Developmental changes in heterogeneous patterns of neurotransmitter receptor binding in the human interpeduncular nucleus

The interpeduncular nucleus (IPN) exhibits many complex features, including multiple subnuclei, widespread projections with the forebrain and brainstem, and neurotransmitter heterogeneity. Despite the putative importance of this nucleus, very little is known about its neurochemical development in the human. The human IPN is cytoarchitectonically simple, unlike the rat IPN, which displays considerable heterogeneity. In the following study, we hypothesized that the developing human IPN is neurochemically heterogeneous despite its cytological simplicity. The chemoarchitecture in this study was defined by neurotransmitter receptor binding patterns by using quantitative tissue autoradiography for the muscarinic, nicotinic, serotoninergic, opioid, and kainate receptors. We examined neurotransmitter receptor binding in the developing human IPN in a total of 15 cases. The midbrains of five midgestational fetuses (19-26 gestational weeks) and six infants (38-74 postconceptional weeks) were examined. The midbrain of one child (4 years) and three adults (20-68 years) were analyzed as indices of maturity. At all ages examined, high muscarinic binding was localized to the lateral subdivision of the IPN, high serotoninergic binding was localized to the dorsal IPN, and high opioid receptor binding was localized to the medial IPN. The developmental profile was unique for each radioligand. We report a heterogenous distribution of neurotransmitter receptor binding in the developing human IPN, which supports a complex role for it in human brain function.

Melanocortin and MCH precursor-derived NEI effects on striatum-midbrain co-cultures

The possibility of developmental effects of POMC-derived melanocortins and analogs on neurons of fetal rat brain regions exhibiting marked developmental melanocortin receptor expression, was studied in serum-free co-cultures of gestational day 18 striatal and mesencephalic cells, and compared with NEI and NGE. These two peptide fragments of the melanin concentrating hormone precursor, occurring in brain areas devoid of POMC terminals, cross-react with alpha-MSH antibodies; NEI elicits grooming similar to alpha-MSH. Neurofilament protein (NF), growth-associated protein (GAP-43) and synaptophysin of the synaptosomal fraction were determined by ELISA as markers for neuritogenesis, growth cones, and nerve terminal differentiation. Cell survival was analyzed by MTT assay, proportions of major cell types by immunocytochemistry. alpha-Melanocyte-stimulating hormone (alpha-MSH, effective concentration 250-2500 nM), the analog Nle4-, D-Phe7-alpha-MSH (NDP, 3.1-750 nM), and NEI (250 nM) increased NF in 3 day cultures by 11%, 17%, and 22%, respectively, whereas ACTH(1-24) and ACTH(1-39) (25 2500 nM) were ineffective. In 11 day cultures, alpha-MSH (250-750 nM), but not NDP, ACTH(1-24) or ACTH(1-39), increased synaptosomal synaptophysin by 11%. GAP-43 and cell survival remained unaffected. These data indicate that selected melanocortins as well as NEI can influence differentiation of neural processes in brain neurons.

Developmental changes in the NGF content in the brain of young, growing, low-birth-weight rats

The NGF content in each region of the brain of four-week-old rats was ranked in the decreasing order of cerebral cortex, hippocampus, cerebellum, midbrain/diencephalon, and pons/medulla oblongata, and the NGF concentration, in the decreasing order of hippocampus, cerebral cortex, cerebellum, midbrain/diencephalon, and pons/medulla oblongata in both AFD and SFD groups. The NGF content and concentration in the cerebral cortex were about the same value at each age between those in the AFD and SFD groups. Those in the hippocampus were a little higher in the SFD group than in the AFD group at the ages of three and four weeks, unlike those in the other regions, where the values for the cerebellum, midbrain/diencephalon and pons/medulla oblongata tended to be somewhat higher in the AFD group than in the SFD group. The NGF concentrations in the hippocampus and cerebral cortex increased with growth: the concentration in the hippocampus at four weeks of age was about 4-fold of that at one week in the AFD group and about 5.7-fold of that at one week in the SFD group; and likewise the concentration in the cerebral cortex at four weeks of age was about 5.3-fold in the AFD group and about 7-fold in the SFD group. The NGF concentrations in the cerebellum decreased, and those in midbrain/diencephalon and pons/medulla oblongata hardly changed with growth in either AFD or SFD group. From these results NGF may have stronger implications for the neuronal growth in the hippocampus compared with those in the lower brain regions of the SFD rats.

Development and survival of rat embryonic mesencephalic dopaminergic neurones in serum-free, antioxidant-rich primary cultures

Mesencephalic dopaminergic neurones typically require the presence of serum for their survival in culture. However, the present study, outlines how neurones from the rat ventral mesencephalon (E14-16) were successfully cultured in serum-free, antioxidant-rich Neurobasal medium supplemented with B27 components. Moreover, immunostaining with mouse monoclonal microtubule-associated protein 2 (MAP2) and glial fibrillary acidic protein (GFAP) from day 1 to 7 in vitro revealed these cultures were primarily neuronal (80-95%). Additionally, immunostaining with tyrosine hydroxylase (TH) revealed these cultures contained a relatively constant population of TH-positive neurones (5%) which were presumed to be dopaminergic. These primary cultures offer considerable advantages for the study of mesencephalic, TH-positive, dopaminergic neurones under conditions where milieu can be readily manipulated in the virtual absence of glia and without the confounding influence of serum.

Dopamine neuron agenesis in Nurr1-deficient mice

Dopamine neurons of the substantia nigra and ventral tegmental area regulate movement and affective behavior and degenerate in Parkinson's disease. The orphan nuclear receptor Nurr1 was shown to be expressed in developing dopamine neurons before the appearance of known phenotypic markers for these cells. Mice lacking Nurr1 failed to generate midbrain dopaminergic neurons, were hypoactive, and died soon after birth. Nurr1 expression continued into adulthood, and brains of heterozygous animals, otherwise apparently healthy, contained reduced dopamine levels. These results suggest that putative Nurr1 ligands may be useful for treatment of Parkinson's disease and other disorders of midbrain dopamine circuitry.

The winged helix gene, Mf3, is required for normal development of the diencephalon and midbrain, postnatal growth and the milk-ejection reflex

The mouse Mf3 gene, also known as Fkh5 and HFH-e5.1, encodes a winged helix/forkhead transcription factor. In the early embryo, transcripts for Mf3 are restricted to the presomitic mesoderm and anterior neurectoderm and mesoderm. By 9.5 days post coitum, expression in the nervous system is predominantly in the diencephalon, midbrain and neural tube. After midgestation, the highest level of mRNA is in the mammillary bodies, the posterior-most part of the hypothalamus. Mice homozygous for a deletion of the mf3 locus on a [129 × Black Swiss] background display variable phenotypes consistent with a requirement for the gene at several stages of embryonic and postnatal development. Approximately six percent of the mf3−/− embryos show an open neural tube in the diencephalon and midbrain region, and another five percent show a severe reduction of the posterior body axis; both these classes of affected embryos die in utero. Surviving homozygotes have an apparently normal phenotype at birth. Postnatally, however, mf3−/− pups are severely growth retarded and approximately one third die before weaning. This growth defect is not a direct result of lack of circulating growth hormone or thyrotropin. Mice that survive to weaning are healthy, but they show an abnormal clasping of the hindfeet when suspended by the tail. Although much smaller than normal, the mice are fertile. However, mf3−/− females cannot eject their milk supply to feed their pups. This nursing defect can be corrected with interperitoneal injections of oxytocin. These results provide evidence that Mf3 is required for normal hypothalamus development and suggest that Mf3 may play a role in postnatal growth and lactation.

Postnatal developmental changes of neurons expressing calcium-binding proteins and GAD mRNA in the pretectal nuclear complex of the cat

The postnatal development of the cat pretectum has been analysed with in situ hybridization and immunohistochemistry with the aim to establish the time course of morphological and neurochemical maturation of parvalbumin (PARV), calbindin-D28k (CALB), and glutamic acid decarboxylase (GAD) expressing neuronal populations. At birth, PARV-ir retinal afferents to the pretectum have already formed distinct termination zones which appear as 3 clusters separated by intercluster regions in coronal sections. The clusters contain two sets of large neurons expressing either PARV or CALB. The two sets of neurons differ in the time at which they grow rapidly. Both sets reach the adult size at P38. PARV-ir retinal fibers contact dendrites of large PARV-negative, and thus presumably CALB-ir neurons. A population of smaller CALB-ir neurons appears within the clusters during the second postnatal week. In intercluster regions, small PARV-ir and CALB-ir neurons are present at birth, but increase in number during development. Only PARV-ir intercluster neurons increase in size between P4 and P38. GAD neurons are present dorsal to the clusters and in intercluster regions from P0 onwards. However, within the clusters GAD neurons do not appear until the second postnatal week. The different onset of marker expression and cellular growth patterns suggest the existence of several populations of CaBP-ir excitatory and inhibitory neurons in the pretectum. The final complement of inhibitory neurons is not present until the second postnatal week. These developmental processes may correlate with the slow maturation of the pretectal motion processing system and the cortico-pretectal projection.

An immunocytochemical study of a G-protein-gated inward rectifier K+ channel (GIRK2) in the weaver mouse mesencephalon

It has been suggested that a mutation in a G-protein-gated inward rectifier K+ channel (GIRK2) is responsible for inducing cell death in the cerebellum of homozygous weaver (wv/wv) mutant mice. These mice also display a progressive, massive loss of mesencephalic dopaminergic neurones. Using an immunocytochemical method, we detected GIRK2-positive cell bodies and fibres in the substantia nigra pars compacta (SNC) and the ventral tegmental area (VTA) of control (+/+) mice. Cell counts of both GIRK2- and tyrosine hydroxylase (TH)-positive neurones demonstrated a marked loss of SNC cell bodies, especially in 12-month-old (12M) wv/wv mice. A considerable proportion of GIRK2-positive cell bodies were preserved, however. In addition, no loss of GIRK2-positive neurones was observed in the VTA of 12M wv/wv mice, despite of a significant reduction in TH-positive cell bodies. These results suggest that expression of the mutated channel is not a sufficient condition to induce cell death in the ventral mesencephalon of the wv/wv mice.

Differential binding profile and internalization process of neurotensin via neuronal and glial receptors

Two G-protein-coupled receptors for the tridecapeptide neurotensin (NT) have been identified and cloned in mammalian brain: a high-affinity (Kd = 0.3 nM) receptor, sensitive to the antagonist SR 48692 but insensitive to levocabastine, and a lower-affinity (Kd = 2-4 nM) receptor, sensitive to levocabastine but with poor affinity for SR 48692. Although there is good evidence that the high-affinity site is predominantly expressed in neurons, little is known of the cellular localization of the low-affinity receptor. In the present study, we identify by confocal microscopy selective levocabastine-sensitive, SR 48692-resistant binding of a fluorescent derivative of NT (fluo-NT) to a subpopulation of glial fibrillary acidic protein-immunoreactive glial cells grown in culture from the midbrain and cerebral cortex of embryonic and neonatal rats, respectively. We also demonstrate, by combining fluo-NT detection with tyrosine hydroxylase immunofluorescence, that these glial binding sites are differentially regulated from the SR 48692-sensitive NT receptor expressed in the same cultures by mesencephalic dopamine neurons. Whereas the latter undergoes rapid ligand-induced internalization followed by centripetal mobilization of ligand-receptor complexes from processes to perikarya and from perikaryal periphery to cell center, the former induces the formation of cell-surface clusters that fail to internalize. It is concluded that NT may exert its effects on both neurons and astrocytes in the CNS. Whereas NT neural signaling is exerted through high-affinity receptors and may be partly effected through internalization of receptor-ligand complexes, glial signaling is exerted through low-affinity NT receptors and appears to be transduced exclusively at the level of the plasma membrane.

Delayed plasticity of the mesolimbic dopamine system following neonatal 6-OHDA lesions

In this study, we determined the ontogenetic profile (at postnatal days 7, 14, 35, and 90) of tyrodine hydroxylase (TH) mRNA in the ventral mesencephalon, and the levels of TH immunoreactivity (TH-IR) and dopamine (DA) transporter (DAT) sites in the striatum of rats that had received intrastriatal 6-hydroxy dopamine (6-OHDA) or vehicle lesions on day of birth (DO) or postnatal day 1 (P1). TH-IR was significantly decreased in all quadrants of the caudate-putamen at all time points, while TH-IR in the nucleus accumbens was unchanged, as compared to controls. Relative to the earliest time point (P7 lesion group), TH-IR recovered significantly in the medial caudate-putamen (CPu) of the P14, P35 and P90 6-OHDA-lesioned groups. Quantitative autoradiography of [3H]-mazindol binding to DAT sites showed significant, lesion-induced losses throughout the caudate-putamen of the 6-OHDA-lesioned groups at all time points and did not show appreciable recovery. Using in situ hybridization, significant (P < .05) decreases in TH mRNA levels were found at all time points in the lateral and medial substantia nigra pars compacta of 6-OHDA-lesioned animals. TH mRNA levels in the rostral ventral tegmental area (VTA), which were significantly decreased at P7, P14 and P35, returned to control levels at P90. TH mRNA levels in the caudal VTA were unchanged through P35 and became significantly elevated as compared to controls (+22%, P < .05) by P90. Thus, recovery of TH-IR in the medial caudate-putamen occurred prior to the elevation in levels of TH mRNA of the VTA. Our findings suggest that compensation exists in early development in certain subpopulations of mesostriatal DA neurons that differs from that in the adult.

Postnatal expression of melanocortin-3 receptor in rat diencephalon and mesencephalon

In situ hybridization was applied to examine the postnatal expression of melanocortin-3 (MC-3) receptor mRNA in the rat brain. Very weak and limited signals were seen in the hypothalamus on postnatal day 0 (P0) and in the dorsal lateral thalamus on P4. A marked increase was noted in several regions of the diencephalon and mesencephalon on P7. The highest levels were reached on P21, which was the time when an adult-like pattern was established. On P21, intense signals were seen in the ventromedial nucleus and the arcuate nucleus of the tuberal hypothalamus, the habenular nucleus of the epithalamus and the ventral tegmental area. [125I] Nle4, D-Phe7-alpha-MSH showed overlapping, but wider labelling of melanocortin receptors, that followed a similar developmental course. alpha-MSH-like immunoreactivity was seen widely in the forebrain and midbrain from P14. In contrast to the staining of alpha-MSH in neurons and their process, gamma 2-MSH-like immunoreactivity was detected strongly in the blood vessels. The neuronal localization of MC-3 receptor mRNA suggests that this receptor may mediate the neurotropic actions of melanocortin peptides in the developing brain.

Epigenetic factors and midbrain dopaminergic neurone development

In the mammalian brain dopamine systems play a central role in the control of movement, hormone release, emotional balance and reward. Alteration of dopaminergic neurotransmission is involved in Parkinson's disease and other movement disorders, as well as in some psychotic syndromes. This review summarises recent findings, which shed some light on signals and cellular interactions involved in the specification and maturation of the dopaminergic function during neurogenesis. In particular we will focus on three major issues: (1) the differentiation of dopaminergic neurones triggered by direct contact with the midbrain floor plate cells through the action of sonic hedgehog; (2) the neurotrophic factors acting on dopaminergic neurones; and (3) the role of target striatal cells on the survival and the axonal growth of developing or grafted dopaminergic neurones.

The extracellular matrix of the midline and non-midline midbrain glia: correlations with neurite growth-supporting abilities

The central nervous system (CNS) midline plays an important role in growth and guidance of axons. At the midline, a multiplicity of cell types establish boundaries that control the navigation of crossed and uncrossed axonal fibers. The extracellular matrix (ECM) molecules of the resident neuroepithelial or committed neuronal or glial cells could be involved in the control of axon growth and axon guidance. This review reports the recent advances in the study of the structure and functional role of the ECM at the midline locus of the CNS. In vivo and in vitro approaches are considered to provide new clues in the understanding of processes involved in the cellular decisions of the CNS midline.

Target and afferents interact to control developmental cell death in the mesencephalic parabigeminal nucleus of the rat

During the period of natural cell death in the developing mammalian brain, both target cells and afferents have been shown to be important for neuronal survival. Here we demonstrate that afferents and targets have interactive roles in the maintenance of cells during development of the mesencephalic parabigeminal nucleus (PB) in rats. Pyknotic nuclei were counted in the PB of developing rats that received a bilateral lesion of the superior colliculus on the day of birth (P0). We observed that simultaneous deafferentation and deeferentation leads to a large peak of cell death at P1-2 in all three divisions of PB. Later the rate of pyknosis decreases and a second period of elevated cell death is observed just before the complete disappearance of the nucleus at P7-8. Counts of healthy neurones indicates two separate periods of increased neuronal loss. The first period occurs at P1-2, and the last and dramatic episode of cell loss at P8 leads to the disappearance of the PB. The combined effects of simultaneous target removal and deafferentation were different from the sum of the individual effects, indicating that the axonal targets and the afferents interact to control cell survival in the PB.

Pre- and postnatal development of dopaminergic neuron numbers in the male and female mouse midbrain

Quantitative information about dopaminergic neuron numbers in the mesencephalon is needed to assess the significance of physiological cell death in the regulation of the development of this neural system. Therefore, stereological techniques were applied to determine absolute numbers of mesencephalic neurons immunoreactive to tyrosine hydroxylase during the ontogenetic period between embryonic day (E) 13 and postnatal day (P) 90. Male and female CBA/J mice were examined separately. The most rapid development with a 2.5-fold increase of total counts of immunostained cells per midbrain took place in the prenatal period. Beginning at E21, immunostained cells were counted separately in their three main locations, substantia nigra (SN), ventral tegmental area (VTA), and retrorubral field (RRF). Neuron numbers in RRF and VTA reached adult levels perinatally. In contrast, counts of immunostained cells in SN continued to increase postnatally. The only sign of cell loss was a transient decrease in VTA cell numbers (but not in total numbers of immunostained midbrain neurons) between E21 and P14. There were no statistically significant sex differences in cell numbers at any time point investigated. It is concluded that physiological cell death is not a major factor in the developmental regulation of dopaminergic cell numbers in the mouse midbrain.

Ontogeny of aromatase messenger ribonucleic acid and aromatase activity in the rat midbrain

Estrogen formation catalyzed by neural aromatase is crucial for the sexual differentiation of the brain. Ontogenic expression of aromatase mRNA and aromatase activity were studied in male and female rat midbrains. Aromatase mRNA was transiently expressed in both sexes showing maximum levels on postnatal day (P)2 and being absent on P20 and in adults. Developmental expression of aromatase mRNA preceded that of aromatase activity. These data demonstrate that the capacity for estrogen formation is present during a distinct phase of midbrain development. Our findings suggest an active role for estrogens in the differentiation of midbrain neurons.

Postmetamorphic changes in auditory sensitivity of the bullfrog midbrain

During metamorphosis, the lateral line system of ranid frogs (Rana catesbeiana) degenerates and an auditory system sensitive to airborne sounds develops. We examined the onset of function and developmental changes in the central auditory system by recording multi-unit activity from the principal nucleus of the torus semicircularis (TSp) of bullfrogs at different postmetamorphic stages in response to tympanically-presented auditory stimuli. No responses were recorded to stimuli of up to 95 dB SPL from late-metamorphic tadpoles, but auditory responses were recorded within 24 hours of completion of metamorphosis. Audiograms from froglets (SVL < 5.5 cm) were relatively flat in shape with high thresholds, and showed a decrease in most sensitive frequency (MSF) from about 2500 Hz to about 1500 Hz throughout the first 7-10 days after completion of metamorphosis. Audiograms from frogs larger than 5.5 cm showed continuous downward shifts in MSF and thresholds, and increases in sharpness around MSF until reaching adult-like values. Spontaneous activity in the TSp increased throughout postmetamorphic development. The torus increased in volume by approximately 50% throughout development and displayed changes in cell density and nuclear organization. These observations suggest that the onset of sensitivity to tympanically presented airborne sounds is limited by peripheral, rather than central, auditory maturation.

Early postnatal changes of the dopaminergic mesencephalic neurons in the weaver mutant mouse

In adult weaver (wv) mutant mice up to 70% of the mesostriatal dopaminergic neurons are lost and major alterations of the dopaminergic dendrites of the substantia nigra have been described. We sought to determine the time of onset of these alterations. Cell counts of the main dopaminergic (DA) mesencephalic cell groups (A8, A9, A10), as labeled with tyrosine hydroxylase immunocytochemistry were done in wild-type and homozygous wv/wv pups. No loss of the DA neurons, was detectable at postnatal day 7 (P7), while reductions in substantia nigra (and retrorubral area) amounted to 35% at P14 and 47% by P21. On the other hand, the severe reduction of dopaminergic dendrites, particularly of their distal compartments was already visible from P3 on. During the first postnatal week, this was associated to abnormal clustering of the dopaminergic neurons. These early neuritic alterations were present, though to a milder degree, in heterozygous (wv/+) mice.

Development of the olfactory and accessory lobes in the American lobster: an allometric analysis and its implications for the deutocerebral structure of decapods

The allometric changes characterizing the growth of the deutocerebrum (midbrain) of the American lobster (Homarus americanus) are studied using computerized three-dimensional reconstructions of serial brain sections. During the embryogenesis of the midbrain, the paired accessory lobes (higher order processing areas) appear later than the paired olfactory lobes (primary olfactory centers), but the former grow faster from their emergence until metamorphosis. The accessory lobes, as they enlarge, shift progressively from a medial to a posterior position in the lateral deutocerebrum. In early juvenile stages the accessory lobes are one of the largest neuropils of the brain. However, these lobes stop growing in adult animals, whereas the brain and olfactory lobes continue to enlarge, albeit at a slow rate. The overall shape of the brain and the relative proportions and locations of the deutocerebral neuropils and associated cell clusters of various lobster ontogenetic stages are similar to those of selected adult decapods. In addition, the relation between deutocerebral organization and brain size seem parallel during lobster development and across crustacean species. Measurements of the brains of 13 species of decapods (illustrated in Sandeman et al. [1993] J. Exp. Zool. 265:112, plus Homarus) indicate the following trends: Small brains possess olfactory lobes but no accessory lobes, larger brains possess accessory lobes that are medial and small relative to the olfactory lobes, and the largest brains contain relatively voluminous posterior accessory lobes. These observations indicate that some differences in the organization of the deutocerebrum are related to absolute brain size in crustaceans and suggest that ontogenetic scaling of proportions may apply to the deutocerebral neuropils of decapods. Peramorphosis and paedomorphosis in the evolution of the decapod brain are considered.

Effects of glial cell line-derived neurotrophic factor on developing and mature ventral mesencephalic grafts in oculo

The search for trophic factors that can support injured dopaminergic neurons and can enhance dopaminergic graft survival and outgrowth for therapeutic uses in Parkinson's disease has lately focused on members of the transforming growth factor (TGF) beta super-family. In this paper we have studied the effects of a member of the TGB beta family, glial cell line-derived neurotrophic factor (GDNF), on immature and mature ventral mesencephalic tissue grafted to the anterior chamber of the eye. The results confirm that GDNF increases survival of TH-positive neurons and enhances TH-immunoreactive nerve fiber formation when the grafts are treated during their development. The distribution of nerve terminals is densest within the area of TH-immunoreactive neurons and at the surface of the grafts. However, there is no change in the number of calcium-binding protein (CaBP)-positive neurons, suggesting that the subpopulation of TH-positive neurons that is increased are the CaBP-negative neurons of the ventral tier of pars compacta. Terminals from those neurons form the striatal patches during normal development. When the grafts are treated with GDNF after maturation, no change in TH-positive cell survival is seen but an increase of nerve terminals is still found within the cell dense area of the graft. Potassium-evoked dopamine release, measured using in vivo chronoamperometry, revealed significantly increased extracellular overflow in transplants treated with GDNF during development. The dopamine uptake blocker nomifensine significantly increased the time for clearance of the released dopamine. These data suggest that GDNF treatment of immature grafts enhances survival of TH-positive neurons, which would have innervated the striatal patches, and also increases TH-immunoreactive nerve fiber formation and dopamine release. Furthermore, GDNF treatment of mature grafts also increases dopamine fiber formation within the TH-positive neuronal area, indicating that adult dopaminergic neurons are also responsive to this agent.

Expression of pS2 gene in rat brain

We have previously shown that the expression of pS2 mRNA, which encodes a secreted 60-amino acid protein of unknown function, is widely distributed throughout the entire body of the mouse including the brain. We report herein that pS2 mRNA is also expressed in the brain and in peripheral tissues of rats. In adult rat brain, pS2 mRNA was predominantly expressed in hippocampus, followed by the cerebral cortex and cerebellum. The developmental expression of pS2 mRNA in hippocampus, which region is known to mature after birth, showed a clear peak in 1- or 3-day-old rats, then gradually decreased by 7 weeks after birth. In midbrain, the maturation of which occurs at an early developmental stage, pS2 mRNA level was retained at a low level from postnatal 1 day to week 7. These results suggest that pS2 protein plays an important role in the development of central nervous system.

Effect of neonatal monosodium glutamate on lipid peroxidation in adult rat brain

Glutamate (glu), an excitatory amino acid (EAA) abundantly present in the brain of mammals, is also a neurotoxin. We examined lipid peroxidation (LPO) potential and antioxidant parameters of midbrain region (MBR) and frontal cortex of adult rats following treatment with monosodium glutamate (MSG) during postnatal day (PND) 1 through PND 10 at a daily dose of 4 mg g-1 body weight. In PND 90 rats MSG increased LPO by 56% and altered antioxidant status of MBR. This indicates that oxidative stress produced by glu in vulnerable brain regions may persist for prolonged periods and could be one of the mechanisms of EAA neurotoxicity resulting in chronic neurodegeneration.

Development of human fetal ventral mesencephalic grafts in rats with 6-OHDA lesions of the nigrostriatal pathway

Neuronal transplantation is an approach that can be exploited to study the development of the human central nervous system as well as being used in attempts to restore neurological function. In the present study, we have examined cellular events that appear to precede the development of dopamine nerve fiber extension by neurons from the human fetal ventral mesencephalon. These cellular events were examined using neuronal cell suspensions from human fetal ventral mesencephalic tissue (gestational ages 7-10 weeks) transplanted into the striatum of unilaterally lesioned 6-hydroxydopamine (6-OHDA) rats. Animals were sacrificed for immunohistochemistry 9-10 weeks after the transplantation prior to the manifestation of behavioral recovery. Histological analysis revealed tyrosine hydroxylase (TH) immunoreactive neurons in the grafts. The majority of these neurons had very short TH positive processes (60-70 microns), indicating that the maturation of grafted dopaminergic neurons was still incomplete. Immunostaining for the human specific intermediate neurofilament (hNF, clone: BF-10) showed dense neuronal fibers in the grafts. These fibers extended deeper into the host brain than the TH positive neuronal processes. The whole striatum, particularly the medial part of the striatum, exhibited long NF positive processes. Glial fibrillary acidic protein (GFAP) immunohistochemistry revealed fine astrocytic processes inside the grafts, which were clearly different from host reactive glial cells surrounding the grafts. These graft-derived glial processes tended to extend into the host brain deeper than the TH positive neuronal processes from the grafts. These early histological findings of the grafted human fetal ventral mesencephalon suggest that the graft-derived NF positive neuronal processes, as well as the glial processes, radiate from the grafted tissue and extend into the host brain prior to the extension of TH positive processes. These results further suggest that human-to-rat xenografts can be used to study the neural development of human fetal brain tissue.

Neurotrophic and neuroprotective effects of neuron-specific enolase on cultured neurons from embryonic rat brain

We previously reported that the gamma gamma-isozyme of enolase, NSE), one of the glycolytic enzymes, promoted the survival of embryonic rat neocortical neurons in culture, but alpha alpha-isozyme (non-neuronal enolase) had no effect. In the present study, the neurotrophic effects of NSE on cultured mesencephalic and spinal neurons from rat embryo were examined. NSE promoted the survival of neurons not only in neocortical cultures but also in mesencephalic and spinal cord cultures. Furthermore, NSE showed neuroprotective action on cultured neocortical neurons in a low-oxygen atmosphere. By contrast, non-neuronal enolase did not show any neurotrophic or neuroprotective activities. To clarify the mechanism of the neurotrophic effect of NSE, the binding of NSE to cultured neurons was determined by radio-receptor assay using 125I-labelled NSE. The specific binding, which was dose-dependent, saturable, and calcium-dependent, could be detected. These results suggest that NSE has neurotrophic and neuroprotective effects on rather a broad spectrum of neurons in the central nervous system. The existence of specific binding of NSE to cultured neurons suggests the possibility that receptor-like or carrier-like molecules on the neuronal surface are involved in the neurotrophic activity of NSE.

Aromatase in the cerebral cortex, hippocampus, and mid-brain: ontogeny and developmental implications

Aromatase activity was measured in explant cultures from the newborn mouse and rat brain and in homogenates of regions of the rat brain sampled between birth and 51 days of age. Conversion of 19-[3H]hydroxy-androstenedione to estradiol and estrone was detected in explant cultures from the mouse preoptic/septal region, anterior cingulate cortex, and midbrain, as well as from the rat preoptic area, septum, hippocampus, anterior cingulate cortex, and midbrain central grey. No detectable estrogen biosynthesis was observed in explants from the cerebellum and spinal cord of either species. Measurements of aromatase in tissue homogenates using 1 beta[3H]androstenedione as substrate revealed detectable enzyme activity in the hypothalamus + preoptic area, amygdala, hippocampus, anterior cingulate cortex, and midbrain, from birth onward. Aromatase activity per milligram of tissue protein was highest in the hypothalamus-preoptic area and amygdala, followed by the hippocampus, midbrain, and cingulate cortex. In all brain regions, aromatase activity was markedly higher at Postnatal Days 1 and 7 than later in life. In both the cingulate cortex and the hippocampus, aromatase was barely detectable above the assay blank in adult (51 day) animals. These results demonstrate that regions of the developing rodent neo- and archicortex have the capacity to convert androgen to estrogen, consistent with a role for local estrogen biosynthesis in the sexual differentiation of higher brain functions.