Compensatory reaction during degeneration of arcuate nucleus dopaminergic neurons in rats

The study has been carried out to verify the authors' hypothesis that degeneration of dopaminergic (DA-ergic) neurons of the hypothalamic tuberoinfundibular system and concomitant development of hyperprolactinemia are accompanied by involvement of compensatory synthesis of dopamine (DA) by non-dopaminergic neurons expressing single complementary enzymes of synthesis of this neurotransmitter. Degeneration of DA-ergic neurons was produced by a stereotaxic injection into the brain lateral ventricles of 6-hydroxydopamine (6-OHDA) - a specific neurotoxin of DA-ergic neurons. 14 and 45 days after the toxin administration there were determined concentration of prolactine in peripheral blood by methods of immunoenzyme and radioimmunological analyses as well as the DA amount in the arcuate nucleus by the method of highly efficient liquid chromatography with electrochemical detection. In a part of the animals, slices were prepared from the mediobasal hypothalamus (arcuate nucleus and medial eminence) and perfused with Krebs-Ringer medium; then the DA concentration was determined in the slices and in the incubation medium. 14 days after the neurotoxin administration there were revealed an increase of blood prolactine concentration and a decrease of DA concentration in the arcuate nucleus in vivo as well a decrease of the total DA amount in the slices and incubation medium in experiments in vitro. 45 days after the neurotoxin administration, all the above parameters returned to the normal level. This, the obtained data indicate that the hyperlactinemia and DA deficit appearing during degeneration of the arcuate nucleus DA-ergic neurons seem to be compensated due to an enhancement of DA synthesis by non-dopaminergic monoenzyme neurons of arctuate nucleus.     

Compensatory reaction during degeneration of arcuate nucleus dopaminergic neurons in rats

The study has been carried out to verify the authors’ hypothesis that degeneration of dopaminergic (DA-ergic) neurons of the hypothalamic tuberoinfundibular system and concomitant development of hyperprolactinemia are accompanied by involvement of compensatory synthesis of dopamine (DA) by non-dopaminergic neurons expressing single complementary enzymes of synthesis of this neurotransmitter. Degeneration of DA-ergic neurons was produced by a stereotaxic injection into the brain lateral ventricles of 6-hydroxydopamine (6-HDA)—a specific neurotoxin of DA-ergic neurons. 14 and 45 days after the toxin administration there were determined concentration of prolactine in peripheral blood by methods of immunoenzyme and radioimmunological analyses as well as the DA amount in the arcuate nucleus by the method of highly efficient liquid chromatography with electrochemical detection. In a part of the animals, sections were prepared from the mediobasal hypothalamus (arcuate nucleus and medial eminence) and perfused with Krebs—Ringer medium; then the DA concentration was determined in the sections and in the incubation medium. 14 days after the neurotoxin administration there were revealed an increase of blood prolactine concentration and a decrease of DA concentration in the arcuate nucleus in vivo as well a decrease of the total DA amount in the sections and incubation medium in experiments in vitro. 45 days after the neurotoxin administration, all the above parameters returned to the normal level. Thus, the obtained data indicate that the hyperlactinemia and DA deficit appearing during degeneration of the arcuate nucleus DA-ergic neurons seem to be compensated due to an enhancement of DA synthesis by non-dopaminergic monoenzyme neurons of arcuate nucleus.     

Electron microscopic analysis of tyrosine hydroxylase, dopamine-beta-hydroxylase and phenylethanolamine-N-methyltransferase immunoreactive innervation of the hypothalamic paraventricular nucleus in the rat

The catecholaminergic innervation of the hypothalamic paraventricular nucleus (PVN) of the rat was studied by preembedding immunocytochemical methods utilizing specific antibodies which were generated against catecholamine synthesizing enzymes. Phenylethanolamine-N-methyltransferase (PNMT)-immunoreactive terminals contained 80-120 nm dense core granules and 30-50 nm clear synaptic vesicles. The labeled boutons terminated on cell bodies and dendrites of both parvo- and magnocellular neurons of PVN via asymmetric synapses. The parvocellular subnuclei received a more intense adrenergic innervation than did the magnocellular regions of the nucleus. Dopamine-beta-hydroxylase (DBH)-immunopositive axons were most numerous in the periventricular zone and the medial parvocellular subnucleus of PVN. Labeled terminal boutons contained 70-100 nm dense granules and clusters of spherical, electron lucent vesicles. Dendrites, perikarya and spinous structures of paraventricular neurons were observed to be the postsynaptic targets of DBH axon terminals. These asymmetric synapses frequently exhibited subsynaptic dense bodies. Paraventricular neurons did not demonstrate either PNMT or DBH immunoreactivity. The fibers present within the nucleus which contained these enzymes are considered to represent extrinsic afferent connections to neurons of the PVN. Tyrosine hydroxylase (TH)-immunoreactivity was found both in neurons and neuronal processes within the PVN. In TH-cells, the immunolabel was associated with rough endoplasmic reticulum, free ribosomes and 70-120 nm dense granules. Occasionally, nematosome-like bodies and cilia were observed in the TH-perikarya. Unlabeled axons established en passant and bouton terminaux type synapses with these TH-immunopositive cells. TH-immunoreactive axons terminated on cell bodies as well as somatic and dendritic spines of paraventricular parvocellular neurons. TH-containing axons were observed to deeply invaginate into both dendrites and perikarya of magnocellular neurons. These observations provide ultrastructural evidence for the participation of central catecholaminergic neuronal systems in the regulation of the different neuronal and neuroendocrine functions which have been related to hypothalamic paraventricular neurons.     

Axonal ephrin-As and odorant receptors: coordinate determination of the olfactory sensory map

Olfactory sensory neurons expressing a given odorant receptor (OR) project with precision to specific glomeruli in the olfactory bulb, generating a topographic map. In this study, we demonstrate that neurons expressing different ORs express different levels of ephrin-A protein on their axons. Moreover, alterations in the level of ephrin-A alter the glomerular map. Deletion of the ephrin-A5 and ephrin-A3 genes posteriorizes the glomerular locations for neurons expressing either the P2 or SR1 receptor, whereas overexpression of ephrin-A5 in P2 neurons results in an anterior shift in their glomeruli. Thus the ephrin-As are differentially expressed in distinct subpopulations of neurons and are likely to participate, along with the ORs, as one of a complement of guidance receptors governing the targeting of like axons to precise locations in the olfactory bulb.     

Evidence for neurotransmitter plasticity in vivo. II. Immunocytochemical studies of rat sweat gland innervation during development

Previous studies of the cholinergic sympathetic innervation of rat sweat glands provide evidence for a change in neurotransmitter phenotype from noradrenergic to cholinergic during development. To define further the developmental history of cholinergic sympathetic neurons, we have used immunocytochemical techniques to examine developing and mature sweat gland innervation for the presence of the catecholamine synthetic enzymes tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH) and for two neuropeptides present in the mature cholinergic innervation, vasoactive intestinal peptide (VIP) and calcitonin gene-related peptide (CGRP). In 7-day old animals, intensely TH- and DBH-immunoreactive axons were closely associated with the forming glands. The intensity of both the TH and DBH immunofluorescence decreased as the glands and their innervation developed. Neither TH-IR nor DBH-IR disappeared entirely; faint immunoreactivity for both enzymes was reproducibly detected in mature animals. In contrast to noradrenergic properties, the expression of peptide immunoreactivities appeared relatively late. No VIP-IR or CGRP-IR was detectable in the sweat gland innervation at 4 or 7 days. In some glands VIP-IR first appeared in axons at 10 days, and was evident in all glands by 14 days. CGRP-IR was detectable only after 14 days. In addition to VIP-IR and CGRP-IR, we examined the sweat gland innervation for several neuropeptides which have been described in noradrenergic sympathetic neurons including neuropeptide Y, somatostatin, substance P, and leu- and met-enkephalin; these peptides were not evident in either developing or mature sweat gland axons. Our observations provide further evidence for the early expression and subsequent modulation of noradrenergic properties in a population of cholinergic sympathetic neurons in vivo. In addition, the asynchronous appearance during development of the two neuropeptide immunoreactivities raises the possibility that the expression of peptide phenotypes may be controlled independently.     

Neurochemical Organization and Connections of the Cerebral Preglomerular Complex of the Masu Salmon

Using immunohistochemical labeling of the cells containing neuronal NO synthase (nNOS), tyrosine hydroxylase (TH), GABA, and parvalbumin (PA), as well as histochemical marking of choline acetyltransferase-containing neurons, we examined the neurochemical organization of the glomerular nuclei and preglomerular complex in the brain of the masu salmon (Oncorhynchus masou). Injections of the carbocyanine dye DiI allowed us to examine projections of neurons of the preglomerular and mammillary nuclei in the salmon brain. We showed that cholinergic, GABA-, PA-, TH-, and nNOS-immunopositive neurons belonging to different morphological types are present in the glomerular and medial preglomerular nuclei. The analysis of correlations between morphometric characteristics of the cells belonging to different neurochemical types and densitometric estimates of amounts of neurochemical agents present in these cells allowed us to hypothesize that there are close morphofunctional interrelations in cell populations possessing different neurochemical and morphometric characteristics. These interrelations of the cells belonging to different chemotypes are, probably, realized as mediatory/modulatory ones. The presence of a great number of small slightly differentiated cells in the preglomerular and glomerular nuclei allows us to suppose that the growth of the greatest sensory center of the salmon brain is provided by neuroblasts that migrate from the proliferative zones in the course of postembryonal neurogenesis. It is also hypothesized that NO, TH, and GABA are involved in paracrine control of the postnatal morphogenesis of the salmon preglomerular complex. The data obtained by hodological analysis indicate that the nuclei of the preglomerular complex obtain afferent projections from the dorsomedial and ventroventral telencephalic regions, preoptic nucleus, periventricular layer of the tectum, and posterior central thalamic nucleus. Our study demonstrated the existence of reciprocal functional connections between the preglomerular complex (most important diencephalic center for transmission of sensory information) and dorsomedial and ventral regions of the telencephalon in the masu salmon.     

Catecholaminergic, cholinergic and peptidergic innervation of gut-associated lymphoid tissue in porcine jejunum and ileum

With its abundance of neurons and immunocytes, the gut is a potentially important site for the study of the interaction between the nervous and immune systems. Using immunohistochemical techniques, we tested the hypothesis that gut-associated lymphoid tissue in the porcine small intestine might receive catecholaminergic, cholinergic and peptidergic innervation. Antibodies against protein gene product (PGP) 9.5 were employed to detect neuronal membranes; antibodies against tyrosine hydroxylase (TH), type 2 vesicular monoamine transporter (VMAT-2) and choline acetyltransferase (ChAT) were used to detect catecholaminergic and cholinergic neurons; and antibodies to neuromedin U-8 (NMU-8), substance P (SP) and vasoactive intestinal peptide (VIP) were also used. PGP9.5-immunoreactive nerve fibers were observed between jejunal Peyer's patch (PP) follicles and in submucosal ganglia localized at the base of continuous ileal PP. Many ChAT-positive and a few TH-/VMAT-2-immunoreactive neurons or axons adjacent to jejunal and ileal PP were observed. Neurons and fibers from ganglia situated between or at the base of PP follicles manifested robust immunoreactivities to VIP and NMU-8; relatively less SP immunoreactivity was observed at these locations. All neuromedin-U 8-positive neurons observed exhibited immunoreactivity to ChAT as did some VIP-positive neurons. The specific chemical coding of enteric neurons in close apposition to jejunal and ileal PP and the differential localization of neuropeptides within the jejunal and ileal PP are indicative of neuroimmunomodulation at these sites.     

Interrelations between monoaminergic afferents and corticotropin-releasing factor-immunoreactive neurons in the rat central amygdaloid nucleus: ultrastructural evidence for dopaminergic control of amygdaloid stress systems

Ample evidence implicates corticotropin-releasing factor (CRF)-producing neurons of the central amygdaloid nucleus (CeA) in vegetative, endocrine, and behavioral responses to stress and anxiety in laboratory rats. Monoaminergic systems are involved in modulating these responses. In the present paper, interrelations between CRF-immunoreactive (ir) neurons, and noradrenergic, serotonergic, and dopaminergic afferents were studied using single and double immunolabeling for light and electron microscopy in the rat CeA. Dopaminergic axons formed dense plexus in the CeA overlapping with the localization of CRF-ir neurons, and their terminals formed frequent associations with CRF-ir somata. Contacts of serotonergic axons on CRF-ir neurons were few, and contacts of noradrenergic axons were the exception. Ultrastructurally, symmetric synapses of dopaminergic terminals on CRF-ir somata and dendrites were found. More than 83% of CRF-ir somata were contacted in single ultrathin sections. About half of these possessed two or more contacts. Of non-ir somata, 37% were contacted by dopaminergic terminals, and only 13% of these had two or more contacts. Correlative in situ hybridization indicated that CeA CRF-ir neurons may express receptor subtype dopamine receptor subtype 2. In conclusion, dopaminergic afferents appear to specifically target CeA CRF neurons. They are thus in a position to exert significant influence on the rat amygdaloid CRF stress system.     

Electron microscopic analysis of tyrosine hydroxylase,dopamine-β-hydroxylase and phenylethanolamine-N-methyltransferase immunoreactive innervation of the hypothalamic paraventricular nucleus in the rat

Summary The catecholaminergic innervation of the hypothalamic paraventricular nucleus (PVN) of the rat was studred by preembedding immunocytochemical methods utilizing specific antibodies which were generated against catecholamine synthesizing enzymes. Phenylethanolamine-N-methyltransferase (PNMT)-immunoreactive terminals contained 80–120 nm dense core granules and 30–50 nm clear synaptic vesicles. The labeled boutons terminated on cell bodies and dendrites of both parvo- and magnocellular neurons of PVN via asymmetric synapses. The parvocellular subnuclei received a more intense adrenergic innervation than did the magnocellular regions of the nucleus. Dopamine--hydroxylase (DBH)-immunopositive axons were most numerous in the periventricular zone and the medial paryocellular subnucleus of PVN. Labeled terminal boutens contained 70–100 nm dense granules and clusters of spherical, electron lucent vesicles. Dendrites, perikarya and spinous structures of paraventricular neurons were observed to be the postsynaptic targets of DBH axon terminals. These asymmetric synapses frequently exhibited subsynaptic dense bodies. Paraventricular neurons did not demonstrate either PNMT or DBH immunoreactivity. The fibers present within the nucleus which contained these enzymes are considered to represent extrinsic afferent connections to neurons of the PVN.Tyrosine hydroxylase (TH)-immunoreactivity was found both in neurons and neuronal processes within the PVN In TH-cells, the immunolabel was associated with rough endoplasmic reticulum, free ribosomes and 70–120 nm dense granules. Occasionally, nematosome-like bodies and cilia were observed in the TH-perikarya. Unlabeled axons established en passant and bouton terminaux type synapses with these TH-immunopositive cells. TH-immunoreactive axons terminated on cell bodies as well as somatic and dendritic spines of paraventricular parvocellular neurons. TH-containing axons were observed to deeply invaginate into both dendrites and perikarya of magnocellular neurons.These observations provide ultrastructural evidence for the participation of central catecholaminergic neuronal systems in the regulation of the different neuronal and neuroendocrine functions which have been related to hypothalamic paraventricular neurons.Supported by NIH Grant NS 19266 to W.K. Paull     

Multiple axon guidance cues establish the olfactory topographic map: how do these cues interact?

Each primary olfactory neuron stochastically expresses one of approximately 1000 odorant receptors. The total population of these neurons therefore consists of approximately 1,000 distinct subpopulations, each of which are mosaically dispersed throughout one of four semi-annular zones in the nasal cavity. The axons of these different subpopulations are initially intermingled within the olfactory nerve. However, upon reaching the olfactory bulb, they sort out and converge so that axons expressing the same odorant receptor typically target one or two glomeruli. The spatial location of each of these approximately 1800 glomeruli are topographically-fixed in the olfactory bulb and are invariant from animal to animal. Thus, while odorant receptors are expressed mosaically by neurons throughout the olfactory neuroepithelium their axons sort out, converge and target the same glomerulus within the olfactory bulb. How is such precise and reproducible topographic targeting generated? While some of the mechanisms governing the growth cone guidance of olfactory sensory neurons are understood, the cues responsible for homing axons to their target site remain elusive.     

Diversity of intersegmental auditory neurons in a bush cricket

Various auditory interneurons of the duetting bush cricket Ancistrura nigrovittata with axons ascending to the brain are presented. In this species, more intersegmental sound-activated neurons have been identified than in any other bush cricket so far, among them a new type of ascending neuron with posterior soma in the prothoracic ganglion (AN4). These interneurons show not only morphological differences in the prothoracic ganglion and the brain, but also respond differently to carrier frequencies, intensity and direction. As a set of neurons, they show graded differences for all of these parameters. A response type not described among intersegmental neurons of crickets and other bush crickets so far is found in the AN3 neuron with a tonic response, broad frequency tuning and little directional dependence. All neurons, with the exception of AN3, respond in a relatively similar manner to the temporal patterns of the male song: phasically to high syllable repetitions and rhythmically to low syllable repetitions. The strongest coupling to the temporal pattern is found in TN1. In contrast to behavior the neuronal responses depend little on syllable duration. AN4, AN5 and TN1 respond well to the female song. AN4 (at higher intensities) and TN1 respond well to a complete duet.     

Opiocortin and catecholamine input to CRF-immunoreactive neurons in rat forebrain

Neural input to distinct and separate populations of CRF-immunoreactive (ir) neurons in rat forebrain was investigated. The relationship of opiocortin and/or catecholamine fibers to different groups of CRF-containing neurons was elucidated using single and dual labeling immunocytochemical procedures. Antibodies to CRF, ACTH(1–39) and the catecholamine synthesizing enzymes which are tyrosine hydroxylase (TH), dopamine β-hydroxylase (DBH) and phenylethanolamine-N-methyltransferase (PNMT) were utilized. CRF-ir neuronal populations are localized predominantly in the following regions of rat forebrain: bed nucleus of stria terminalis, medial preoptic area, suprachiasmatic and paraventricular (PVN) nuclei of hypothalamus and central nucleus of amygdala. The present study demonstrates that CRF-ir neuronal groups in rat forebrain are not homogenous in that each population received a characteristic neural input. CRF-ir neurons in the PVN received a dense input of ACTH-, TH-, DBH-, and PNMT-ir fibers. In contrast, CRF-ir neurons in the central nucleus of amygdala are colocalized predominantly with TH-ir fiber/terminals. In the ventral portion of the bed nucleus of stria terminalis, TH-, ACTH- and DBH-ir fibers are demonstrated in close anatomical proximity to CRF-containing perikarya; in the dorsal portion of this nucleus, TH-ir fiber/terminals are colocalized with CRF-ir neurons. In the suprachiasmatic nucleus, neither opiocortin- nor catecholamine-immunostained fibers are observed in association with CRF-ir neurons. Our data suggest that there is a transmitter specificity of neural input to each CRF-ir neuronal population in rat forebrain.     

Neuropeptide-Y and ACTH-immunoreactive innervation of corticotropin releasing factor (CRF)-synthesizing neurons in the hypothalamus of the rat. An immunocytochemical analysis at the light and electron microscopic levels

Corticotropin releasing factor (CRF), synthesized in neurons of the hypothalamic paraventricular nucleus (PVN), is one of the main regulators of the pituitary-adrenal cortex endocrine axis. In order to elucidate the possible involvement of the central neuropeptide-Y (NPY)- and adrenocorticotroph hormone (ACTH)-immunoreactive (IR) systems in the innervation of hypophysiotrophic CRF-synthesizing neurons, immunocytochemical double labelling studies were conducted in the hypothalamus of the rat to localize CRF-synthesizing neurons, as well as neuronal fibers exhibiting NPY and ACTH-immunoreactivity, respectively. The parvocellular subnuclei of the PVN received an intense NPY- and ACTH-IR innervation. At the light microscopic level, these peptidergic axons were associated with the dendrites and perikarya of CRF-IR neurons. Ultrastructural analysis revealed that NPY- and ACTH-IR axons established synaptic specializations with parvocellular neurons expressing CRF-immunoreactivity. These findings indicate that both neuropeptide-Y and adrenocorticotroph hormone containing neuronal systems of the brain are capable of influencing adrenal function via synaptic interactions with hypophysiotrophic CRF-synthesizing neurons. The data also support the concept that NPY and ACTH might be utilized as neuromodulators within the PVN.     

Innervation and motor patterns of the abdominal superficial flexor muscles in larval lobsters

The pattern of innervation and motor program of the abdominal superficial flexor muscle was investigated electrophysiologically in larval lobsters (Homarus americanus). The muscle receives both excitatory and inhibitory innervation in the larval as well as in the embryonic stages. Individual muscle fibers receive a single inhibitory neuron (f5) and a maximum of three excitors. Based on spike heights these axons belong to either the small (f1 or f2) or large (f3, f4) motoneurons. While the small axons preferentially innervate the medial muscle fibers the large axons innervate medial as well as lateral fibers. This larval pattern of innervation resembles the pattern in the adult lobster. The resemblance extends to the firing patterns as well with both large and small excitors firing spontaneously. Furthermore, evoked activity in the larvae produces reciprocal (and occasionally cyclical) bursts of excitor and inhibitor neurons denoting abdominal extension and flexion and resembling the firing patterns in adults. Consequently motor programs employed in steering the pelagic larvae are reminiscent of the programs for maintaining posture in the benthic adult lobsters.     

Intrinsic organization of the medial cerebral cortex of the lizard Lacerta pityusensis: A golgi study

The morphology of cells and the organization of axons were studied in Golgi-Colonnier and toluidine blue stained preparations from the medial cerebral cortex of the lizard Lacerta pityusensis. In the medial cortex, six strata were distinguished between the superficial glial membrane and the ependyma. Strata I and II formed the outer plexiform layer, stratum III formed the cellular layer, and strata IV go VI the inner plexiform layer. The outer plexiform layer contained smooth bipolar neurons; their dendrites were oriented anteroposteriorly and their axons were directed towards the posterior zone of the brain. Five neuronal types were observed in the cellular layer. The spinous pyramidal neurons had well-developed apical dendrites and poorly developed basal ones. Their axons entered the inner plexiform layer and gave off collaterals oriented anteroposteriorly. The small, sparsely spinous pyramidal neurons had poorly developed dendrites and their axons entered the inner plexiform layer. The spinous bitufted neurons had well-developed apical and basal dendritic tufts. Their axons gave off collaterals that reached the outer and inner plexiform layers of both the dorsomedial and dorsal cortices. The sparsely spinous horizontal neurons had dendrites restricted to the outer plexiform layer. Their axons entered the inner plexiform layer. The sparsely spinous, multipolar neurons had their soma close to stratum IV and their axons entered the outer plexiform layer. In stratum V of the inner plexiform layer were large, spiny polymorphic neurons; they had dendrites with long spines, and their axons reached the cellular layer. On the basis of these results, we have subdivided the medial cortex into two subregions: the superficial region, which contains the neurons of the cellular layer and their dendritic domains, and the deep region, strata V and VI, which contains the large, spiny polymorphic neurons. The neurons in the medial cortex of these lizards resembles those in the area dentata of mammals. On this basis, the superficial region may be compared to the dentate gyrus and the deep region to the hilar region of the hippocampus of mammals.     

Development of a glial network in the olfactory nerve: role of calcium and neuronal activity

In adult olfactory nerves of mammals and moths, a network of glial cells ensheathes small bundles of olfactory receptor axons. In the developing antennal nerve (AN) of the moth Manduca sexta, the axons of olfactory receptor neurons (ORNs) migrate from the olfactory sensory epithelium toward the antennal lobe. Here we explore developmental interactions between ORN axons and AN glial cells. During early stages in AN glial-cell migration, glial cells are highly dye coupled, dividing glia are readily found in the nerve and AN glial cells label strongly for glutamine synthetase. By the end of this period, dye-coupling is rare, glial proliferation has ceased, glutamine synthetase labeling is absent, and glial processes have begun to extend to enwrap bundles of axons, a process that continues throughout the remainder of metamorphic development. Whole-cell and perforated-patch recordings in vivo from AN glia at different stages of network formation revealed two potassium currents and an R-like calcium current. Chronic in vivo exposure to the R-type channel blocker SNX-482 halted or greatly reduced AN glial migration. Chronically blocking spontaneous Na-dependent activity by injection of tetrodotoxin reduced the glial calcium current implicating an activity-dependent interaction between ORNs and glial cells in the development of glial calcium currents.     

A Qualitative Assessment of Neuron Populations Expressing the Enzymes of Dopamine Synthesis in the Rat Accurate Nucleus during Ontogeny

The ratio of neuron populations expressing either tyrosine hydroxylase or aromatic L-amino acid decarboxylase, which are enzymes of dopamine synthesis, was estimated quantitatively in the accurate nucleus of male and female rats on the 21st day of intrauterine development, the 9th day of postnatal development, and in adult animals. The enzymes in neurons were revealed by double immunocytochemical labeling, followed by identification under a fluorescence microscope. At all the developmental stages, three neuron populations differing in the expression of these enzymes were revealed. By the end of the prenatal period, most of the neurons (99%) contained only one of the enzymes, and the proportion of neurons expressing both enzymes (dopaminergic neurons) did not exceed 1%. During postnatal development, the proportion of neurons with one enzyme proved to decrease, whereas that of dopaminergic neurons increased. However, the latter proportion, even in adult animals, did not exceed 50% of the total number of neurons expressing the enzymes of dopamine synthesis. Thus, the population of neurons expressing both enzymes increases during rat ontogeny, whereas the number of neurons expressing only one enzyme decreases.     

Neuropeptide-Y and ACTH-immunoreactive innervation of corticotropin releasing factor (CRF)-synthesizing neurons in the hypothalamus of the rat

Summary Corticotropin releasing factor (CRF), synthesized in neurons of the hypothalamic paraventricular nucleus (PVN), is one of the main regulators of the pituitaryadrenal cortex endocrine axis. In order to elucidate the possible involvement of the central neuropeptide-Y (NPY)-and adrenocorticotroph hormone (ACTH)-immunoreactive (IR) systems in the innervation of hypophysiotrophic CRF-synthesizing neurons, immunocytochemical double labelling studies were conducted in the hypothalamus of the rat to localize CRF-synthesizing neurons, as well as neuronal fibers exhibiting NPY and ACTH-immunoreactivity, respectively.The parvocellular subnuclei of the PVN received an intense NPY-and ACTH-IR innervation. At the light microscopic level, these peptidergic axons were associated with the dendrites and perikarya of CRF-IR neurons. Ultrastructural analysis revealed that NPY- and ACTH-IR axons established synaptic specializations with parvocellular neurons expressing CRF-immunoreactivity. These findings indicate that both neuropeptide-Y and adrenocorticotroph hormone containing neuronal systems of the brain are capable of influencing adrenal function via synaptic interactions with hypophysiotrophic CRF-synthesizing neurons. The data also support the concept that NPY and ACTH might be ntilized as neuromodulators within the PVN.Dedicated to Professor Dr. T.H. Schiebler on the occasion of his 65th birthday     

Role of IGF signaling in olfactory sensory map formation and axon guidance

Olfactory neurons project their axons to spatially invariant glomeruli in the olfactory bulb, forming an ordered pattern of innervation comprising the olfactory sensory map. A mirror symmetry exists within this map, such that neurons expressing a given receptor typically project to one glomerulus on the medial face and one glomerulus on the lateral face of the bulb. The mechanisms underlying an olfactory neuron's choice to project medially versus laterally remain largely unknown, however. Here we demonstrate that insulin-like growth factor (IGF) signaling is required for sensory innervation of the lateral olfactory bulb. Mutations that eliminate IGF signaling cause axons destined for targets in the lateral bulb to shift to ectopic sites on the ventral-medial surface. Using primary cultures of olfactory and cerebellar neurons, we further show that IGF is a chemoattractant for axon growth cones. Together these observations reveal a role of IGF signaling in sensory map formation and axon guidance.