Transient expression of tyrosine hydroxylase immunoreactivity in some neurons of the rat neocortex during postnatal development

Thoracolaparoscopic esophagectomy for esophageal cancer with a cervical or abdominal incision to extract specimen

Surgery is the only curative approach for resectable esophageal cancer. This retrospective study was to investigate the immediate effect and operative complications of conventional and modified thoracolaparoscopic esophagectomy with a cervical or abdominal incision to extract specimen for the treatment of patients with esophageal cancer. Eighty-one patients were enrolled, among which 55 patients underwent conventional McKeown thoracolaparoscopic esophagectomy (conventional MTE) and 26 patients underwent modified MTE with a cerivical incision (modified MTE). The clinical, surgical, and postoperative data were analyzed. No significant (P > .05) difference was detected in the clinical data between two groups. The surgical procedure was successful in all patients (100%). The surgical time was significantly (P = .018) shorter in the conventional MTE group than in the modified MTE group (280 min vs 317 min). However, no significant (P > .05) difference was found in blood loss (200 mL vs 180 mL), intensive care unit (ICU) stay (31.3 ± 11.3 vs 25.2 ± 6.4 hours), first flatus after surgery (2.9 ± 1.9 vs 3.3 ± 1.6 days), postoperative hospital stay (12.9 ± 5.6 vs 12.6 ± 3.3 days), total number of lymph nodes dissected (27.9 ± 4.1 vs 26.7 ± 5.7), types of carcinoma, and pathological classification. No significant (P > .05) differences were detected in postoperative complications between the two groups. Assessment of postoperative pain using the visual analogue scale (VAS) score showed a significant (P < .05) difference in the VAS score at day 2 (4.81 ± 1.70 vs 3.87 ± 1.14) and day 3 (5.10 ± 0.83 vs 4.61 ± 1.12) between the conventional and modified MTE groups. The modified McKeown thoracolaparoscopic esophagectomy with only one cervical incision is more minimally invasive, more cosmetic, and less painful than the conventional approach.

Distribution of tyrosine-hydroxylase-immunoreactive neurons in the hypothalamus of tree shrews

The tree shrew (Tupaia belangeri chinensis) is the closest living relative of primates. Yet, little is known about the anatomical distribution of tyrosine hydroxylase (TH)-immunoreactive (ir) structures in the hypothalamus of the tree shrew. Here, we provide the first detailed description of the distribution of TH-ir neurons in the hypothalamus of tree shrews via immunohistochemical techniques. TH-ir neurons were widely distributed throughout the hypothalamus of tree shrew. The majority of hypothalamic TH-ir neurons were found in the paraventricular hypothalamic nucleus (PVN) and supraoptic nucleus (SON), as was also observed in the human hypothalamus. In contrast, rare TH-ir neurons were localized in the PVN and SON of rats. Vasopressin (AVP) colocalized with TH-ir neurons in the PVN and SON in a large number of neurons, but oxytocin and corticotropin-releasing hormone did not colocalize with TH. In addition, colocalization of TH with AVP was also observed in the other hypothalamic regions. Moreover, TH-ir neurons in the PVN and SON of tree shrews expressed other dopaminergic markers (aromatic l-amino acid decarboxylase and vesicular monoamine transporter, Type 2), further supporting that TH-ir neurons in the PVN and SON were catecholaminergic. These findings provide a detailed description of TH-ir neurons in the hypothalamus of tree shrews and demonstrate species differences in the distribution of this enzyme, providing a neurobiological basis for the participation of TH-ir neurons in the regulation of various hypothalamic functions.

Molecular and cellular reorganization of neural circuits in the human lineage

To better understand the molecular and cellular differences in brain organization between human and nonhuman primates, we performed transcriptome sequencing of 16 regions of adult human, chimpanzee, and macaque brains. Integration with human single-cell transcriptomic data revealed global, regional, and cell-type-specific species expression differences in genes representing distinct functional categories. We validated and further characterized the human specificity of genes enriched in distinct cell types through histological and functional analyses, including rare subpallial-derived interneurons expressing dopamine biosynthesis genes enriched in the human striatum and absent in the nonhuman African ape neocortex. Our integrated analysis of the generated data revealed diverse molecular and cellular features of the phylogenetic reorganization of the human brain across multiple levels, with relevance for brain function and disease.

Tyrosine hydroxylase-producing neurons in the human cerebral cortex do not colocalize with calcium-binding proteins or the serotonin 3A receptor

Interneurons of the cerebral cortex play a significant role in cortical information processing and are of clinical interest due to their involvement in neurological disorders. In the human neocortex, three subsets of interneurons can be identified based on the production of the calcium-binding proteins parvalbumin, calretinin or calbindin. A subset of interneurons in the mouse cortex expresses the serotonin 3A receptor (5-HT_3AR). Previous work in humans has also demonstrated the presence of a subgroup of cortical neurons that produces the catecholaminergic enzyme tyrosine hydroxylase (TH). Many TH-producing cells in the rat cortex coexpress calretinin and are adjacent to blood vessels. However, little is known about the phenotype of these TH interneurons in humans. Here we immunohistochemically examined the coexpression of TH with parvalbumin, calretinin, calbindin or 5-HT_3AR in human Brodmann's areas 10 and 24, cortical regions with high densities of TH-containing neurons. Colocalization of TH with these calcium-binding proteins and with 5-HT_3AR was not detected in either area. Cortical TH cells were rarely apposed to blood vessels, denoted by immunolabeling for the gliovascular marker aquaporin-4. Our results suggest that the TH-immunoreactive cells in the human cortex do not overlap with any known neurochemically-defined subsets of interneurons and provide further evidence of differences in the phenotype of these cells across species.

Lrp5/6 are required for cerebellar development and for suppressing TH expression in Purkinje cells via β-catenin

BACKGROUND

The cerebellum is responsible for coordinating motor functions and has a unique laminated architecture. Purkinje cells are inhibitory neurons and represent the only output from the cerebellar cortex. Tyrosine hydroxylase (TH) is the key enzyme for the synthesis of catecholamines, including dopamine and noradrenaline, and it is normally not expressed in cerebellar neurons.

RESULTS

We report here that the low-density lipoprotein receptors (Lrp) 5 and 6, Wnt co-receptors, are required for the development of the cerebellum and for suppressing ectopic TH expression in Purkinje cells. Simultaneous inactivation of Lrp 5 and 6 by Nestin-Cre results in defective lamination and foliation of the cerebellum during postnatal development. Surprisingly, TH is ectopically expressed by Purkinje cells, although they still keep its other neurochemical characteristics. These phenotypes are also observed in the cerebellum of GFAP-Cre;β-catenin(flox/flox) mice, and AAV2-Cre-mediated gene deletion leads to ectopic TH expression in Purkinje cells of β-catenin(flox/flox) mice as well.

CONCLUSIONS

Our results revealed a new role of the canonical Lrp5/6-β-catenin pathway in regulating the morphogenesis of the cerebellum during postnatal development.

Brain neurons partly expressing dopaminergic phenotype: location, development, functional significance, and regulation

In addition to catecholaminergic neurons possessing all the enzymes of catecholamine synthesis and the specific membrane transporters, neurons partly expressing the catecholaminergic phenotype have been found a quarter of a century ago. Most of them express individual enzymes of dopamine (DA) synthesis, tyrosine hydroxylase (TH), or aromatic l-amino acid decarboxylase (AADC), lacking the DA membrane transporter and the vesicular monoamine transporter, type 2. These so-called monoenzymatic neurons are widely distributed throughout the brain in ontogenesis and adulthood being in some brain regions even more numerous than dopaminergic (DA-ergic) neurons. Individual enzymes of DA synthesis are expressed in these neurons continuously or transiently in norm and pathology. It has been proven that monoenzymatic TH neurons and AADC neurons are capable of producing DA in cooperation. It means that l-3,4-dihydroxyphenylalanine (l-DOPA) synthesized from l-tyrosine in monoenzymatic TH neurons is transported to monoenzymatic AADC neurons for DA synthesis. Such cooperative synthesis of DA is considered as a compensatory reaction under a failure of DA-ergic neurons, for example, in neurodegenerative diseases like hyperprolactinemia and Parkinson's disease. Moreover, l-DOPA, produced in monoenzymatic TH neurons, is assumed to play a role of a neurotransmitter or neuromodulator affecting the target neurons via catecholamine receptors. Thus, numerous widespread neurons expressing individual complementary enzymes of DA synthesis serve to produce DA in cooperation that is a compensatory reaction at failure of DA-ergic neurons.

Selective preservation of MeCP2 in catecholaminergic cells is sufficient to improve the behavioral phenotype of male and female Mecp2-deficient mice

Rett syndrome (RTT) is a neurodevelopmental disorder caused primarily by mutations of the X-linked MECP2 gene. Although the loss of MeCP2 function affects many neural systems, impairments of catecholaminergic function have been hypothesized to underlie several of the cardinal behavioral deficits of RTT patients and Mecp2-deficient mice. Although recent Mecp2 reactivation studies indicate that RTT may be a reversible condition, it remains unclear whether specifically preserving Mecp2 function within a specific system will be sufficient to convey beneficial effects. Here, we test whether the selective preservation of Mecp2 within catecholaminergic cells will improve the phenotype of Mecp2-deficient mice. Our results show that this targeted preservation of Mecp2 significantly improves the lifespan, phenotypic severity and cortical epileptiform discharge activity of both male and female Mecp2-deficient mice. Further, we found that the catecholaminergic preservation of Mecp2 also improves the ambulatory rate, rearing activity, motor coordination, anxiety and nest-building performances of Mecp2-deficient mice of each gender. Interestingly, our results also revealed a gender-specific improvement, as specific cortical and hippocampal electroencephalographic abnormalities were significantly improved in male, but not female, rescue mice. Collectively, these results support the role of the catecholaminergic system in the pathogenesis of RTT and provide proof-of-principle that restoring MeCP2 function within this specific system could represent a treatment strategy for RTT.

Alterations of neocortical development and maturation in autism: insight from valproic acid exposure and animal models of autism

Autism spectrum disorder (ASD) is a behaviourally defined brain disorder affecting approximately 1 in 88 children. Many pathological studies have shown that ASD is frequently associated with grey and white matter changes that can be described by their deviations from the normal trajectory of cortical maturation. For example, during the early (i.e. <2 years) postnatal period there is marked and selective tissue overgrowth in the higher-order temporal and frontal networks involved in emotional, social, and communication functions. In this focused review we first summarize some basic principles of neocortical neural organization and how they are disrupted in ASD. We will then highlight some of the potential mechanisms by which the normal developmental trajectory and organization of neocortical networks can be altered based on animal studies of valproic acid, a teratogen widely used in animal models of ASD. We argue that the trajectory of postnatal cerebral neocortex development may be influenced by several cellular and molecular mechanisms that may all converge to produce a neuropathology characterized by premature or accelerated neuronal growth.

Building authentic midbrain dopaminergic neurons from stem cells - lessons from development

The challenge with controlling the differentiation of human pluripotent cells to generate functional dopaminergic neurons for the treatment of Parkinson’s disease has undergone significant progress in recent years. Here, we summarize the differences between newer and older protocols for generating midbrain dopaminergic neurons from human pluripotent stem cells, and we highlight the importance of following developmental pathways during differentiation. The field has now developed to a point where it is timely to take human pluripotent stem cells one step closer to clinical use, and cell criteria to be fulfilled for such developments are outlined in this review.

Increasing proportions of tyrosine hydroxylase-immunoreactive interneurons colocalize with choline acetyltransferase or vasoactive intestinal peptide in the developing rat cerebral cortex

Cortical interneurons are critical for information processing, and their dysfunction has been implicated in neurological disorders. One subset of this diverse cell population expresses tyrosine hydroxylase (TH) during postnatal rat development. Cortical TH-immunoreactive neurons appear at postnatal day (P) 16. The number of TH cells sharply increases between P16 and P20 and subsequently decreases to adult values. The absence of apoptotic markers in these cells suggests that the reduction in cell number is not due to cell death but is due to a decline in TH production. Cortical TH cells lack all additional catecholaminergic enzymes, and many coexpress GABA and calretinin, but little else is known about their phenotype or function. Because interneurons containing choline acetyltransferase (ChAT) or vasoactive intestinal peptide (VIP) share characteristics with cortical TH neurons, the coexpression of TH with ChAT or VIP was examined throughout the neocortex at P16, P20, and P30. The proportions of TH cell profiles double-labeled for ChAT or VIP significantly increased between P16 and P30. Based on their proximity to blood vessels, intrinsic cholinergic and VIPergic cells have been hypothesized to regulate cortical microcirculation. Labeling with the gliovascular marker aquaporin-4 revealed that at least half of the TH cells were apposed to microvessels at these ages, and many of these cells contained ChAT or VIP. Cortical TH neurons did not coproduce nitric oxide synthase. These results suggest that increasing proportions of cortical TH neurons express ChAT or VIP developmentally and that a subset of these TH neurons may regulate local blood flow.

Non-dopaminergic neurons partly expressing dopaminergic phenotype: distribution in the brain, development and functional significance

Besides the dopaminergic (DA-ergic) neurons possessing the whole set of enzymes of DA synthesis from l-tyrosine and the DA membrane transporter (DAT), the neurons partly expressing the DA-ergic phenotype have been first discovered two decades ago. Most of the neurons express individual enzymes of DA synthesis, tyrosine hydroxylase (TH) or aromatic l-amino acid decarboxylase (AADC) and lack the DAT. A list of the neurons partly expressing the DA-ergic phenotype is not restricted to so-called monoenzymatic neurons, e.g. it includes some neurons co-expressing both enzymes of DA synthesis but lacking the DAT. In contrast to true DA-ergic neurons, monoenzymatic neurons and bienzymatic non-dopaminergic neurons lack the vesicular monoamine transporter 2 (VMAT2) that raises a question about the mechanisms of storing and release of their final synthetic products. Monoenzymatic neurons are widely distributed all through the brain in adulthood being in some brain regions even more numerous than DA-ergic neurons. Individual enzymes of DA synthesis are expressed in these neurons continuously or transiently in norm or under certain physiological conditions. Monoenzymatic neurons, particularly those expressing TH, appear to be even more numerous and more widely distributed in the brain during ontogenesis than in adulthood. Most populations of monoenzymatic TH neurons decrease in number or even disappear by puberty. Functional significance of monoenzymatic neurons remained uncertain for a long time after their discovery. Nevertheless, it has been shown that most monoenzymatic TH neurons and AADC neurons are capable to produce l-3,4-dihydroxyphenylalanine (L-DOPA) from l-tyrosine and DA from L-DOPA, respectively. L-DOPA produced in monoenzymatic TH neurons is assumed to play a role of a neurotransmitter or neuromodulator acting on target neurons via catecholamine receptors. Moreover, according to our hypothesis L-DOPA released from monoenzymatic TH neurons is captured by monoenzymatic AADC neurons for DA synthesis. Such cooperative synthesis of DA is considered as a compensatory reaction under a failure of DA-ergic neurons, e.g. in neurodegenerative diseases like hyperprolactinemia and Parkinson's disease.Thus, a substantial number of the brain neurons express partly the DA-ergic phenotype, mostly individual complementary enzymes of DA synthesis, serving to produce DA in cooperation that is supposed to be a compensatory reaction under the failure of DA-ergic neurons.

Neurochemical characterization of tyrosine hydroxylase-immunoreactive interneurons in the developing rat cerebral cortex

Understanding the development of cortical interneuron phenotypic diversity is critical because interneuron dysfunction has been implicated in several neurodevelopmental disorders. Here, tyrosine hydroxylase (TH)-immunoreactive neurons in the developing and adult rat cortex were characterized in light of findings regarding interneuron neurochemistry and development. Cortical TH-immunoreactive neurons were first observed 2 weeks postnatally and peaked in number 3 weeks after birth. At subsequent ages, the number of these cell profiles was gradually reduced, and they were seen less frequently in adults. No DNA fragmentation or active caspase 3 was observed in cortical TH cells at any age examined, eliminating cell death as an explanation for the decrease in cell number. Although cortical TH cells reportedly fail to produce subsequent catecholaminergic enzymes, we found that the majority of these cells at all ages contained phosphorylated TH, suggesting that the enzyme may be active and producing L-DOPA as an end-product. Morphological criteria and colocalization of some TH cells with glutamic acid decarboxylase suggest that these cells are interneurons. Previously, parvalbumin, somatostatin, and calretinin were demonstrated in non-overlapping subsets of interneurons. Cortical TH neurons colocalized with calretinin but not with parvalbumin or somatostatin. These findings suggest that the transitory increase in TH cell number is not due to cell death but possibly due to alterations in the amount of detectable TH present in these cells, and that at least some cortical TH-producing interneurons belong to the calretinin-containing subset of interneurons that originate developmentally in the caudal ganglionic eminence.

P2 receptor expression in the dopaminergic system of the rat brain during development

Extracellular ATP facilitates the release of dopamine via P2 receptor activation in parts of the mesolimbic system. To characterize P2X/Y receptor subtypes in the developing dopaminergic system, their expression in organotypic slice co-cultures including the ventral tegmental area/substantia nigra (VTA/SN) complex and the prefrontal cortex (PFC) was studied in comparison to the receptor expression in 3-5 day-old and adult rats. Reverse transcriptase-polymerase chain reaction (RT-PCR) with specific primers for the P2X(1,2,3,4,6,7) and P2Y(1) receptors in the tissue extracts of organotypic co-cultures revealed the presence of the P2X and P2Y receptor mRNAs investigated. Multiple immunofluorescence labeling of the P2X/Y receptor protein indicated differences in the regional expression in the organotypic co-cultures after 10 days of cultivation (VTA/SN, P2X(1,2,3,4,6,7), P2Y(1,6,12); PFC, P2X(1,3,4,6,7), P2Y(1,2,4,6,12)). At postnatal days 3-5, an immunofluorescence mostly comparable to that of adult rats was observed (VTA/SN and PFC: P2X(1,2,3,4,6,7), P2Y(1,2,4,6,12)). There was one important exception: the P2X(7) receptor immunocytochemistry was not found in adult tissue, suggesting a potential role of this receptor in the development. Only few P2 receptors (e.g. P2X(1), P2Y(1)) were expressed at fibers interconnecting the dopaminergic VTA/SN with the PFC in the organotypic co-cultures. The treatment of the cultures with the ATP analogues 2-methylthio-ATP and alpha,beta-methylene-ATP induced an increase in axonal outgrowth and fiber density, which could be inhibited by pre-treatment with the P2X/Y receptor antagonist pyridoxal-phosphate-6-azophenyl-2',4'-disulphonic acid. The co-localization of the dopamine-(D1) receptor with the P2X(1) receptor in organotypic slice cultures was evident. In the PFC of the co-cultures, and that of young but not adult rats, a number of tyrosine hydroxylase (TH)-positive cells also possessed P2Y(1)-immunoreactivity (IR). Additionally, a strong P2Y(1)-IR was observed on astrocytes. The present results show a time-, region- and cell type-dependent in vitro and in vivo expression pattern of different P2 receptor subtypes in the dopaminergic system indicating the involvement of ATP and its receptors in neuronal development and growth.

Methamphetamine induces ectopic expression of tyrosine hydroxylase and increases noradrenaline levels within the cerebellar cortex

Methamphetamine produces locomotor activation and typical stereotyped motor patterns, which are commonly related with increased catecholamine activity within the basal ganglia, including the dorsal and ventral striatum. Since the cerebellum is critical for movement control, and for learning of motor patterns, we hypothesized that cerebellar catecholamines might be a target of methamphetamine. To test this experimental hypothesis we injected methamphetamine into C57 Black mice at the doses of 5 mg/kg two or three times, 2 h apart. This dosing regimen is known to be toxic for striatal dopamine terminals. However, we found that in the cerebellum, methamphetamine increased the expression of the primary transcript of the tyrosine hydroxylase (TH) gene, followed by an increased expression of the TH protein. Increased TH was localized within Purkinje cells, where methamphetamine increased the number of TH-immunogold particles, and produced a change in the distribution of the enzyme by increasing the cytoplasmic percentage. Increased TH expression was accompanied by a slight increase in noradrenaline content. This effect was highly site-specific for the cortex of posterior vermal lobules, while only slight effects were detectable in the hemispheres. The present data indicate that the cerebellum does represent a target of methamphetamine, which produces specific and fine alterations of the catecholamine system involving synthesis, amount, and compartmentalization of TH as well as increased noradrenaline levels. This may be relevant for motor alterations induced by methamphetamine. In line with this, inherited cerebellar movement disorders in various animal species including humans are associated with increased TH immunoreactivity within intrinsic neurons of the same lobules of the cerebellar cortex.

Tyrosine hydroxylase (TH)- and aromatic-L-amino acid decarboxylase (AADC)-immunoreactive neurons of the common marmoset (Callithrix jacchus) brain: an immunohistochemical analysis

From the perspective of comparative morphology, the distribution of non-monoaminergic neurons in the common marmoset (Callithrix jacchus) was investigated using an immunohistochemical method with specific antibodies to tyrosine hydroxylase (TH) and aromatic-L-amino acid decarboxylase (AADC).TH-immunoreactive (IR) neurons (but not AADC-IR) neurons were observed in the olfactory tubercle, preoptic suprachiasmatic nucleus, periventricular hypothalamic nucleus, arcuate nucleus, paraventricular nucleus, periaqueductal gray matter, medial longitudinal fasciculus, substantia nigra, and nucleus solitaris. In contrast, AADC-IR (but not TH-IR), small, oval and spindle-shaped neurons were sparsely distributed in the following areas: the hypothalamus from the anterior nucleus to the lateral nucleus, the dorsomedial nucleus, the dorsomedial area of the medial mammillary nucleus and the arcuate nucleus; the midbrain, including the stria medullaris and substantia nigra; and the medulla oblongata, including the dorsal area of the nucleus solitaris and the medullary reticular nucleus. The distribution of AADC-IR neurons was not as extensive in the marmoset as it is in rats. However, these neurons were located in the marmoset, but not the rat substantia nigra. Furthermore, AADC-IR neurons that are present in the human striatum were absent in that of the marmoset. The present results indicate that the distribution of non-monoaminergic neurons in the brain of the common marmoset is unique and different from that in humans and rodents.

Dopamine neuron systems in the brain: an update

The basic organization of the catecholamine-containing neuronal systems and their axonal projections in the brain was initially worked out using classical histofluorescence techniques during the 1960s and 1970s. The introduction of more versatile immunohistochemical methods, along with a range of highly sensitive tract-tracing techniques, has provided a progressively more detailed picture, making the dopamine system one of the best known, and most completely mapped, neurotransmitter systems in the brain. The purpose of the present review is to summarize our current knowledge of the diversity and neurochemical features of the nine dopamine-containing neuronal cell groups in the mammalian brain, their distinctive cellular properties, and their ability to regulate their dopaminergic transmitter machinery in response to altered functional demands and aging.

Prenatal cocaine exposure accelerates morphological changes and transient expression of tyrosine hydroxylase in the cochlea of developing rats

Prenatal cocaine exposure causes alterations in auditory brainstem response in children and experimental animals and has adverse effects on auditory information processing and language skills in children. These effects may result from lesions in the cochlea since this organ is particularly sensitive to chemical insults during the development. We have thus studied here the effect of prenatal cocaine exposure on the maturation of the rat cochlea using the transient non-catecholaminergic expression of tyrosine hydroxylase in spiral ganglion neurons as an index of cochlear maturation and morphometry to evaluate the maturation of primary auditory neurons and the organ of Corti. We showed that prenatal cocaine exposure accelerated the cochlear maturation. In the basal coil of cochleas from PND8 cocaine-treated pups, the Kölliker's organ had disappeared, the tunnel of Corti was opened, and the stria vascularis no longer contained undifferentiated marginal cells. The maximum expression of tyrosine hydroxylase in type I primary auditory neurons occurred at PND8 instead of PND12 in pair-fed controls. On the other hand, the prenatal cocaine exposure had no effect on the width and height of the organ of Corti, spiral ganglion volume and number and size of primary auditory neurons. In conclusion, our data suggest that prenatal cocaine exposure, though not lethal to primary auditory neurons, accelerates aspects of the cochlear sensorineural maturation. This accelerated cochlear maturation in cocaine-treated rat pups could cause auditory dysfunctions by desynchronizing the development of the whole auditory pathway.

Age-dependent (+)MDMA-mediated Neurotoxicity in Mice

In the present study the effects of a neurotoxic regimen of (+)-MDMA (20 mg/kgx4, s.c.) in 4- and 10-week-old C57Bl/6J mice during treatment and 7 days post-treatment were examined. Rectal temperatures monitored between (+)-MDMA injections (30 min post-injection/2 h intervals) revealed hyperthermic responses in both age groups, with the magnitude of the response significantly greater in older mice. Seven days post-treatment, immunoblot analyses of the vesicular monoamine transporter 2 (VMAT2), and tyrosine hydroxylase (TH) revealed significant reductions (-37 and -58%, respectively) in the older animals, but not in the younger group, compared to age-matched controls. Dopamine transporter (DAT) expression was significantly reduced in both 4- and 10-week-old animals (26 and 69.7%, respectively). (+)-MDMA-treated animals also exhibited significantly lower levels of striatal dopamine, and 3,4-dihydroxyphenylacetic acid than controls, again the effect being more pronounced in the older animals. Although both age groups showed evidence of (+)-MDMA-induced toxicity, our data revealed that older animals exhibited a greater hyperthermic response to (+)-MDMA and were also are more susceptible to subsequent dopaminergic damage than the younger animals.

Tyrosine hydroxylase and acetylcholinesterase in the domestic pig mesencephalon: An immunocytochemical and histochemical study

The mesencephalon of the young domestic pig was studied by tyrosine hydroxylase (TH) immunocytochemistry and acetylcholinesterase (AChE) histochemistry with focus on the substantia nigra (SN), the ventral tegmental area (VTA), and related areas. The purpose was to obtain information on the organization of the mesencephalic, TH immunoreactive (TH-i), and dopaminergic areas of the pig, in order to provide the necessary background for the possible use of the pig as an alternative large animal experimental model for research on Parkinson's disease, including the use of encapsulated pig dopaminergic neurons for intracerebral xenotransplantation. Significant findings in the pig, compared to observations in other species, included the presence of prominent bundles of TH-i dendrites passing in a dorsoventral direction from pars compacta into pars reticulata at middle and caudal levels of the SN, and the presence of a distinct TH-i substantia nigra pars lateralis (SNL). Caudally in the pig mesencephalon, the retrorubral field (RRF) was found to be very extensive. The view of the RRF, SN, and VTA as parts of the same integrated system was indicated by the crisscrossing of TH-i dendrites at the transitions between these areas. Estimation of the number of TH-i neurons in the SN and the VTA showed that these nuclei were of equal size in the pig. Further, it was found that TH-i nerve cells were present in the midline between the VTA in the interfascicular and rostral linear groups. TH-i nerve cells were also present in the otherwise serotoninergic dorsal raphe nuclei, just as other TH-i cells formed a perirubral cell group. AChE-positive neurons were present in both SN and VTA, and appeared to have the same size and morphology as the TH-i neurons in these areas. Within both nuclei, there were local differences in the AChE staining density, but perhaps more significantly were some marked differences in the structure of the AChE-positive neuropil of the two areas. We anticipate that the present description of the cellular organization of the TH-i dopaminergic areas in the domestic pig ventral mesencephalon will be useful for the development of a nonprimate, large animal, experimental model of Parkinson's disease.

Cortical and striatal expression of tyrosine hydroxylase mRNA in neonatal and adult mice

1. Elucidating the mechanisms underlying regulation of the dopamine (DA) phenotype during development and in adult animals was a major focus of many of the students and postdoctoral fellows in the Laboratory of Dr Donald Reis. In one series of studies, expression of tyrosine hydroxylase (TH), the first enzyme in the DA biosynthetic pathway, was induced in primary cultures prepared from the cortical anlage of embryonic day 13 (E13)-E17 rat embryos. On the basis of these data, the current studies investigated whether under appropriate conditions TH expression might occur in forebrain regions that do not normally contain DA neurons. 2. A transgenic mouse strain harboring a 9-kb TH promoter/EGFP (enhanced green fluorescent protein) reporter construct was analyzed as adults for coexpression of the fluorescent reporter and the endogenous gene, the latter using a sensitive nonradioactive in situ hybridization procedure. The latter procedure was also used to determine the development of neonatal cortical endogenous TH expression. 3. Cortical and striatal cells containing TH mRNA were observed at postnatal day 5 (P5), but not P2, increased in number at P7 and were found in adults. Many cells in the cortex and striatum coexpressed TH mRNA and EGFP, but TH protein was not detected in these brain regions indicating independent transcriptional and translational regulation of TH expression. Overlapping expression of the two transcriptional indicators and TH protein in olfactory bulb occurred only in those DA neurons that receive afferent stimulation from receptor cells. 4. These findings suggest that partial DAergic differentiation may occur in some cortical and striatal cells, but that full expression of the phenotype requires synaptic activation or activity-dependent release of an as-yet unidentified factor(s).

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.

Cannabinoids and gene expression during brain development

Cannabis is the most commonly used illicit drug in western societies, in particular among young people. It is consumed even by women during pregnancy and lactation, which result in a variety of disturbances in the development of their offspring, because, like other habit-forming drugs, cannabinoids, the psychoactive ingredients of marijuana, can cross the placental barrier and be secreted in the maternal milk. Through this way, cannabinoids affect the ontogeny of various neurotransmitter systems leading to changes in different behavioral patterns. Dopamine and endogenous opioids are among the neurotransmitters that result more affected by perinatal cannabinoid exposure, which, when animals mature, produce changes in motor activity, drug-seeking behavior, nociception and other processes. These disturbances are likely originated by the capability of cannabinoids to influence the expression of key genes for both neurotransmitters, in particular, the enzyme tyrosine hydroxylase and the opioid precursor proenkephalin. In addition, cannabinoids seem to be also able to influence the expression of genes encoding for neuron-glia cell adhesion molecules, which supports a potential influence of cannabinoids on the processes of cell proliferation, neuronal migration or axonal elongation in which these proteins are involved. In support of this possibility, CB1 receptors, which represent the major targets for the action of cannabinoids, are abundantly expressed in certain brain regions, such as the subventricular areas, which have been involved in these processes during brain development. Finally, cannabinoids might also be involved in the apoptotic death that occurs during brain development, possibly by influencing the expression of Bcl-2/Bax system. Also in support of this option, CB1 receptors are transiently expressed during brain development in different group of neurons which do not contain these receptors in the adult brain. This paper will review all evidence relating cannabinoids to the expression of key genes for neural development, trying to establish the future research addressed to elucidate the mechanisms involved in the epigenetic action of cannabinoids during brain development.

Catecholamine-independent transient expression of tyrosine hydroxylase in primary auditory neurons is coincident with the onset of hearing in the rat cochlea

During the last stages of neuronal maturation, tyrosine hydroxylase is transiently expressed in the absence of the other catecholamine-synthesizing enzymes. We show here that it is expressed in rat spiral ganglion neurons between postnatal days 8 and 20, with a peak of expression at postnatal day 12. These tyrosine hydroxylase-immunoreactive neurons did not display aromatic amino acid decarboxylase- or dopamine-beta-hydroxylase-immunoreactivities, ruling out the possibilities of dopamine or noradrenaline synthesis. They also did not display peripherin- or intense neurofilament 200-kDa-immunoreactivities, two indicators of type II primary auditory neurons. Tyrosine hydroxylase-immunoreactive dendrites were seen in synaptic contact with the inner hair cells and expressed the GluR2 subunit of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors, further confirming the type I nature of the neurons transiently expressing the enzyme. The end of the tyrosine hydroxylase expression was not due to cell death because the immunoreactive neurons did not show TUNEL-labelled nuclei. Finally, all the type I neurons expressed the tyrosine hydroxylase mRNA at postnatal day 12, suggesting that the expression of the enzyme is a maturational step common to all these neurons and that the expression of the protein is not synchronized. Because the period of transient expression of tyrosine hydroxylase in type I neurons parallels the periods of maturation of evoked exocytosis in inner hair cells and of appearance and maturation of the cochlear potentials, we propose that the expression of the enzyme indicates the onset of hearing in individual type I primary auditory neurons. This enzyme expression could rely on a Ca2+ activation of its encoding gene subsequent to a sudden and massive Ca2+ entry through voltage-activated Ca2+ channels.

Abnormal postnatal ontogeny of the locus coeruleus in the epileptic mutant mouse quaking

The tonic-clonic convulsions of the quaking mutant mice have been shown to be associated with the hyperplasia of the nucleus locus coeruleus, the origin of most brain noradrenergic neurons. In the present study, the postnatal ontogeny of the locus coeruleus has been studied by tyrosine hydroxylase immunolabeling in the mutant mice quaking and their controls at postnatal days 1, 30 and 90. In the control mice, the number of immunoreactive neuronal cell bodies increased significantly in the rostral half of the locus coeruleus between birth and postnatal day 30, while it decreased significantly in the caudal half between birth and adulthood. Thus, during postnatal maturation, the distribution of locus coeruleus neurons was shifted in the rostral direction. In the quaking mutant mice, while the increase of immunolabeling between birth and postnatal day 30 was observed in the rostral half of the locus coeruleus, no diminution could be found in the caudal half between birth and adulthood. As a result, the rostral shift of tyrosine hydroxylase immunoreactivity was not observed. Consequently, in adult mice, the caudal part of the mutants locus coeruleus appeared to contain significantly more neurons than the corresponding region in the controls. These results indicate that the hyperplasia of the locus coeruleus of the quaking mice that we had previously reported results from an alteration of the postnatal maturation of this nucleus. This developmental abnormality might be a primary determinant of the inherited epilepsy of the quaking mutant mice.

Changing distribution of monoaminergic markers in the developing human cerebral cortex with special emphasis on the serotonin transporter

This article reviews the current knowledge of the early onset of the monoaminergic innervation in the developing cerebral cortex in humans and of changes in the distribution of tyrosine hydroxylase (TH) immunoreactivity in different neuronal populations of the developing telencephalon. The early genesis of the central monoaminergic neurons in mammals has led to postulations of a trophic role of monoamines in brain morphogenesis--especially in the cerebral cortex. The developmental effects of amines can be linked to the transient expression of different molecules linked to dopamine or serotonin neurotransmission. We present novel data on the immunocytochemistry of the vesicular monoamine transporter (VMAT2) and of the high-affinity serotonin transporter (SERT) in human fetuses. SERT is a marker of the serotoninergic axons and allows visualization of the serotonin afferents of the raphe in the human telencephalon. In addition, during a restricted time period corresponding to 12-14 postovulatory weeks, we found SERT-immunolabeled fibers in the rostral and caudal limbs of the internal capsule that do not correspond to serotoninergic fibers, but do coincide with the calbindin D28k-labeled thalamocortical fiber tracts. The present observations are correlated with findings in rodents, in which a transient expression of SERT is visible in the thalamocortical axons during early postnatal life. The function of this transporter has been shown to be important for the fine-tuning of cortical sensory maps during the critical period of development of these maps. Although the present observation does not allow ascertainment of which neurons transiently express SERT, it lends support to the notion that serotonin and serotonin uptake could have important developmental roles, during the formation of brain connections in humans, as they have in rodents.

Prenatal cocaine exposure produces consistent developmental alterations in dopamine-rich regions of the cerebral cortex

Administration of cocaine to pregnant rabbits produces robust and long-lasting anatomical alterations in the dopamine-rich anterior cingulate cortex of offspring. These effects include increased length and decreased bundling of layer III and V pyramidal neuron dendrites, increases in parvalbumin expression in the dendrites of interneurons, and increases in detectable GABAergic neurons. We have now examined multiple cortical regions with varying degrees of catecholaminergic innervation to investigate regional variations in the ability of prenatal cocaine exposure to elicit these permanent changes. All regions containing a high density of tyrosine hydroxylase-immunoreactive fibers, indicative of prominent dopaminergic input, exhibited alterations in GABA and parvalbumin expression by interneurons and microtubule-associated protein-2 labeling of apical dendrites of pyramidal neurons. These regions included the medial prefrontal, entorhinal, and piriform cortices. In contrast, primary somatosensory, auditory and motor cortices exhibited little tyrosine hydroxylase staining and no measurable cocaine-induced changes in cortical structure. From these data we suggest that the presence of dopaminergic afferents contributes to the marked specificity of the altered development of excitatory pyramidal neurons and inhibitory interneurons induced by low dose i.v. administration of cocaine in utero.

Autoradiographic studies using L-[(14)C]DOPA and L-DOPA reveal regional Na(+)-dependent uptake of the neurotransmitter candidate L-DOPA in the CNS

We previously proposed that L-3,4-dihydroxyphenylalanine (L-DOPA) is a neurotransmitter in the CNS. Receptor and transporter molecules for L-DOPA, however, have not been determined. In the present study, in order to localize the uptake sites of L-DOPA in the CNS, we performed autoradiographic uptake studies using L-[14C]DOPA and L-[3H]DOPA in the uptake study on rat brain slice preparations, and further analyzed the properties of L-DOPA uptake. Image analysis of the L-[14C]DOPA autoradiogram showed a unique heterogeneous distribution of uptake sites in the brain. The intensity was relatively high in the cerebral cortex, the hypothalamus, the cerebellum and the hippocampus, while the density was moderate or even low in the striatum and the substantia nigra. L-DOPA and phenylalanine, but not dopamine (10mM) were able to almost completely inhibit the uptake of L-[14C]DOPA to basal levels. Microautoradiographic studies using L-[3H]DOPA revealed accumulation of dense grains in the median eminence, the supraoptic nucleus of the hypothalamus, the cerebral cortex (layer I) and the hippocampus. In the cerebellum, grains formed in clusters surrounding the Purkinje cells. This grain accumulation was concluded to be in Bergmann glial cells, since the morphological pattern of grain accumulation was similar to that of the immunoreactivity of the glutamate aspartate transporter, a marker protein for Bergmann glial cells. In the hippocampus, the grain density significantly decreased under Na(+)-free conditions. In addition, grain density also decreased in the absence of Cl(-). In contrast, grains in the choroid plexus and the ependymal cell layer, were not affected by the absence of Na(+). These findings indicated that the uptake of L-DOPA occurs via various types of large neutral amino acid transport mechanisms. It appears that neuronal and/or glial cells, which take up L-DOPA in a Na(+)-dependent manner, exist in the CNS. Our finding further supports the concept that L-DOPA itself may act as a neurotransmitter or neuromodulator.

Neurotransmitters, neuropeptides and calcium binding proteins in developing human cerebellum: a review

Many endogenous neurochemicals that are known to have important functions in the mature central nervous system have also been found in the developing human cerebellum. Cholinergic neurons, as revealed by immunoreactivities towards choline acetyltransferase or acetylcholinesterase, appear early at 23 weeks of gestation in the cerebellar cortex and deep nuclei. Immunoreactivities gradually increase until the first postnatal month. Enkephalin is localized in the developing cerebellum, initially in the fibers of the cortex and deep nuclei at 16-20 weeks and then also in the Purkinje cells, granule cells, basket cells and Golgi cells at 23 weeks onward. Another neuropeptide, substance P, is localized mainly in the fibers of the dentate nucleus from 9 to 24 weeks but substance P immunoreactivity declines thereafter. GABA, an inhibitory neurotransmitter of the central nervous system, starts to appear at 16 weeks in the Purkinje cells, stellate cells, basket cells, mossy fibers and neurons of deep nuclei. GABA expression is gradually upregulated toward term forming networks of GABA-positive fibers and neurons. Catecholaminergic fibers and neurons are also detected in the cortex and deep nuclei at as early as 16 weeks. Calcium binding proteins, calbindin D28K and parvalbumin, make their first appearance in the cortex and deep nuclei at 14 weeks and then their expression decreases toward term, while calretinin appears later at 21 weeks but its expression increases with fetal age. The above findings suggest that many neurotransmitters, neuropeptides and calcium binding proteins (1) appear early during development of the cerebellum; (2) have specific temporal and spatial expression patterns; (3) may have functions other than those found in the mature neural systems; and (4) may be able to interact with each other during early development.

Catecholamine systems in the brain of vertebrates: new perspectives through a comparative approach

A comparative analysis of catecholaminergic systems in the brain and spinal cord of vertebrates forces to reconsider several aspects of the organization of catecholamine systems. Evidence has been provided for the existence of extensive, putatively catecholaminergic cell groups in the spinal cord, the pretectum, the habenular region, and cortical and subcortical telencephalic areas. Moreover, putatively dopamine- and noradrenaline-accumulating cells have been demonstrated in the hypothalamic periventricular organ of almost every non-mammalian vertebrate studied. In contrast with the classical idea that the evolution of catecholamine systems is marked by an increase in complexity going from anamniotes to amniotes, it is now evident that the brains of anamniotes contain catecholaminergic cell groups, of which the counterparts in amniotes have lost the capacity to produce catecholamines. Moreover, a segmental approach in studying the organization of catecholaminergic systems is advocated. Such an approach has recently led to the conclusion that the chemoarchitecture and connections of the basal ganglia of anamniote and amniote tetrapods are largely comparable. This review has also brought together data about the distribution of receptors and catecholaminergic fibers as well as data about developmental aspects. From these data it has become clear that there is a good match between catecholaminergic fibers and receptors, but, at many places, volume transmission seems to play an important role. Finally, although the available data are still limited, striking differences are observed in the spatiotemporal sequence of appearance of catecholaminergic cell groups, in particular those in the retina and olfactory bulb.

Dopamine D(3) receptor is selectively and transiently expressed in the developing whisker barrel cortex of the rat

The rodent primary somatosensory cortex (SI) contains a map of the body surface, the most conspicuous part of which are "barrels," neuronal aggregates in layer IV that receive somatotopic projections from whiskers on the rodent's snout. We report that the D(3) dopamine receptor (D(3)R) is selectively and transiently expressed in SI during the first 2 weeks of postnatal development. D(3)R binding sites and mRNA overlap completely and are limited to layer IV of SI. D(3)R/mRNA are organized in a pattern corresponding to somatotopic representations of the body (e.g., whiskers, jaws, paws, etc.) with the highest expression in the barrel field. D(3) mRNA is first detected at postnatal day (P)4, increases rapidly until P7-10, and sharply decreases after P14. D(3)R binding sites are detectable at P6, peak at P14, and decline afterwards. D(1), D(2), D(4), or D(5) mRNAs display dissimilar expression pattern. D(1) mRNA is mostly confined to infragranular layers throughout the cortex. D(4) mRNA expression in layer IV rises by 4 weeks postnatal, when D(3)R expression is virtually undetectable. Quantitative analysis of D(3) mRNA expression demonstrates that the proportion of D(3) mRNA-positive cells decreases between P7 and P14, whereas mRNA concentration per cell remains stable. Moreover, D(3)R number continues to rise, whereas mRNA levels begin to decline. Thus, a process limiting D(3)R expression to fewer cells may occur that also induces changes in post-transcriptional regulation of D(3)R expression in remaining cells. These findings indicate that dopamine acting via D(3)R may play an important role in the development or function of the SI.

Neurocircuitries of the basal ganglia studied in organotypic cultures: focus on tyrosine hydroxylase, nitric oxide synthase and neuropeptide immunocytochemistry

The nigrostriatal and mesolimbic systems of the rat were reconstructed using an organotypic culture model, whereby neonatal brain tissue was grown in vitro for approximately one month. The nigrostriatal system comprised of tissue from the substantia nigra, the dorsal striatum and the frontoparietal cortex, while the mesolimbic system included the ventral tegmental area, ventral striatum (including the fundus striati, accumbens nucleus, olfactory tubercle, lateral septum, ventral pallidum and piriform cortex) and cingulate cortex. These regions were also cultured alone or in pairs. The cultures were monitored in vitro, and after one month fixed in a formalin-picric acid solution, and processed for immunohistochemistry using antibodies raised against tyrosine hydroxylase, nitric oxide synthase, preprocholecystokinin, glutamate decarboxylase, neuropeptide Y, dopamine- and cyclic AMP-regulated phosphoprotein-32 and glial fibrillary acidic protein. The tissue survived in single, double or triple cultures, although differences were found depending upon the source and combination of cultured region. Neurons had localization and shape as in vivo. Local networks were especially prominent in the mesencephalon, where both tyrosine hydroxylase-positive axons spread from the "substantia nigra" to the rest of the tissue, and where nitric oxide synthase-positive networks also surrounded tyrosine hydroxylase-positive neurons. Glutamate decarboxylase-positive nerve terminals formed dense networks around tyrosine hydroxylase-positive neurons. In the striatum, nitric oxide synthase and dopamine- and cyclic AMP-regulated phosphoprotein-32 neurons were surrounded by tyrosine hydroxylase-positive nerve terminals. The nigral and ventral tegmental area dopamine neurons projected to striatal and cortical structures, but the projection from the ventral tegmental area to the cingulate cortex was more prominent. With regard to co-existence, preprochole-cystokinin-like immunoreactivities was found in many tyrosine hydroxylase-positive neurons and neuropeptide Y- and nitric oxide synthase-like immunoreactivity co-existed in striatal and cortical tissues. In general terms, the chemical neuroanatomy in the cultures was similar to that described earlier in vivo. Nitric oxide synthase staining was particularly intense. Taken together, the organotypic model captures many of the morphological and neurochemical features seen in vivo, providing a valuable model for studying neurocircuitries of the brain in detail, where 'normal' and 'pathological' conditions can be simulated.

Maternal separation followed by early social deprivation affects the development of monoaminergic fiber systems in the medial prefrontal cortex of Octodon degus

The influence of early postnatal socio-emotional deprivation on the development of tyrosine hydroxylase- and 5-hydroxytryptamine-immunoreactive fiber innervation in the medial prefrontal cortex was quantitatively investigated in the precocial rodent Octodon degus. Forty-five-days-old degus from two groups were compared: (i) degus which were repeatedly separated from their mothers during the first three postnatal weeks and after weaning reared in complete isolation; and (ii) degus which were reared under normal undisturbed social conditions. The two monoaminergic fiber systems in the four subregions of the medial prefrontal cortex responded differentially to the deprivation. While the infralimbic cortex was the only subregion that displayed an increase in 5-hydroxytryptamine-positive fiber densities (129.2%) but no changes in tyrosine hydroxylase-immunoreactive fibers, the precentral medial (82.2%), anterior cingulate (74.6%) and prelimbic cortex (86.9%) showed significantly reduced tyrosine hydroxylase-positive fiber innervation, but no changes in 5-hydroxytryptamine-immunoreactive fiber densities. The number of tyrosine hydroxylase-positive somata in the ventral tegmental area and in the substantia nigra remained unchanged. In cortical areas the number of tyrosine hydroxylase-immunoreactive somata was increased (depending on the medial prefrontal cortex subregion between 241.8% and 398.7%) in deprived animals. This altered balance between the serotonergic and dopaminergic cortical innervation in the different subregions of the medial prefrontal cortex may reflect a counter-regulative anatomical and functional adaptation, which may be triggered by an altered activity of these transmitter systems during the phases of maternal separation and social isolation.

The endogenous cannabinoid system and brain development

Cannabinoid receptors and their endogenous ligands constitute a novel modulatory system that is involved in specific brain functions, such as nociception, control of movement, memory and neuroendocrine regulation. Recently, it has also been suggested that this system is involved in brain development. Studies have used a variety of techniques to elucidate the effects of cannabinoids during development, as well as to characterize the presence of elements of the endogenous cannabinoid system (receptors and ligands) in the developing brain. Collectively, they suggest that endocannabinoids participate in brain development through the activation of second-messenger-coupled cannabinoid receptors.

Anatomical and functional reconstruction of the nigrostriatal system in vitro: selective innervation of the striatum by dopaminergic neurons

To study development of the nigrostriatal pathway in an in vitro model system, organotypic slices obtained from rat pups (P4) and containing the striatum and the cortex were grown together with apposed embryonic (E13.5) mesencephalic blocks according to the static slice culture method of Stoppini et al. (1991; J. Neurosci. Methods 37:173-182). Under these conditions, mesencephalic dopaminergic (DA) fibers rapidly grow through the slice, preferentially its striatal portion. This innervation provides a true synaptic innervation to the striatum, as shown by the presence of DA terminals on striatal neurons. DA fibers are able to exert a functional influence, as seen by their ability to modulate c-Fos expression in striatal neurons in the same way as in vivo. Thus, blockade, under basal conditions, of the effect of spontaneously released dopamine by the D2 receptor antagonist haloperidol leads to the activation of c-Fos expression in the striatum. Furthermore, stimulation of DA release by amphetamine induces striatal c-Fos expression in a D1 receptor-dependent manner. Next, the mechanisms of the selective striatal innervation were examined. Indeed, DA fibers innervated specifically the striatum, avoiding the cortical portion of the slice. This selectivity seems to be specific for DA neurons; no selectivity could be observed when noradrenergic neurons were substituted for DA neurons. Short-term cocultures in a collagen gel of mesencephalic blocks with striatal blocks failed to reveal any oriented outgrowth of DA fibers from the mesencephalon, suggesting that the selective innervation observed in the organotypic slices results from some contact-dependent, presumably adhesive interactions rather than from the presence of some diffusible substance orienting the growth of DA fibers towards the striatum. On the other hand, DA neurons seeded onto striatal slices did not attach selectively onto the striatal portion of the slice, indicating that the putative specific adhesive interactions governing the selective striatal innervation are not the same as those determining the adhesion of the DA neurons. These results show that cocultures of cortex-striatum and mesencephalic slices result in a system that displays a number of the morphological and functional traits of the normal nigrostriatal system and that can be relied on as a good in vitro model of in vivo development.

Immunocytochemical characterization of catecholaminergic neurons in the rat striatum following dopamine-depleting lesions

It is possible either permanently or transiently to deplete the rat striatum of dopamine. Following such depletions, striatal neurons immunoreactive for tyrosine hydroxylase (TH), aromatic L-amino acid decarboxylase (AADC) or dopamine appear. The presence of dopamine-producing neurons in the striatum has relevance for the treatment of Parkinson's disease, but whether these catecholaminergic phenotypes all produce dopamine is unclear. In the present study we establish that after unilateral 6-hydroxydopamine lesions or methamphetamine administration, striatal TH-immunoreactive neurons differ in size, morphology and location from those that are immunopositive for AADC or dopamine. The TH-positive cells which were localized either to ventral parts of the striatum or to the central and dorsal areas of the caudate-putamen generally have the morphological features of projection neurons, whereas those containing AADC or dopamine were confined to subcallosal positions in the dorsal medial quadrant of the caudate-putamen and resemble small, local-circuit neurons. The fact that AADC-immunoreactive neurons overlap in size, morphology and location with the cells that produce dopamine suggests strongly that this population is dopaminergic. However, the simultaneous appearance of neurons that contain the TH enzyme but clearly do not make dopamine raises questions about the functional role of these cells and the cellular mechanisms responsible for their induction following striatal dopamine loss.

Role of endocannabinoids in brain development

In addition to those functions that have been extensively addressed in this special issue, such as nociception, motor activity, neuroendocrine regulation, immune function and others, the endogenous cannabinoid system seems to play also a role in neural development. This view is based on a three-fold evidence. A first evidence emerges from neurotoxicological studies that showed that synthetic and plant-derived cannabinoids, when administered to pregnant rats, produced a variety of changes in the maturation of several neurotransmitters and their associated-behaviors in their pups, changes that were evident at different stages of brain development. A second evidence comes from studies that demonstrated the early appearance of elements of the endogenous cannabinoid system (receptors and ligands) during the brain development. The atypical location of these elements during fetal and early postnatal periods favours the notion that this system may play a role in specific molecular events related to neural development. Finally, a third evidence derives from studies using cultures of fetal glial or neuronal cells. Cannabinoid receptors are present in some of these cultured cells and their activation produced a set of cellular effects consistent with a role of this system in the process of neural development. All this likely supports that endocannabinoids, early synthesized in nervous cells, play a role in events related to development, by acting through the activation of second messenger-coupled cannabinoid receptors.

Early appearance of acetylcholinergic, serotoninergic, and peptidergic neurons and fibers in the developing human central nervous system

Animal experiments have already shown that neurotransmitters and neuropeptides are not only important for normal functioning of the adult central nervous system (CNS) but are also crucial to its development. However, information on the spatio-temporal distribution of these endogenous substances in the developing human CNS is still scarce. With the use of immunocytochemical staining and a constant supply of properly fixed human abortuses from southern China, an early appearance of acetylcholinesterase, enkephalin, and substance P immunoreactivities was detected first in the spinal cord (weeks 5 to 7 of gestation), then in the brainstem nuclei (weeks 11 to 12). Their overlapping localizations in many regions of the CNS suggest possible interactions among neurons containing these substances, which are in turn important for the proper establishment of the neuronal circuitry. Immunoreactivity for neuropeptide Y appeared initially in the lateral region of upper segments of the spinal cord at week 12 of gestation, then spread latero-medially and cranio-caudally to the sacral region. In the hippocampus, neuropeptide Y neurons appeared from week 15 onwards. Serotoninergic neurons were found in the dorsal raphe nucleus at week 10 and then decreased in number as the fetus grew older. Somatostatin releasing inhibitory factor, vasopressin, and oxytocin were detected in the hypothalamus from weeks 12 to 14 onwards, and monoamine oxidase, succinic dehydrogenase, parvalbumin, calbindin D28K, and vasoactive intestinal peptide were found in the visual cortex at midgestation. The early appearance and the abundance of the neurotransmitters and neuropeptides in the developing CNS indicate that they may play a key role in neuronal differentiation.

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.

CRE and TRE sequences of the rat tyrosine hydroxylase promoter are required for TH basal expression in adult mice but not in the embryo

Tyrosine hydroxylase (TH), the rate-limiting enzyme in the biosynthesis of catecholamine neurotransmitters, is expressed in a restricted number of areas, and subject to numerous regulations during development and in adulthood. Two transcription factor binding sites present in the proximal region of the TH gene, the TPA-responsive element (TRE) and the c-AMP responsive element (CRE), have been shown to play important roles in TH gene regulation in vitro. In order to elucidate in vivo the role of these two sites, we produced transgenic mice bearing a 5.3-kb fragment from the 5' flanking sequence of the TH gene with mutations in either the CRE-or TRE-sites. Using the intact 5.3-kb fragment fused to two different reporter genes (HSV1-tk and lacZ), we show that this promoter fragment is able to specifically direct expression in catecholaminergic tissues both in adult mice and embryos. Interestingly, the CRE- and TRE-mutated transgenes were not expressed in adult mice, contrary to the situation in embryos where they were specifically expressed in catecholaminergic regions. These results demonstrate that the CRE and TRE play an essential role in basal TH expression in adult tissues in vivo. Moreover, they suggest that distinct transcription factors are involved in TH regulation in developing and adult tissues. In support of this, gel mobility shift experiments revealed a complex present only in embryonic tissues. Taken together, these data highlight the diversity of the mechanisms underlying the establishment and maintenance of the catecholaminergic phenotype.

Laminar distribution of neuropeptide Y-immunoreactive neurons in human prefrontal cortex during development

Neuropeptide Y (NPY) is present in neurons of the adult human cerebral cortex. In view of the reported roles of NPY in the central nervous system in health and during certain disease conditions, we have studied normal development of NPY immunoreactivity (-ir) in the human prefrontal cortex (PFC), Brodmann areas 9 and 46. Twenty-six specimens ranging from the ages of 14 postovulatory weeks to 34 years exhibited patterns that revealed six periods in the development of the laminar distribution and density of NPY-ir neurons. Changes during prenatal and perinatal periods reflect the onset, development, and resolution of the transient fetal telencephalic compartments, including the subplate zone, in which NPY-ir neurons are especially abundant. Before the age of 1 year, the majority of NPY-ir neurons were found in the subplate zone, whereas, after 1 year, the majority were seen in the cortical layers. This is in contrast with the human visual cortex, where the majority of NPY-ir neurons were still located in the white matter. The density of cortical NPY-ir neurons increased in the fifth developmental period (ages 4-7 years), coinciding with the increase of cortical volume and marked progression of cognitive functions. The adult pattern of a relatively low density of cortical NPY-ir neurons was reached in period 6 (from about 8 years), when individual variation also became apparent. Our data point to a protracted maturation of NPY-ir in the human PFC and to different distribution patterns of NPY-ir neurons in different cortical areas.

Coexistence of tyrosine hydroxylase and serotonin in the raphe nucleus of the laboratory shrew (Suncus murinus) during postnatal life

Immunoreactivity (IR) of tyrosine hydoroxylase (TH), which is the rate-limiting enzyme of catecholamine (CA) synthesis, was observed in the serotonergic neurons of the raphe nucleus (RN) of the newborn laboratory shrew from postnatal day (P) 0 to P14. Using an immunohistochemical method involving highly specific antibodies produced in our laboratory, we found that these RN neurons were TH-, GTP cyclohydrolase I-, aromatic L-amino acid decarboxylase-immunoreactive, but DOPA- and dopamine-immunonegative. In addition, they were tryptophan-, 5-hydroxytryptophan- and serotonin-immunoreactive. These results suggest that TH in serotonergic neurons of RN of laboratory shrew has no function as a CA-synthesizing enzyme but may play some role as a regulator or a subsidiary factor in the postnatal development of serotonergic neurons.

Distribution of tyrosine hydroxylase-immunoreactive afferents to the cerebellum differs between species

The indirect antibody peroxidase-antiperoxidase technique was used to determine the laminar and lobular distribution of catecholaminergic afferents in the adult mouse, opossum, and cat cerebellum. A monoclonal antibody to tyrosine hydroxylase (TH) revealed a plexus of thin varicose fibers that exhibited a different density and distribution pattern for each species. In the cat, TH-immunoreactive fibers were sparsely distributed to all laminae, lobules, and nuclei of the cat cerebellum except for an area of elevated density in the ventral folia of lobules V and VI. In the opossum, TH-positive fibers were uniformly and densely distributed in the granule and Purkinje cell layers; they were more abundant in vermal lobules V-VI than in more anterior and posterior lobules, particularly I and X. Numerous TH-immunoreactive fibers were found in all four cerebellar nuclei of the opossum. In the mouse, TH-positive fibers formed a dense plexus within all cerebellar lobules, laminae, and nuclei. The mouse also exhibited numerous TH-immunoreactive Purkinje cells that were localized predominantly within vermal lobules VI-X, the paraflocculus, and flocculus. In addition to the interspecies differences in the distribution of catecholaminergic fibers within the cerebellum, comparison of this plexus to that previously described for serotonin in these species reveals that the relative densities and distribution patterns of catecholaminergic and serotoninergic fibers also vary between species. It is thus hypothesized that in each species a given monoamine has a unique net effect on cerebellar output that is determined by its effects on different neuronal populations within the cerebellum.

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.

Transient expression of neuropeptide Y (NPY) immunoreactivity in the developing hamster paraventricular thalamic area is due to apoptosis

1. A new population of neurons with transient expression of NPY immunoreactivity was described in the developing hamster paraventricular thalamic area. The present study was performed to discover whether this phenomenon is due to programmed cell death or apoptosis. 2. Toward this aim, immunocytochemical and electron microscopic examination of the paraventricular thalamic region, as well as DNA electrophoresis of tissue extracted from the described area, was performed on different stages of embryonic and postnatal development. 3. A sudden increase in neuropeptide Y immunoreactivity (NPY-IR) in the paraventricular thalamic area at embryonic day 14 (E14) was the first symptom of neuronal degeneration. 4. Electron microscopy revealed many neurons with large masses of condensed chromatin within nuclei and extracellular bodies. The affected cells had a convoluted shape and condensed cytoplasm. 5. DNA electrophoresis revealed a ladder of bands between 150 and 1000 bp that is specific for internucleosomal DNA fragmentation. 6. The data strongly suggest that developmental disappearance of NPY-IR neurons within the hamster dorsal thalamic area is due to apoptosis.