development, suggesting discrete roles for these proteins in normal cerebella development.

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.

Early-life undernutrition causes deficits in rat dentate gyrus granule cell number

Recently developed stereological methods have been used in experiments to examine the effects of two levels of undernutrition during early postnatal life on the total number of rat dentate gyrus granule cells. This study has shown that previously undernourished rats have significant deficits in the total number of this particular type of neuron.

Neonatal undernutrition and self-grooming development in the rat: long-term effects

The effect of neonatal undernutrition on six different self-grooming components was examined in male rats during the pre- and postweaning periods. Rats underfed by the maternal nipple-ligation procedure before weaning did not exhibit significant score differences in the various self-grooming measurements. In contrast, after weaning they showed a significant increment in the duration of face-washing, head-washing, fur licking and body-scratching. In all cases, the total postweaning self-grooming activity was significantly increased in the formerly underfed rats. Present data suggest that neonatal undernutrition may presumably interfere with the sequential maturational processes of central and/or peripheral mechanisms underlying some components of self-grooming behavior.

Developing rat cerebellum--III. Effects of abnormal thyroid states and undernutrition on gangliosides

Alteration of rat postnatal cerebellar development produced by undernutrition, thyroxine treatment and thyroid deficiency also involves ganglioside deposition. The distribution of the different ganglioside types is apparently unaffected but quantitative alterations are present that reflect the reduction of cell number and cell process surface in the adult, and either acceleration or slowing down or reduction of cell formation and maturation occurring during cerebellar development in the three experimental situations.

Effects of a lengthy period of undernutrition from birth and subsequent nutritional rehabilitation on the synapse: granule cell neuron ratio in the rat dentate gyrus

Recent evidence showing alterations in spatial memory due to a period of undernutrition during early life has implicated the hippocampus as one of the brain centres that may be particularly adversely affected. However, there are very few quantitative morphological studies that have examined the neuronal and synaptic populations of the hippocampi from undernourished animals. We decided to carry out such experiments, paying particular attention to the granule cell of the dentate gyrus. Male rats were undernourished from the 18th day of gestation until 21, 75, or 150 days of age. Some of these previously undernourished rats were nutritionally rehabilitated between 150 and 250 days of age. Groups of well-fed control and experimental rats were killed by intracardiac perfusion with 2.5% sodium-cacodylate-buffered glutaraldehyde. The right hippocampus from each rat was dissected out and processed for electron microscopy. Stereological procedures at the light and electron microscopical levels were used to estimate the numerical densities of granular cell neurons and molecular layer synapses in the dorsal lip of the dentate gyrus. These estimates were used to calculate synapse: neuron ratios. There were 5,056 +/- 347 (mean +/- SE) and 5,002 +/- 190 synapses per neuron in 21-day-old control and undernourished rats, respectively. By 75 days these values had increased to 9,215 +/- 588 and 6,683 +/- 237. The difference was statistically significant. By 150 days of age the value for control animals had fallen once again to 6,518 +/- 209 whereas undernourished rats had increased slightly to 7,689 +/- 288 (P less than .01); 250-day-old rats, previously undernourished from birth to 150 days of age, showed a substantial increase in the synapse: neuron ratio during the period of nutritional rehabilitation. Thus these nutritionally rehabilitated rats had 9,407 +/- 365 synapses per neuron whereas age-matched controls had only 6,323 +/- 239 (P less than .01). These results indicate that the rat dentate gyrus is vulnerable to undernutrition even during the postweaning period and that a lengthy period of undernutrition can alter the developmental growth curve for synapse: neuron ratios.

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.

Comparison of cerebellar Purkinje cell simple spike discharges in adult rats after undernutrition during the suckling period and nutritionally normal rats

The spontaneous activity of cerebellar Purkinje cells was compared in 100- to 130-day-old rats undernourished during the suckling period (i.e. 0-21 days) and subsequently nutritionally rehabilitated (PU rats), with that in rats of the same strain and of similar age fed normally (age controls), and in normally fed rats of the same strain but approximately one month younger (weight controls). Simple spike activity of single cells was recorded with extracellular microelectrodes in pentothal-anaesthetized animals. The discharge patterns were assessed by on-line computer analysis of the interspike interval distributions with subsequent transformation of the data to enable the results to be evaluated by an analysis of variance. In addition, the distribution of the mean interval, the percentage of intervals less than 30 ms, the percentage of intervals greater than or equal to 150 ms, and the time spent in intervals greater than 150 ms, were compared for the PU rats and pooled controls by a nonparametric statistical test on the untransformed data. None of the results indicated that there were any significant differences between the simple spike activity of Purkinje cells from age- and weight- control rats nor between that in PU rats and the control groups. These results are discussed in relation to the previously reported deficits of granule cells in the cerebella of PU rats.

Sex differences in effects of environmental stimulation on brain weight of previously undernourished rats

Neonatally undernourished male and female rats were housed under differential (enriched vs standard) environmental conditions during refeeding from 30 days post-partum (dpp). Animals were killed at 170 dpp and whole brain, forebrain and cerebellar weights compared with those of normally-fed, differentially housed control animals. A sex difference was observed in the response to environmental enrichment. Enriched females showed significantly increased brain weights, irrespective of previous nutritional history. Enriched males failed to show any significant alteration in brain weight. Autopsy results indicated that the enriched condition was stressful to males but not to females. The results cast doubt on the notion that infantile undernutrition may limit later effects of differential experience on the brain.

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 effects of refeeding after varying periods of neonatal undernutrition on the morphology of Purkinje cells in the cerebellum of the rat

Undernutrition of the rat for the first 30 days of postnatal life is known to permanently alter Purkinje cell (PC) dendritic morphology. The effects of earlier nutritional rehabilitation have not previously been determined. Neonatal rat pups were undernourished by limiting their access to the lactating dam. After 10, 15, or 20 days of food restriction, animals were either killed for histological comparison with normally fed controls, or provided with ad libitum food until 80 dpp, and then killed. Network analysis of Golgi Cox impregnated PCs from the undernourished animals revealed alterations in dendritic length, segment frequency, and branching pattern, which first became apparent at 15 dpp, accompanied by a reduction in the number of granule cells (GCs) per PC. If undernourished animals were refed from 10 or 15 days, however, the total lengths and segment frequencies of their PC trees were indistinguishable from those of controls at 80 dpp, although the 15-day group showed persistent topological alterations. The GC:PC ratios of these refed groups were also found to be similar to those of the controls. In animals refed after 20 days of undernutrition, network size remained reduced, as did the GC:PC ratio. The different degrees of recovery of PC dendritic field parameters recorded in the refed animals could be related either to enhanced GC replication afforded by refeeding, or to the existence of intrinsic mechanisms which limit the growth capacity of the PC dendrites.

The influence of pre- and postnatal undernutrition on the developing brain stem reticular core: a quantitative Golgi study

Neurons of the brain stem reticular core were examined in rats which had been exposed to prenatal or postnatal undernutrition. Prenatal undernutrition was induced by restricting maternal diet to 2/3 of ad libitum prior to and during the gestation period. Postnatal restriction to 20 days of age was induced by increasing the litter to 14 and removing the dam for 8 h each day. Both imposed experimental conditions tended to delay the course of reticular neuron development as indicated by altered number of dendritic protospines and varicosities. However, the effects of prenatal undernutrition were more severe. At birth, the amount of DNA in the brain stem was reduced (-24%) while average dendritic extent and branching were greatly increased. Early undernutrition appears to have a profound effect on the quality of the neuropil, both neuronal and glial, while postnatal exposure does not influence the structure of the dendritic arbor.

Morphological development of the brain stem reticular core in prenatally undernourished rats

The development of brain stem reticular core neurons in prenatally undernourished rats was investigated using the Golgi technique to determine the effect of immediate postnatal nutritional rehabilitation. Quantitative measurements of dendritic extent of branching and of cell size were compared in experimental and control neurons. An assessment of developmental dendritic status was achieved by counting numbers of dendritic protospines and varicosities on proximal and distal segments of dendrite. The protein and DNA content of the brain stem was also examined. The deficit of brain stem cell number at birth was rapidly restored by 11 days of age as was the delay of dendritic development. The number of dendritic protospines was comparable to control levels by 20 days but dendritic varicosities were more numerous on proximal segments. The dendritic extent increased during this period with rehabilitation though not as greatly as in control cells. The pattern of dendritic branching and size of somata were restored. Cell replication with rehabilitation probably represents a return of glial numbers which may impede distal dendritic growth of reticular core dendrites. Proximal growth is enhanced and the afferent supply to the reticular core may be increased during this time.

Malformation of Purkinje cell dendrites induced by graft-versus-host disease

Impairment of cerebral Purkinje cell growth was assessed in Golgi-Cox stained tissue in 14 day old (Fischer X DA)F1 hybrid rats subjected to graft versus host disease (GVHD). GVHD was induced by grafting parental strain lymph node cells (PSLNC) into the anterior facial vein on the day of birth. We have previously described GVHD induced changes in nucleotide and protein content [12] and RNA function [14] as well as alterations in cell numbers and areas of the external granular and molecular layers in diseased animals [13]. In this report some effects of GVHD on the gross morphology of Purkinje cells in 14 day old animals are enumerated. Most Purkinje cells (62%) from GVHD animals had a height to width ratio greater than 1, whereas most from control animals (71%) had ratios of less than 1. The majority of Purkinje cells (67%) from diseased animals had elongated main dendrites which were devoid of branches and often (13%) these elongated main dendrites were S-shaped. In addition, comparison of Purkinje cells from GVHD and control animals revealed a greater tendency (15%) toward retention of extrasomal process in GVHD animals. These findings suggest that GVHD affects nondividing, differentiating cell populations as well as those which are proliferating and migrating. Our evidence that, as a result of GVHD, the protein synthesizing capacity of the cerebellum is altered [14] and that Purkinje cells are more closely spaced at day 11 suggests that both intrinsic and extrinsic factors are involved in producing the changes in dendritic shape reported here.

A stereological analysis of the cerebellar granule and Purkinje cells of 30-day-old and adult rats undernourished during early postnatal life

Male rats undernourished from birth to 30 days of age were nutritionally rehabilitated till 160 days of age. Quantitative stereological procedures at the light microscope level were used to estimate, among other things, the numerical densities of cerebellar granule and Purkinje cells on a "per unit volume of cortex" basis. These were subsequently used to calculate granule-to-Purkinje cell ratios. The 30-day-old undernourished rats had a mean +/- S.E. of 290 +/- 27 granule cells for every Purkinje cell present, compared to 395 +/- 34 for the controls. This was a deficit of about 27% (p < 0.05). At 160 days of age, the previously undernourished rats still showed a persisting deficit of about 25% (p < 0.05) in this ratio, despite the lengthy nutritional rehabilitation. There were no statistically significant age-related changes in this ratio. The numerical density of Purkinje cells, but not that of granule cells, was significantly greater in the previously undernourished rats than in controls, for both age groups, Increasing age caused a fall in the numerical density of both cell types. Granule and Purkinje cell nuclear diameters were unaffected by nutrition. However, Purkinje cell nuclei decreased in size by between 7%--13% with increasing age. These results indicate that undernutrition during early life can cause a permanent distortion of the relative number of the various cell types in the cerebellum.

Synapse-to-neuron ratios of the frontal and cerebellar cortex of 30-day-old and adult rats undernourished during early postnatal life

Male rats undernourished from birth to 30 days were nutritionally rehabilitated till 160 days of age. Quantitative stereological procedures at the light and electron microscopical levels were employed to estimate, among other things, the synapse-to-neuron ratios in the frontal cortex and granular layer of the cerebellum. In the frontal cortex, the 30-day-old undernourished rat had a mean +/- SE of about 14,020 +/- 1,540 synapses-per-neuron compared with 22,270 +/- 3,250 for the controls. This was a deficit of 37% (p < 0.05). By 160 days of age the previously undernourished rats showed no statistically significant deficit in this ratio compared with controls (11,800 +/- 690 and 13,360 +/- 1,110 respectively, p > 0.1). This was due mainly to a fall in the synapse-to-neuron ratio with age. A much larger fall in the ratio occurred in the control than in the previously undernourished group. In the granular layer of the cerebellum the 30-day-old undernourished rats had 341 +/- 17 synapses-per-neuron compared with 495 +/- 25 for the controls. This was a deficit of 31% (p < 0.01). By 160 days of age the previously undernourished rats again showed no statistically significant deficit in this ratio compared with controls (627 +/- 56 and 688 +/- 38, respectively (p > 0.1). These results show that the previously undernourished rats are capable of at least some (if not complete) "catch-up" with regard to the synapse-to-neuron ratio.

Organization and development of brain stem auditory nuclei of the chicken: dendritic gradients in nucleus laminaris

Nucleus laminaris (NL) is a third-order auditory nucleus in the avian brain stem which receives spatially-segregated binaural inputs from the second-order magnocellular nuclei. The organization of dendritic structure in NL was examined in Golgi-impregnated brains from hatchling chickens. Quantitative analyses of dendritic size and number were made from camera lucida drawings of 135 neurons sampled from throughout the nucleus. The most significant results of this study may be summarized as follows: (1) The preponderant neuron in n. laminaris may be characterized as having a cylindrical-to-ovoid cell body, about 20 micrometer in diameter. The neurons comprising NL were found to be nearly completely homogeneous in issuing their dendrites in a bipolar fashion: one group of dendrites is clustered on the dorsal surface of the cells, the other group on the ventral. The dendrites of NL are contained within the glia-free neuropil surrounding the nucleus. From the rostromedial to the caudolateral poles of NL there is a gradient of increasing extension of the dendrites, increasing number of tertiary and higher-order dendrites, and increasing distance from the somata of the occurrence of branching. (2) The total dendritic size (sum of the dorsal) and ventral dendritic lengths of the cells) increases 3-fold from the rostromedial to the caudolateral poles of NL. About 50% of the variance in dendritic size is accounted for by the position of the cells in NL, and the gradient of dendritic size increase has the same orientation across NL as the tonotopic gradient of decreasing characteristic frequency in NL. (3) From the rostromedial pole to the caudolateral pole of NL there is an 11-fold decrease in the number of primary dendrites along a gradient coinciding with the length and frequency gradients. Sixty-six percent of the variance in dendrite number is accounted for by position in the nucleus. (4) The correlation of dorsal and ventral dendritic size on a cell-by-cell basis is not high (r = 0.47), indicating a fair amount of variability on the single-cell level. On the other hand, the average dorsal dendritic length within an isofrequency band in NL correlates very highly with the average ventral dendritic length. Thus, on an areal basis, the amount of dendritic surface area offered to the dorsal and ventral afferents is tightly regulated. (5) The dorsal and ventral dendrites have separate gradients of increasing length and number across NL. The dorsal gradients are skewed toward the rostrocaudal axis, while the ventral dendritic gradients are skewed mediolaterally. (6) There was no correlation between either dendritic size or number of primary dendrites and the size of the somata in NL, which remains relatively constant throughout the nucleus. Several hypotheses about the ontogenetic control of dendritic structure are examined in light of the above data. Of these, the hypotheses that the ontogeny of dendritic size and number is largely under afferent control receives a great deal of circumstantial support.

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.

The effects of postnatal lead exposure on Purkinje cell dendritic development in the rat

Rat pups, suckled by mothers maintained after parturition on a diet containing 4% lead acetate, were killed at 30 days and their cerebella examined. The blood lead was greatly increased in these animals (258.20 +/- 6.72 micrograms/100 ml) as compared with controls (4.75 +/- 0.75 micrograms/100 ml) and their mean body weight was reduced by 28%. Cerebellar weight, however, remained unchanged. Histologically the vermis showed vacuolation of the white matter and an increase in the size of Purkinje cell bodies. The total number of Purkinje and granule cells and their densities were unchanged except in animals with encephalopathy when these parameters were reduced. Network analysis of the dendritic trees of Purkinje cells indicated a 34.8% reduction in total dendritic length, due to reduction in total segment number and in the length of distal segments. Dendritic density and the frequency of trichotomous branching were unchanged by the experimental treatment. The density of dendritic spines over the periphery of the network was normal. The topology of the dendritic trees of Purkinje cells was abnormal in that branching patterns deviated from the normal pattern generated by random terminal growth. These results suggest that lead causes changes in Purkinje cell metabolism which reduce the rate of dendritic growth and cause abnormal branching. It remains to be determined whether these are direct effects or secondary to the vascular changes known to occur in the cerebellum during lead intoxication.