Early evidence of catecholaminergic cell groups in 5- and 6-week-old human embryos using tyrosine hydroxylase and dopamine-beta-hydroxylase immunocytochemistry

The Central Noradrenergic System in Neurodevelopmental Disorders: Merging Experimental and Clinical Evidence

The aim of this article is to highlight the potential role of the locus-coeruleus-noradrenergic (LC-NA) system in neurodevelopmental disorders (NdDs). The LC is the main brain noradrenergic nucleus, key in the regulation of arousal, attention, and stress response, and its early maturation and sensitivity to perinatal damage make it an interesting target for translational research. Clinical data shows the involvement of the LC-NA system in several NdDs, suggesting a pathogenetic role in the development of such disorders. In this context, a new neuroimaging tool, LC Magnetic Resonance Imaging (MRI), has been developed to visualize the LC in vivo and assess its integrity, which could be a valuable tool for exploring morphological alterations in NdD in vivo in humans. New animal models may be used to test the contribution of the LC-NA system to the pathogenic pathways of NdD and to evaluate the efficacy of NA-targeting drugs. In this narrative review, we provide an overview of how the LC-NA system may represent a common pathophysiological and pathogenic mechanism in NdD and a reliable target for symptomatic and disease-modifying drugs. Further research is needed to fully understand the interplay between the LC-NA system and NdD.

Transient compartmentalization and accelerated volume growth coincide with the expected development of cortical afferents in the human neostriatum

The neostriatum plays a central role in cortico-subcortical circuitry underlying goal-directed behavior. The adult mammalian neostriatum shows chemical and cytoarchitectonic compartmentalization in line with the connectivity. However, it is poorly understood how and when fetal compartmentalization (AChE-rich islands, nonreactive matrix) switches to adult (AChE-poor striosomes, reactive matrix) and how this relates to the ingrowth of corticostriatal afferents. Here, we analyze neostriatal compartments on postmortem human brains from 9 postconceptional week (PCW) to 18 postnatal months (PM), using Nissl staining, histochemical techniques (AChE, PAS-Alcian), immunohistochemistry, stereology, and comparing data with volume-growth of in vivo and in vitro MRI. We find that compartmentalization (C) follows a two-compartment (2-C) pattern around 10PCW and is transformed into a midgestational labyrinth-like 3-C pattern (patches, AChE-nonreactive perimeters, matrix), peaking between 22 and 28PCW during accelerated volume-growth. Finally, compartmentalization resolves perinatally, by the decrease in transient "AChE-clumping," disappearance of AChE-nonreactive, ECM-rich perimeters, and an increase in matrix reactivity. The initial "mature" pattern appears around 9 PM. Therefore, transient, a 3-C pattern and accelerated neostriatal growth coincide with the expected timing of the nonhomogeneous distribution of corticostriatal afferents. The decrease in growth-related AChE activity and transfiguration of corticostriatal terminals are putative mechanisms underlying fetal compartments reorganization. Our findings serve as normative for studying neurodevelopmental disorders.

The Development of the Mesoprefrontal Dopaminergic System in Health and Disease

Midbrain dopaminergic neurons located in the substantia nigra and the ventral tegmental area are the main source of dopamine in the brain. They send out projections to a variety of forebrain structures, including dorsal striatum, nucleus accumbens, and prefrontal cortex (PFC), establishing the nigrostriatal, mesolimbic, and mesoprefrontal pathways, respectively. The dopaminergic input to the PFC is essential for the performance of higher cognitive functions such as working memory, attention, planning, and decision making. The gradual maturation of these cognitive skills during postnatal development correlates with the maturation of PFC local circuits, which undergo a lengthy functional remodeling process during the neonatal and adolescence stage. During this period, the mesoprefrontal dopaminergic innervation also matures: the fibers are rather sparse at prenatal stages and slowly increase in density during postnatal development to finally reach a stable pattern in early adulthood. Despite the prominent role of dopamine in the regulation of PFC function, relatively little is known about how the dopaminergic innervation is established in the PFC, whether and how it influences the maturation of local circuits and how exactly it facilitates cognitive functions in the PFC. In this review, we provide an overview of the development of the mesoprefrontal dopaminergic system in rodents and primates and discuss the role of altered dopaminergic signaling in neuropsychiatric and neurodevelopmental disorders.

Vitamin D and schizophrenia: 20 years on

Many epidemiological studies have highlighted the link between vitamin D deficiency and schizophrenia. In particular, two prominent studies report an association between neonatal vitamin D deficiency and an increased risk of schizophrenia. In parallel, much has been learnt about the role of vitamin D in the developing central nervous system over the last two decades. Studies in rodent models of developmental vitamin D (DVD)-deficiency describe how brain development is altered leading to a range of neurobiological and behavioral phenotypes of interest to schizophrenia. While glutamate and gamma aminobutyric acid (GABA) systems have been little investigated in these models, alterations in developing dopamine systems are frequently reported. There have been far more studies reporting patients with schizophrenia have an increased risk of vitamin D deficiency compared to well controls. Here we have conducted a systematic review and meta-analysis that basically confirms this association and extends this to first-episode psychosis. However, patients with schizophrenia also have poorer general health, poorer diets, are frequently less active and also have an increased risk of other medical conditions, all factors which reduce circulating vitamin D levels. Therefore, we would urge caution in any causal interpretation of this association. We also summarize the inconsistent results from existing vitamin D supplementation trials in patients with schizophrenia. In respect to animal models of adult vitamin D deficiency, such exposures produce subtle neurochemical alterations and effects on cognition but do not appear to produce behavioral phenotypes of relevance to schizophrenia. We conclude, the hypothesis that vitamin D deficiency during early life may increase the risk of schizophrenia remains plausible and warrants ongoing research.

The Influence of Donor Age on the Survival of Solid and Suspension Intraparenchymal Human Embryonic Nigral Grafts

In many species, graft survival and graft-derived behavioral recovery are affected by the embryonic donor age. We compared the ability of solid and suspension grafts of human embryonic mesencephalic dopaminergic (DA) neurons at different embryonic stages to survive intra-parenchymal transplantation into 6-OHDA lesioned immunosuppressed rats. Suspension grafts survived best when donor age was between postconception (PC) days 34 and 56. Transplants displayed numerous healthy tyrosine hydroxylase immunoreactive (TH-IR) neurons which sent extensive neuritic processes into the host striatum. Suspension grafts survived poorly when donor age was greater than 65 days. Solid implants displayed comparable viability of TH-IR neurons when donor age was between 44 and 65 days. No solid grafts contained TH-IR cells when donor tissue was older than 72 days. The suspension and solid methods of transplantation resulted in comparable survival of robust grafts, but solid grafts resulted in more intergraft variability than suspension grafts, particularly among the more marginal implants. Our results demonstrate that the upper limit for survival of human embryonic DA suspension grafts correlates well with the period of development of the human nigrostriatal pathway. The “window” for donor age of solid human embryonic DA grafts appears to be extended by about 9 days in comparison to suspension grafts. These data suggest that the upper age limit for grafting human mesencephalic DA neurons should be PC day 56 for suspension grafts, and PC day 65 for solid implants. Older donors are likely to produce grafts with fewer surviving DA neurons.

The Effect of Perinatal Hypoxic/Ischemic Injury on Tyrosine Hydroxylase Expression in the Locus Coeruleus of the Human Neonate

We have previously shown that perinatal hypoxic/ischemic injury (HII) may cause selective vulnerability of the mesencephalic dopaminergic neurons of human neonate. In the present study, we investigated the effect of perinatal HII on the noradrenergic neurons of the locus coeruleus (LC) of the same sample. We studied immunohistochemically the expression of tyrosine hydroxylase (TH, first limiting enzyme for catecholamine synthesis) in LC neurons of 15 autopsied infants (brains collected from the Greek Brain Bank) in relation to the neuropathological changes of acute or chronic HII of the neonatal brain. Our results showed that perinatal HII appears to affect the expression of TH and the size of LC neurons of the human neonate. In subjects with neuropathological lesions consistent with abrupt/severe HII, intense TH immunoreactivity was found in almost all neurons of the LC. In most of the neonates with neuropathological changes of prolonged or older injury, however, reduction in cell size and a decrease or absence of TH staining were observed in the LC. Intense TH immunoreactivity was found in the LC of 3 infants of the latter group, who interestingly had a longer survival time and had been treated with anticonvulsant drugs. Based on our observations and in view of experimental evidence indicating that the reduction of TH-immunoreactive neurons occurring in the LC after perinatal hypoxic insults persists into adulthood, we suggest that a dysregulation of monoaminergic neurotransmission in critical periods of brain development in humans is likely to predispose the survivors of perinatal HII, in combination with genetic susceptibility, to psychiatric and/or neurological disorders later in life.

Cannabis, the pregnant woman and her child: weeding out the myths

To review and summarise the literature reporting on cannabis use within western communities with specific reference to patterns of use, the pharmacology of its major psychoactive compounds, including placental and fetal transfer, and the impact of maternal cannabis use on pregnancy, the newborn infant and the developing child. Review of published articles, governmental guidelines and data and book chapters. Although cannabis is one of the most widely used illegal drugs, there is limited data about the prevalence of cannabis use in pregnant women, and it is likely that reported rates of exposure are significantly underestimated. With much of the available literature focusing on the impact of other illicit drugs such as opioids and stimulants, the effects of cannabis use in pregnancy on the developing fetus remain uncertain. Current evidence indicates that cannabis use both during pregnancy and lactation, may adversely affect neurodevelopment, especially during periods of critical brain growth both in the developing fetal brain and during adolescent maturation, with impacts on neuropsychiatric, behavioural and executive functioning. These reported effects may influence future adult productivity and lifetime outcomes. Despite the widespread use of cannabis by young women, there is limited information available about the impact perinatal cannabis use on the developing fetus and child, particularly the effects of cannabis use while breast feeding. Women who are using cannabis while pregnant and breast feeding should be advised of what is known about the potential adverse effects on fetal growth and development and encouraged to either stop using or decrease their use. Long-term follow-up of exposed children is crucial as neurocognitive and behavioural problems may benefit from early intervention aimed to reduce future problems such as delinquency, depression and substance use.

Developmental origins of brain disorders: roles for dopamine

Neurotransmitters and neuromodulators, such as dopamine, participate in a wide range of behavioral and cognitive functions in the adult brain, including movement, cognition, and reward. Dopamine-mediated signaling plays a fundamental neurodevelopmental role in forebrain differentiation and circuit formation. These developmental effects, such as modulation of neuronal migration and dendritic growth, occur before synaptogenesis and demonstrate novel roles for dopaminergic signaling beyond neuromodulation at the synapse. Pharmacologic and genetic disruptions demonstrate that these effects are brain region- and receptor subtype-specific. For example, the striatum and frontal cortex exhibit abnormal neuronal structure and function following prenatal disruption of dopamine receptor signaling. Alterations in these processes are implicated in the pathophysiology of neuropsychiatric disorders, and emerging studies of neurodevelopmental disruptions may shed light on the pathophysiology of abnormal neuronal circuitry in neuropsychiatric disorders.

The vitamin D receptor in dopamine neurons; its presence in human substantia nigra and its ontogenesis in rat midbrain

There is growing evidence that vitamin D is a neuroactive steroid capable of regulating multiple pathways important for both brain development and mature brain function. In particular, there is evidence from rodent models that prenatal vitamin D deficiency alters the development of dopaminergic pathways and this disruption is associated with altered behavior and neurochemistry in the adult brain. Although the presence of the vitamin D receptor (VDR) has been noted in the human substantia nigra, there is a lack of direct evidence showing that VDR is present in dopaminergic cells. Here we confirm that the VDR is present in the nucleus of tyrosine hydroxylase (TH)-positive neurons in both the human and rat substantia nigra, and it emerges early in development in the rat, between embryonic day 12 (E12) and E15. Consistent evidence based on immunohistochemistry, real-time PCR and western blot confirmed a pattern of increasing VDR expression in the rat midbrain until weaning. The nuclear expression of VDR in TH-positive neurons during critical periods of brain development suggests that alterations in early life vitamin D status may influence the orderly development of dopaminergic neurons.

Molecular mechanisms of maternal cannabis and cigarette use on human neurodevelopment

Prenatal development is highly sensitive to maternal drug use due to the vulnerability for disruption of the fetal brain with its ongoing neurodevelopment, resulting in lifelong consequences that can enhance risk for psychiatric disorders. Cannabis and cigarettes are the most commonly used illicit and licit substances, respectively, among pregnant women. Although the behavioral consequences of prenatal cannabis and cigarette exposure have been well-documented in epidemiological and clinical studies, only recently have investigations into the molecular mechanisms associated with the developmental impact of early drug exposure been addressed. This article reviews the literature relevant to long-term gene expression disturbances in the human fetal brain in relation to maternal cannabis and cigarette use. To provide translational insights, we discuss animal models in which protracted molecular consequences of prenatal cannabis and cigarette exposure can be better explored and which enable future evaluation of epigenetic pathways, such as DNA methylation and histone modification, that could potentially maintain abnormal gene regulation and related behavioral disturbances. Altogether, this information may help to address the current gaps of knowledge regarding the impact of early drug exposure that set in motion lifelong molecular disturbances that underlie vulnerability to psychiatric disorders.

Molecular genetics of the developing neuroendocrine hypothalamus

Formation of the mammalian endocrine system and neuroendocrine organs involves complex regulatory networks resulting in a highly specialized cell system able to secrete a diverse array of peptide hormones. The hypothalamus is located in the mediobasal region of the brain and acts as a gateway between the endocrine and nervous systems. From an endocrinology perspective, the parvicellular neurons of the hypothalamus are of particular interest as they function as a control centre for several critical physiological processes including growth, metabolism and reproduction by regulating hormonal signaling from target cognate cell types in the anterior pituitary. Delineating the genetic program that controls hypothalamic development is essential for complete understanding of parvicellular neuronal function and the etiology of congenital disorders that result from hypothalamic-pituitary axis dysfunction. In recent years, studies have shed light on the interactions between signaling molecules and activation of transcription factors that regulate hypothalamic cell fate commitment and terminal differentiation. The aim of this review is to summarize the recent molecular and genetic findings that have advanced our understanding of the emergence of the known important hypophysiotropic signaling molecules in the hypothalamus. We have focused on reviewing the literature that provides evidence of the dependence on expression of specific genes for the normal development and function of the cells that secrete these neuroendocrine factors, as well as studies of the elaboration of the spatial or temporal patterns of changes in gene expression that drive this development.

Neurobiological consequences of maternal cannabis on human fetal development and its neuropsychiatric outcome

Despite the high prevalence of marijuana use among pregnant women and adolescents, the impact of cannabis on the developing brain is still not well understood. However, growing evidence supports that the endocannabinoid system plays a major role in CNS patterning in structures relevant for mood, cognition, and reward, such as the mesocorticolimbic system. It is thus clear that exposure to cannabis during early ontogeny is not benign and potential compensatory mechanisms that might be expected to occur during neurodevelopment appear insufficient to eliminate vulnerability to neuropsychiatric disorders in certain individuals. Both human longitudinal cohort studies and animal models strongly emphasize the long-term influence of prenatal cannabinoid exposure on behavior and mental health. This review provides an overview of the endocannabinoid system and examines the neurobiological consequences of cannabis exposure in pregnancy and early life by addressing its impact on the development of neurotransmitters systems relevant to neuropsychiatric disorders and its association with these disorders later in life. It posits that studying in utero cannabis exposure in association with genetic mutations of neural systems that have strong relationships to endocannabinoid function, such as the dopamine, opioid, glutamate, and GABA, might help to identify individuals at risk. Such data could add to existing knowledge to guide public health platform in regard to the use of cannabis and its derivatives during pregnancy.

[Development of human hypothalamus at the end of the first and in the second trimester of gestation]

INTRODUCTION

The paper deals with the embryonic development of human hypothalamus at the end of the first and during the second trimesters of gestation. Bearing in mind that the mammal brain, as an entity, develops from the prosencephalic, mesencephalic and rhombencephalic vesicles, which are noticeable in the cranial portion of the neural tube in the 4th week of gestation, and that diencephalon is manifested in the eye vesicle at the same gestational age, authors presented the neuronal secretory activity in that period.

SECRETORY ACTIVITY OF HYPOTHALAMIC NEURONS

The secretory activity of both neurons and hypothalamic nuclei, as well as their maturation, were followed-up by certain immunohistochemical and immunoradiological methods based on structural identification of some factors (primarily protein molecules), which made it possible to determine the specificity of secretory activity of hypothalamic nuclei (ex. tuberohypophyseal pathways), as well as the levels of the hormone release into the hypothalamo-hypophysial complex.

CONCLUSION

The aim of this work was to estimate the catecholamine activity during the development of the respective part of the brain in the 5th, 6th, 11th and 13th week of gestation and later.

The amygdaloid complex and the medial and lateral ventricular eminences in staged human embryos

The amygdaloid complex was investigated in 36 serially sectioned staged human embryos, including 20 impregnated with silver. This is the first such account based on graphic reconstructions, 28 of which were prepared. Significant findings in the human include the following. (1) The medial (first) and (then) lateral ventricular eminences arise independently at stages 14 and 15, and unite only at stage 18 to form the floor of the lateral ventricle. (2) The future amygdaloid region is discernible at stage 14 and the amygdaloid primordium at stage 15. (3) The anterior amygdaloid area and the corticomedial and basolateral complexes appear at stage 16. (4) These three major divisions arise initially from the medial ventricular eminence, which is diencephalic. (5) Individual nuclei begin to be detectable at stages 17-21, the central nucleus at stage 23 and the lateral nucleus shortly thereafter. (6) The ontogenetic findings in the human embryonic period accord best with the classification used by Humphrey. (7) The lateral eminence, which is telencephalic, contributes to the cortical nucleus at stage 18. (8) The primordial plexiform layer develops independently of the cortical nucleus. (9) Spatial changes of the nuclei within the amygdaloid complex and of the complex as a whole begin in the embryonic period and continue during the fetal period, during the early part of which the definitive amygdaloid topography in relation to the corpus striatum is attained. (10) The developing amygdaloid nuclei are closely related to the medial forebrain bundle, which has already appeared in stage 15. (11) Fibre connections develop successively between the amygdaloid nuclei and the septal, hippocampal and diencephalic formations, constituting the beginning of the limbic system before the end of the embryonic period. Although the nucleus accumbens also appears relatively early (stage 19), connections between it and the amygdaloid complex are not evident during the embryonic period. (12) Influence of the olfactory bulb and tubercle on initial amygdaloid development, as postulated for rodents, is unlikely in the human. The findings exemplify the necessity of beginning developmental studies with the embryonic period proper.

Systemic prenatal insults disrupt telencephalon development: implications for potential interventions

Infants born prematurely are prone to chronic neurologic deficits including cerebral palsy, epilepsy, cognitive delay, behavioral problems, and neurosensory impairments. In affected children, imaging and neuropathological findings demonstrate significant damage to white matter. The extent of cortical damage has been less obvious. Advances in the understanding of telencephalon development provide insights into how systemic intrauterine insults affect the developing white matter, subplate, and cortex, and lead to multiple neurologic impairments. In addition to white matter oligodendrocytes and axons, other elements at risk for perinatal brain injury include subplate neurons, GABAergic neurons migrating through white matter and subplate, and afferents of maturing neurotransmitter systems. Common insults including hypoxia-ischemia and infection often affect the developing brain differently than the mature brain, and insults precipitate a cascade of damage to multiple neural lineages. Insights from development can identify potential targets for therapies to repair the damaged neonatal brain before it has matured.

Development of A9/A10 dopamine neurons during the second and third trimesters in the African green monkey

Disruption in the development of dopamine-containing neurons has been postulated to underlie several CNS disorders. However, there have been no quantitative studies on the normal development of primate dopamine neurons. Thus, the fetal maturation of primate midbrain dopamine neurons was examined to establish changes that occur in the A9/A10 groups during the second and third trimesters. Eleven fetal African green monkey midbrains were immunostained for tyrosine hydroxylase (TH-ir) as a marker for dopamine neurons and quantified using stereological techniques (nucleator method). The number and size of defined dopamine neurons and the volume occupied by A9/A10 neurons increased in near linear fashion throughout the term. The estimated number of defined dopamine neurons in each hemisphere rose from approximately 50,000 at embryonic day (E) 70 to 225,000 at birth (E165), similar to the adult population. The size and the area occupied by them at birth were, however, well below the estimated adult levels. Additionally, the younger fetal midbrains had far less diversity in dopamine cell volumes compared with older fetuses and adult brains. Until midway through gestation (E81), clusters of apparently immature midbrain TH-ir cells were observed, but could not be counted. Even though the majority of cells destined to become dopamine neurons are generated in the first trimester, phenotypical maturation of A9 and A10 cell bodies continues steadily throughout gestation and extends well into the postnatal period. These data have relevance to transplantation studies that employ fetal dopaminergic grafts, and to disorders hypothesized to result from damage to developing midbrain dopamine neurons.

Development of paraventricular nucleus (PVN) associated with immunoreactivity to tyrosine hydroxylase (TH) in the second half of gestation

The aim of this study was to shed more light on the developmental characteristics of human paraventricular nucleus (PVN) and hypothalamus in general, using modern immunohistochemical techniques to detect the activity of tyrosine hydroxylase (TH) in the synthesis of catecholamine (CA). Fetal brains were examined at 12, 16, 20 and 23 weeks gestation. Immunohistochemical staining used for sections is a qualitative method for detection and distribution of the chosen protein. The amplification of positive signals was carried out using AVIDIN/BIOTIN technique. The first positive results were obtained at 16th week of gestation and immunoreactivity) grew with the advencement of gestation and that there was no homogenisation of immunoreactivity in some parts of the nucleus. The PVN showed to be an oval formation. nearly parallel with the lateral wall of the 3rd cerebral ventricle, where the upper apex of the nucleus is situated closer to the ependymal ventricular layer. There was an ascendant dorsal movement of the nucleus in the embryonic phase of hypothalamus development.

Phenotypic expression of monoamines and GABA in the early development of human telencephalon, transient or not transient

We review the phenotypic expression of molecules involved in monoamine and GABA neurotransmission in the developing human brain. Recent experimental reports have analyzed neurotransmitter signaling before the onset of synaptogenesis, which could act to influence early developmental events such as proliferation, migration, and differentiation of animal brain development. Such signaling may also occur in human development. The expression of molecules involved in neurotransmission in precocious human brain may reflect either the differentiation of a permanent neurotransmitter system of the adult brain or transient expression to serve specific developmental functions different from those in the adult brain. We review the changes observed in the expression of various catecholamine markers such as tyrosine-hydroxylase (TH) immunoreactivity in various neuronal populations of the developing human telencephalon. The specific transporter for serotonin, serotonin transporter (SERT) has been detected in fibers of the internal capsule (IC) during the restricted time period of 12-14 gestational weeks in humans. These serotonin-containing fibers do not correspond to serotoninergic ascending axons from the raphe nuclei. They may be the human counterpart of the thalamo-cortical axons that have been shown to uptake serotonin during the critical period of development of the sensory systems in rodents. GABA phenotypes are expressed in numerous cells of the human ganglionic eminence (GE) and cerebral wall at the end of the embryonic period proper. These results are similar to that described at comparable developmental stages in the mouse and support the hypothesis of an early migration from ganglionic progenitors in humans. But one cannot exclude a transient expression of GABA within the post-mitotic neurons, which could influence early developmental events. In conclusion, data showing the phenotypic expression of molecules in discrete areas of the brain at various points in the protracted human development require careful interpretation.

Differential expression and distribution of alpha-, beta-, and gamma-synuclein in the developing human substantia nigra

Although the functions of alpha-, beta-, and gamma-synuclein (alphaS, betaS, gammaS, respectively) are unknown, these synaptic proteins are implicated in the pathogenesis of Parkinson's disease (PD) and related disorders. For example, alphaS forms Lewy bodies (LBs) in substantia nigra (SN) neurons of PD. However, since it is not known how these hallmark PD lesions contribute to the degeneration of SN neurons or what the normal function of alphaS is in SN neurons, we studied the developing human SN from 11 weeks gestational age (GA) to 16 years of age using immunohistochemistry and antibodies to alphaS, betaS, gammaS, other synaptic proteins, and tyrosine hydoxylase (TH). SN neurons expressed TH at 11 weeks GA and alphaS, betaS, and gammaS appeared initially at 15, 17, and 18 weeks GA, respectively. These synucleins first appeared in perikarya of SN neurons after synaptophysin, but about the same time as synaptotagmin and synaptobrevin. Redistribution of alphaS from perikarya to processes of SN neurons occurred by 18 weeks GA in parallel with synaptophysin, while betaS and synaptotagmin were redistributed similarly between 20 and 28 weeks GA and this also occurred with gammaS and synaptobrevin between 33 weeks GA and 9 months postnatal. These data suggest that alphaS, betaS, and gammaS may play a functional role in the development and maturation of SN neurons, but it remains to be determined how sequestration of alphaS as LBs in PD contributes to the degeneration of SN neurons.

Neurobiological mechanisms of the onset of puberty in primates

An increase in pulsatile release of LHRH is essential for the onset of puberty. However, the mechanism controlling the pubertal increase in LHRH release is still unclear. In primates the LHRH neurosecretory system is already active during the neonatal period but subsequently enters a dormant state in the juvenile/prepubertal period. Neither gonadal steroid hormones nor the absence of facilitatory neuronal inputs to LHRH neurons is responsible for the low levels of LHRH release before the onset of puberty in primates. Recent studies suggest that during the prepubertal period an inhibitory neuronal system suppresses LHRH release and that during the subsequent maturation of the hypothalamus this prepubertal inhibition is removed, allowing the adult pattern of pulsatile LHRH release. In fact, y-aminobutyric acid (GABA) appears to be an inhibitory neurotransmitter responsible for restricting LHRH release before the onset of puberty in female rhesus monkeys. In addition, it appears that the reduction in tonic GABA inhibition allows an increase in the release of glutamate as well as other neurotransmitters, which contributes to the increase in pubertal LHRH release. In this review, developmental changes in several neurotransmitter systems controlling pulsatile LHRH release are extensively reviewed.

Structure of longitudinal brain zones that provide the origin for the substantia nigra and ventral tegmental area in human embryos, as revealed by cytoarchitecture and tyrosine hydroxylase, calretinin, calbindin, and GABA immunoreactions

In a previous work, mapping early tyrosine hydroxylase (TH) expressing primordia in human embryos, the tegmental origin of the substantia nigra (SN) and ventral tegmental area (VTA) was located across several neuromeric domains: prosomeres 1-3, midbrain, and isthmus (Puelles and Verney, [1998] J. Comp. Neurol. 394:283-308). The present study examines in detail the architecture of the neural wall along this tegmental continuum in 6-7 week human embryos, to better define the development of the SN and VTA. TH-immunoreactive (TH-IR) structures were mapped relative to longitudinal subdivisions (floor plate, basal plate, alar plate), as well as to radially superposed strata of the neural wall (periventricular, intermediate, and superficial strata). These morphologic entities were delineated at each relevant segmental level by using Nissl-stained sections and immunocytochemical mapping of calbindin, calretinin, and GABA in adjacent sagittal or frontal sections. A numerous and varied neuronal population originates in the floor plate area, and some of its derivatives become related through lateral tangential migration with other neuronal populations born in distinct medial and lateral portions of the basal plate and in a transition zone at the border with the alar plate. Some structural differences characterize each segmental domain within this common schema. The TH-IR neuroblasts arise predominantly within the ventricular zone of the floor plate and, more sparsely, within the adjacent medial part of the basal plate. They first migrate radially from the ventricular zone to the pia and then apparently move laterally and slightly rostralward, crossing the superficial stratum of the basal plate. Several GABA-IR cell populations are present in this region. One of them, which might represent the anlage of the SN pars reticulata, is generated in the lateral part of the basal plate.

Expression of calbindin D28K in the dopaminergic mesotelencephalic system in embryonic and fetal human brain

A subset of tyrosine-hydroxylase (TH) neurons of the substantia nigra (A9) containing calbindin D28K (CaBP) appeared to be less vulnerable to cell death induced by Parkinson's disease than the subset containing dopamine (DA) alone. Because grafting procedures of fetal human neurons are increasingly used in the therapy of Parkinson's disease, it is important to study the development of DA neurons coexpressing CaBP. In humans, the genesis of TH immunoreactivity of A9, of the ventral tegmental area (A10), and of the retrorubral area (A8) occurred during a 2-week period from the 4. 5th gestational week (g.w.) in the ventricular zone of the floor plate and the contiguous basal plate of the mesencephalon and diencephalon, i.e., the prosomeres p1-p3. Double-immunolabeled TH-CaBP neurons were detected from 5.5 g.w. on, in the first wave of DA neuron's migration, and were observed in their final residence in the dorsal A9 by 10.5 g.w. Calretinin immunoreactivity was expressed in TH-immunoreactive (IR) neurons from 10.5 g.w. on. Ascending TH-CaBP-IR axons were observed toward the telencephalon from 6-7 g.w. , reaching the anlage of the nucleus accumbens and amygdaloid complex at 10.5 g.w., but were not detected in the ganglionic eminence at this latter stage. Dopaminergic patches were detected at 13 g.w. in the anlage of the putamen, but no TH-CaBP-IR fibers were observed in the matrix at this stage. In conclusion, even if CaBP immunoreactivity was detected in TH-IR cell bodies during the embryonic period, the TH-CaBP-IR axonal terminal was observed earlier in some limbic-related areas than in the matrix compartment of the basal ganglia in humans.

Effects of methamphetamine-induced neurotoxicity on the development of neural circuitry: a hypothesis

Exposure of the developing brain to methamphetamine has well-studied biochemical and behavioral consequences. We review: (1) the effects of methamphetamine on mature serotonergic and dopaminergic pathways; (2) the mechanisms of methamphetamine neurotoxicity and (3) the role of serotonergic and dopaminergic signaling in sculpting developing neural circuitry. Consideration of these data suggest the types of neural circuit alterations that may result from exposure of the developing brain to methamphetamine and that may underlie functional defects.

Ontogeny of the dopamine D2 receptor mRNA expressing cells in the human hippocampal formation and temporal neocortex

The study details the cellular expression of the dopamine D2 receptor mRNA in the human temporal lobe during prenatal development. At 13 embryonic weeks (E13) D2 mRNA was widely expressed in the temporal lobe. At this time point in the dentate gyrus D2 mRNA positive cells first appeared at the outer border of the granular layer and their number increased with development. The CA1 exhibited the highest level of D2 mRNA expression. By E19-25 the hippocampal formation underwent rapid morphological maturation. D2 mRNA expression became more uniform and dense in the ammonic subfield. At all ages the subiculum appeared more mature morphologically but less intensely stained for D2 mRNA than the ammonic fields. In the entorhinal cortex D2 mRNA expression was most conspicuous in the future layer II at all ages. In the temporal neocortex D2 mRNA-positive cells were detected in the subplate and cortical plate. Differentiation of the cortical plate was accompanied by concentration of D2 mRNA-positive cells in layer V. The most conspicuous cells expressing D2 mRNA were found in the marginal zone of all regions and resembled Cajal-Retzius cells in morphology and location. Density of putative Cajal-Retzius cells expressing D2 mRNA decreased with development. They all but disappeared from the hippocampal areas by mid gestation, but in the temporal neocortex occasional cells were seen even at term. Early and widespread but region and cell type specific expression of D2 receptor mRNA suggests an important role of this DA receptor subtype in prenatal development of the human temporal lobe.

Safety and tolerability assessment of intrastriatal neural allografts in five patients with Huntington's disease

This study describes issues related to the safety and tolerability of fetal striatal neural allografts as assessed in five patients with Huntington's disease. Huntington's disease (HD) is characterized by motor, cognitive, and behavioral disturbances. The latter include psychological disturbances and, as a consequence, we took particular care to analyze behavioral changes, in addition to the usual "safety" follow-up. We conducted multidisciplinary follow-up at least 2 years before and 1 year after grafting. Psychological care extended to close relatives. The grafting procedure itself was altogether safe and uneventful, and there were no apparent clinical deleterious effects for 1 year. The immunosuppressive treatment, however, was complicated by various problems (irregular compliance, errors of handling, side effects). Direct psychological consequences of the transplantation procedure were rare and not worrisome, although mood alteration requiring treatment was observed in one patient. Indirectly, however, the procedure required patients and relatives to accept constraints that tended to complicate familial situations already marred by aggressivity and depression. All patients and close relatives expressed major expectations, in spite of our strong and repeated cautioning. It is clearly important to be aware of these particular conditions since they may eventually translate into psychological difficulties in coping with the long-term clinical outcome of the procedure, if not beneficial. Despite an overall good tolerance, therefore, this follow-up calls for caution regarding the involvement of HD patients in experimental surgical protocols.

Cocaine upregulates the dopamine transporter in fetal rhesus monkey brain

Cocaine is a highly addictive drug that binds to the dopamine transporter (DAT), inhibits the reuptake of dopamine, and initiates multiple actions within midbrain dopaminergic systems. Using the rhesus monkey, we have investigated the consequences of in utero cocaine exposure on the expression of DAT in the fetal brain. By using the selective DAT ligand [125I]RTI-121 and tyrosine hydroxylase (TH) immunocytochemistry, we found that DAT binding sites are highly developed by day 70 of gestation and show a distribution pattern similar to TH. The rank order of specific 3beta-(4-[125I]iodophenyl)tropane-2beta-carboxylic acid isopropyl ester ([125I]RTI-121) binding densities was substantia nigra-ventral tegmental area > putamen > caudate > lateral hypothalamus > accumbens > linear/interfascicular nuclei >/= globus pallidus > prefrontal cortex. Furthermore, we observed that DAT mRNA was differentially expressed within fetal midbrain dopamine neurons with the highest levels detected in the ventral tier of the substantia nigra pars compacta, and the lowest levels in the ventral tegmental area and the linear/interfascicular nuclei. In utero cocaine exposure between days 22 and 70 significantly increased DAT mRNA expression, and the density of [125I]RTI-121 binding sites within midbrain dopamine neurons in the 70-d-old fetus. This increased DAT expression is accompanied by other presynaptic and postsynaptic neuronal changes, which collectively suggest that midbrain dopamine neurons are hypoactive after prolonged cocaine exposure, a state that may be a contributing factor in the development of attention deficit disorders observed in subjects exposed prenatally to cocaine.

Distribution of the catecholaminergic neurons in the central nervous system of human embryos and fetuses

The catecholaminergic cell groups in the human brain, denominated from A1 to A17, display some striking anatomical differences with those described in the rodent. These differences are essentially observed in the extent of the dopaminergic neurons and especially their axonal fields in the telencephalon. Immunocytochemistry for tyrosine-hydroxylase and dopamine-ss-hydroxylase allowed the visualization of the precocious human catecholaminergic groups as early as 4.5 postovulatory weeks. Maps of tyrosine-hydroxylase positive neurons generated in the different rhombomeres, midbrain, and prosomeres are shown following the prosomeric model introduced by Puelles and Rubenstein [(1993) Trends Neurosci. 16:472-476]. Such a description is convenient to compare catecholaminergic systems in different mammalian species and provide clear anatomical landmarks of the embryonic substantia nigra (midbrain and prosomeres 1 and 2), that are necessary for transplantation of neural tissue in Parkinson's disease. The development and early specification of the dopaminergic neurons expressing calbindin D28K phenotype in the substantia nigra and in the ventral tegmental area are described. The catecholaminergic axons enter the anlage of the cerebral cortex just after the formation of the cortical plate, from 7 postovulatory weeks on. They invade the subplate layer where they wait for 4 weeks before penetrating the cortical plate. At midgestation, the different areas and layers of the frontal cerebral wall are invaded by the catecholaminergic axons, before the layering of the cortex is completed, in a pattern of fiber distribution similar to that described in the adult human brain. The early pattern of development of the catecholamine systems appeared to be phylogenetically well preserved in mammals, but specific features emerging during the differentiation period are unique to humans.

Fetal tissue transplantation [correction of transplanation] in Parkinson's disease

Since the first successful attempts in 1990, human embryonic tissue transplantation has attracted the attention of multiple investigators and clinicians as a serious candidate therapy for Parkinson's disease. Although over two hundred patients have undergone the procedure, multiple issues and questions remain unresolved. We will address this topic emphasizing the recent advances in the technical aspects of the transplantation procedure in light of the limited animal and clinical experience available.

Early neuromeric distribution of tyrosine-hydroxylase-immunoreactive neurons in human embryos

A segmental mapping of brain tyrosine-hydroxylase-immunoreactive (TH-IR) neurons in human embryos between 4.5 and 6 weeks of gestation locates with novel precision the dorsoventral and anteroposterior topography of the catecholamine-synthetizing primordia relative to neuromeric units. The data support the following conclusions. (1) All transverse sectors of the brain (prosomeres in the forebrain, midbrain, rhombomeres in the hindbrain, spinal cord) produce TH-IR neuronal populations. (2) Each segment shows peculiarities in its contribution to the catecholamine system, but there are some overall regularities, which reflect that some TH-IR populations develop similarly in different segments. (3) Dorsoventral topology of the TH-IR neurons indicates that at least four separate longitudinal zones (in the floor and basal plates and twice in the alar plate) found across most segments are capable of producing the TH-IR phenotype. (4) Basal plate TH-IR neurons tend to migrate intrasegmentally to a ventrolateral superficial position, although some remain periventricular; those in the brainstem are related to motoneurons of the oculomotor and branchiomotor nuclei. (5) Some alar TH-IR populations migrate superficially within the segmental boundaries. (6) Most catecholaminergic anatomical entities are formed as fusions of smaller segmental components, each of which show similar histogenetic patterns. A nomenclature is proposed that partly adheres to previous terminology but introduces the distinction of embryologically different cell populations and unifies longitudinally analogous entities. Such a model, as presented in the present study, is convenient for resolving problems of homology of the catecholamine system across the diversity of vertebrate forms.

Neural transplantation in Parkinson's disease

Parkinson's disease is a neurodegenerative disorder that affects about 1% of Canadians between the ages of fifty and seventy. The medical management for these patients consists of drug therapy that is initially effective but has limited long term benefits and does not alter the progressive course of the disease. The recalcitrance of longstanding Parkinson's disease to medical management has prompted the use of alternative surgical therapies. Many neurosurgical procedures have been utilized in order to improve the disabling symptoms these patients harbour. Although most of the current procedures involve making destructive lesions within various basal ganglia nuclei, neural transplantation attempts to reconstitute the normal nigrostriatal pathway and restore striatal dopamine. The initial success of neural transplantation in the rodent and primate parkinsonian models has led to its clinical application in the treatment of parkinsonian patients. Currently, well over one hundred patients throughout the world have been grafted with fetal tissue in an effort to ameliorate their parkinsonian symptoms. Although the results of neural transplantation in clinical trials are promising, a number of issues need to be resolved before this technology can become a standard treatment option. This review focuses on the current status of neural transplantation in Parkinson's disease within the context of other surgical therapies in current use.

Morphometric characteristics of cryopreserved mesencephalic dopamine neurons in culture

Blocks of embryonic rat mesencephalon were freeze-stored for 1-2 years in liquid nitrogen at -196 degrees C with 7.5% dimethyl sulfoxide (DMSO) as cryoprotectant. After thawing, pooled mesencephalic tissues were mechanically dissociated. The cells, plated at two different densities (4.10[5] and 2.10[5]/cm2) were cultured in a serum-supplemented medium for at least 2 weeks before immunocytochemical staining with highly specific antidopamine (DA) antibodies. The cryopreserved DA-immunoreactive (IR) neurons were compared, by means of computerized morphometry, to the fresh ones plated at the same densities. A separate analysis of the dendritic and axonal morphometric parameters revealed that the cryopreserved DA-IR cells, whatever the experimental conditions, had significantly larger dendritic fields and, less significantly, larger axonal fields than their fresh counterparts. A principal component analysis, mainly based on the dendritic morphometric parameters, allowed to individualize only two populations (cryopreserved and fresh) among the four groups studied. These findings underline the role of dendrites as potential sites of release and/or re-uptake of dopamine and their possible implications in functionally effective cryopreserved nigral grafts.

Ontogeny of the striatal neurons expressing the D2 dopamine receptor in humans: an in situ hybridization and receptor-binding study

D2 dopamine receptor (D2R) gene expression was analyzed by in situ hybridization and D2R ligand autoradiography in the human striatum during ontogeny. D2R mRNA and ([3H]YM-09151-2)-binding sites were detected in the striatum from week 12 of fetal life. At this time, D2R mRNA and binding sites were predominant in the putamen and occurred in a pattern of clusters. D2R-binding sites displayed a similar pattern. The signal in the caudate nucleus was weak from weeks 12 to 16. From week 20 of fetal life, D2R mRNA and D2R-binding sites signals became intense in the ventral striatum. At birth, D2R mRNA became homogeneously distributed while D2R-binding sites kept an heterogeneously distribution. Comparative topological and temporal analysis of the D2R, enkephalin and D1 dopamine receptor (D1R) mRNAs showed a distinct developmental pattern for each mRNA. Before birth, the neurons expressing enkephalin and D1R mRNAs were preferentially distributed in the matrix and in the striosomes, respectively, while the neurons expressing D2R mRNA did not display a preferential localization. At birth, high levels of enkephalin mRNA were restricted to the matrix; D1R mRNA level was homogeneous throughout the striatum. D2R mRNA was heterogeneously distributed in the whole striatum with high signals located both in the striosomes and the matrix. These results demonstrate that functional D2R are expressed as early as week 12 in the striatum with a heterogeneous distribution. Our findings also demonstrate that, in contrast to what was expected from similar studies in rodents, D2R mRNA and enkephalin mRNA do not display identical, overlapping expression patterns in striatal neurons during human ontogeny.

Initial development of gamma-aminobutyric acid immunoreactivity in the human cerebral cortex

The development of cortical cells immunoreactive for gamma-aminobutyric acid (GABA) was studied in human cerebral cortex in the first trimester of gestation (from 4 to 13 gestational weeks; g.w.). The first GABA-immunoreactive (IR) cells were observed at 6.5 g.w., i.e., before the appearance of the cortical plate, which gives rise to a majority of the adult cortical layers. GABA-IR cells were found initially in the telencephalic wall, where a lateromedial gradient in the density of GABA-positive cells was observed at this early developmental time point, but not at later stages. At 7 g.w., as the cortical plate emerged in the ventrolateral region of the cerebral vesicle, GABA-immunoreactive cells were found dorsal and ventral to the developing cortical plate. At this stage, immunoreactivity was also observed in the other transient developmental zones of the cortical anlage: in the subplate layer and in the intermediate, subventricular and ventricular zones. From 8 to 9 g.w. and continuing throughout the end of the studied period (13 g.w.), GABA-IR cells were distributed throughout the full width of the telencephalic wall, and, at 13 g.w., the newly formed subpial granular layer contained GABA-immunoreactive cells, as well. However, the predominant sites for GABA immunoreactivity remained the prospective layer I and the subplate. The population of GABA-positive cells described here was not immunoreactive for glial fibrillary acidic protein (GFAP) at any gestational age examined and, therefore, probably represents GABA-containing neurons. The observation that GABA-IR neurons appear in human developing cortex slightly before the cortical plate formation and beginning of synaptogenesis (6.5 g.w.) suggests that GABA plays an important role in the initial organization of the developing human cerebral cortex.

Molecular anatomy of the development of the human substantia nigra

A series of 15 fetal and perinatal human brains (from week 12 of fetal life to day 2 after birth) was studied in order to describe the anatomical and molecular correlates of the substantia nigra ontogeny. In situ hybridization, immunohistochemistry and binding studies were used to detect D2 dopamine receptor (D2R) mRNA, D2R binding sites, dopamine membrane transporter (DAT) mRNA, tyrosine hydroxylase (TH) protein D1 dopamine receptor (D1R) protein and D1R binding sites. Dopaminergic (DA) neurons of the substantia nigra were detected through TH immunoreactivity from week 12. At week 16, the substantia nigra was clearly delineated as a compact group of intermingled neurons and fibers. From week 19, groups of DA neurons were segregated from the pars reticulata. These groups have been divided into the substantia nigra pars compacta, the ventral tegmental area and the retrorubral area. The DA neurons exhibited a gradual increase in size and branching development until birth. From week 12 onward they expressed several other markers of dopamine transmission, i.e., D2R mRNA, D2R binding sites and DAT mRNA. The ventral tegmental area expressed lower levels of mRNA for DAT and D2R than the pars compacta. From week 12, D1R immunoreactivity and D1R binding sites were also present in the substantia nigra pars reticulata. This suggests that projecting striatonigral neurons, known to express the D1R gene, have developed pathways connecting with the substantia nigra by week 12. Our results demonstrate that the developing substantia nigra in human displays early transcriptional and translational activity for the main constituents of dopaminergic transmission from week 12 and receives at this time dopaminoceptive inputs bearing D1 receptors from the striatum.

Comigration of tyrosine hydroxylase- and gonadotropin-releasing hormone-immunoreactive neurons in the nasal area of human embryos

Tyrosine hydroxylase (TH) immunoreactive (IR) central catecholaminergic neurons have been observed in human CNS from 4.5 gestational weeks (g.w.) on [Verney, C., Zecevic, N. and Puelles, L. Eur. J. Neurosci., Suppl. 8 (1995) 7044; Zecevic, N. and Verney, C., J. Comp, Neurol., 351 (1995) 509-535]. We describe here a discrete TH-IR cell population localized in the rostral nasal region during embryonic development. Tyrosine hydroxylase-IR cells spread from the olfactory placode towards the basal and medial telencephalon. They follow the same migration path as the gonadotropin-releasing hormone (GnRH)-IR hypothalamic neurons. Tyrosine hydroxylase-IR neurons are first detected at 4.5 g.w., while GnRH-IR cells are visualized later at 5.5 g.w. Double immunocytochemical labeling reveals the presence of three neuronal populations comigrating along the developing vomeronasal-nervus terminalis complex. These populations express either one or both TH and GnRH phenotypes depending on their position in the migration route. At 6 g.w., most of the neurons express TH immunoreactivity as they leave the vomeronasal organ whereas most of the GnRH-IR neurons are detected closer to the CNS and in the CNS itself. These results emphasize the early phenotypic heterogeneity of the different migrating neuronal populations generated in the olfactory placode in humans. At later stages, very few TH-IR neurons are detected in the anterior forebrain suggesting a transient expression of TH immunoreactivity within these neuronal populations.

Effects of in utero cocaine exposure on the expression of mRNAS encoding the dopamine transporter and the D1, D2 and D5 dopamine receptor subtypes in fetal rhesus monkey

The effects of in utero cocaine exposure on the development of the mRNAs encoding the dopamine transporter (DAT) and the D1, D2 and D5 dopamine receptor subtypes were determined in fetal monkey brains at day 45 and day 60 of gestation. Pregnant monkeys were treated with cocaine 3 mg/kg or saline i.m., four times a day from day 18 of gestation until the pregnancy was terminated at day 45 or day 60. The fetal brains were dissected, and tissue RNA extracted and quantified using ribonuclease protection assay analysis. In day 45 fetal monkeys, dopamine D1 and D2 receptor subtype mRNAs and DAT mRNA were found in low quantities both in control and cocaine-treated subjects. In day 60 fetal monkeys, D1 receptor mRNA levels were highest in the frontal cortex/striatal area, and low to moderate quantities were found in diencephalic and mesencephalic fetal brain regions. Dopamine D2 receptor mRNA levels were highest in the frontal cortex/striatal area, diencephalon and the midbrain, moderate in the brainstem and low in the caudal temporal lobe and surrounding cortical areas. Dopamine D5 receptor mRNA was expressed in low quantities throughout the day 60 fetal monkey brain, whereas DAT mRNA was found in the midbrain only. In utero cocaine exposure caused a significant increase in dopamine D1, D2 and D5 receptor subtype mRNAs in the frontal cortex/striatal area of day 60 fetal monkeys. These results support the hypothesis that dopamine synthesis and release may be reduced in cocaine-treated fetuses, which results in dopamine receptor up-regulation.

Bilateral fetal nigral transplantation into the postcommissural putamen in Parkinson's disease

We performed fetal nigral transplantations in 4 Parkinson's disease (PD) patients. Solid grafts were bilaterally implanted into the postcommissural putamen using 3 to 4 donors per side aged 6 1/2 to 9 weeks postconception. Transplant deposits were separated by no more than 5 mm in three dimensions. Cyclosporine was employed for a total of 6 months. Patients were evaluated at baseline and at 1, 3, and 6 months postoperatively. Striatal 18-fluorodopa uptake was assessed by positron emission tomography at baseline and at 6 months postoperatively. The procedure was well tolerated in all patients. One patient had a clinically asymptomatic superficial cortical hemorrhage along the needle tract and a second had transient postoperative confusion and hallucinations. All patients experienced clinically meaningful benefit. Significant improvement (p < 0.05) was detected in total UPDRS score during the "off" state, Schwab-England disability score during the "off" state, percent "off" time, and percent "on" time with dyskinesia. Increased striatal fluorodopa uptake was observed bilaterally in each patient, with mean increases of 53% on the right (p = 0.01) and 33% on the left (p = 0.08). Our study demonstrated clear and consistent improvement in clinical features and striatal fluorodopa uptake following fetal tissue transplantation in patients with advanced PD whose condition was not improved preoperatively by drug manipulation. These preliminary results are encouraging and support further studies to evaluate grafting strategies as a therapy for PD.

Primary dissociated cultures of human brainstem cells: a useful tool for their characterization and neuroprotection study

Dissociated cell cultures were prepared from brainstems of 5- to 10-week-old human fetuses. Catecholamine- as well as indolamine-containing cells were visualized using respectively dopamine (DA), noradrenaline (NA) and serotonin (5HT) as immunocytochemical markers. NA-, DA-, and 5HT-stained cells were characterized in the rhombencephalic cultures, representing respectively the fetal localization of the locus coeruleus and raphe nuclei. DA-stained cells were characterized in the mesencephalic cultures; these DA-cells originating from the substantia nigra presented morphological aspects different from the DA-rhombencephalic cells. Two types of GABA neurons and glial cells presenting glial fibrillary acidic protein (GFA-P) reactivity were also found in all the cultures. Two non-competitive N-methyl-D-aspartate antagonists, 1-[1-(2-thienyl)cyclohexyl]piperidine (TCP) and cis-Pip/Me 1-[1-(2-thienyl)-2-methylcyclohexyl]piperidine (GK11) in enantiomeric form (-), have been investigated for survival on rhombencephalic cultured cells. The number of 5HT-cells was found to be greater in the treated cultures than in the control ones. This in vitro system appears to be a useful tool for the investigation of the development of central nervous system (CNS) cells as well as the study of neuroprotection.

Neuropathological evidence of graft survival and striatal reinnervation after the transplantation of fetal mesencephalic tissue in a patient with Parkinson's disease

BACKGROUND

Trials are under way to determine whether fetal nigral grafts can improve motor function in patients with Parkinson's disease. Some studies use fluorodopa uptake on positron-emission tomography (PET) as a marker of graft viability, but fluorodopa uptake does not distinguish between host and grafted neurons. There has been no direct evidence that grafts of fetal tissue can survive and innervate the striatum.

METHODS

We studied a 59-year-old man with advanced Parkinson's disease who received bilateral grafts of fetal ventral mesencephalic tissue in the postcommissural putamen. The tissue came from seven embryos between 6 1/2 and 9 weeks after conception. The patient died 18 months later from a massive pulmonary embolism. The brain was studied with the use of tyrosine hydroxylase immunohistochemical methods.

RESULTS

After transplantation, the patient had sustained improvement in motor function and a progressive increase in fluorodopa uptake in the putamen on PET scanning. On examination of the brain, each of the large grafts appeared to be viable. Each was integrated into the host striatum and contained dense clusters of dopaminergic neurons. Processes from these neurons had grown out of the grafts and provided extensive dopaminergic reinnervation to the striatum in a patch-matrix pattern. Ungrafted regions of the putamen showed sparse dopaminergic innervation. We could not identify any sprouting of host dopaminergic processes.

CONCLUSIONS

Grafts of fetal mesencephalic tissue can survive for a long period in the human brain and restore dopaminergic innervation to the striatum in patients with Parkinson's disease. In the patient we studied, clinical improvement and enhanced fluorodopa with uptake on PET scanning were associated the survival of the grafts and dopaminergic reinnervation of the striatum.

Immunocytochemical localization of growth-associated protein GAP-43 in early human development

Fibers labelled with antibody to the growth associated protein (GAP-43) were observed as early as 4 gestational weeks (g.w.) in the nervous system of human embryos. At 6 g.w. these fibers could be traced throughout the brainstem and the diencephalon. None of the immunolabeled fibers entered the telencephalic wall at that point, but 2 weeks later at 8 g.w., GAP-43 positive fibers were observed below the newly formed cortical plate of the cerebral cortex. GAP-43 positive fiber bundles had the same distribution as those previously labeled with tyrosine hydroxylase antibodies at the same age. These results strongly suggest that this growth associated protein is localized in the early growing dopaminergic fibers.

Development of the catecholamine neurons in human embryos and fetuses, with special emphasis on the innervation of the cerebral cortex

The cathecholaminergic (CA) systems have been described as appearing early in the development of the mammalian central nervous system (CNS), but their exact distribution in humans has been studied only following gestational week (g.w.) 13. Furthermore, it is not known when CA fibers initially penetrate the developing cerebral cortex. In this study, the CA cells groups and fibers are described in the human central nervous system from 6 to 13 g.w. as revealed with immunocytochemical techniques, with antibodies raised against three synthetic enzymes of the catecholamine (CA) pathway: tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH), and phenylethanolamine-N-methyltransferase (PNMT). At 6 g.w., TH-like immunoreactive (TH-IR) cell groups were widespread through the caudorostral extension of the CNS corresponding to the different dopaminergic mesencephalic and hypothalamic groups. Noradrenergic groups also were labeled in the medulla oblongata and in the locus coeruleus as well as in other areas in the pons. Additional TH-IR cell groups might represent a transient developmental expression of TH similar to that observed in the rat. DBH immunoreactivity labeled primarily the noradrenergic pontic cell groups and, to a lesser extent, groups located in the medulla oblongata. Rare PNMT-IR neurons were detected in the medulla oblongata only at 13 g.w. The main CA bundles described in the adult were also observed in human embryos and fetuses. At 6 g.w., TH-IR pathways extended caudorostrally within the central tegmental tract and the dorsal tegmental bundle, the latter merging with the dopaminergic mesotelencephalic pathway giving rise to the medial forebrain bundle in the basal forebrain. At 7-8 g.w., TH-IR fibers extended to the basal ganglia and the telencephalic wall. The first TH-IR and, to a much lesser extent, DBH-IR fibers penetrated the frontal lateral cortical anlage through the intermediate zone and sparsely through the marginal zone but not through the thin cortical plate. A second stream entered the telencephalic anlage frontomedially, ventral to the septal area. At 11 g.w., numerous TH-IR fibers invaded the subplate layer, but they penetrated the cortical plate only at 13 g.w. At that time, TH-IR and DBH-IR fibers had reached the occipital cortex in a rostrocaudal gradient. The appearance of well-organized CA system already in embryonic stages in humans could be of great importance for normal shaping of the nervous system as well as for development of cortical circuitry.

Development of catecholamine systems in the brain of the lizard Gallotia galloti

For a better insight into general and derived traits of developmental aspects of catecholaminergic (CA) systems in amniotes, we have studied the development of these systems in the brain of a lizard, Gallotia galloti, with tyrosine hydroxylase (TH)- and dopamine (DA) immunohistochemical techniques. Two main groups of TH-immunoreactive (THi) perikarya appear very early in development: one group in the midbrain which gives rise to the future ventral tegmental area, substantia nigra and retrorubral cell groups, and another group in the tuberomammillary hypothalamus. Somewhat later in development, TH/DA-immunoreactive cells are observed in the thalamus, rostrodorsal hypothalamus and spinal cord, and, with another delay, in the suprachiasmatic nucleus, the periventricular organ, and the pretectal posterodorsal nucleus. CA cell groups that appear rather late in development include the cells in the olfactory bulb, the locus coeruleus and the caudal brainstem. As expected, the development of immunoreactive fibers stays behind that of the cell bodies, but reaches the adult-like pattern just prior to hatching. The present study revealed considerable variation in the relation between the state of cytodifferentiation and first expression of TH/DA immunoreactivity between CA cell groups. Catecholamine cells in the midbrain and tuberomammillary hypothalamus are still migrating, immature (absence of dendrites) and express only TH immunoreactivity at the time of first detection. Cells which appear at later developmental stages lie already further away from the ventricle, possess two or more dendritic processes, and generally express both TH- and DA immunoreactivity.

The response of human and rat fetal ventral mesencephalon in culture to the brain-derived neurotrophic factor treatment

Brain-derived neurotrophic factor (BDNF) has been shown to increase the survival of dopaminergic neurons in rodent mesencephalic cultures. The mRNAs of BDNF and trkB receptor have been found to be expressed in the substantia nigra of rat. In this study, the action of BDNF was studied on the survival and transmitter-specific differentiation of dopaminergic neurons of fetal human CNS aged 9-10-week in vitro. Dopaminergic neuron viability and phenotypic expression were monitored by tyrosine hydroxylase (TH) immunohistochemistry and measurement of dopamine (DA) content with HPLC, respectively. After seven days of treatment with BDNF there were 2.2-fold greater number of TH+ neurons surviving than in untreated cultures. Although very low levels of DA were detectable in human tissue, considerable amounts of DA was found in the culture medium from around 13 days in vitro (DIV), indicating that DA in human fetal tissue tended to be synthesised and released into the incubation medium more readily than from cultured rat fetal tissue during the same period. The content of DA in the BDNF-treated cultures was approximately double that of untreated cultures after 7 days. In rat fetal tissue, the capacity of each TH+ neuron to produce DA was not changed in the BDNF-treated cultures (7 DIV) compared with control cultures, suggesting that BDNF does not up-regulate the production of DA but rather acts to reduce cell death rates. Ciliary neurotrophic factor (CNTF) treatment of rat mesencephalic culture failed to improve the period of survival of fetal dopaminergic neurons and had no effect on the production of DA in cultures.(ABSTRACT TRUNCATED AT 250 WORDS)