Changes in tyrosine hydroxylase gene expression in mesencephalic catecholaminergic neurons of immature and adult male rats perinatally exposed to cannabinoids

We have previously reported that the perinatal exposure of pregnant rats to cannabinoids affected the activity of tyrosine hydroxylase (TH) in the striatum of their male offspring at peripubertal ages. In the present work, we examined whether this effect was accompanied by modifications in TH gene expression. The amount of TH-mRNA--measured by Northern blot analysis with a specific TH probe--in the mesencephalon of 15- and 20-day-old male rats perinatally exposed to hashish extracts was higher than that measured in aged-matched controls. No differences appeared at 30 and 40 days after birth, a priori because they correspond to ages after the hashish withdrawal occurring on day 24 after birth. However, a significant decrease in the amount of TH-mRNA was observed in adult animals (70 days of life) perinatally exposed to hashish. The increase in TH-mRNA concentrations observed in hashish-exposed 15-day-old animals corresponded to an increase in the amount of TH protein, measured by Western blot analysis, in the mesencephalon, with no differences in the striatum. However, the amount of TH protein in both tissues was not modified by perinatal hashish treatment in adult animals, where TH-mRNA amounts had been decreased. In summary, perinatal cannabinoid exposure enhances the expression of the TH gene in mesencephalic catecholaminergic neurons during early peripubertal ages, coinciding with hashish treatment. Normality was found after hashish withdrawal and an interesting decrease in the amount of TH-mRNA appeared in adulthood, although with no reflection on the amount of TH protein.

Target cells modulate dopamine transporter gene expression during brain development

We have analysed the expression of the dopamine transporter (DAT) gene and compared it with that of tyrosine hydroxylase, neuronal GABA transporter and synaptic vesicle monoamine transporter genes during pre- and post-natal development of rat mesencephalic dopaminergic (DA) neurones. Our results show that DAT transcripts are not detectable until embryonic day (E) 15, whilst those of the other genes analysed are already present at E12. In vitro, the level of DAT gene transcription in mesencephalic E13 DA neurones is increased in coculture with target striatal cells. Thus striatal targets cells regulate, at the transcriptional level, a key step of dopaminergic neurotransmission during DA neurone development.

Morphometric evaluation of neonatal brainstem development by means of the ultrasonographic method

Development of the midbrain in 260 newborn infants was studied by means of the ultrasonographic method. The 260 infants were divided into four groups; 211 appropriate-for-date (AFD) infants without intracranial abnormalities or chromosomal disorders, 41 light-for-date (LFD) infants without intracranial abnormalities or chromosomal disorders, 5 cases of Down syndrome and 3 cases of trisomy 18. The midbrain area (MBA) was measured in transverse sections using a Sonos 1000 (YHP) within 24 h of birth. MBA of the 211 AFD infants was correlated with gestational age (GA), the standard curve being -0.0029(GA)2 + 0.2611(GA) -3.335 (r = 0.87, P < 0.0001). MBA of the other three groups were compared with this standard curve. Thirty-seven of the 41 LFD cases and all the Down syndrome infants showed MBA within 1.5 S.D. of the standard curve. However, all the infants with trisomy 18 had smaller MBA than -1.5 S.D. of the standard curve. The standard curve should be useful for assessing the gestational age of newborn infants and for detecting abnormal development of the brainstem in developmental disorders.

Dopamine neoinnervation in the substantia nigra and hyperinnervation in the interpeduncular nucleus of adult rat following neonatal cerebroventricular administration of 6-hydroxydopamine

An aberrant network of dopamine axons was found to pervade the rat substantia nigra following neonatal destruction of its dopamine nerve cell bodies and dendrites by cerebroventricular administration of 6-hydroxydopamine. Light-microscopic immunocytochemistry with a primary monoclonal antibody directed against dopamine-glutaraldehyde-protein was used to investigate the time-course of development and the critical period of induction of this ectopic dopamine innervation (neoinnervation). In rats 6-hydroxydopamine-lesioned at postnatal day 3 (P3) and examined at P7, P10, P15, P30 or later, some dopamine fibers were already present in the substantia nigra at P7; their number increased sharply until P15 and only slightly thereafter, assuming a topographic distribution reminiscent of the missing dopamine nerve cell bodies and dendrites. A similar growth of dopamine fibers took place in the substantia nigra after lesions made at P6, P9 and P12, but was less pronounced after lesion at P15 and absent after lesion at P21 or later. Excessive innervation by dopamine axons (hyperinnervation) was concomitantly observed in the nearby interpeduncular nucleus. The sprouting of dopamine axons in both regions was therefore rapid and coincided in time and space with the developmental redistribution of mesencephalic dopamine neurons in normal rat. It is conceivable that these aberrant dopamine innervations play a role in the peculiar behavior and responsiveness to dopaminergic agents manifested by neonatally 6-hydroxydopamine-lesioned rats. It will be of particular interest to investigate the functional consequences of the dopamine neoinnervation in the substantia nigra, where an eventual axonal release might thus be replacing the normal somatodendritic release of this amine.

Pattern formation in the developing superior colliculus: ontogeny of the periodic architecture in the intermediate layers

The superior colliculus of mammals contains a striking neurochemical architecture in which histochemically identifiable compartments are distributed in an iterative arrangement in the intermediate layers. We used stains for acetylcholinesterase activity as a compartment marker to trace ontogenesis of this architecture during pre- and postnatal development in the domestic cat. We found that compartmentation in the intermediate collicular layers is virtually absent at birth, and only gradually emerges during the first weeks of postnatal life. Over the same postnatal period, acetylcholinesterase activity shifts from a predominantly perikaryal expression pattern immediately postnatally to a nearly exclusive localization in the neuropil at maturity. Remarkably, a striking compartmentation of the superior colliculus was readily apparent with acetylcholinesterase histochemistry prenatally. The first appearance of a periodic architecture in the superior colliculus was observed at embryonic day 34, a time at which the collicular plate had not yet become laminated. The compartments characterized by high levels of acetylcholinesterase activity then gained in prominence until late in the prenatal period, when they receded and disappeared. The loss of the acetylcholinesterase-positive compartments in the perinatal period did not reflect a loss of compartmentation altogether. Neonatally, there was a distinct compartmental architecture visible with enkephalin immunohistochemistry. The virtual absence of acetylcholinesterase-positive compartments in the superior colliculus at birth therefore reflects developmental regulation of enzyme expression in the compartments, not regulation of the compartments as structural entities. We conclude that the periodic architecture, which characterizes the intermediate collicular layers in the adult cat, arises early in ontogenesis. These observations raise the possibility that the histochemical compartments are ontogenetic units that undergo remodeling as the superior colliculus matures.

New subdivision schema for the avian torus semicircularis: neurochemical maps in the chick

Chemoarchitectonic subdivisions in the chicken torus semicircularis were mapped by means of acetylcholinesterase histochemistry and immunocytochemical labeling of leucine-enkephalin, choline acetyltransferase, neuropeptide Y, and calbindin/calretinin in adjacent sections. The torus semicircularis was found to consist of three main divisions: intercollicular area, toral nucleus, and preisthmic superficial area. All three appear variously subdivided. The intercollicular area is a mid-mesencephalic ventral periventricular region and appears subdivided into core and shell intercollicular regions. The toral nucleus is formed by a large caudal periventricular cytoarchitectonic complex, consisting of a periventricular lamina subdivided into core and shell regions, a pericentral, diffuse external nucleus, a central nucleus subdivided into core and shell regions, a caudomedial shell nucleus, a paracentral nucleus, and a posterior hiliar nucleus, apart from other minor parcellations. The preisthmic superficial area extends superficially at the caudomedial end of the toral nucleus, reaching the paramedian dorsal brain surface just rostral to the isthmo-optic nucleus. It is subdivided into core and shell regions. This previously unnoticed area is distinguished here from the intercollicular area and from the caudomedial shell and paracentral nuclei, all of which are frequently mixed in the literature under the concept "intercollicular nucleus." The revised terminology and subdivision for the avian torus clarifies many chemoarchitectonic and hodological mappings reported in the literature. It also suggests new research subjects and eliminates some causes of confusion.

Naltrexone administration effects on regional brain monoamines in developing rats

The effects of the opioid antagonist naltrexone (NALTX) daily administration (1 mg/kg SC) from birth on the levels of dopamine (DA), serotonin (5-HT), and their respective major metabolites, in the striatum, midbrain, and hypothalamus of 7-, 14-, and 22-day-old rats were investigated. Naltrexone treatment increased the striatal HVA/DA ratio on postnatal day 7. At day 14, two subpopulations (A and B) were found among the treated animals. The subpopulation A showed decreased HVA/DA and increased DOPAC/DA ratios, whereas the subpopulation B presented a higher DA concentration. No significant effect appeared on the striatal dopaminergic system in 22-day-old pups. The serotonergic system was affected by exposure to naltrexone only from day 14. The subpopulation A showed a reduction in all the parameters measured in the three regions studied, although in the subpopulation B, lower 5-HIAA/5-HT ratios appeared in the midbrain and hypothalamus. At 22 days of age NALTX treatment elevated striatal 5-HT and 5-HIAA and the ratio of 5-HIAA/5-HT in the midbrain and hypothalamus. These data suggest an endogenous opioid modulation on the central aminergic systems during the neonatal period and point out the consequences of opioid plasticity on related neurotransmitter systems.

Ontogenic development of brain asymmetry in dopaminergic neurons

In the present study the right-left brain asymmetry of central dopamine (DA) systems during postnatal brain development is evaluated. DA and dihydroxyphenylacetic acid (DOPAC) levels increased from neonatal to adult life in both the forebrain and mesencephalon. This increase was not similar in the right and left brain sides. From neonatal life to adulthood a fall was observed in (a) DA percentage in the DA high-brain side in the mesencephalon and (b) DOPAC percentage in the DOPAC high-brain side in both the forebrain and mesencephalon. The percentage of lateralized rats (more than 65% of DA or DOPAC levels in either brain side) also decreased during ontogeny. Thus, biochemical lateralization decreases during ontogeny. The right-left brain correlation for DA level and DA turnover was used to evaluate the inter-hemispheric regulation of dopaminergic systems. The correlation coefficient was near to 0 during postnatal life and around -0.8 during adulthood in both forebrain and mesencephalon. Taken together, these data suggest that the ontogenic decrease of in brain asymmetry for DA or DOPAC levels is related to the postnatal development of an inter-hemispheric regulatory system that control dopaminergic neurons activity.

Re-initiated growth from mature ventral mesencephalon: an in oculo transplant study of nigrostriatal co-grafts

The ability of mature dopaminergic neurons derived from ventral mesencephalon to re-initiate growth after making contact with a non-innervated target was studied using the intra-ocular grafting model. Foetal ventral mesencephalic tissue or brain stem including the locus coeruleus area was grafted to the anterior chamber of the eye. Two weeks, 6 weeks or 1 year after the first implantation, foetal striatal tissue was placed in contact with the nigral graft or grafted alone. The size of the transplants was measured through the cornea. The final size of the striatal grafts was significantly larger when placed alone than when co-grafted with 1-year-old or 6-week-old dopaminergic grafts. Striatum grafted together with 2-week-old nigra was larger than when grafted adjacent to mature substantia nigra, but not significantly so. Nerve fibre outgrowth into the iris from the nigral transplants did not increase after maturation, but the re-innervated area of the host iris progressively increased around the locus coeruleus grafts. Ingrowth of tyrosine hydroxylase (TH) immunoreactive nerve fibres into the striatal grafts was studied 6 weeks after the second implantation. TH immunohistochemistry revealed innervation of the striatal piece in all cases, except for the group where striatum alone was grafted. With the short survival time for co-grafts of 6 weeks, TH-positive nerve fibres innervated a larger volume, had a patchy appearance and the density was higher in striatum grafted to 2 week-old nigral transplants than that seen in striatal transplants grafted to mature nigral grafts. The patchy pattern of TH-immunoreactive nerve terminals was also seen in striatum co-grafted with 6-week-old or 1-year-old nigral transplants. No difference in striatal innervation volume was detected between those latter two groups. When striatum was implanted adjacent to mature ventral mesencephalon and grown together for 6 months--the longer survival time--the same dense TH-positive innervation as seen in striatum co-grafted with immature nigral tissue at the shorter survival time was found. Additionally, the nigral part of the co-grafts showed increased TH-immunoreactive nerve fibre density. In conclusion, dopaminergic neurites from mature ventral mesencephalic transplants can re-initiate growth if placed in contact with non-innervated striatal tissue. The nigral grafts do not progressively re-innervate the host iris, while locus coeruleus grafts do. The intra-ocular grafting model can be used to study the in vivo effects of trophic factors on mature dopaminergic neurons.

Antennular projections to the midbrain of the spiny lobster. III. Central arborizations of motoneurons

The central organization of antennular motoneurons in the brain of the spiny lobster, Panulirus argus, was analyzed by combining biocytin backfills with serial reconstructions of the antennular nerves and the brain. Eighty-nine to 99 antennular motoneurons occur in each hemibrain. The somata of the motoneurons are distributed in a consistent pattern in two complex soma clusters, the ventral paired mediolateral cluster of the deutocerebrum and the dorsal unpaired median cluster of the tritocerebrum. The motoneurons arborize ipsilaterally in the lateral and median antennular neuropils and the tegumentary neuropil. The backfills indicate a minimum of five morphological types of motoneurons with different arborization patterns. The innervation pattern of the motoneurons, together with previously reported innervation patterns of antennular sensory afferents, suggest that the lateral antennular neuropil is a lower motor center driving local antennular reflexes in response to chemical and mechanical stimulation of the antennule, whereas the median antennular neuropil is a lower motor center for equilibrium responses.

Neonatal 6-OHDA lesions upregulate adult expression of tyrosine hydroxylase mRNA

We explored the consequences of postnatal day 1 (P1) intrastriatal 6-hydroxydopamine (6-OHDA) lesions on the developing mesostriatal dopamine system by performing in situ hybridization histochemistry for tyrosine hydroxylase (TH) in the substantia nigra-ventral tegmental area (SN-VTA) complex of neonatally-lesioned and non-lesioned animals at P90. There were significant reductions in the expression of TH mRNA from both the rostral and caudal levels of the lateral and medial SNc of 6-OHDA treated animals. The VTA was preferentially spared from the neurotoxic effects of 6-OHDA and showed elevated levels of TH mRNA in the caudal VTA compared with controls. This heterogeneous pattern of TH mRNA expression suggests that early intrastriatal 6-OHDA lesions selectively damage certain DA systems and affect the development of other systems.

Development of the mesencephalic nucleus of the trigeminal nerve in chick embryos: target innervation, neurotrophin receptors, and cell death

The goal of this study was to determine whether processes of neurons in the mesencephalic nucleus of the trigeminal nerve (Mes V) of chick embryos arrive in their peripheral target prior to the period of developmental cell death, and to determine whether neurons with early target contact survive to a greater extent than neurons with processes that reach their peripheral target later. The arrival of Mes V nerve fibers in the masticatory muscles was determined by injecting the fluorescent tracer DiI, and the position of labeled and unlabeled neurons was mapped in subdivisions of the Mes V nucleus. Developmental changes in the numerical configuration of Mes V subdivisions were studied in DiI-labeled as well as Nissl-stained material. The expression of low-affinity (p75) neurotrophin receptors was investigated throughout development of the Mes V nucleus with in situ hybridization to assess whether and how levels of expression of this trophic receptor may relate to target innervation and cell death. The extent of cell death was evaluated by counting pyknotic nuclei. Processes of Mes V neurons invade their peripheral target between 5 and 7 days of incubation (E5-7). At E7-12, between 800 and 1,400 labeled Mes V neurons were distributed throughout the two main subdivisions of the Mes V nucleus, the tectal commissure and the optic tectum. Only few Mes V neurons were labeled in the posterior commissure or outside the brain. Cell counts in Nissl-stained material from E7-13 revealed that the numbers of Mes V neurons in the optic tectum decreased to about 40-60%, and in the tectal commissure to 20-25%, whereas Mes V neurons in the posterior commissure disappeared almost entirely. Few Mes V neurons remained in the leptomeninges at E8-10, but a considerable number was found outside the midbrain at E11, indicating ongoing migration of some Mes V neurons. Neurotrophin receptors were differentially expressed in the Mes V nucleus: Before and after the period of cell death, 90-100% of Mes V neurons expressed neurotrophin receptors, whereas during, and immediately preceding the period of developmental cell death (E9-E13), merely 70% of Mes V neurons expressed this receptor. These findings are consistent with the hypothesis that early target contact may provide an advantage for the survival of Mes V neurons and that competition for trophic factors may occur in the peripheral target of this nucleus prior to the period of cell death.

Neuromelanin accumulation with age in catecholaminergic neurons from Macaca fascicularis brainstem

Neuromelanin (NM) is an auto-oxidation by-product of catecholamine synthesis which is observed almost exclusively in primates. We have estimated the distribution and the number of NM-positive neurons of the upper brainstem and the degree of their melanization from birth to the onset of senescence in 5 monkeys (Macaca fascicularis) aged 0, 1.5, 3.5, 8 and 13 years. Series of sections taken at 640-microns intervals were examined either unstained to detect unstained NM, stained for NM with Masson silver impregnation or processed by tyrosine hydroxylase (TH) immunohistochemistry to analyze catecholaminergic neurons. The proportion of NM-containing cells among TH-positive neurons varied from one catecholaminergic region to another: low in the hypothalamus and central gray substance (cgs); moderate in the cell group A8, and high in the ventral tegmental area (VTA), locus coeruleus (LC) and substantia nigra (SN). TH-positive neurons were detected in the SN, VTA, catecholaminergic cell group A8, LC, cgs and hypothalamus. At birth, although no unstained NM-positive neurons were detected, Masson-stained cells were observed, though only in the LC. At 1.5 and 3.5 years, Masson-positive neurons were observed despite the absence of visible pigment. At 8 and 13 years, unstained NM was present in Masson-positive neurons. The number of unstained NM-positive neurons and Masson-positive neurons and the amount of NM per neuron increased with age in each subregion studied. Nevertheless, some TH-positive neurons were found to be without NM. The data indicate a differential increased NM content with age in the neurons of midbrain catecholaminergic cell groups. However, its functional significance remains to be determined.

Long distance directed axonal growth from human dopaminergic mesencephalic neuroblasts implanted along the nigrostriatal pathway in 6-hydroxydopamine lesioned adult rats

Dissociated ventral mesencephalon of 6 to 8-week-old human embryos were implanted by stereotaxic injection at different sites along the nigrostriatal pathway in adult rats, previously subjected to a 6-hydroxydopamine lesion of the intrinsic mesotelencephalic dopamine pathways. The recipients were immunosuppressed by daily injections of cyclosporin A to prevent rejection. At 13-20 weeks after transplantation, the implanted human neurons and their associated fiber outgrowths were visualized with a species-specific antibody recognizing human, but not rat, intermediary neurofilaments (HNF). From implants placed in the host rostral mesencephalic region, HNF-positive axonal projections were seen to extend in large numbers rostrally along the medial forebrain bundle and the internal capsule, and ramify within the caudate putamen, the ventral striatum and the amygdaloid nuclei (a distance of about 5-6 mm), and more sparsely in the frontal cortex and the olfactory bulb (a distance of about 10 mm). From implants placed in the internal capsule, abundant HNF-positive axons extended in the rostral, but not caudal, direction along the myelinated fiber bundles into the caudate putamen and the ventral striatum. Tyrosine hydroxylase (TH) immunohistochemistry revealed that the vast majority of the rostrally projecting HNF-positive axons were also TH-positive, and that the graft-derived axons gave rise to dense TH-positive terminal networks, above all in large areas of the previously denervated caudate putamen. From control implants of cortical neuroblasts, axonal projections were seen along the medial forebrain bundle and the internal capsule, but the axons were TH-negative and showed only sparse projections to the striatal areas. Instead, dense projections were seen, e.g., in the frontal cortex. The results demonstrate a remarkable ability of human mesencephalic neuroblasts to extend axons along the trajectories of the nigrostriatal and mesolimbocortical pathways to reach and innervate the principal striatal and limbic target areas in the forebrain. This shows that the basic requirements for the formation of long axonal pathways may be present in the adult mammalian central nervous system (CNS) at least for certain types of projection neurons. Furthermore, it implies that the developing human neuroblasts can escape the inhibitory features known to be present along myelinated growth trajectories in the adult mammalian brain. In addition, the present approach may offer new possibilities for functional neural grafting in the rat Parkinson model, since transplanted nigral neurons placed in their natural position within the rostral mesencephalon could provide an anatomically and functionally more integrated system than the standard model with ectopically placed intrastriatal nigral grafts.

NCAM as a differentiation marker of postmigratory immature neurons in the developing human nervous system

The regional distribution and cellular localization of the neural cell adhesion molecule were investigated in the developing nervous system of human embryos and fetuses, by using immunocytochemistry with antibodies against the human neural cell adhesion molecule. Embryos and fetuses with crown-rump lengths ranging from 15 to 80 mm (corresponding approximately to 6-12 ovulation weeks) were examined. In the telencephalon, immunoreactivity was found in the primordial plexiform layer and in the early cortical plate. During later stages, immunoreactivity was present in the marginal zone, cortical plate, developing subplate zone and radiations of the internal capsule. In the mesencephalon and rhombencephalon, neuronal perikarya were outlined and strong staining was present in fiber bundles. In the spinal cord, strong immunostaining was present in fiber tracts and in dorsal and ventral roots. Immunostaining outlined perikarya of dorsal and ventral gray columns; the neuropil of the developing gray matter was also stained. Contrary to findings in some other species, precursor cells in the proliferating zones, i.e. all cells of ventricular zones and the external granular layer in the proliferation were not stained. Reactivity, however, was also observed in single mature-looking nerve cell bodies and their processes, which were localized in proliferating zones. All peripheral nervous structures including nerve fibers and peripheral nervous tissue components derived from the neural crest (i.e. sensory and autonomic ganglia) expressed the neural cell adhesion molecule. At the cellular level staining always appeared to be associated with the entire cell membrane of a given neuron including its outgrowing processes. Immunocytochemical staining for neural cell adhesion molecule is an excellent method for the identification of single nerve fibers, nerves and nerve cell bodies in situ in the developing peripheral and early central nervous system. The neural cell adhesion molecule is suggested as a marker of postmigratory immature neurons in the developing human nervous system.

Differential expression of tyrosine hydroxylase mRNA in the developing rat mesencephalon

1. With respect to the mesostriatal projection, the mesencephalon is composed of two dopaminergic (DA) cell populations, called dorsal tier and ventral tier. Strong evidence suggests differences in both the spatial and the temporal sequence of the innervation of the striatum between the two groups, with the ventral tier neurons innervating striatal patches prenatally and dorsal tier cells innervating striatal matrix postnatally. 2. Using in situ hybridization, we have examined the expression of the gene coding for tyrosine hydroxylase (TH) in mesencephalic DA neurons with respect to their postnatal development. Two ontogenic patterns of expression were observed: (a) dorsal tier neurons of the medial mesencephalon exhibited a sharp increase in expression beginning after birth, peaking on day 14, then decreasing and, finally, stabilizing; and (b) ventral tier neurons and dorsal tier cells from the lateral and the medial-dorsal mesencephalon showed only a slight increase in TH mRNA, reaching a plateau at P10. 3. The time course of the observed increase in TH gene expression in the first group, generally parallels the innervation of their target cells in the striatal matrix, suggesting that TH gene expression in these cells may be influenced by their postsynaptic cells or by the innervation process.

Differentiation of the brain stem structures in the salamander, Hynobius nebulosus

Differentiation of the internal structure of the brain stem was analyzed in the salamander with special reference to neurons distributed in the marginal layer. It was found that the salamander brain stem was at first composed exclusively of the mantle layer. The marginal layer later differentiated peripherally. In these developmental stages, the mantle and marginal layers were clearly differentiated: the former was made up exclusively of the somata, while the latter was composed mainly of nerve fibers. As the development proceeded, these organization patterns were modified: a few cells migrated into the marginal layer. Cells migrating into the marginal layer formed various nuclei and layers such as the raphe nuclei, reticular formation and superficial cellular layers of the optic tectum. In later development stages, fibers in the marginal layer were myelinated, and neurons in the marginal layer were observed to become embedded among numerous myelinated fibers. Cytologically, the majority of neurons in early developmental stages were unipolar, extending a process peripherally into the marginal layer. In later developmental stages, neurons in a deep zone of the mantle layer remained unipolar, whereas those in the marginal layer and in the superficial zone of the mantle layer differentiated into multipolar cells. Thus, (1) the marginal layer differentiated peripherally as a cell free region; (2) cells in the mantle layer later migrated into the marginal layer, changing into multipolar neurons; (3) cells in the marginal layer formed reticular formation as well as various nuclei and layers in the peripheral white matter; and (4) as development proceeded, fibers in the marginal layer became myelinated.

Temporal and compartmental restriction of neuron-specific enolase expression in the rat mesostriatal system

The striatum and the mesencephalic dopamine neurons which innervate it, are each organized into developmentally and biochemically distinct compartments. Striatal patches, characterized in the neonate by high concentrations of opiate receptors and substance P, are innervated prenatally by fibers originating in one group of midbrain dopamine neurons, the ventral tier. By the third postnatal day, a dense dopamine projection from neurons in the dorsal tier of the mesostriatal group innervates non-patch areas of the striatum, i.e. the matrix, and is followed by the appearance there of neurotensin, somatostatin and calcium binding protein. We have recently observed that the period of establishment of connections between dorsal tier dopamine neurons and their target cells in the striatal matrix is accompanied by a surge in expression of the gene coding for tyrosine hydroxylase (TH). In order to determine the overall metabolic state of mesencephalic and striatal neurons during the period of up-regulation of TH gene expression, we have applied immunocytochemistry for neuron specific enolase (NSE), and cytochrome oxidase histochemistry, known markers for neuronal activity, as well as TH immunohistochemistry to the mesencephalon and striatum of postnatally developing rats. At birth, both NSE and cytochrome oxidase were expressed almost exclusively in the patches, appearing in the matrix only after the 2nd postnatal day. Patches of NSE remained visible thru the 14th day. In the mesencephalon, cytochrome oxidase and immunoreactive NSE cells in adjacent sections, were present only in the pars reticulata (i.e. ventral tier). By day 8, both techniques identified nigral cells in the dorsal as well as ventral tiers.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunohistochemistry and neurochemistry of the habenulo-interpeduncular connection after partial developmental depletion of habenular cholinergic neurons in the rat

The habenulo-interpeduncular system of the rat constitutes an interesting model to address quantitatively problems related to synaptogenesis and to the interactions between neuronal populations after selective alteration of these elements during development. In the present study this has been achieved by experimentally reducing, through gestational treatment with methylazoxymethanol acetate (MAM), the population of cholinergic neurons of the medial habenula which projects to the interpeduncular nucleus. Immunohistochemical analysis gave evidence that the topographical localization of the cholinergic and the substance P-containing populations in the medial habenula was not altered by MAM treatment. Furthermore, the topographical distribution of cholinergic fibers and terminals in the interpeduncular nucleus, which reflects the habenulo-interpeduncular projection as well as cholinergic projections coming from different sources, was substantially preserved. The same was also true concerning the terminal distribution of substance P in the interpeduncular nucleus. Quantitative radioassays demonstrated a sizable decrease of overall ChAT activity in both the habenulae and the interpeduncular nucleus. By comparison of 1 month-old and 3 month-old animals it appeared that this effect was partially reversed with age in the interpeduncular nucleus.

Dopaminergic neuron development in rats: biochemical study from prenatal life to adulthood

Dopaminergic cell development has been studied mainly using morphological techniques and especially histofluorescence. However, the biochemical characteristics of dopamine (DA) neuron development and its physiological role during ontogeny are much less known. In the present article, the biochemical development of DA neurons, from day 13 of prenatal life to adulthood, is evaluated in Sprague-Dawley rats. DA was first detected on day 14 of gestation. The brain increase in this neurotransmitter begins on day 17 in the proencephalon and on day 18 in the mesencephalon, reaching on day 20 a level similar to that found during adulthood in the latter but not in the former. DA levels in the proencephalon rise slowly to adulthood level when compared to DA in the mesencephalon. The modifications observed in tyrosine levels are also largely similar to those reported for DA. Finally, the study of the first 48 h of life shows an increase in tyrosine levels and a decrease in dihydroxyphenylacetic acid levels (with a reduction of DA turnover) during the first 4-5 h of postnatal life. Since the serotonergic modification was completely different from DA modification, we conclude that the biochemical alteration of DA neurons during early postnatal development is specific. The present data suggest that DA neurons play different roles before and after reaching adult development.

Midbrain dopamine neurons regulate preprotachykinin-A mRNA expression in the rat forebrain during development

Intracerebroventricular 6-hydroxydopamine injections were performed at postnatal days 3 and 6 in animals pretreated with the norepinephrine uptakeblocker desimipramine in order to generate a selective lesion of dopamine neurons. In situ hybridization was then used to analyze preprotachykinin-A (PPT-A) mRNA expression in the lesioned as well as in saline-injected control animals. The midbrain dopaminergic lesion caused a 22-25% increase in the level of PPT-A mRNA in cingulate cortex and frontoparietal cortex when analysed at 2 weeks of age, compared to saline-injected control animals. In contrast, the lesion caused no change in PPT-A mRNA expression in the neonatal caudate-putamen. These results indicate that dopamine neurons downregulate the expression of PPT-A mRNA specifically in cingulate cortex and frontoparietal cortex during early postnatal brain development. In the adult rat forebrain, lesioned at P3 and P6, no change in the level of PPT-A mRNA was seen in cingulate cortex and frontoparietal cortex. However, a 29% decrease in PPT-A mRNA was seen in the lateral caudate-putamen with no significant change in neurons of medial caudate-putamen. Thus, dopamine neurons appears to exert a region specific influence on PPT-A mRNA expression during brain development.

Target-specific outgrowth from human mesencephalic tissue grafted to cortex or ventricle of immunosuppressed rats

Human fetal mesencephalic tissue was grafted to rats with unilateral lesions of the nigrostriatal pathway. The animals were immunosuppressed with cyclosporine A. Grafts were placed either into the lateral ventricle ipsilateral to the lesion or in the cingulate cortex above corpus callosum. The grafts and newly formed fibers were visualized by immunohistochemistry with antibodies against tyrosine hydroxylase (TH) and the human Thy-1 glycoprotein. TH-positive fibers covered the total volume of striatum when the graft was placed either in the ventricle or in the cortex. When the transplant was located in the ventricle, TH-positive cells migrated from the graft into host striatum. No cell migration was seen into any other areas than striatum. Cortex and septum were sparsely reinnervated by the graft, but not to a density higher than that normally seen. Globus pallidus was totally devoid of TH-positive fibers. When the graft was placed in cingulate cortex, fiber bundles penetrated through corpus callosum into either striatum, to arborize in its dorsal parts, or followed the medial side of the lateral ventricle to ventral limbic areas, where a fiber network also was formed. Human specific Thy-1-immunohistochemistry revealed positivity only on the lesioned side. These data suggest that dopamine neurons in human mesencephalic tissue, grafted to the rat brain, can migrate specifically into host striatum. Furthermore, TH-positive fiber outgrowth occurred only into dopamine denervated areas of the host, avoiding areas that are normally not innervated by nigral neurons, but also able to reach distant target cells.

The development of cholecystokinin in the interpeduncular nucleus of rats

This study describes the development and late disappearance of cholecystokinin-like immunoreactivity (CCK-LI) in the interpeduncular nucleus (IPN) of rats. Between one and 7 days of age, CCK-positive fiber labeling was sparse and restricted to the lateral subnuclei of the caudal IPN. By 28 days of age the density of CCK-positive fibers increased and labeling was found in the lateral, rostral and apical subnuclei, and medial to the dorsolateral subnuclei. At 35 days of age CCK-LI fiber labeling was absent in the lateral subnuclei and medial to the dorsolateral subnuclei. No additional changes in fiber labeling were observed after 35 days of age. These results suggest that significant anatomical or biochemical reorganization may occur in projections to the IPN between 28 and 35 days of age.

Mesencephalic dopaminergic cells exhibit increased density of neural cell adhesion molecule and polysialic acid during development

In the developing mesencephalon of the rat, the dopaminergic neurons are generated in the ventricular zone of the basal plate between E11 and E15 and then migrate along radial glia to the ventral surface of the developing mesencephalon. To study the factors that control migration and maturation of the dopaminergic neurons, we immunolabeled embryo and pups, ages E12-P21, for neural cell adhesion molecule (NCAM), polysialic acid (PSA) - a polysaccharide found in high amounts on NCAM during development, tyrosine hydroxylase (TH) - a marker of mesencephalic dopaminergic cells, and vimentin - the major cytoskeletal protein in radial glia in the rat. At E13, we noted that cells throughout the mesencephalon contained NCAM-immunoreactive (NCAM-IR) material but that cells along the ventral surface of the mesencephalon contained an increased amount of NCAM-IR material and PSA-immunoreactive (PSA-IR) material. At this age, we first noted a small number of TH-immunoreactive (TH-IR) cells adjacent to the marginal zone of the ventral surface of the mesencephalon. Many of the TH-IR cells contained an increased density of NCAM-IR material. At age E14, the pattern of increased density of NCAM-IR material on cells along the ventral surface of the mesencephalon persisted and a conspicuous amount of PSA-IR material was also noted on cells in this region. TH-IR cells were more numerous, and a striking number of the TH-IR cells also contained an increased amount of NCAM-IR material and PSA-IR material. With increasing age the distribution of NCAM-IR material and PSA-IR material in the mesencephalon became more uniform. Our work suggests that NCAM may be involved in control of migration and synthesis of TH in the dopaminergic cells of the developing mesencephalon.

Influence of altered afferent input on the number of trochlear motor neurons during development

A loss of about half of the trochlear motor neurons occurs during the course of normal development. The present investigation was undertaken to examine the role of afferent input in regulating the number of surviving or dying trochlear motor neurons. A majority of the afferent input to the trochlear nucleus comes from the vestibular nuclei of the hindbrain via the medial longitudinal fasciculus. Portions of the hindbrain were lesioned in duck embryos on embryonic day 3, considerably prior to the time motor neurons send their axons out and cell death begins. The effectiveness of hindbrain lesion was verified by electron microscopical examination of synapses. There was a significant decrease in the number of synapses on trochlear motor neurons following hindbrain lesion. Cell counts made after the period of cell death indicated a significant decrease in the final number of surviving trochlear motor neurons. Cell counts made prior to the onset of cell death indicated that there was a drastic reduction in the initial number of trochlear motor neurons produced in hindbrain lesion embryos. In spite of a significant reduction in the initial number of neurons, the percentage loss of neurons was about the same as during normal development. Since trochlear motor neurons are generated prior to the formation of afferent synapses on them, it is unlikely that the reduction in the number of motor neurons initially produced is due to reduced afferent synaptic input. Since the percentage of cell loss in hindbrain lesion and normal embryos is about the same, it seems that the magnitude of cell death is genetically programmed.(ABSTRACT TRUNCATED AT 250 WORDS)