The structure of cerebral cortex in the rat following prenatal administration of 6-hydroxydopamine

Catecholaminergic Innervation of Periventricular Neurogenic Regions of the Developing Mouse Brain

The major catecholamines—dopamine (DA) and norepinephrine (NE)—are not only involved in synaptic communication but also act as important trophic factors and might ultimately be involved in mammalian brain development. The catecholaminergic innervation of neurogenic regions of the developing brain and its putative relationship to neurogenesis is thus of pivotal interest. We here determined DA and NE innervation around the ventricular/subventricular zone (VZ/SVZ) bordering the whole ventricular system of the developing mouse brain from embryonic day 14.5 (E14.5), E16.5, and E19.5 until postnatal day zero (P0) by histological evaluation and HPLC with electrochemical detection. We correlated these data with the proliferation capacity of the respective regions by quantification of MCM2⁺ cells. During development, VZ/SVZ catecholamine levels dramatically increased between E16.5 and P0 with DA levels increasing in forebrain VZ/SVZ bordering the lateral ventricles and NE levels raising in midbrain/hindbrain VZ/SVZ bordering the third ventricle, the aqueduct, and the fourth ventricle. Conversely, proliferating MCM2⁺ cell counts dropped between E16.5 and E19.5 with a special focus on all VZ/SVZs outside the lateral ventricles. We detected an inverse strong negative correlation of the proliferation capacity in the periventricular neurogenic regions (log-transformed MCM2⁺ cell counts) with their NE levels (r = −0.932; p < 0.001), but not their DA levels (r = 0.440; p = 0.051) suggesting putative inhibitory effects of NE on cell proliferation within the periventricular regions during mouse brain development. Our data provide the first framework for further demandable studies on the functional importance of catecholamines, particularly NE, in regulating neural stem/progenitor cell proliferation and differentiation during mammalian brain development.

Gestational exposure to the organophosphate chlorpyrifos alters social-emotional behaviour and impairs responsiveness to the serotonin transporter inhibitor fluvoxamine in mice

BACKGROUND

The organophosphate chlorpyrifos (CPF) is a pesticide largely used worldwide. Studies from animal models indicate that CPF exposure during development at low doses can target different neurotransmitter systems in the absence of overt cholinergic effects.

METHODS

Late gestational exposure (gestational days 14-17) to CPF at the dose of 6 mg/kg was evaluated in CD-1 mice at adulthood. Neurobehavioural effects likely involving serotonin (5-hydroxytryptamine, 5HT) transmission were assessed both in males and females, through the light-dark exploration test to assess CPF effects on anxiety profiles and the forced swimming test to evaluate the response to the 5HT transporter (5HTT) inhibitor fluvoxamine (30 mg/kg). In females only, we evaluated the effects of gestational exposure to CPF on maternal aggression, under basal condition or after injection of fluvoxamine.

RESULTS

Gestational CPF exposure increased anxiety levels only in female mice, as shown by the augmented thigmotaxis behaviour and the lower latency to enter in the dark compartment. In the forced swimming test, no differences between CPF and control mice were found when assessed under basal condition (saline administration), but both male and female CPF mice missed to show the typical behavioural effects of the 5HTT inhibitor fluvoxamine. During maternal aggression, CPF females showed lower propensity to and intensity of aggressive behaviour, together with mild decreased responsiveness to fluvoxamine administration.

CONCLUSIONS

Overall, the present results confirm a specific and sex-dependent vulnerability of affective/emotional domains to developmental CPF exposure. Furthermore, data provide clear indication on the disrupting effects of prenatal CPF on serotoninergic transmission.

Histological brain alterations following prenatal methamphetamine exposure in rats

When pregnant women abuse methamphetamine, the foremost concern is the potential adverse effect of this substance on fetal development. Clinical studies in humans have found that exposure to methamphetamine during brain development can cause neurobehavioral abnormalities, such as aggressive behavior, learning problems, and poor social adaptation. In the present study, we examined the effects of prenatal methamphetamine exposure on brain development in rats. The first group of pregnant rats was administered methamphetamine at a dose of 5 mg/kg/day during gestational day (GD 10 to GD 20 [MA]. The second group of pregnant rats was injected with saline vehicle only [SAL]. On GD 21 their fetuses were removed and fetal brains were observed. We found various types of morphological damage in MA fetal brains, including microgyria, ectopia, and hemorrhage. In some cases, abnormal distribution of the leptomeninx, such as breach or accumulation, was observed in addition to these histological abnormalities. Therefore, we examined the expression of laminin, which is an important component of the pia mater, in the fetal brains. However, Western blot analysis revealed that there was no difference in expression amount of laminin in whole fetal brain between the MA and SAL groups. We concluded that methamphetamine use during pregnancy can cause histological brain alterations in fetuses. Morphological alterations of brain seen in the present study and previous human studies following prenatal exposure to methamphetamine might be related to the neurobehavioral abnormalities seen in patients who had been exposed to methamphetamine in utero.

Effects of prenatal alcohol exposure on the development of the vibrissal somatosensory cortical barrel network

We have previously shown that the serotonin (5-HT) and its thalamocortical afferents are compromised by prenatal alcohol exposure (PAE). The development of the sensory cortical barrels is regulated by 5-HT-rich thalamocortical afferents. Therefore, it is hypothesized that PAE will deleteriously affect the postnatal development of the cortical barrel formations. On embryonic day (E)7, C57BL/6 mice were grouped into: Alcohol (Alc), Pair-fed (PF), or Chow, and maintained on diet until E18. On postnatal day 7, cortices were stained with 5-HT for thalamocortical fibers, and a NeuN for identification of mature neurons. The area of the posterior medial barrel subfield (PMBSF), was measured as well as the number of NeuN+ neurons within the barrel patches. Though brain weight and brain volume were similar among the three groups, a significant reduction was seen in total area of the PMBSF, and in the average individual barrel area in the Alc group as compared to Chow. Furthermore, the volumes of the B, but not C row barrels were significantly reduced. Barrels were found missing in layer IV, specifically in the posterior aspects of the A, B, and straddler row in the Alc group. Cell counts demonstrated a nearly 50% reduction in NeuN+ neuron number in both rows. This reduction in size of the PMBSF and fewer neurons within these sensory barreloids may underlie a change in the development of the discriminatory sensitivity of the whiskers and serves as an excellent model for the study of a compromised sensory modality following PAE.

A morphogenetic role for acetylcholine in mouse cerebral neocortex

Recently, cholinergic afferents to cerebral cortex have met renewed attention regarding the regulation of plasticity as well as cognitive processing. My laboratory has developed a mouse neonatal basal forebrain lesion paradigm that has contributed considerably to the understanding of cholinergic mechanisms in cortical development. We have shown that transient cholinergic deafferentation, beginning at birth, precipitates alterations in neuronal differentiation and synaptic connectivity that persist into maturity, and contribute to altered cognitive behavior. These data are in general agreement with studies in rats in which the cholinergic basal forebrain is lesioned very early in development but contrast with effects of later developmental lesions. Moreover, in mouse, both morphological and behavioral consequences of the lesion are sex dependent. Studies of receptors and secondary messengers that are instrumental in morphogenesis and plasticity suggest that sex dependent molecular alterations occur within days if not hours following cortical cholinergic deafferentation.

The cholinergic basal forebrain system during development and its influence on cognitive processes: important questions and potential answers

This review seeks to address, though perhaps not answer fully, four important questions about the cholinergic basal forebrain (BF) system in developing mammals. First, what role does the cholinergic basal forebrain system play in the development of cognitive functions? Second, does the cholinergic BF system play a fundamentally similar role in development vs. adulthood? Third, does sexual dimorphism of the developing cholinergic BF system influence cognition differently in the two sexes? Finally, what role does the developing cholinergic BF system play in developmental disorders such as Down syndrome and Rett syndrome? Examples from the literature, primarily studies in mice and rats, are given in an attempt to answer these important questions.

Central chemosensitivity and breathing asleep in unilateral medullary lesion patients: comparisons to animal data

The rostro-ventrolateral medulla (RVLM) is a site of chemosensitivity in animals; such site(s) have not been defined in humans. We studied the effect of unilateral focal lesions in the rostrolateral medulla (RLM) of man, on the ventilatory CO(2) sensitivity and during awake and sleep breathing. Nine patients with RLM lesions (RLM group), and six with lesions elsewhere (non-RLM group) were studied. The ventilatory CO(2) sensitivity was lower in the RLM compared with the non-RLM group (mean (S.D.), RLM, 1.4 (0.9), non-RLM 3.0 (0.6) L min(-1) mmHg(-1)). In both groups resting breathing was normal. During sleep all RLM patients had frequent arousals, four had significant sleep disordered breathing (SDB), only one non-RLM patient had SDB. Our findings in humans resemble those in animals with focal RVLM lesions. This review provides evidence that in humans there is an area of chemosensitivity in the RLM. We propose that in humans, dorsal displacement of the RVLM area of chemosensitivity in animals, arises from development of the olive plus the consequences of the evolution of the cerebellum/inferior peduncle.

Experimentally induced leptomeningeal glioneuronal heterotopia and underlying cortical dysplasia of the lateral limbic area in rats treated transplacentally with methylmercury

Leptomeningeal glioneuronal heterotopia (LGH) is a developmental anomaly sometimes observed at the surface of human brains with severe malformations. We experimentally induced LGH in brains of rat pups by transplacental exposure to methylmercury. Histopathological profiles of the induced LGH, including the spatio-temporal predominance of the manifestation, suggest some aspects of the histogenesis of this malformation. Pregnant rats on embryonic day 8 (E8), E11, E13, E16, E18 or E21 were treated orally with a single administration of 20 mg/kg methylmercury chloride, and the brains of their delivered offspring were examined on postnatal day 7 (P7) and P28. The incidence of LOH varied significantly according to the treatment day: it was almost exclusively restricted to individuals treated on E13. Furthermore, all the induced LGH was confined to the subarachnoid space dorsal to the rhinal fissure, unilaterally or bilaterally. A part of the nest was connected to the underlying cortical surface of the lateral limbic area, where glia limitans and basal lamina were disrupted. Narrow stripes of disarrangement of cortical neurons underlying the bridges were observed. The P7 LGHs consisted mainly of neurons, some of which were GABA-immunolabeled. and a small number of astrocytes as well as endogenous blood vessels and fibroblasts. LGHs in P28 brains consisted mainly of GFAP-positive astrocyte processes. An additional experiment with double administrations of 5-bromo-2-deoxyuridine (BrdU) and methylmercury on E13 disclosed an abnormally widespread distribution of labeled neurons throughout all cortical layers underlying the LGH in P28 brains. Thus, cerebral LGH would be induced if a developing brain were insulted at the early stage of neurogenesis. accompanied by cortical dysplasia.

Neonatal 6-hydroxydopamine treatment affects GABA(A) receptor subunit expression during postnatal development of the rat cerebellum

Neurotoxic elimination of noradrenergic terminals by 6-hydroxydopamine (6-OHDA) leads to alteration of the granule cell layer formation. We have studied the developmental expression of GABA(A) receptor subunits in rat cerebellum after neonatal administration of 6-OHDA during the first postnatal month of life. 6-OHDA was injected subcutaneously. The expression of GABA(A) receptor subunits was studied by in situ hybridization and immunohistochemistry. The alterations were observed in the neocerebellum - the part of the cerebellum which starts development postnatally. The migration of granule cells was delayed, and the total area of the granule cell layer in the neocerebellum from 6-OHDA-treated rats was reduced to 22.6+/-5% of the corresponding area from control rats. In situ hybridization with subunit-specific antisense oligonucleotide probes was performed for alpha1, alpha2, alpha3, alpha5, alpha6, beta1, beta2, gamma1 and gamma2 subunits of the GABA(A) receptor. In neocerebellum, 6-OHDA treatment caused a significant reduction in the alpha1, alpha6 and gamma2 subunit mRNA levels. The expression of the other subunits was not changed. It has been shown that in the postnatal cerebellum alpha1 and alpha6 subunits can be detected in granule cells only when the cells had migrated to their final destination. Our findings indicate that a noradrenergic influence may be necessary for the normal maturation and migration of cerebellar granule cells.

Ectopic noradrenergic hyperinnervation does not functionally compensate for neonatal forebrain acetylcholine lesion

Adult rats who have undergone neonatal 192 IgG-saporin induced lesions of forebrain acetylcholine (ACH) neurons are normal on many behavioral tasks. In this study we determined whether ectopic hippocampal ingrowths, a documented consequence of these neonatal cholinergic lesions, functionally compensate for ACH denervation in these rats. Neonatal rats underwent systemic 6-hydroxydopamine (6-OHDA) injections on postnatal days (PND) 1-3 to prevent the ingrowths, and/or intraventricular 192 IgG-saporin injections on PND 7. The 192 IgG-saporin profoundly reduced basal forebrain p75 neurotrophin receptor (p75(NTR)) immunoreactive (IR) neurons. The 6-OHDA treatment abolished hippocampal and cortical dopamine-beta-hydroxylase (DBH) IR terminals, indicating the absence of normal norepinephrine (NE) innervation. Ectopic DBH IR and p75(NTR) IR varicosities which occurred in the hippocampus of 192 IgG-saporin treated rats were also eliminated by 6-OHDA treatment. Behavioral testing in adulthood indicated no effect of the treatments on the Morris water maze. 192 IgG-saporin treatment caused perseveration during delayed spatial alternation (DSA) and increased working but not reference memory errors on the radial arm maze (RAM). The 6-OHDA plus 192 IgG-saporin treated rats did not differ from the 192 IgG-saporin only rats on any task. These results indicate that ectopic hippocampal NE ingrowths do not functionally compensate for neonatal ACH lesions. Neonatal forebrain ACH lesion impairs working memory on the RAM but the absence of an effect on DSA contraindicates a basic dysfunction of short term memory. Despite severe combined neonatal loss of forebrain ACH and NE innervation, behavior is remarkably intact.

The functions of the preplate in development and evolution of the neocortex and hippocampus

Recently, it has been shown that the early developmental organization of the archicortical hippocampus resembles that of the neocortex. In both cortices at embryonic stages, a preplate is present, which is split by the formation of the cortical plate into a marginal zone and a subplate layer. The pioneer neurons of the preplate are believed to form a phylogenetically ancient cortical structure. Neurons in these preplate layers are the first postmitotic neurons and have important roles in the development of the cerebral cortex. Cajal-Retzius cells in the marginal zone regulate the phenotype of radial glial cells and may direct neuronal migration establishing the inside-out gradient of corticogenesis. Furthermore, pioneer neurons form the initial axonal connections with other (sub)cortical structures. A significant difference between the hippocampus and neocortex, however, is that in the hippocampus, most afferents are guided by the pioneer neurons in the prominent marginal zone, while in the neocortex most ingrowing afferent axons enter via the subplate. At later developmental periods, most pioneer neurons disappear by cell death or transform into other neuronal shapes. Here, we review the early developmental organization of the mammalian cerebral cortex (both neocortex and hippocampus) and discuss the functions and fate of pioneer neurons in cortical development, in particular that of Cajal-Retzius cells. Evaluating the developmental properties of the hippocampus and neocortex, we present the hypothesis that the distribution of the main ingrowing afferent systems in the developing neocortex, which differs from the one in the hippocampal region, may have enabled the specific evolution of the neocortex.

Degeneration of Cajal-Retzius cells in the developing cerebral cortex of the mouse after ablation of meningeal cells by 6-hydroxydopamine

In the central nervous system, the neurotoxic drug 6-hydroxydopamine (6-OHDA) selectively deletes central catecholaminergic neurons and meningeal cells. Meningeal cells are known to contribute to brain development and their specific degeneration leads to disorganized neuronal positioning. We have analyzed whether a particular population of cortical pioneer neurons, the Cajal-Retzius (CR) cells, which lie just below meningeal cells, is also affected by 6-OHDA treatment. We show that application of 6-OHDA to the cortical surface leads to a rapid degeneration of CR cells, without affecting other cortical neurons. The ablation of CR cells was prevented by normetanephrine, which blocks the 6-OHDA uptake into meningeal cells. These results indicate that the disappearance of CR cells after 6-OHDA treatment may be a result of the ablation of the meningeal cells and suggest a trophic dependence of CR cells upon meningeal cells.

Postnatal development of adrenergic terminals in rat locus coeruleus, with special reference to growth of noradrenergic neurons

The postnatal development of noradrenergic (NA) neurons and adrenergic (AD) terminals in the rat locus coeruleus (LC) was studied immunohistochemically. Cell body size was measured after staining of NA neurons with anti-tyrosine hydroxylase (TH) serum, and AD terminals were visualized with anti-phenylethanolamine N-methyltransferase serum. NA neurons in the LC were strongly TH-immunoreactive throughout the postnatal period. At birth, their mean cell body volume was 660 +/- 30 microns 3. It reached a maximum of 2580 +/- 230 microns 3 at postnatal day (PD) 14, and decreased thereafter to 930 +/- 50 microns 3 at PD 60. This transient enlargement of NA neurons may be closely related to the development of the cerebral cortex. AD afferents to the LC had terminals forming predominantly asymmetric junctions at birth (about 96% of all junctions). They occasionally made axo-somatic contact, suggesting that AD input already modulated the activity of LC neurons at this stage. AD terminals making axo-spinous synapses increased in number until PD 31, but still represented a minor proportion of these LC terminals, since there were more than 80% in contact with dendritic shafts at all ages examined.

Developmental regulation of adult cortical morphology and behavior: an animal model for mental retardation

The purpose of this study was to examine the behavioral performance in adult mice which, as neonates, had received lesions to cortically projecting, cholinergic basal forebrain neurons. The nucleus basalis magnocellularis (nBM) provides the primary cholinergic innervation to cerebral cortex. Lesions in the nBM in neonatal mice result in transient cholinergic denervation and persistent abnormalities in cortical morphology and cytoarchitecture. These cortical abnormalities resemble pathologies observed in a number of developmental disabilities in humans, including Down Syndrome. Balb/CByJ mice received lesions to the nBM 12-24 hr after birth; littermates served as controls. Behavioral testing began 8 weeks after the lesion and included assessments of spontaneous motor activity, retention (a passive avoidance task) and cognition (the Morris swim task). Following behavioral testing, a subset of mice was killed for Nissl and acetylcholinesterase (AChE) histology. The cortical morphology in these brains was evaluated and ranked by the experimenter, who was blind to the lesion and behavioral studies. The lesioned mice exhibited increased spontaneous activity as compared to littermate controls. The lesioned mice were also severely impaired in performance of the retention and cognitive task; they showed decreased passive avoidance retention latencies and increased swim maze latencies as compared to controls. The brains of all of the lesioned mice exhibited cortical morphological abnormalities that ranged from slight to severe. Cortical AChE intensity and distribution in the brains of the lesioned mice, however, were comparable to those of controls. In correlation studies of behavioral and morphological data, motor activity did not correlate with either passive avoidance retention or swim maze latencies. Additionally, cortical cytoarchitectural abnormalities did not correlate with motor activity. Cortical cytoarchitectural abnormalities did, however, correlate with both passive avoidance and swim maze latencies, i.e. severely abnormal cortical morphology predicted low passive avoidance retention latencies and high swim maze latencies. These data indicate that cortical cytoarchitectural abnormalities resulting from nBM lesions in neonates correlate with impairments on the cognitive task, but not with the activity measures, in adult mice. Thus, in this lesion model, and by extrapolation in developmental disabilities in humans, structural changes in the cortex which result from transient disruption of cortical cholinergic innervation may lead to persistent cognitive impairments in adulthood.

Monoaminergic afferents to cortex modulate structural plasticity in the barrelfield of the mouse

Electrolytic lesions of the follicles of a set of mystacial vibrissae, and their innervation, of the mouse placed during the early postnatal period result in a modification in appearance of the corresponding and of adjacent barrels in the somatosensory cortex of the adult animal. These changes can be evoked during the first 6 days of postnatal life--the so-called critical period. The pattern of these modifications varies with the age of the animal at which the lesion was placed. In order to evaluate the contribution of the monoaminergic cortical input to this type of plasticity, the noradrenergic and/or serotonergic afferents to the cerebral cortex of newborn mice were destroyed by systemic administration of various selective neurotoxic drugs (6-hydroxydopamine, 5,7-dihydroxytryptamine, N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine). The animals were then subjected, on postnatal day 3 (P3; P0 = day of birth), to a lesion of the follicles of the large, caudal mystacial vibrissae of row C. Control animals were injected with vehicle solution only but had the same follicles lesioned. Compared with animals with intact monoaminergic afferents, those treated with neurotoxins showed a different changed barrel pattern, i.e. one that corresponded to a pattern normally obtained after a lesion placed at an earlier stage of development, i.e. at P2 or P1. Thus, monoaminergic depletion of the cortex results in a retardation of the maturation of the parietal cortex as defined by its plastic response to peripheral nerve injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunocytochemical evidence of well-developed dopaminergic and noradrenergic innervations in the frontal cerebral cortex of human fetuses at midgestation

The catecholaminergic (CA) innervation of the frontal lobe was visualized in 20- to 24-week-old human fetuses with immunocytochemical techniques, by use of antibodies raised against three synthetic enzymes of the CA pathway, tyrosine-hydroxylase (TH), dopamine-beta-hydroxylase (DBH), and phenylethanolamine-N-methyltransferase (PNMT). DBH-like immunoreactivity (IR) was probably labeling the noradrenergic (NA) fibers and terminals in the cerebral cortex since no PNMT-IR fibers were detected. In double-labeling TH-DBH experiments, 92-95% of the DBH-IR afferents were not labeled with TH antibodies, indicating that TH-like immunoreactivity (TH-IR) was found primarily in dopaminergic (DA) fibers. Although cortical layering had not yet occurred at this stage, the widespread CA innervation observed in the different areas and layers of the fetal frontal cortex was comparable to that previously described in the adult (Gaspar, Berger, Febvret, Vigny, and Henry: J. Comp. Neurol. 279:249-271, '89). At midgestation, the distribution of CA innervation was region and laminar specific: 1) The densest dopaminergic innervation in the cerebral cortex was located caudal to the genu of the corpus callosum: TH-IR fibers were abundant throughout all layers, from the medial telencephalon (future cingulate) to the dorsal areas (presumed motor cortices) and the lateral insular areas; 2) TH-IR fibers were less dense in the rostral prefrontal cortical anlage; 3) DBH-IR noradrenergic afferents were less numerous than the dopaminergic ones in all the cortical areas studied; 4) in all areas, the highest amount of TH and DBH-IR terminals was found in the upper subplate and in the lower part of the cortical plate, followed by the molecular layer and the intermediate zone. The deep subplate exhibited a lower number of positive fibers but contained TH-IR cell bodies. The presence of dense CA innervation in the immature cortical anlage of the human frontal lobe does not exclude a reorganization of DA and NA innervations within the different cortical layers and areas during the protracted pre- and postnatal period of development.

Neonatal brain dopamine depletion and the cortical and behavioral consequences of enriched postweaning environment

This study investigated the effects of neonatal intraventricular administration of 6-hydroxydopamine (6-OHDA, 15 micrograms total with and without desmethylimipramine pretreatment) on the cortical thickening and behavioral effects of 35 days of enriched postweaning housing (ENR) in the rat. The 6-OHDA treatment depleted cortical dopamine (DA) to about 40% of control. It did not affect the thickness of the cerebral cortex nor did it affect the capacity for the cortex to be thickened by ENR. In addition, it did not alter the superior performance on two spatial water maze tasks that was caused by ENR. Thus, the potential for neurobehavioral plasticity was not changed by neonatal DA depletion. ENR eliminated the spatial learning/memory deficits that were caused by neonatal DA depletion and that were manifested when the rat was raised in standard (impoverished) laboratory conditions. Hence, environmental factors can modulate the cognitive effects of neonatal DA depletion. ENR did not attenuate the hyperactivity of the neonatal DA-depleted rat. This may reflect the subcortical mediation of this behavioral abnormality.

Host dopaminergic afferents affect the development of DARPP-32 immunoreactivity in transplanted embryonic striatal neurons

Homotopic transplantation provides an interesting way to observe the relationships between developing cells and ingrowing host afferents. We have performed a complete and selective elimination of the mesostriatal dopaminergic system in adult rats to observe the influence of its absence on the development and chemical differentiation of embryonic striatal cells. Cell suspensions from striatal primordia of 14-15-day-old embryos were transplanted into host striata that were (i) neuron-depleted by kainic acid (control group) or (ii) deprived of dopamine by 6-hydroxydopamine prior to the neuronal depletion by kainic acid (experimental group). The expression of dopamine- and adenosine 3',5'-monophosphate-regulated phosphoprotein (DARPP-32) by transplanted cells was observed in correlation with their innervation by host dopaminergic afferents which in turn were identified by tyrosine hydroxylase immunohistochemistry. Observations were made between four days and three months after transplantation. Four days after transplantation, no immunoreactivity for DARPP-32 was observed in transplants of control animals despite the presence of tyrosine hydroxylase-immunopositive fibers growing from the host to discrete cell clusters in the transplant. DARPP-32-labeled cells appeared soon afterwards. Six days after transplantation they displayed varying intensities of immunoreaction, ranging from just detectable to normal levels and were specifically targeted by developing tyrosine hydroxylase-immunopositive fibers. The number of DARPP-32-labeled cells increased rapidly and they formed increasingly compact clusters. Fourteen days after transplantation and afterwards, all the DARPP-32-labeled cells displayed an intensity of immunoreaction and a distribution comparable to that observed in long-term transplants. Transplants in the experimental hosts displayed the same organization and developmental features as the control transplants with the exception of DARPP-32 labeling which was not detected before eight days after transplantation. Ten days after transplantation, the distribution and intensity of DARPP-32 labeling was similar to that observed at six days in the control group. The evolution of DARPP-32 labeling after 10 days in the experimental group paralleled that observed six days post-transplantation and beyond in the control group. Dopaminergic mesostriatal host afferents are able to provide developing cells in grafted striatal tissues with normal innervation very rapidly. Despite this rapidity, the innervation does not seem to have any trophic influence on the general development of the transplant but does affect the onset time of the expression of neurochemical markers that are directly related to its synaptic function.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of noradrenergic denervation by neonatal DSP-4 on peptide neurotransmitter systems in the rat brain

The specific effects of a neonatal treatment of rats with the noradrenergic neurotoxin DSP-4 were investigated in the adult rat by measuring monoamine and peptide transmitter levels in eight brain regions. When applied concomitantly with a 5-hydroxytryptamine uptake blocker, neonatal DSP-4 induced a selective depletion of noradrenaline (NA) in cortex, hippocampus and amygdala. An increase of NA was observed in the medulla and substantia nigra/ventral tegmental area and a decrease in dopamine was observed in the thalamus. The vasoactive intestinal polypeptide levels were markedly elevated in the DSP-4 treated rats in almost all CNS regions whereas those of three other neuropeptides remained unchanged. It is concluded that certain adaptational changes can be observed in the peptide systems of the CNS upon disruption of the development of the noradrenergic innervation.

Destruction of meningeal cells over the medial cerebral hemisphere of newborn hamsters prevents the formation of the infrapyramidal blade of the dentate gyrus

Meningeal cells participate in the development of the cerebellum both by stabilizing the extracellular matrix of the pial surface and by organizing the radial glial scaffold and the lamination of the cerebellar cortex. In the present study we investigated possible influences of meningeal cells on the development of the dentate gyrus, whose ontogenesis has many similarities to that of the cerebellum. Meningeal cells were selectively destroyed by injecting newborn hamsters with 25 micrograms 6-hydroxydopamine (6-OHDA) into the interhemispheric fissure. Twenty-four hours postinjection (p.i.) the meningeal cells over the medial cerebral hemispheres were completely destroyed. Thirty days p.i. the infrapyramidal blade of the dentate gyrus was almost completely missing, while the suprapyramidal blade was hypertrophied, extending with its medial tip almost up to the medial surface of the cortex. In order to ascertain that this maldevelopment was caused by the destruction of meningeal cells, another group of hamsters was pretreated with normetanephrine (NMN) which inhibits the extraneuronal uptake of 6-OHDA into meningeal cells. In this group the meningeal cells were unaffected by the treatment, and the morphology of the dentate gyrus was normal 30 days p.i. of 6-OHDA plus NMN. When the meningeal cells were destroyed in later stages of development (postnatal days 1-5), alterations of the dentate gyrus could be induced only up to the fourth postnatal day; thereafter, 6-OHDA treatment left it unchanged. This indicates a critical period of meningeal cell influence that coincides with the period of existence of the subpial dentate matrix. Analysis of the time course of the defective development revealed that in the first 5 days p.i. 1) meningeal cells over the medial cerebral hemisphere were destroyed and removed, 2) the pial basement membrane over both the dentate anlage and the diencephalon thinned and ruptured, and the adjacent brain parts fused focally, 3) many cells of the subpial dentate matrix disappeared from their subsurface position, 4) the number of "immature" cells increased in the hilus and the subgranular zone of the suprapyramidal blade, 5) the suprapyramidal blade elongated and thickened considerably, while the infrapyramidal blade did not form. Beyond 5 days p.i. those parts of the pial surface of the dentate anlage that had not fused with the diencephalon were repopulated with meningeal cells. This reappearance of meningeal cells was accompanied by 1) the restitution of the normal morphology of the basement membrane, 2) the reappearance of neuronal and glial cells below the pial surface, and 3) the formation of fragments of the infrapyramidal blade which later developed a normal appearing lamination.(ABSTRACT TRUNCATED AT 400 WORDS)

In vivo neurotoxin administration alters immune responses in chickens (Gallus domesticus)

1. 6-Hydroxydopamine (6-OHDA) administered in ovo enhanced in primary immune response to sheep red blood cells (SRBC) in chicks 2. Splenic norepinephrine levels increased during the peak anti-SRBC response. 3. Cell-mediated immunity as measured by delayed-type hypersensitivity to phytohemagglutinin-P (PHA-P) was not affected by treatment with 6-OHDA.

Ultrastructural analysis of the serotonin hyperinnervation in adult rat neostriatum following neonatal dopamine denervation with 6-hydroxydopamine

Serotonin (5-HT) immunocytochemistry was used at the electron microscopic level to characterize the ultrastructural features of 5-HT axon terminals (varicosities) hyperinnervating the neostriatum of adult rats, 3 months after a neonatal destruction of the nigrostriatal dopamine system by intraventricular 6-hydroxydopamine. 5-HT-immunostained terminals from the anterior half of the hyperinnervated neostriatum were examined in single thin sections, and compared to their counterparts in vehicle-injected controls with respect to shape, size, organelle content, presence of a synaptic membrane differentiation and composition of the microenvironment. The intrinsic and relational features of the 5-HT-immunostained varicosities were essentially the same in 5-HT-hyperinnervated and control tissue. In particular, the frequency with which these varicosities made synaptic contacts was similarly low in both conditions (6-8% for whole varicosities), as already described in normal adult rat neostriatum. The distributional frequency of elements juxtaposed to the 5-HT-immunostained varicosities was also comparable in control and 5-HT-hyperinnervated tissue. However, in both conditions, there were much fewer dendritic spines in the microenvironment of 5-HT varicosities than around unlabeled terminals randomly selected from the same thin sections. This difference seemed entirely due to the numerous axo-spinous synaptic contacts made by the randomly selected, unlabeled varicosities. Together with recent observations on the 5-HT-hyperinnervation of adult rat hippocampus after grafts of fetal neurons, these data lead to the suggestion that mostly non-junctional neostriatal 5-HT terminals are not committed to a specific intratissular microenvironment. This might in part explain why they grow in excess when reinnervating adult tissue after a lesion or a graft.

Postnatal development of the noradrenergic projection from locus coeruleus to the olfactory bulb in the rat

Norepinephrine (NE) may play a role in the developing brain by modulating synaptic plasticity during critical periods of circuit formation (Kasamatsu and Pettigrew, 1976; 1979; Bear and Singer, 1986). In the olfactory bulb, NE input from the locus coeruleus (LC) appears to be necessary for the newborn rat to form a learned odor preference (Sullivan and Leon, 1986; Wilson and Leon, 1988; Sullivan et al., 1989). However, little is known about the development of NE innervation of the olfactory bulb. Thus, it is not clear how the maturation of the LC projection to the bulb correlates with the formation of olfactory bulb circuits during the period when NE modulates early olfactory learning. In this study, the postnatal development of the NE input from the LC to the main and accessory bulbs was characterized with tract tracing, immunocytochemistry, and quantitative image analysis methods. By birth there is already a substantial input to the olfactory bulb from the LC; as many as 200 LC neurons can be retrogradely labelled with wheatgerm agglutinin-horseradish peroxidase injection in the olfactory bulb. This compares with an estimated 400-600 neurons labelled by similar procedures in adult rats (Shipley et al., 1985). In order to study the development of NE fibers innervating the olfactory bulb, immunocytochemistry with antibodies to dopamine-beta-hydroxylase was employed. Image analysis was used to facilitate visualization and to quantitate the development of fiber densities. At birth, immunocytochemically labelled NE fibers were identified in all layers of the main and accessory olfactory bulb. The innervation was strongly preferential for infraglomerular layers at all stages of postnatal development. The fibers were densest in the internal plexiform and granule cell layers, less dense in the external plexiform layer, and sparse in the glomerular layer. The density of the fibers increased during development. There were no significant shifts in the relative distribution of the fibers in different layers of the bulb during development. This consistent laminar innervation by NE fibers suggests that if these fibers have a developmental role, their influence is probably limited to neuronal elements in inframitral cell layers.

Early development of the nucleus basalis-cortical projection but late expression of its cholinergic function

The aim of this study was to examine the development of the basalocortical pathway by using choline acetyltransferase and nerve growth factor receptor immunocytochemistry, acetylcholinesterase histochemistry and retrograde axonal transport. The observations were made in the ferret because in this species brain development occurs over a much more protracted period than in the rat. Staining for choline acetyltransferase immunoreactivity in the brain was minimal before birth. Adult levels of staining for the enzyme were not seen in cell bodies until three weeks after birth and in axons up to six weeks after birth. This, however, did not mean that presumptive cholinergic pathways are absent early in development. There was strong staining for nerve growth factor receptor in basal forebrain neurons from at least two weeks before birth. Positive staining for acetylcholinesterase was found in axons that begin to invade the cerebral cortex a week before birth. The retrograde axonal transport technique showed that the basalocortical pathway has a normal organization in the neonate. The conclusion is that cholinergic pathways form early in the prenatal period in the ferret but express their transmitter function late in postnatal development.

Morphometrical and microdensitometrical studies on peptide- and tyrosine hydroxylase-like immunoreactivities in the forebrain of rats prenatally exposed to methylazoxymethanol acetate

Methylazoxymethanol acetate (MAM Ac) injected into pregnant rats at a dose of 25 mg/kg at gestational day 15 causes microcephaly due to an atrophy of various telencephalic areas, mainly neocortex, hippocampus and basal ganglia. Previous studies demonstrated alterations in various neurochemical markers of classical transmitter systems in these regions. The present paper deals with changes in peptide and tyrosine hydroxylase (TH)-containing neurons in MAM Ac-induced microcephaly using immunocytochemistry coupled with computer-assisted morphometry and microdensitometry. No change in the number of vasoactive intestinal polypeptide (VIP)-immunoreactive neurons in the neocortex and neuropeptide Y (NPY)-immunoreactive neurons in the nucleus caudatus-putamen was found whereas cholecystokinin (CCK)-and NPY-immunoreactive neurons in the neocortex and CCK- and VIP-immunoreactive neurons in the hippocampus were decreased. The reduction of the latter peptide containing neuronal populations led to a maintained density of cells in MAM Ac-exposed rats, due to the parallel reduction of the overall mass of these regions. TH immunoreactivity was found to be unchanged in the basal ganglia, and increased in the cerebral cortex in agreement with previous reports on noradrenaline cortical system after MAM Ac exposure. The present results show a heterogenous vulnerability of different peptide immunoreactive neuronal populations to MAM Ac exposure. The sparing of VIP- and NPY-immunoreactive neurons may be due to their late development in the neocortex and striatum, respectively. The hypothesis is introduced that cortical VIP interneurons can develop independent of marked alterations in the intrinsic circuitry of the cortical region.

Noradrenaline neuron plasticity in developing rat brain: effects of neonatal 6-hydroxydopamine demonstrated by dopamine-beta-hydroxylase immunocytochemistry

The present study was conducted to assess the morphological changes produced by neonatal administration of 6-hydroxydopamine (6-OHDA) in the noradrenergic innervation of the developing and adult rat brain. As demonstrated by dopamine-beta-hydroxylase (DBH) immunohistochemistry, the major alterations are the following. First, neocortical and hippocampal noradrenergic innervation is permanently eliminated by the treatment, with lesser effects on other telencephalic structures. These changes appear by postnatal day 5 and are permanent in nature. In adult treated animals, most thalamic nuclei are hyperinnervated by DBH-immunoreactive axons as are the cerebellum and a number of brainstem nuclei. The hyperinnervation of these structures occurs after postnatal day 20, and is extremely specific, with the pattern of organization and distribution of noradrenergic axons in treated animals identical to that of controls. In contrast, the noradrenergic innervation of the hypothalamus is relatively unaffected by 6-OHDA treatment. The principal exception is the development of an anomalous plexus of DBH immunoreactive axons in the lateral hypothalamus. The timing and organization of the changes produced by neonatal 6-OHDA administration are consistent with the hypothesis that noradrenergic neurons, and particularly those of the locus coeruleus, are programmed to produce a defined amount of axon and terminal field, with any developmental loss resulting in a 'pruning effect' such that the total terminal field appears conserved. Given the specificity of the hyperinnervation, inductive influences from the target nuclei probably play a major role in determining the pattern of the noradrenergic innervation.

6-Hydroxydopamine induces serotonergic axon sprouting in cerebral cortex of newborn rat

Newborn rats were administered the neurotoxin 6-hydroxydopamine (6-OHDA) to determine whether neonatal ablation of the noradrenergic (NE) innervation produces augmented growth (i.e., sprouting) of serotonergic (5-HT) raphe-cortical axons. Following NE denervation at birth, the density of 5-HT axons in motor cortex (AG1) was determined at 4 days postnatal. Using a computer microscope system, the positions of all 5-HT-positive axons were mapped in radial strips of cortex from treated and control rats. Cumulative axon length, expressed as a function of area inspected, was used as a parameter of innervation density. Following 6-hydroxydopamine, the cumulative length of 5-HT axons in motor cortex increases by 32% (P less than 0.05) while cortical serotonin levels measured by HPLC concomitantly increase by 29% (P less than 0.005). The combined increases in 5-HT axon density and in neurotransmitter levels indicate that NE denervation produces increased growth of the cortical 5-HT innervation by the 4th postnatal day. The amount of transmitter stored per unit length of 5-HT axons appears unchanged. In 6-OHDA-treated rats, 5-HT axons exhibit augmented growth in all layers of motor cortex. In the treated rats, the relative density of 5-HT axons in each cortical layer is roughly proportional to the normal innervation density. Accordingly, in motor cortex, the magnitude of 5-HT axon sprouting is greatest in layer VI, which normally receives a dense 5-HT innervation, and is less in layer V, which has a lower innervation density. Qualitative assessment of other cortical areas following 6-OHDA reveals that 5-HT axon density appears increased in cortical zones that normally receive a dense 5-HT innervation, while the density remains low in zones with sparse innervation. The absence of axonal sprouting is particularly striking in those zones which receive a dense NE innervation but are sparsely innervated by 5-HT axons. Thus, while 5-HT axons undergo sprouting, they do not appear to replace ablated NE terminals in areas with a sparse 5-HT innervation. Hence, normal laminar and regional specificity of 5-HT axons is preserved despite ablation of NE afferents. These data indicate that, while NE denervation may trigger serotonergic sprouting, competition between NE and 5-HT fibers for the same postsynaptic sites is not the main factor that regulates postnatal growth of these axonal projections. The present findings demonstrate that the early development of raphe-cortical projections is influenced by NE cortical innervation.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of neonatal thermal lesioning of the mesocortical dopaminergic projection on the development of the rat prefrontal cortex

The role of dopamine (DA) in the development of the prefrontal cortex (PFC) was investigated by depleting the dopaminergic innervation of the PFC. A new stereotaxic procedure made it possible to produce small lesions in 1-day-old rats confined to the A10 group of dopaminergic cell bodies in the ventral tegmentum, from which the dopaminergic projection to the PFC originates. The variety in the lesions revealed a clear topographical organization of the efferent connections of the ventral tegmental area (VTA) to the prefrontal cortex. As far as we know from the literature the data presented in this study are a first direct indication of a neurotrophic role for dopamine in the development of the prefrontal cortex. When the prefrontal cortex was depleted of the dopaminergic innervation from birth on, by lesioning the cells of origin on postnatal day 1, the cortical thickness in the medial PFC was reduced by about 6%. Although coagulative lesions in the ventral tegmentum cause also a depletion of cortical serotonin, cortical reduction seems to be rather the result of the absence of dopamine during its development. This is indicated by the absence of a significant cortical thickness reduction in the dysgranular part of the first somatosensory cortex, which receives a serotonergic but no dopaminergic innervation.

Effects of neonatal 6-hydroxydopamine treatment upon morphological organization of the posteromedial barrel subfield in mouse somatosensory cortex

While recent studies indicate that proposed regulation of visual cortex plasticity by norepinephrine (NE) probably involves 6-hydroxydopamine (6-OHDA) effects other than NE depletion, reports of diminished neuronal maturation and reduced postweaning sensitivity to environmental conditions in animals treated with anti-adrenergic compounds continue to suggest a role for NE in neocortical development. To assess its possible role in development of a highly organized neocortical structure, the effects of postnatal 6-OHDA administration upon development of the somatosensory cortical posteromedial barrel subfield (PMBSF), which subserves the large facial whiskers, were observed in mice with whiskers in the middle row of the face removed unilaterally. Treatment with 6-OHDA caused 96-98% depletion of NE in parietal cortex. There were no effects of (or lesion interactions with) 6-OHDA treatment on barrel size in measures of Nissl-stained neurons, and 6-OHDA effects on numerical measures of dendritic branching of Golgi-impregnated non-pyramidal neurons in PMBSF were negligible. There were, however, effects of 6-OHDA treatment upon the highly ordered arrangement of dendrites within barrels. In 6-OHDA-treated animals, the class I (spiny and sparsely spined) cell dendrites were less attracted to the barrel hollow. In controls, for class I cells with their somata within the barrel wall, there was a high correlation between the distance from the soma to the hollow and the amount of dendrite in the wall, reflecting the distance the dendrite traverses to the hollow. In 6-OHDA-treated animals, this correlation was absent, i.e., cells at any distance from the hollow tended to have a high percentage of dendrite in the wall.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional differences in 5-hydroxytryptamine and catecholamine uptake in primary astrocyte cultures

The uptake of 3H-labelled 5-hydroxytryptamine (5-HT, serotonin) norepinephrine ([3H]NE), and 3,4-dihydroxyphenylethylamine ([ 3H]dopamine, [3H]DA) was studied in primary astrocyte cultures prepared from the cerebral cortex, corpus striatum, and hippocampal regions of neonatal rat brain. Na+-dependent uptake showed marked regional differences. For [3H]5-HT the magnitude of uptake was corpus striatum greater than or equal to cerebral cortex greater than hippocampus, whereas for [3H]NE the order was hippocampus greater than corpus striatum greater than cerebral cortex. For [3H]DA, only the hippocampal cultures showed significant Na+-dependent uptake. [3H]5-HT uptake was specifically inhibited by 10(-7) M fluoxetine whereas [3H]NE uptake was preferentially inhibited by 10(-7) M desipramine. These results may reflect regional brain specialization and/or different developmental patterns of high affinity uptake of serotonin and catecholamines by astrocytes in situ.

Effects of neonatal forebrain noradrenaline depletion on recovery from brain damage: performance on a spatial navigation task as a function of age of surgery and postsurgical housing

The experiments examined the contributions of forebrain noradrenaline and environmental enrichment to recovery of place navigation ability in rats after hemidecortication in infancy or adulthood. Noradrenaline depletion did not affect recovery from neonatal hemidecortication, although the early hemidecortications did allow sparing of function relative to adult operates. Noradrenaline depletion also failed to attenuate the positive effects of enriched housing on otherwise normal rats. Noradrenaline depletion did retard recovery of adult hemidecorticate rats housed in standard laboratory cages, but it did not retard recovery of adult hemidecorticate rats housed in enriched environments. The results suggest that noradrenaline is importantly involved in enhancing recovery from brain damage when other sources of compensation (e.g., neonatal injury, enriched environment) are absent.

Acetylcholine-rich neuronal grafts in the forebrain of rats: effects of environmental enrichment, neonatal noradrenaline depletion, host transplantation site and regional source of embryonic donor cells on graft size and acetylcholinesterase-positive fibre outgrowth

The importance of several factors influencing the survival of cholinergic-rich embryonic tissue transplanted to the adult rat forebrain and the extent of acetylcholinesterase-positive fibre innervation of the host brain was investigated in 3 experiments. In the first two experiments, embryonic ventral forebrain tissue was grafted to the neocortex of rats in which the intrinsic cortical cholinergic innervation had been removed by nucleus basalis lesions. Housing the host rats in an enriched environment produced a temporary enhancement of fibre outgrowth 4 weeks after transplantation, but this was not maintained after 10 weeks. Fibre outgrowth was greater when the grafts were transplanted to the noradrenaline-depleted neocortex than to the intact neocortex. Neither environmental enrichment nor noradrenaline depletion influenced graft survival or size. In the third experiment, the embryonic donor tissue was dissected to separate regions containing precursors of the nucleus basalis cholinergic cells from regions containing precursors of the septal cholinergic cells, and transplanted to either the neocortex following nucleus basalis lesions or to the hippocampus following fimbria-fornix lesions. Nucleus basalis grafts showed greater growth in size than septal grafts, and grafts placed into the hippocampus showed greater growth in size than grafts placed into the neocortex. More interestingly, the extent of fibre outgrowth depended on the appropriateness of the donor tissue to the host transplantation site: nucleus basalis tissue showed greater acetylcholinesterase-positive outgrowth than septal tissue in the neocortex, whereas septal tissue showed greater outgrowth than nucleus basalis tissue in the hippocampus.

Postnatal development of serotonin nerve fibers in the somatosensory cortex of mice studied by immunohistochemistry

Postnatal serotonin (5HT) innervation in the cerebral cortex of mice has been studied by 5HT immunohistochemistry. 5HT-like immunoreactive (5HT-LI) nerve fibers and terminals appeared to increase transiently, particularly in the somatosensory (Sm) cortex during early postnatal days. As pups grow, 5HT afferent inputs decreased rapidly to reach a similar pattern of distribution to that in adult animals. Since the transient increase was seen at a critical period (seventh postnatal day) for the differentiation of layer IV, it is suggested that increased 5HT concentrations might have an effect on thalamocortical inputs and/or cortical lamination of the developing brains.

Influences of meningeal cells on brain development. Findings and hypothesis

Destruction of meningeal cells during brain development results in alterations of the extracellular matrix over the surface of the central nervous system, and a regional disruption of the external glial limiting membrane, associated with a reorganization of the glial scaffold. These changes of the glial organization have repercussions on neuronal migration and aggregation leading to a failure of neurons to segregate into spatially separated layers and lobules. We propose that meningeal cells stabilize the labile outer surface of the brain and the glial scaffold during development by specifically controlling the composition of the extracellular matrix at the interface with glial end-feet.

Disruption of corticospinal plasticity by 6-hydroxydopamine as measured by intracortical microstimulation in rats

Intracortical microstimulation in normal, adult rats evoked low-threshold contralateral and high-threshold ipsilateral forelimb movements. In comparison, stimulation of the intact cortex in adult rats that sustained unilateral cortical lesions at birth evoked ipsilateral movements at abnormally low-threshold levels in addition to normal contralateral movements. Depletion of cortical and spinal cord noradrenaline levels by treatment with 6-hydroxydopamine prior to the placement of neonatal cortical lesions eliminated the low-threshold ipsilateral movements when tested at maturity. These findings suggest that the noradrenergic system may influence corticospinal plasticity.

Selective destruction of meningeal cells by 6-hydroxydopamine: a tool to study meningeal-neuroepithelial interaction in brain development

The effects of 6-hydroxydopamine (6-OHDA) on meningeal cells were studied at different ages in conjunction with blockade of the neuronal uptake 1 for catecholamines using nomifensine (NMF) and of the extraneuronal uptake 2 using normetanephrine (NMN). Our results show that maximal numbers of meningeal cells over the cerebellum of the newborn rat are destroyed by a threshold dose of 6-OHDA of 25 micrograms. The morphological characteristics which mark the time course of degeneration of meningeal cells were used to assess the effects of 6-OHDA given in conjunction with either NMF or NMN to differentiate between neuronal (uptake 1) and extraneuronal (uptake 2) effects of 6-OHDA. Uptake of 6-OHDA into meningeal cells and their subsequent degeneration was prevented by pretreatment with NMN but not with NMF. This finding indicates that meningeal cells have uptake 2 capacity but no uptake 1 membrane pump and explains both their uptake of 6-OHDA and their extreme sensitivity to the toxic effects of this drug. Application of this pharmacological regimen using NMF and NMN in conjunction with 6-OHDA thus allows selective destruction of meningeal cells which may be used experimentally to study the contribution of meningeal cells to brain development.

Immunohistochemical analysis of the early ontogeny of the neuropeptide Y system in rat brain

The distribution of neuropeptide Y in the developing rat brain was studied with immunocytochemistry, using the peroxidase-antiperoxidase method. Immunoreactive perikarya were first seen on embryonic day 13 and staining of fibres appeared from embryonic day 15 onwards: perikaryal staining was generally more intense prenatally than after birth. Areas rich in neuropeptide Y immunostaining included the monoaminergic regions of the brain stem from embryonic day 13 (especially the lateral reticular nucleus and the medullary reticular formation), the dorsal mesencephalon (with spots of immunoreactivity in the outer subventricular zone at embryonic days 13 or 14 and many cells and fibres in the inferior colliculus from embryonic days 16-20) and the olfactory tubercle/ventral striatum from embryonic day 15 until birth. The period of development of cortical neurones extended from embryonic day 19 until postnatal day 21. A hitherto unreported feature unique to neuropeptide Y was the presence in certain parts of the cerebral cortex of transient cells at the base of the cortical plate bearing radial processes which transverse its width. They were present from embryonic day 17 until postnatal day 4 and were maximally developed at embryonic days 20 or 21, contributing at this age a substantial fibre projection through the immature corpus callosum. The abundance of neuropeptide Y in the prenatal rat brain suggests it may play an important role in development.

alpha 1- and beta-adrenergic receptors are co-regulated during both noradrenergic denervation and hyperinnervation

Changes in the density of alpha 1- and beta-adrenergic receptors were studied following denervation of rat cerebral cortex and hyperinnervation of cerebellum and motor trigeminal nucleus, caused by neonatal 6-hydroxydopamine treatment. Four well-defined thalamic projection zones to cortex were studied separately using tissue punch methodology. Both alpha 1- and beta-adrenergic receptors were unevenly distributed in motor, sensory, visual and auditory cortex. The density of alpha 1-adrenergic receptors correlated better with the norepinephrine content of the punches (r = 0.62) than did the density of beta-adrenergic receptors (r = 0.38). Noradrenergic denervation increased both alpha 1- and beta-adrenergic receptor density in almost all cortical areas studied, however the percentage increase was larger for beta- than alpha 1-adrenergic receptors. The change in receptor density was largest in visual cortex and smallest in somatosensory cortex for both receptor sub-types. Noradrenergic hyperinnervation caused a 15-18% decrease in both alpha 1- and beta-adrenergic receptor density in the motor trigeminal nucleus of the pons, but did not change the density of either receptor type in the cerebellum. In general, following either noradrenergic denervation or hyperinnervation the change in alpha 1-adrenergic receptor density was correlated (r = 0.64, P less than 0.005) with the change in beta-adrenergic receptor density in each region, suggesting that these different receptor sub-types are under similar control mechanisms.

The angiogenesis of micrencephalic rat brains caused by methylazoxymethanol acetate. I. Superficial venous system. A quantitative analysis

The angiogenesis of the rat cerebrum was studied under pathologic conditions caused by the administration of the neurotoxin methylazoxymethanol acetate (MAMAc) in the time (E14) of neuroblast migration. The sinovenous junction of the main superficial cerebral veins and the morphological changes of the veins were examined by a quantitative analytic method. The hypoplastic areas of the brains showed extremely malformed venous systems with pathologic changes of the sinovenous junctions depending on the degree of disturbance of the neuroblast migration. These findings suggest the primary role of the neuronal maturation in the angioarchitectonic development and the direct dependency of the vascular differentiation on the neuroblast migration of the drained territory.

A single gene error of noradrenergic axon growth synchronizes central neurones

One strategy for deciphering inherited neurological disease is to examine the expression of individual genes controlling the assembly and physiology of specific cell groups within the developing mammalian central nervous system (CNS). This neurogenetic approach, using defined single-locus mutations arising on coisogeneic mouse strains, has recently been used to analyse a major class of neuronal membrane diseases involving abnormal excitability, the epilepsies, and to identify examples of hereditary variation in signalling properties at central synapses. An interesting mutation, the Tottering (tg) gene, causes a delayed onset, recessive neurological disorder in the mouse featuring a stereotyped triad of ataxia, intermittent myoclonus and cortical spike-wave discharges accompanied by behavioural absence seizures which resemble petit mal epilepsy. Axon branches of the locus coeruleus, a noradrenergic brain-stem nucleus, hyperinnervate specific target regions of the tg brain. The number of parent coerulean perikarya is unaffected, indicating a true proliferation of the terminal axonal arbor. With the exception of this unusually precise error of axonal growth, no other cytopathology has been identified in the tg brain. Here I present evidence that selective lesions of the central noradrenergic axons early in development limit the expression of the disease.

Events governing organization of postmigratory neurons: studies on brain development in normal and reeler mice

The purpose of the present work is to examine some of the mechanisms responsible for the early architectonic differentiation of the central nervous system, as well as for the abnormal development which occurs in certain hereditary malformations. In order to approach these questions, the embryonic development of the cerebral cortex, the cerebellum, the inferior olivary complex and the facial nerve nucleus has been studied in normal and reeler mutant mice, using morphological methods. The adult reeler phenotype is characterized not only by extreme laminar abnormalities of cell positioning in the telencephalic and cerebellar cortices, but also by relatively less extreme, though distinct abnormal architectonics in non-cortical structures such as the inferior olive and the facial nerve nucleus. Study of the embryonic development of these structures reveals that neurons are generated at the normal time and migrate along normal pathways. Moreover, the processes of directional axonal growth, differentiation of class specific features of neurons and glia, and synaptogenesis appear similar in both genotypes and are probably not directly affected by the reeler mutation. However, in all instances, the early architectonic organization achieved by reeler cortical, Purkinje, olivary or facial neurons at the end of their migration is consistently less regular than in normal embryos. In addition, these anomalies become amplified during the later developmental period. This evidence for the early appearance of abnormalities in reeler embryos indicates that the disposition of neurons at maturity cannot be exclusively regarded as secondary to the maturation of cells, neurites and connections, but is contingent upon a specific mechanism. One may infer that the presence of a normal allele at the reeler locus is necessary for the normal completion of this histogenetic step, which consequently is submitted to genetic control. Although the factor(s) responsible for the stable configuration of the early architectonics is unknown, various hypotheses are considered. Several lines of evidence are presented which argue against a major role being played by diffusible factors, mesodermal components and afferent fiber systems. Two mechanisms are considered particularly worth evaluating: (1) a diminution of relative adhesivity between neurons and radial glial fibers at the end of migration, and (2) a stabilization of neuronal configuration by selective recognition-adhesion among postmigratory neurons. The reeler gene could, directly or indirectly, affect these cell-cell interactions.(ABSTRACT TRUNCATED AT 400 WORDS)

Comparative development of striatal opiate receptors and dopamine revealed by autoradiography and histofluorescence

The pattern alignment of dopamine and mu opiate receptors in the rat neostriatum during pre- and postnatal development was investigated by means of catecholamine histofluorescence and receptor autoradiography in alternate sections. On embryonic day (E) 14, dopamine and mu opiate receptors appear in the striatum, but neither is yet distributed in patches. On E19, patches and a lateral rim of intense, punctate dopamine fluorescence begin to form, while patches of dense opiate receptors within a less dense matrix are apparent on E20. From the emergence of patterns in the two systems until the disappearance of dopamine fluorescent patches after postnatal day (P) 16, dopamine and opiate receptor patches in the dorsal striatum are in topographic register. After P16, dopamine fluorescence is diffuse and homogeneous in the dorsal striatum, and opiate receptors continue to mature into their heterogeneous adult pattern. In the accumbens nucleus, opiate receptors appear on E18, whereas dopamine fluorescence is not discerned until E20. The patterning of the two systems in the accumbens nucleus lags behind that of the caudate-putamen, and from P6 through adulthood, areas of dim fluorescence correspond to dense opiate receptor patches. The register of dorsal striatal dopamine and opiate receptors and their negative association in the accumbens nucleus are discussed in relation to dual dopamine and opiate systems. The role that these systems play as developmental determinants is discussed.

The development of catecholaminergic nerves in the spinal cord of rat. II. Regional development

The development of noradrenergic and dopaminergic nerves in 5 regions of the developing spinal cord of rat, from fetal day (FD) 16, to the young adult stage was studied. The normal synthetic capacity of adrenergic nerves in the ventral horn of the cervical and lumbar regions developed at the same time, and at the same rate, despite their spatial separation, and before similar development of the noradrenergic nerves in the dorsal horn and zona intermedia. In the ventral horn, the synthesis of NE from injected L-DOPA, as well as the release and metabolism of NE are well-established at 12 h (ND 0.5) after birth. In the dorsal horn these developments occur later at ND 4. Except in the dorsal horn of the cervical region, there was no easily observable, consistent pattern in the development of regional spinal dopaminergic innervation. The capacity of the developing cord to synthesize dopamine (DA) from injected DOPA is significantly developed at FD 16 (the earliest time studied), and peaked in all regions as early as ND 4. Control experiments indicate that 100%, and only 10% respectively of NE and DA synthetized from injected DOPA, occurred in descending monoaminergic fibers. Norepinephrine is synthesized exclusively in noradrenergic nerves. Cells appear transiently in the developing cord at FD 18, that are capable of synthesizing catecholamines (probably mainly DA) from injected DOPA. During postnatal development of the cord, and to a less extent in the adult, the network of catecholaminergic nerves actually present, is more extensive than that normally revealed during routine fluorescence microscopy. The results are discussed in the context of current attempts to understand the functional importance of catecholaminergic nerves in the mammalian spinal cord, and elsewhere in the CNS.