A quantitative electron microscopic study of synaptogenesis in the dentate gyrus of the rat

Rate of maturation of the hippocampus and the developmental progression of children's performance on the delayed non-matching to sample and visual paired comparison tasks

Although it has been widely speculated that the hippocampus, and the type of memory dependent upon the hippocampus, develops late in primates just as it does in rats (e.g., Nadel & Zola-Morgan, 1984; Bachevalier & Mishkin, 1984; Schacter & Moscovitch, 1984), the evidence to date would not seem to support this. Instead, there is behavioral evidence of very early recognition memory and anatomical evidence of very early hippocampal maturation in human and non-human primates. It is true, however, that the standard delayed non-matching to sample task, which requires recognition memory, is not mastered until quite late. The reason for this late mastery would appear to be the late emergence of some other ability required for the task, not recognition memory. The candidates for what that ability might be are (1) the capacity to plan and execute an indirect, two-action sequence, (2) the capacity to understand that the object stands for the reward, but is not the reward itself, (3) the ability to deduce an abstract rule, (4) the ability to make explicit on testing what can be shown implicitly during play, (5) the ability to quickly encode visual stimuli (speed of encoding), and (6) the ability to resist interference. Only empirical work will enable us to decide among these candidate abilities; that work is currently underway.

Contributions of dendritic spines and perforated synapses to synaptic plasticity

The dynamic nature of synaptic connections has presented morphologists with considerable problems which, from a structural perspective, have frustrated the development of ideas on synaptic plasticity. Gradually, however, progress has been made on concepts such as the structural remodelling and turnover of synapses. This has been considerably helped by the recent elaboration of unbiased stereological procedures. The major emphasis of this review is on naturally occurring synaptic plasticity, which is regarded as an ongoing process in the postdevelopmental CNS. The focus of attention are PSs, with their characteristically discontinuous synaptic active zone, since there is mounting evidence that this synaptic type is indicative of synaptic remodelling and turnover in the mature CNS. Since the majority of CNS synapses can only be considered in terms of their relationship to dendritic spines, the contribution of these spines to synaptic plasticity is discussed initially. Changes in the configuration of these spines appears to be crucial for the plasticity, and these can be viewed in terms of the significance of the cytoskeleton, of various dendritic organelles, and also of the biophysical properties of spines. Of the synaptic characteristics that may play a role in synaptic plasticity, the PSD, synaptic curvature, the spinule, coated vesicles, polyribosomes, and the spine apparatus have all been implicated. Each of these is assessed. Special emphasis is placed on PSs because of their ever-increasing significance in discussions of synaptic plasticity. The possibility of their being artefacts is dismissed on a number of grounds, including consideration of the results of serial section studies. Various roles, other than one in synaptic plasticity have been put forward in discussing PSs. Although relevant to synaptic plasticity, these include a role in increasing synaptic efficacy, as a more permanent type of synaptic connection, or as a route for the intercellular exchange of metabolites or membrane components. The consideration of many estimates of synaptic density, and of PS frequency, have proved misleading, since studies have reported diverse and sometimes low figures. A recent reassessment of PS frequency, using unbiased stereological procedures, has provided evidence that in some brain regions PSs may account for up to 40% of all synapses. All ideas that have been put forward to date regarding the role of PSs are examined, with particular attention being devoted to the major models of Nieto-Sampedro and co-workers.(ABSTRACT TRUNCATED AT 400 WORDS)

Protein synthesis in the neuropil of the rat dentate gyrus during synapse development

Previous studies have shown that there are dramatic accumulations of polyribosomes under developing synapses on dendrites of CNS neurons. The present study was designed to evaluate what types of proteins might be synthesized by the synapse-associated polyribosomes. Hippocampal slices from rat pups sacrificed at 4, 7, 10, 12, 14, and 21 days after birth as well as slices from adult animals were incubated in a modified Eagle's medium containing 3H-leucine. After a 30 min exposure to radiolabeled amino acids, the slices were microdissected, separating the dendritic enriched molecular layer from the cell bodies of the dentate gyrus and the hippocampus proper. The level of protein synthetic activity was assessed by comparing the incorporation in cell body and dendritic laminae. Polypeptides present in each dissected zone were separated electrophoretically on 1D SDS-polyacrylamide gels according to their molecular weight and the newly synthesized proteins were analyzed through gel fluorography. The overall level of 3H-amino acid incorporation into protein (measured as cpm/microgram protein) was higher than that of the adult at all postnatal ages. When the entire slice was analyzed, the maximum incorporation was at 12 days after birth. In the dissected subregions of the slice the peak protein synthetic activity in cell-body-enriched regions of dentate gyrus and hippocampus proper was at 4-7 days postnatal, declining between 7 and 21 days to values comparable to the adult. By contrast, protein synthesis in the molecular layer of the dentate gyrus did not peak until 12 days after birth, decreasing toward adult rates after 14 days. The overall pattern of Coomassie stained polypeptides present in the dentate molecular layer was comparable at all ages examined. Moreover, one-dimensional gel analysis showed no qualitative differences in the proteins that were synthesized in the three dissected zones across ages.(ABSTRACT TRUNCATED AT 250 WORDS)

Morphological changes in cultures of hippocampus following prenatal irradiation in the rat

The effect of prenatal irradiation was studied in organotypic cultures of hippocampus, prepared from newborn rats that had been exposed to whole-body irradiation of 1 Gy from a 60Co-source at day 13 of pregnancy. Light and electron microscopic observations showed remarkable damage to neuronal mitochondria accompanied by extensive swelling, vacuolation of the Golgi complex, and formation of multilamellar bodies and vesicles of the lysosomal type. In contrast to neuronal alterations, no delay in synaptogenesis or onset of myelination was observed based upon the absence of significant morphological changes in synapses and myelin sheaths. Using this tissue culture model it could be confirmed that prenatal exposure to irradiation, even at low doses, induces specific morphological changes in the brain.

Gender differences in the dendritic tree of granule neurons in the hippocampal dentate gyrus of weaning age rats

The dendritic tree was quantified in granule cells from the dentate gyrus in rats at weaning age. While the number of dendritic branch segments was at adult levels, the length of dendritic segments was shorter than in adults. There were sex differences in the number of dendritic segments (female greater than male) but not in the length of individual segments or in the total length of the dendritic tree. Comparisons to adult sex differences indicate that the sex differences in the dendritic tree of weaning age rats are not permanent.

Development and characterization of clonal cell lines derived from septal cholinergic neurons

Studies employing primary cells to determine the molecular basis of neuronal development and selective synaptogenesis in the central nervous system are limited by cellular heterogeneity. Clonal hybrid cell lines derived from a particular region of brain, which express differentiated characteristics typical of the cells of origin, offer a potentially powerful alternative approach. We previously demonstrated the feasibility of deriving such cell lines from septal cholinergic cells. We now delineate the methods employed, and describe the development of additional cholinergic cell lines expressing neuronal and cholinergic features from later developmental stages. One cell line has been studied in detail and found to form neurites, express choline acetyltransferase (ChAT) and neurofilament protein (NFP), and display typical neuronal ultrastructural characteristics, including puncta adherens, neuritic varicosities, vesicles, and growth cones.

Changes in excitatory amino acid modulation of phosphoinositide metabolism during development

Two different developmental patterns of stimulation of phosphoinositide (PI) metabolism by excitatory amino acid (EAA) receptors were observed during the postnatal maturation of various brain regions. A 'burst' in PI metabolism was seen at postnatal day 6 (PND6) in olfactory bulb and cerebellum and at PND9 in hippocampus. In cortex and thalamus/hypothalamus high levels of PI metabolism were observed initially, and then began to decline at PND15 and PND18, respectively. NMDA inhibition of PI metabolism was generally found to parallel the EAA activation but the persistence of inhibition varied in the different brain regions.

Physiological and pathophysiological roles of excitatory amino acids during central nervous system development

Recent studies suggest that excitatory amino acids (EAAs) have a wide variety of physiological and pathophysiological roles during central nervous system (CNS) development. In addition to participating in neuronal signal transduction, EAAs also exert trophic influences affecting neuronal survival, growth and differentiation during restricted developmental periods. EAAs also participate in the development and maintenance of neuronal circuitry and regulate several forms of activity-dependent synaptic plasticity such as LTP and segregation of converging retinal inputs to tectum and visual cortex. Pre- and post-synaptic markers of EAA pathways in brain undergo marked ontogenic changes. These markers are commonly overexpressed during development; periods of overproduction often coincide with times when synaptic plasticity is great and when appropriate neuronal connections are consolidated. The electrophysiological and biochemical properties of EAA receptors also undergo marked ontogenic changes. In addition to these physiological roles of EAAs, overactivation of EAA receptors may initiate a cascade of cellular events which produce neuronal injury and death. There is a unique developmental profile of susceptibility of the brain to excitotoxic injury mediated by activation of each of the EAA receptor subtypes. Overactivation of EAA receptors is implicated in the pathophysiology of brain injury in several clinical disorders to which the developing brain is susceptible, including hypoxia-ischemia, epilepsy, physical trauma and some rare genetic abnormalities of amino acid metabolism. Potential therapeutic approaches may be rationally devised based on recent information about the developmental regulation of EAA receptors and their involvement in the pathogenesis of these disorders.

Neurons, numbers and the hippocampal network

Anatomists involved with studies of the hippocampal formation are being prodded by computational modelers and physiologists who demand detailed and quantitative information concerning hippocampal neurons and circuits. The beautiful camera lucida drawings of old, and the elegant descriptions of dendritic form that accompanied them are giving way to computer-reconstructed and three-dimensionally analyzed cells with rigorous determination of dendritic lengths and volumes, branching pattern and spine distribution. We will review certain quantitative aspects of hippocampal organization in the rat based on a survey of available literature and on our own intracellular labeling studies of granule cells of the dentate gyrus and pyramidal cells of the hippocampus. Some of the potential implications of these data for hippocampal information processing will be discussed.

Spontaneous activity mediated by NMDA receptors in immature rat entorhinal cortex in vitro

Intracellular recordings were made from cells in layer II of entorhinal cortex slices from 9 to 13-day-old rats. The majority of these cells showed pronounced spontaneous synaptic activity which could summate into large depolarizing events and give rise to bursts of spikes. These events could be associated with an apparent decrease in membrane conductance. They were reduced in amplitude by hyperpolarization of the cell and tended to increase on depolarization. Perfusion with 2-amino-5-phosphonovalerate abolished the spontaneous activity. Thus, in layer II of the entorhinal cortex at this stage of development there seems to be a functional enhancement of ongoing synaptic activity mediated via activation of N-methyl-D-aspartate receptors.

Prenatal ethanol exposure decreases hippocampal mossy fiber zinc in 45-day-old rats

The long-term consequences of prenatal ethanol exposure on histochemically detectable hippocampal mossy fiber zinc was examined using a recently developed quantitative histofluorescence procedure. Pregnant Sprague-Dawley rats were maintained throughout gestation on one of three dietary regimens: (a) a liquid diet containing either 3.35% ethanol, (b) an isocalorically matched liquid diet pair-fed to the 3.35% ethanol group, or (c) lab chow ad libitum. At 45 days of age, offspring from each of the three diet groups were sacrificed for determination of hippocampal mossy fiber zinc and zinc analysis of selected tissues by atomic absorption spectroscopy. Hippocampal mossy fiber zinc was reduced by 36% in dorsal and 20% in ventral hippocampal formation stratum lucidum of rats exposed to the 3.35% ethanol diet compared to the offspring of the pair-fed control and ad libitum control dams. No significant differences in zinc:TS-Q histofluorescence were observed between the ad libitum and pair-fed control groups. No significant differences were observed among groups in tissue wet weight or tissue zinc concentration in any of the brain or other body regions analyzed. These results indicate a long lasting prenatal ethanol exposure-induced reduction in hippocampal mossy fiber zinc in the absence of changes in any indices of total body zinc nutriture. These results suggest that prenatal exposure to relatively low blood ethanol levels (30-40 mg/dl) has subtle, yet long-lasting effects in the hippocampal formation, a brain region important in the process of memory consolidation.

Transient increase in the number of cholinergic neurons in the developing rat dentate gyrus

Using a monoclonal antibody against choline acetyltransferase (ChAT), we have examined the distribution of cholinergic neurons in the rat dentate gyrus during development. ChAT-positive neurons were occasionally detected in the hilus on postnatal day 2 (P2). There was a transient abrupt increase in the number and density of ChAT-positive neurons between P15 and P20 and then a decline to the adult level with few ChAT-immunoreactive neurons. A few ChAT-positive varicose fibers and punctae were first seen at P5. They increased in number and density until P20 when they reached the adult level and distribution. These observations suggest the occurrence of a transient expression of cholinergic markers in the hippocampus.

Development of NADPH diaphorase-positive pedunculopontine nucleus neurons

Nicotinamide adenine dinucleotide phosphate (NAD-PH) diaphorase histochemistry was used to localize cholinergic neurons in the pedunculopontine nucleus of neonatal and adult rats. Measurements of cell body areas revealed an average area around 200 microns2 at birth, followed by a significant increase to approximately 500 microns2 by 2 weeks of age. Thereafter, there was a decrease in cell area such that by 5 weeks of age the neurons had attained their adult size of around 300 microns2. The marked increase in cell size at the end of 2 weeks of age is discussed in relation to significant events in the development of locomotor and other rhythmic function control systems.

Effects of hypothyroidism on high-affinity vasopressin binding sites in developing hippocampal synaptosomes

Binding sites of vasopressin (VP) have been characterized in the hippocampal synaptic plasma membranes of developing normal and hypothyroid rats using a highly specific tritiated VP antagonist, d(CH2)5Tyr(Me)VP (V1 type). This antagonist bound to an apparently homogeneous population of specific sites with an affinity ten times higher than that of VP itself. The total amount of synaptosomal protein in 15-day-old normal rats represented about 50% of the adult value, but the density of binding sites was already maximal and remained constant thereafter, supporting the concept of an early development of an extrahypophyseal vasopressinergic hippocampal system. Thyroid deficiency specifically reduced the amount of synaptosomal protein. However, the binding site density in the synaptsomal fraction appeared to be relatively well preserved from hypothyroidism, although there was a transient decrease in the apparent affinity of the ligand. These data suggest that thyroid hormones are slightly involved in the early development of high-affinity VP receptors.

Calcium dependency of N-methyl-D-aspartate toxicity in slices from the immature rat hippocampus

The literature on ionic requirements for excitotoxicity is largely contradictory. Depending on the experimental paradigms, it has been concluded that either Ca2+ or Na+ and Cl- mediate excitotoxicity. In the present study, the dependence on Ca2+ of N-methyl-D-aspartate-induced damage to neurons in immature rat hippocampal slices was investigated with light microscopy. In addition N-methyl-D-aspartate-induced cell damage was followed by measurement of release of lactate dehydrogenase from slices. When incubated in N-methyl-D-aspartate-containing (100 microM) buffer for 30 min, hippocampal neurons displayed fine chromatin aggregation and swelling of neuronal nuclei and neuropil. Slices incubated in standard medium for 90 min after exposure to N-methyl-D-aspartate contained a large number of neurons that failed to recover from the initial lesion. The acute edema was at least as severe in slices incubated in N-methyl-D-aspartate-containing, Ca2+-free buffer. In contrast, clumping of the chromatin could not be observed. CA1 neurons recovered completely from the acute changes, and granule cells recovered to some extent. While omission of Ca2+ had no obvious morphological effects on the tissue in its own right, the efflux of lactate dehydrogenase was significantly increased after incubation in Ca2+-free medium. Slices exposed to N-methyl-D-aspartate released approximately twice as much lactate dehydrogenase as controls 1-5 h after the exposure, and the same rate of release was seen if Ca2+ was absent during N-methyl-D-aspartate treatment. The morphological results suggest that N-methyl-D-aspartate toxicity is Ca2+-dependent in pyramidal cells whereas the toxicity in granule cells is partly Ca2+-independent.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of nerve growth factor on the development of septal cholinergic neurons in reaggregate cell cultures

Recent studies suggest that nerve growth factor is present within the central nervous system where it may exert selective trophic effects on cholinergic neurons. We have measured the effects of nerve growth factor on septal cholinergic neurons in three-dimensional reaggregating cell cultures, a system which closely simulates the cellular environment in situ. Septal cells obtained from 15-day-old mouse embryos were dissociated into a single cell suspension and then allowed to reaggregate in culture in a rotary incubator shaker. After 17 days in culture, half of the reaggregates from a flask were sonicated for measurement of choline acetyltransferase activity, and the remaining reaggregates were processed for acetylcholinesterase histochemistry. Addition of nerve growth factor to medium containing septal reaggregates resulted in greater than a three-fold increase in choline acetyltransferase activity and in the number of acetylcholinesterase-positive cells, as well as an enhancement in the staining of acetylcholinesterase-positive fibers. All of these effects of nerve growth factor could be neutralized by antibodies to nerve growth factor. In order to evaluate the possible role of endogenous hippocampal-derived nerve growth factor, antiserum to nerve growth factor was added to the culture media containing septal-hippocampal coaggregates. After 21 days in culture, the presence of nerve growth factor antibodies did not qualitatively affect the pattern or density of cholinergic fibers observed. Synapse formation between cholinergic axons and hippocampal target cells was still in evidence as revealed by electron microscopy. However, there was a modest decrease in choline acetyltransferase activity (20%) and cholinergic cell number (30%) when compared with coaggregates grown in culture medium either without nerve growth factor antiserum or with non-immune serum. The magnitude of these effects was markedly less than the effects observed when exogenous nerve growth factor was added to septal cells grown alone in reaggregate culture. These results suggest that nerve growth factor may play a role during central cholinergic development, but that additional trophic mechanisms are likely to be required.

First month of development of fetal neurons transplanted as a cell suspension into the adult CNS

It has been demonstrated elsewhere that fetal thalamic tissue, when transplanted as a cell suspension into the excitotoxically neuron-depleted adult somatosensory thalamus, can grow, differentiate, and receive projections from host afferents. In the present study, we used the same paradigm to analyse the transplanted neurons during their morphogenesis, i.e. during the first month after transplantation. Using various anatomical criteria, at the light and electron microscope levels, we compared the development of transplanted neurons with the normal ontogeny of homologous neuronal populations. Confined solely to the mechanically lesioned area during implantation at seven days post-grafting, the transplant increased in size to occupy most of the previously neuron-depleted area by the third week after grafting. The final size of the transplant thus depended upon the size of the lesion. At seven days post-grafting, the neurons were small in size and the cellular density was high. At this immature stage few synaptic contacts were visible and the ultrastructure was characterized by large extracellular spaces. At 10 days post-grafting, the size of the neurons had increased and the cellular density had decreased. Both an extensive dendritic proliferation and a simultaneous active synaptogenesis could also be observed. All these events continued to evolve and during the third week the neuropil progressively acquired more mature ultrastructural characteristics. Synaptic contacts exhibiting characteristics comparable to those observed in the intact thalamus also became more numerous. At 20 days post-grafting, axonal myelination had started, the development of the graft apparently stopped and the various criteria had stabilized. Until that developmental stage, growth of grafted neurons compared to that of normal thalamic ones. At later stages, however, grafted neurons failed to grow larger and did not reach the size of the homologous population in the adult animal. It seems, therefore, that transplants of thalamic fetal neurons can be used as a tool with which to study thalamic neuronal development, within definable limits.

The time course of hippocampal cholinergic innervation in the developing hypothyroid rat. A combined histochemical and biochemical study of acetylcholinesterase activity

Development of cholinergic innervation in the hippocampal formation of normal and hypothyroid rats was studied by a combined biochemical and histochemical analysis of acetylcholinesterase (AChE) activity in normal and hypothyroid rats. The normal developmental pattern of cholinergic activity suggests an entrance of septal cholinergic fibers from the fimbria to different zones of the hippocampal formation mainly during the first postnatal week. By 10 days of age, the regional distribution of staining was similar to that in the adult. Thereafter, the intensity of staining increased without major changes in the laminar organization. As shown by closely related histochemical and biochemical findings, hypothyroidism led to a delay in the arrival of cholinergic afferences and a possible subsequent cholinergic hyperinnervation of the hippocampal formation in adulthood. These results are discussed taking into account the time course of structural development in the two synaptic compartments, namely the extrinsic septal neurons and intrinsic pyramidal and granule cells, in comparison with the development of thyroid function.

Developmental changes in protein phosphorylation in chicken forebrain. I. cAMP-stimulated phosphorylation

The net level of cyclic AMP-stimulated protein phosphorylation was investigated in cytosolic and membrane fractions from chicken forebrain between embryonic day 13 (E13) and 52 days post-hatching. Throughout this period the majority of the net level of cAMP-stimulated phosphorylation of endogenous proteins was in the cytosolic fractions. Between day -8 (E13) and adult, the net level of cAMP-stimulated phosphorylation of endogenous proteins in the cytosol (S3) and crude synaptic plasma membrane (P2-M) fractions fell by 3 and 4 fold, respectively, when expressed per mg protein and rose by 5 and 10 fold, respectively, when expressed per fraction. The changes in specific activity were completed by 6-15 days post-hatching. The occluded cytosol (P2-S) fraction showed little change in the net level of cAMP-stimulated phosphorylation of endogenous proteins per mg protein. Major changes in phosphoprotein patterns involving both decreases and increases in phosphorylation occurred in all fractions from day -8 (E13) to day 6 post-hatch; thereafter the phosphoprotein bands and their relative intensities were unchanged. Three bands (P90 in S3; P41 and P31 in P2-M) contained major cAMP-stimulated phosphoproteins in embryonic brain but were absent after hatching. When cAMP-stimulated phosphorylation activity was measured in S3 and P-2M using an exogenous peptide substrate (Kemptide) there was no change in kinase activity per mg protein between day -8 (E13) and 30 days post-hatch. This suggests that the decrease in the net level of cAMP stimulated phosphorylation of endogenous proteins was due to the decrease in levels of endogenous phosphoproteins rather than protein kinase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Ultrastructural evidence for hippocampal target cell-mediated trophic effects on septal cholinergic neurons in reaggregating cell cultures

We have previously demonstrated at the light microscopic level that when embryonic day-15 septal neurons are co-cultured for 21 days with their target cells from the hippocampus, increased numbers of septal cholinergic neurons are present as compared with co-cultures employing cells from the non-target cerebellum. In addition, fine varicose axon-like cholinergic fibers are found to be associated with the hippocampal cells but not with cerebellar cells. We now provide ultrastructural evidence for hippocampal target cell-enhanced cholinergic neuronal survival, axonal proliferation, and synapse formation in this culture system. Dissociated cell suspensions from septal, hippocampal, and cerebellar areas were obtained from 15-day mouse embryos; and hippocampal and cerebellar cells were internally labeled with rhodamine-conjugated wheat germ agglutinin. Combinations of septal and hippocampal cells, and septal and cerebellar cells were allowed to reaggregate in rotation mediated culture for either 15 or 21 days. The reaggregates were then fixed, embedded, sectioned, and processed for acetylcholinesterase-positive acetylcholinesterase-positive cells and fibers, and under fluorescence to locate rhodamine-labeled cell populations. Representative reaggregate profiles were then re-embedded for electron microscopic examination. In both types of reaggregates, either labeled hippocampal target or cerebellar non-target cells segregated from the septal cells so that areas containing each of the respective cell populations could be studied. In sections of septal-hippocampal reaggregates from 15-day cultures, 571 out of 665 (85%) cholinergic neurons examined were intact, whereas 15% of the cells showed some ultrastructural features of degeneration. Similarly, at day 21, 297 out of 335 (88%) of the cholinergic neurons were intact. In sections of septal-cerebellar reaggregates from 15-day cultures, 473 out of 572 (83%) cholinergic neurons were intact. By day 21 of culture, however, only 15 out of 110 (14%) cholinergic neurons examined were intact from the septal-cerebellar reaggregates. In areas of septal-hippocampal reaggregates occupied by rhodamine-labeled hippocampal cells, profiles of acetylcholinesterase-labeled axons were identified, and synaptic specializations were observed between cholinergic terminals and dendrites as well as somata of hippocampal target cells. In contrast, areas of septal-cerebellar reaggregates occupied by rhodamine-labeled cerebellar cells were devoid of cholinergic fibers.(ABSTRACT TRUNCATED AT 400 WORDS)

Synaptogenesis in the hippocampal dentate gyrus: effects of in utero ethanol exposure

In animal models of Fetal Alcohol Syndrome, ethanol causes a number of changes in brain development, with many of these changes being very transient. This is especially true for the process of synaptogenesis in different brain areas. Our quantitative electron microscopic study of synaptogenesis in the molecular layer of the rat dentate gyrus supports the above statement, by demonstrating that ethanol has no effect on the appearance of synapses in the dentate gyrus during early postnatal life (10-30 days old). However, prenatal ethanol exposure does appear to affect the process of synapse turnover, which is indicated by the significantly delayed appearance of complex (curved) synapses and multiple synaptic contacts on single axonal terminals. Efficient synapse turnover is thought to be required for the normal maintenance of neuronal plasticity, which in turn ensures an animal's ability to respond to novel environments, tasks and injuries. It would seem that the prenatal neurotoxicology of ethanol may manifest itself by more subtle mechanisms at sites of structural and functional importance.

Light-microscopic immunolocalization of the growth- and plasticity-associated protein GAP-43 in the developing rat brain

Growth-associated protein-43 (GAP-43) is a developmentally regulated, fast-axonally transported phosphoprotein whose synthesis and transport are enhanced during periods of growth and synaptic terminal formation. GAP-43 is a substrate of protein kinase C and is identical to protein F1, a phosphoprotein which is regulated during long-term potentiation in the hippocampus. In order to characterize the cellular localization of GAP-43, we have raised a specific antiserum against it, and used this as a probe to show that GAP-43 is neuron-specific, and is localized to growing neuronal processes in developing rat brain, and to presynaptic terminals in both the peripheral and central nervous system. In the mature CNS, GAP-43 immunoreactivity is present in most neuropil areas, but is especially dense in the molecular layers of the cerebellum, neocortex, and the hippocampus, structures known to exhibit synaptic plasticity. Its localization, together with biochemical data concerning the dynamics of its synthesis and its identity as protein F1, suggest that GAP-43 may be involved in axon growth in the developing nervous system, and in some aspect of synaptic plasticity in the mature CNS. These data also suggest that axon growth and synaptic plasticity in the brain may be regulated by a common mechanism, both involving the protein kinase C-mediated phosphorylation of GAP-43.

Differentiation of granule cells in relation to GABAergic neurons in the rat fascia dentata. Combined Golgi/EM and immunocytochemical studies

Golgi impregnation was used to study the dendritic differentiation of granule cells in the rat fascia dentata. The impregnated granule cells were gold-toned allowing for a fine structural study of the same identified neurons and of the input synapses onto their cell bodies and dendrites. Due to the long postnatal formation of these cells it was possible to describe a sequence of maturational stages coexisting on the same postnatal day (P5). Characteristic features of the dendritic development of granule cells were i) occurrence of varicose swellings along the dendrites, ii) growth cones on dendritic tips, iii) transient formation of basal dendrites, and iv) progressive development of dendritic spines. Incoming synapses on the differentiating granule cells were mainly found on dendritic shafts. Their membrane specializations were symmetric. At least some of these symmetric synapses were GABAergic because immunostaining of Vibratome sections from the same postnatal stage (P5) demonstrated a well-developed GABAergic axon plexus in the fascia dentata (antibodies against glutamate decarboxylase (GAD), the GABA synthesizing enzyme). Electron microscopy of the immunostained axon plexus revealed numerous GABAergic terminals that formed symmetric synaptic contacts, mainly on shafts of differentiating dendrites but also on cell bodies of granule cells. Our results thus indicate that the plexus of inhibitory GABAergic axons is already well developed at a stage when the target neurons, the granule cells, are still being formed.

A monoclonal antibody, WCC4, recognizes a developmentally regulated ganglioside containing alpha-galactose and alpha-fucose present in the rat nervous system

A monoclonal antibody, WCC4, raised against PC12 cells, recognizes a ganglioside which is present in low concentrations in the postnatal rat nervous system. The antigen is also present in the adrenal and kidney, as determined immunohistochemically, but is not detectable in liver or spleen. A neutral glycosphingolipid is also immunoreactive. In the present report, the chemical characterization of this ganglioside, isolated from PC12 cells, and the anatomical distribution of the antigens recognized by the WCC4 antibody are described. By enzymatic cleavage of terminal saccharide moieties, the ganglioside is identified as alpha-galactosyl, (alpha-fucosyl) GM1. The ganglioside increases in concentration postnatally to day 35 (P35) and is present in a slightly diminished concentration in the adult. Immunohistochemical studies revealed that this glycolipid is also present on neuronal cell soma throughout the cerebrum, cerebellum and spinal cord. It is expressed in highest concentration in the molecular layer of the dentate gyrus and is also present in the olfactory bulb, the molecular layer of the hippocampus, the piriform cortex, the olfactory tubercle and the entorhinal cortex. The dentate molecular layer receives most of its innervation from neurons in the entorhinal cortex, and gangliosides are known to have an effect on plasticity following entorhinal cortical lesions. Therefore, the WCC4 antibody should prove to be a useful tool for the study of the role of endogenous gangliosides in this region of the nervous system.

The development of carbachol-induced EEG 'theta' examined in hippocampal formation slices

The development of carbachol-induced EEG theta (theta) activity was studied in the CA1 and dentate regions of hippocampal formation slices obtained from neonatal rats (4, 6, 8, 10, 12 and 14 days of age). When perfused with carbachol (50 microM), 4- and 6-day-old hippocampal slices exhibited only short-lasting irregular activity. The initial appearance of carbachol-induced rhythmic waves were observed in slices obtained from 8-day-old rats. From the time that theta appeared at 8 days of age, a steady increase in amplitude and frequency was noted. This observed in vitro developmental pattern of hippocampal theta-rhythm closely resembles the development of theta activity in in vivo preparations.

Ultrastructural organization of normal and transplanted rat fascia dentata: I. A qualitative analysis of intracerebral and intraocular grafts

Few studies have dealt with the general ultrastructure and synaptic organization of grafted brain tissue. This study was therefore performed to extend current light microscopic observations on intracerebral and intraocular grafts of hippocampal tissue to the ultrastructural level. Blocks of tissue containing the hippocampus and fascia dentata from day 21 embryonic rats were grafted into the brain of developing and adult rats and to the anterior eye chamber of adult rats. After 100 or 200 days of survival the recipient rat brains or eyes were processed for electron microscopy. Tissue containing the graft dentate molecular layer and adjacent granule cell layer was selected for ultrastructural analysis, together with a few samples of the hilus and CA3. Normal dentate tissue was analyzed as control. At the light microscopic level most intracerebral and intraocular grafts displayed an organotypic organization with clearly recognizable cell and neuropil layers. Under the electron microscope the grafted granule cells had normal-appearing dendrites bearing the normal types of spines and forming the normal types of synapses. This was the case even in the absence of the normal major extrinsic afferents like the perforant path. The graft dentate granule cells formed axons and terminals with characteristics of the normal mossy fiber system in the hilus and CA3, in addition to aberrant supragranular mossy fiber terminals known from light microscopic studies of dentate transplants. Abnormal structures included a few dendritic growth cones and an increased occurrence of polyribosomes in spines. Their occurrence indicates ongoing dendritic plasticity even 100 days after transplantation. There was also an increased density of glial elements, particularly in the intraocular grafts. In some of these grafts the granule cells displayed immature traits in terms of nuclear indentations. Dentate interneurons of the basket cell type were present in both the intracerebral and the intraocular grafts. We conclude that grafted dentate granule cells, in different surroundings and without the normal, major perforant path input, can develop a basically normal cellular morphology, which includes the normal ultrastructural characteristics of the dendrites with spines and synapses, and the mossy fibers and its terminals.

Ultrastructural organization of normal and transplanted rat fascia dentata: II. A quantitative analysis of the synaptic organization of intracerebral and intraocular grafts

As part of an ultrastructural analysis of the normal rat fascia dentata and intracerebral and intraocular dentate transplants the synapses in the dentate molecular layer were quantified. Hippocampal and dentate tissue from 21-day-old rat embryos were grafted into the brain of developing and adult rats and to the anterior eye chamber of adult rats. After 100 or 200 days of survival the recipient rat brains and the recipient eyes were processed for electron microscopy, and the graft dentate molecular layer with the adjacent granule cell layer selected for ultrastructural analysis. Tissue from the dentate molecular layer of normal adult rats served as controls. The dentate synapses were classified as asymmetric (Gray's type 1) or symmetric (Gray's type 2), and according to the postsynaptic element (cell body, dendritic shaft, dendritic spine). The spine synapses were further classified into simple and complex types according to the spine-terminal configuration. Also, the length of synaptic contacts of the individual synaptic types was measured in some grafts, just as the percentage of the cross sectional area of the neuropil covered by blood vessels. The results showed that the synaptic density, expressed as number per unit area of neuropil, to a large extent was the same within the different parts of the normal dentate molecular layer. Compared with this the synaptic density was reduced with 16.4% in dentate molecular layer of the intracerebral graft, primarily because of a 17.6% reduction of simple synapses on dendritic spines and almost halving of the symmetric synapses on dendritic shafts. The synaptic density was independent of the age of the recipient, the intracerebral location of the graft, and the survival time. Although the synaptic length of some of the individual synaptic types increased, this did not compensate for the loss of synapses. In the intraocular grafts the synaptic density was lower than in the intracerebral grafts. Despite the reduced synaptic density, which mainly involved two synaptic types, we conclude that grafted dentate granule cells can develop a remarkably normal, ultrastructural synaptic organization even in the absence of major afferent inputs. This outcome must accordingly be achieved by reorganization of the available intrinsic afferents.

The susceptibility of rats to pilocarpine-induced seizures is age-dependent

Behavioral, electroencephalographic and morphological changes induced by systemic administration of pilocarpine hydrochloride were studied in 3-90-day-old rats. Pilocarpine, 100, 200 and 380 mg/kg, presented a characteristic array of behavioral patterns in developing rats. Hyper- or hypoactivity, tremor, loss of postural control, scratching, head bobbing and myoclonic movements of the limbs dominated the behavior in 3-9-day-old rats. No overt motor seizures were observed in this age group. More intense behavioral signs evolving in some animals to limbic seizures and status epilepticus occurred when pilocarpine was administered in 12-day-old-rats. The electrographic activity in these animals progressed from low voltage spiking registered concurrently in the hippocampus and cortex during the first week of life into localized epileptic activity in the hippocampus, which spread to cortical recordings during the second week of life. No morphological alterations were detected in the brains of 3-12-day-old rats subjected to the action of pilocarpine, 100-380 mg/kg. The adult pattern of behavioral and electroencephalographic sequelae after pilocarpine was encountered in 15-21-day-old rats. Akinesia, tremor and head bobbing progressed in 15-21-day-old rats given pilocarpine, 100-380 mg/kg, to motor limbic seizures and status epilepticus. The lethal toxicity of pilocarpine reached 50% during the third week of life. This increased susceptibility to the convulsant action of pilocarpine was characterized by a shortened latency for behavioral and electrographic signs, and an increased severity of seizures relative to older and younger rats. In 15-21-day-old rats subjected to pilocarpine-induced convulsions high voltage fast activity superposed over hippocampal theta-rhythm, progressed into high voltage spiking and spread to cortical records. The electrographic activity became well synchronized and then developed into seizures and status epilepticus. Morphological analysis of frontal forebrain sections in 15-21-day-old rats which underwent status epilepticus after pilocarpine revealed no damage or an attenuated pattern of damage. In 15-21-day-old rats which presented epilepsy-related brain damage, morphological breakdown was seen in the hippocampus, amygdala, olfactory cortex, neocortex and certain thalamic nuclei. No damage was detected in the substantia nigra and lateral thalamic nucleus. An adult pattern of the damage to the brain, in terms of extent and topography, was present in 4-5-week-old rats.(ABSTRACT TRUNCATED AT 400 WORDS)

Development of cholinergic neurons in the septal/diagonal band complex of the rat

In the present study we employed immunohistochemical techniques using a polyclonal antibody against choline acetyltransferase (ChAT) to determine the distribution and cytological features of cholinergic neurons in the developing septal/diagonal band complex of the rat. ChAT-positive perikarya were first clearly detected in this region on embryonic day 17, although the neurons were faintly labeled and lacked the cytological details found in the adult. After birth we observed a dramatic increase in the intensity of the immunolabeling which continued until postnatal day 23. Thereafter, the ChAT-positive neurons assumed their adult-like characteristics.

Decreased level of nerve growth factor (NGF) and its messenger RNA in the aged rat brain

Trophic factors such as nerve growth factor (NGF) are thought to support survival, differentiation and maintenance of neurons. Recent results indicate that NGF produced in cortical and hippocampal areas is required for the function of cholinergic neurons in the basal forebrain. With the use of enzyme immunoassay and RNA blot hybridization we studied the NGF protein and NGF mRNA, respectively, in regions of the brain innervated by basal forebrain cholinergic neurons in adult and aged rats. Levels of NGF protein were decreased by 40% in hippocampus of aged (28 months) Fischer 344 rats compared with adults (6 months), whereas no alterations were observed in cerebral cortex. Moreover, a reduction by 50% in the NGF mRNA was found in samples of the aged forebrain (cerebral cortex, hippocampus, basal forebrain and hypothalamus) compared to the adult. NGF deficiencies may thus account for the loss of cholinergic neurons in the basal forebrain generally found to accompany normal aging and resulting in altered cognitive functions.

Cholecalcin (28-kDa calcium-binding protein) in the rat hippocampus: development in normal animals and in altered thyroid states. An immunocytochemical study

An immunocytochemical study of cholecalcin (28-kDa calcium-binding protein, CaBP, calbindin) was carried out during the development of the rat hippocampus. In normal animals, the protein appeared from Postnatal Day 3 in the granule cells of the dentate gyrus and from Day 5 in the CA1-CA2 pyramidal cells of Ammon's horn. The cells of both regions thus showed positive cholecalcin labeling about 1 week after their formation. The sequence of labeling of the granule cells was a reflection of the major sequences of neurogenesis. Cholecalcin could not be detected in hippocampal cells until dendritic arborization and axon growth had occurred. There was a good correlation between the appearance of cholecalcin and the onset of synaptogenesis. In animals with an experimentally altered thyroid state, in which hippocampal development is retarded or accelerated due to abnormal cell maturation, cholecalcin appearance was similarly retarded or accelerated. Cholecalcin seems to be synthesized at the same time as the hippocampal cells become functional.

Spectral analysis of the electroencephalogram in the developing rat

Power spectral measures of the EEG obtained from the frontal cortex and hippocampal formation during different vigilance states in the developing rat have been computed and compared. The most significant ontogenetic changes were observed in the hippocampal power spectra obtained during the vigilance state of REM sleep. These spectral analyses have revealed in the hippocampus: (1) a significant increase in the frequency at which the peak power occurs in the theta-frequency (4-11 Hz) band from 14 to 45 days of age; (2) a decrease in the quality factor of the peak from 14 to 45 days of age; (3) a decrease in the relative power co-ordinate for the center of spectral mass associated with the 0-4-Hz frequency band coupled with an increase in the frequency coordinate of the 4-11-Hz frequency band from 14 to 45 days of age, and; (4) a significant decrease in the average percent relative power associated with the 0-4-Hz frequency band from 14 to 22 days of age. For the EEG obtained from the frontal cortex, the major findings of note were: (1) a dominant contribution of relative power in the 0-4-Hz frequency band which was observed at every age and during every vigilance state tested, and; (2) a significant increase in the average percent relative power associated with this band at 18, 22, and 45 days of age. The results of this study provide a quantitative description of the electroencephalographic (EEG) ontogeny of the hippocampal formation and the frontal cortex in the rat. These ontogenetic changes in EEG activity relate closely to development of the internal circuitry and synaptic maturation in the hippocampal formation and frontal cortex.

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.

Developmental changes of nerve growth factor and its mRNA in the rat hippocampus: comparison with choline acetyltransferase

Previous experiments have demonstrated that in the septo-hippocampal system choline acetyltransferase (ChAT) is induced by nerve growth factor (NGF) (Gnahn et al. (1983) Dev. Brain Res. 9, 45-52) and that hippocampal NGF and mRNANGF levels are correlated with the density of cholinergic innervation (Korsching et al. (1985) EMBO J. 4, 1389-1393). In the present investigation we have compared the developmental changes of ChAT, NGF, and mRNANGF levels in this system. During the postnatal development of the hippocampus the time courses of NGF and ChAT were well correlated including the most rapid increase between P12 and P14. This increase in hippocampal NGF was preceded by a corresponding increase in mRNANGF. The developmental changes in hippocampal NGF levels were also closely reflected by corresponding changes in the septum. This, together with previous observations (Korsching et al., 1985) that the adult septum, in spite of relatively high NGF levels, does not contain measurable quantities of mRNANGF, suggests that the NGF levels in the septum are determined by the quantity of NGF transported retrogradely from the field of innervation rather than by local synthesis. During the prenatal period hippocampal NGF levels were relatively high, whereas the mRNANGF was below the level of detection. Since the ingrowth of septal fibers, and with that also the removal of NGF by retrograde transport, begins around birth, the relatively high prenatal NGF levels probably result from an accumulation produced by a small copy number of mRNANGF prior to the removal of NGF by retrograde axonal transport. It is concluded that the correlation of the developmental changes in NGF and mRNANGF with the ChAT activity in the hippocampus further supports the concept of a physiological role of NGF in the central nervous system.

Sulfated glucuronic acid-containing glycoconjugates are temporally and spatially regulated antigens in the developing mammalian nervous system

Monoclonal antibody 4F4, which was raised against a cell suspension of embryonic rat forebrain, reacts with acidic glycolipids and several high-molecular-weight glycoproteins in rodent brain. The major reactive glycolipid is maximally expressed at Embryonic Day 15 (E15) and is no longer detectable at Postnatal Day 14 (P14) in the rat. 4F4 antibody reacts with a glucuronic acid- and sulfate-containing lipid isolated from human sciatic nerve as well as with lipids from mouse and rat embryonic brain tissue. Although the glycolipid disappears postnatally, the immunoreactive glycoproteins continue to be expressed in brain until adulthood. Both sciatic nerve and embryonic brain glycolipids are hydrolyzed by glucuronidase/sulfatase treatment but are insensitive to all other glycosidases tested. In addition, the observed 4F4 reactivity with extracted glycolipids, glycoproteins, and tissue sections of embryonic brain is identical to the reactivity demonstrated by HNK-1 antibodies. Immunocytochemical studies in developing brain showed stage-specific distribution of this carbohydrate antigen. At E10 in the mouse, immunoreactivity is associated with the mantle layer of the neural tube. At E15 in the cortex, the most intense staining is associated with the molecular layer and the subplate, and weaker staining is seen in the intermediate zone and cortical plate, suggesting that the antigen is highly concentrated on postmigratory cells in the embryonic nervous system.

Prenatal protein malnutrition affects synaptic potentiation in the dentate gyrus of rats in adulthood

Long-term potentiation (LTP) was studied in the dentate gyrus of anesthetized normal and prenatally protein malnourished rats in adulthood. LTP was initiated by high-frequency stimulation of the perforant path. Potentiation of both population excitatory postsynaptic potential (EPSP) slope and population spike was studied at various times after conditioning out to 5 h. The results indicate that prenatal protein malnutrition has a differential effect on LTP. Although potentiation of the population spike was relatively unaffected, prenatal protein malnutrition did lead to a significant reduction in potentiation of the population EPSP. Several possibilities are proposed as to the cause of the differential effect.

The development of kindled seizures is accelerated in the genetically epilepsy-prone rat

The kindling phenomenon was examined in genetically epilepsy-prone (GEPR) and non-epileptic control Sprague-Dawley rats. Kindling stimulations were administered three times a day until each rat had exhibited three Class 5 kindled motor seizures. The mean total number of kindling stimulations required for each experimental group to exhibit three motor seizures of each motor seizure class was determined. The results indicated that the early stage of kindling development was accelerated significantly in both the GEPR-3 and GEPR-9 rats, compared to non-epileptic control rats. Later stages of kindling development were accelerated in GEPR-9 but not GEPR-3 rats. Thus a differential acceleration of kindling development was exhibited by GEPR-3 and GEPR-9 rats. The results suggest the possibility that some brain region(s) involved in the early stages of kindling development may be hyperexcitable in both GEPR-3 and GEPR-9 rats. Other brain region(s) involved with the later stages of kindling development may be more excitable in GEPR-9 rats. These putative alterations may, in part, contribute to the seizure prone state of GEPR rats and the differential seizure responses of GEPR-3 and GEPR-9 rats.

Early handling increases hippocampal long-term potentiation in young rats

The hippocampal formation undergoes major anatomical and physiological changes postnatally, and thus might be expected to be particularly sensitive to early handling effects. Long-term potentiation (LTP) in the hippocampal formation, a form of brain plasticity thought to be important in learning and memory, was examined in young rats following early handling or control treatments. The amplitude of LTP was reliably greater in rats receiving the early handling regime. Possible mechanisms and consequences of enhanced LTP were discussed.

Nerve growth factor increases choline acetyltransferase activity in developing basal forebrain neurons

Nerve growth factor (NGF) is a neuronotrophic protein. Its effects on developing peripheral sensory and sympathetic neurons have been extensively characterized, but it is not clear whether NGF plays a role during the development of central nervous system neurons. To address this point, we examined the effect of NGF on the activity of neurotransmitter enzymes in several brain regions. Intracerebroventricular injections of highly purified mouse NGF had a marked effect on the activity of choline acetyltransferase (ChAT), a selective marker of cholinergic neurons. NGF elicited prominent increases in ChAT activity in the basal forebrain of neonatal rats, including the septum and a region which contains neurons of the nucleus basalis and substantia innominata. NGF also increased ChAT activity in the hippocampus and neocortex, terminal regions for the fibers of basal forebrain cholinergic neurons. In analogy with the response of developing peripheral neurons, the NGF effect was shown to be selective for basal forebrain cholinergic cells and to be dose-dependent. Furthermore, septal neurons closely resembled sympathetic neurons in the time course of their response to NGF. These observations suggest that endogenous NGF does play a role in the development of basal forebrain cholinergic neurons.

Characterization and cellular localization of a developmentally regulated rat neural sialidase

A developmentally regulated neural sialidase has been identified in particulate, subcellular fractions of rat brain. Enzyme activity, measured using a [3H]sialoganglioside substrate, was linear with time and had a pH optimum of 4.0-4.5. Protein linearity was only observed at low protein concentrations. This appeared to be caused by enzyme access to a lipophilic substrate, as activity was significantly stimulated by membrane-fluidizing agents. Enzyme activity was developmentally expressed in P2 pellets coincident with in vivo synaptogenesis. It was located on the synaptosome and was particularly high in myelin-containing fractions. Its cellular distribution was confined to neuronal cells and centrally derived oligodendrocytes.

Angular bundle kindling is accelerated in rats with a genetic predisposition to acoustic stimulus-induced seizures

Limbic kindling was examined in genetically epilepsy-prone (GEPR) and non-epileptic control rats. The early stage of kindling development was accelerated in both groups of GEPR rats compared to controls. Later stages of kindling were accelerated in GEPR-9 but not GEPR-3 rats. These results indicate that GEPR rats have an enhanced susceptibility to limbic kindling and suggest that limbic brain alterations may contribute to acceleration of the early stage kindling development in GEPR rats.

Development and regional expression of beta nerve growth factor messenger RNA and protein in the rat central nervous system

The presence of nerve growth factor (NGF) mRNA and protein in the rat central nervous system is documented. Blot-hybridization analysis showed an abundance of NGF mRNA in the hippocampus, cerebral cortex, and olfactory bulb. Enzyme immunoassay confirmed significant levels of a NGF-like protein in the hippocampus and cerebral cortex. Bioassay of a NGF-like immunoaffinity-purified protein from these regions was physiologically indistinguishable from NGF. Immunohistochemistry revealed a widespread distribution of NGF-like reactivity in the adult brain, preferentially in fiber tracts. NGF mRNA accumulation began at birth, with adult levels reached 3 weeks postnatally. Enzyme immunoassay detected the presence of a NGF-like protein in the embryonic rat brain. Postnatally, the level of NGF-like protein reached a maximum at 3 weeks. Additionally, a distinct fetal form of NGF may exist.

Power spectral analysis of hippocampal and cortical EEG activity following severe prenatal protein malnutrition in the rat

We have studied the effects of prenatal protein malnutrition on development of the hippocampal and frontal cortical electroencephalographic (EEG) activity. Using power spectral analyses in rats of several age groups we found that protein malnutrition, instituted prenatally and continued postnatally, produces marked alterations in power spectral measures, i.e., alterations in peak theta frequency in the hippocampus during rapid eye movement (REM) sleep. Peak theta frequency was found to be significantly retarded in malnourished animals, especially during the preweaning period of development. Protein malnutrition, therefore, appears to affect mechanisms responsible for generating the tonic component of theta activity.

Changes in the subcellular distribution of calmodulin-kinase II during brain development

Subcellular fractions prepared from rodent forebrain at different postnatal ages were examined for calmodulin-binding proteins using [125I]calmodulin and a gel overlay technique. Synaptic junction (SJ) fractions from newborn brain, which display purity comparable to adult SJ fractions, contain low but detectable amounts of 60 and 50 kdalton calmodulin-binding polypeptides; the latter being the major postsynaptic density protein. These polypeptides have recently been shown to be the calmodulin-binding protein subunits of calmodulin-dependent protein kinase II (CaM-kinase II). CaM-kinase II polypeptides represented the predominent calmodulin-binding proteins in nearly every subcellular fraction examined, regardless of postnatal age. Large increases were observed in the CaM-kinase II content of every subcellular fraction throughout postnatal development. During development, a striking shift in the subcellular distribution of CaM-kinase Ii was observed. Over 4 times as much CaM-kinase II was cytosolic relative to particulate in newborn brain while this ratio was completely reversed in adult brain. Large age-dependent increases in particulate-associated CaM-kinase II were observed in highly purified synaptic plasma membrane (5-fold) and SJ (14-fold) fractions. The CaM-kinase II content of SJ fractions increased approximately 70% between days 24 and 90, a period in development that follows the most active stages of synapse formation in situ. In adult brain, approximately 60% of CaM-kinase II in crude synaptosomal fractions (P2-INT) was recovered in SJ fractions. The CaM-kinase II in SPM fractions from all developmental ages resists solubilization in Triton X-100 and greater than 90% is recovered in SJ fractions. These studies indicate that during brain development the accumulation of SJ-associated CaM-kinase II represents an important process in the molecular and enzymatic maturation of CNS postsynaptic structures.