Multiple effects of artemin on sympathetic neurone generation, survival and growth

To define the role of artemin in sympathetic neurone development, we have studied the effect of artemin on the generation, survival and growth of sympathetic neurones in low-density dissociated cultures of mouse cervical and thoracic paravertebral sympathetic ganglia at stages throughout embryonic and postnatal development. Artemin promoted the proliferation of sympathetic neuroblasts and increased the generation of new neurones in cultures established from E12 to E14 ganglia. Artemin also exerted a transient survival-promoting action on newly generated neurones during these early stages of development. Between E16 and P8, artemin exerted no effect on survival, but by P12, as sympathetic neurones begin to acquire neurotrophic factor independent survival, artemin once again enhanced survival, and by P20 it promoted survival as effectively as nerve growth factor (NGF). During this late period of development, artemin also enhanced the growth of neurites from cultured neurones more effectively than NGF. Confirming the physiological relevance of the mitogenic action of artemin on cultured neuroblasts, there was a marked reduction in the rate of neuroblast proliferation in the sympathetic ganglia of mice lacking the GFRα3 subunit of the artemin receptor. These results indicate that artemin exerts several distinct effects on the generation, survival and growth of sympathetic neurones at different stages of development.

Development of electrophysiological and morphological diversity in autonomic neurons

The generation of neuronal diversity requires the coordinated development of differential patterns of ion channel expression along with characteristic differences in dendritic geometry, but the relations between these phenotypic features are not well known. We have used a combination of intracellular recordings, morphological analysis of dye-filled neurons, and stereological analysis of immunohistochemically labeled sections to investigate the development of characteristic electrical and morphological properties of functionally distinct populations of sympathetic neurons that project from the celiac ganglion to the splanchnic vasculature or the gastrointestinal tract of guinea pigs. At early fetal stages, neurons were significantly more depolarized at rest compared with neurons at later stages, and they generally fired only a single action potential. By mid fetal stages, rapidly and slowly adapting neurons could be distinguished with a topographic distribution matching that found in adult ganglia. Most rapidly adapting neurons (phasic neurons) at this age had a long afterhyperpolarization (LAH) characteristic of mature vasomotor neurons and were preferentially located in the lateral poles of the ganglion, where most neurons contained neuropeptide Y. Most early and mid fetal neurons showed a weak M current, which was later expressed only by rapidly-adapting and LAH neurons. Two different A currents were present in a subset of early fetal neurons and may indicate neurons destined to develop a slowly adapting phenotype (tonic neurons). The size of neuronal cell bodies increased at a similar rate throughout development regardless of their electrical or neurochemical phenotype or their topographical location. In contrast, the rate of dendritic growth of neurons in medial regions of the ganglion was significantly higher than that of neurons in lateral regions. The apparent cell capacitance was highly correlated with the surface area of the soma but not the dendritic tree of the developing neurons. These results demonstrate that the well-defined functional populations of neurons in the celiac ganglion develop their characteristic electrophysiological and morphological properties during early fetal stages of development. This is after the neuronal populations can be recognized by their neurochemical and topographical characteristics but long before the neurons have finished growing. Our data provide strong circumstantial evidence that the development of the full phenotype of different functional classes of autonomic final motor neurons is a multi-step process likely to involve a regulated sequence of trophic interactions.

Developmental changes in galanin in lumbosacral sympathetic ganglionic neurons innervating the avian uterine oviduct and galanin induction by sex steroids

We recently found lumbosacral sympathetic ganglionic galanin neurons innervating the quail uterine oviduct. Galaninergic innervation of the uterine muscle may be essential for avian oviposition, as galanin evoked oviposition through a mechanism of induction of vigorous uterine contraction. The questions arising from these findings are: what changes occur in galanin expression in the sympathetic ganglionic galanin neuron during development, and what is the hormonal factor(s) that induces galanin expression in this neuron? Therefore, the present study examined the developmental changes in galanin of the quail sympathetic ganglionic neuron and uterus, and the effect of administration of ovarian sex steroids on galanin induction. Immature birds reared under long-day photoperiods from 4 weeks of age demonstrated progressive increases in galanin levels both per unit ganglionic protein (concentration) and per ganglia (content) concurrent with ganglionic development during weeks 4--13. The uterine galanin content and uterine weight also increased progressively during the same period, but the galanin concentration in the uterus at 4 weeks was high due to the much smaller tissue mass. Immunocytochemical analysis with anti-galanin serum showed that immunoreactive ganglionic cells were few and small at 4 weeks and increased progressively thereafter. Administration of oestradiol-17 beta to immature birds at 3 weeks of age for 1 week increased both the galanin concentration and content in the ganglia without ganglionic growth. A marked increase in galanin-immunoreactive ganglionic cells was detected following oestradiol treatment. In contrast, progesterone increased ganglionic galanin levels, but the effects were low. Expression of the mRNAs encoding oestrogen receptor-alpha and -beta (ER alpha and ER beta) in the ganglionic tissue was verified by RT-PCR/Southern blot analysis. Immunocytochemical staining with anti-ER serum further revealed an intense immunoreaction restricted to the nucleus of ganglionic neurons. These results suggest that ovarian sex steroids, in particular oestradiol-17 beta, contribute as hormonal factors to galanin induction, which takes place in the lumbosacral sympathetic ganglionic neurons innervating avian uterine oviduct during development. Oestradiol may act directly on this ganglionic neuron through intra-nuclear receptor-mediated mechanisms to induce galanin.

The development of synaptophysin immunoreactivity in the human sympathetic ganglia

Using an indirect immunohistochemical method, synaptophysin immunoreactivity (SYN-IR) has been studied in cryostat sections of stellate and thoracic ganglia in human fetuses, neonates, infants and adults. In the course of development, a progressive increase in SYN-IR in axonal terminals and around nerve cells was demonstrated. In contrast, large clusters of small intensely fluorescent (SIF) cells and paraganglionic cells increased in number in fetuses and premature neonates at 24-25 weeks. Such SIF cell clusters varied in form and often occurred at pole or subcapsular areas of sympathetic ganglia close to blood vessels or paraganglia. With increasing gestational age and during infancy, a decrease in sizes of SIF cell groups and paraganglionic cells as well as changes in their distribution were found. The results show that the amount and distribution of SYN-IR is temporally related to the maturation and functional activity of human sympathetic ganglia neurons. It was suggested that numerous SIF cells and paraganglia in human prenatal sympathetic ganglia were both indicative of incomplete cell migration and an important source of regulation of ganglionic microcirculation under the conditions of relative hypoxia and immature nervous regulation.

3',5'-cyclic adenosine monophosphate regulates expression of synaptotagmin in neonatal sympathetic ganglia in vitro

The expression of the synaptic vesicle protein, synaptotagmin, in developing rat superior cervical ganglia is influenced by transsynaptic factors associated with membrane depolarization. The present study examines the role of cyclic AMP in the regulation of synaptotagmin in neonatal superior cervical ganglia maintained in explant culture. Ganglia were treated for 48 h in vitro with the Na+-channel ionophore, veratridine, or with pharmacological agents that alter cyclic AMP levels. Levels of cyclic AMP and synaptotagmin were determined by radioimmunoassay. Veratridine treatment significantly increased cyclic AMP in cultured ganglia, with a long time course, and also increased synaptotagmin levels. Drugs that elevate cyclic AMP levels significantly increased synaptotagmin levels, with similar magnitude to that produced by veratridine treatment. These pharmacological agents did not alter neuron survival or total ganglionic protein content. No additive effects were observed after combined treatment with veratridine and pharmacological agents that increased cyclic AMP. Agents that blocked adenylyl cyclase blocked the veratridine-induced increase in synaptotagmin levels. The results suggest that regulation of expression of synaptotagmin in neonatal sympathetic neurons is mediated partially by cyclic AMP.

Apoptosis in cells of rat sympathetic ganglia during early ontogeny: electron microscopic study

Postnatal ontogeny of sympathetic ganglia includes both proliferative processes and programmed cell death. Electron microscopy helps to evaluate the intensity and the relationship between these processes.

Spontaneous synaptogenesis in ex vivo sympathetic ganglion and the blockade by serum treatment

Central denervation for more than 1 month has been shown to cause an increase in the number of adrenergic synapses in sympathetic ganglia in vivo. Here, we report several lines of evidence that adrenergic synapses may be generated de novo in ex vivo superior cervical ganglion (SCG) of adult rats only several hours after the isolation. Structures immunoreactive for synaptophysin, a marker of presynaptic elements, were drastically decreased 6 days after the preganglionic denervation. A significant increase in number of synaptophysin positive boutons was observed over 3-8 hours in the denervated SCGs maintained ex vivo at 36 degrees C in oxygenated physiologic saline, and this increase was blocked by adding normal serum in the saline. Electron microscopic analysis confirmed that the number of adrenergic synapses specifically labeled with 5-hydroxydopamine was increased by several-fold under the same condition. Intracellular labeling of SCG neurons revealed an increase in the incidence (from 8 to 50%) of neurons having dendritic plexus after the in vitro incubation. No evidence of axonal sprouting within the ganglion was observed. Intracellular recordings from single neurons of denervated SCGs revealed that maximum amplitudes of inhibitory postsynaptic potentials, which were completely blocked by yohimbine, an alpha2-adrenoceptor antagonist, in response to focal stimulation were increased over the several hours. These results suggest that dendrites of SCG neurons rapidly develop and exhibit local efferent characteristics that underlie the inhibitory synaptic transmission once they are subjected to serum deprivation.

Developmental changes in the transmitter properties of sympathetic neurons that innervate the periosteum

During the development of sweat gland innervation, interactions with the target tissue induce a change from noradrenergic to cholinergic and peptidergic properties. To determine whether the change in neurotransmitter properties that occurs in the sweat gland innervation occurs more generally in sympathetic neurons, we identified a new target of cholinergic sympathetic neurons in rat, the periosteum, which is the connective tissue covering of bone, and characterized the development of periosteal innervation of the sternum. During development, sympathetic axons grow from thoracic sympathetic ganglia along rib periosteum to reach the sternum. All sympathetic axons displayed catecholaminergic properties when they reached the sternum, but these properties subsequently disappeared. Many axons lacked detectable immunoreactivities for vesicular acetylcholine transporter and vasoactive intestinal peptide when they reached the sternum and acquired them after arrival. To determine whether periosteum could direct changes in the neurotransmitter properties of sympathetic neurons that innervate it, we transplanted periosteum to the hairy skin, a noradrenergic sympathetic target. We found that the sympathetic innervation of the transplant underwent a noradrenergic to cholinergic and peptidergic change. These results suggest that periosteum, in addition to sweat glands, regulates the neurotransmitter properties of the sympathetic neurons that innervate it.

Intraventricular infusion of nerve growth factor as the cause of sympathetic fiber sprouting in sensory ganglia

OBJECT

The results of previous clinical trials have indicated that intraventricular infusion of nerve growth factor (NGF) in patients with Alzheimer's disease is frustrated by the appearance of weight loss and diffuse back pain. The present study tested whether NGF induces sympathetic sprouting in sensory ganglia. Such sprouting has been implicated in previous studies as a possible mechanism of sympathetically maintained pain in neuropathic animals.

METHODS

Nineteen Long-Evans rats underwent intraventricular infusion of either artificial cerebrospinal fluid (ACSF; seven animals) or NGF (12 animals). After 14 days of infusion, the sensory ganglia of the trigeminal nerve and the C-2, C-8, T-1, L-4, and L-5 dorsal roots were examined for sympathetic sprouting by using tyrosine hydroxylase immunohistochemical analysis.

CONCLUSIONS

In the animals receiving NGF, 52 of 144 ganglia showed sympathetic fiber sprouting. In the control animals receiving ACSF, only two of 72 ganglia showed minor sympathetic fiber sprouting. A preferential sprouting of sympathetic fibers was demonstrated at lower lumbar ganglia compared with the cervical and thoracic ganglia. The data presented here demonstrate that in the rat intraventricular NGF infusion caused sympathetic sprouting in dorsal root ganglia (p < 0.01). These findings may have importance both for the treatment of Alzheimer's disease and the understanding of neuropathic pain.

Catecholamine synthesis is mediated by tyrosinase in the absence of tyrosine hydroxylase

Catecholamine neurotransmitters are synthesized by hydroxylation of tyrosine to L-dihydroxyphenylalanine (L-Dopa) by tyrosine hydroxylase (TH). The elimination of TH in both pigmented and albino mice described here, like pigmented TH-null mice reported previously (Kobayashi et al., 1995; Zhou et al., 1995), demonstrates the unequivocal requirement for catecholamines during embryonic development. Although the lack of TH is fatal, TH-null embryos can be rescued by administration of catecholamine precursors to pregnant dams. Once born, TH-null pups can survive without further treatment until weaning. Given the relatively rapid half-life of catecholamines, we expected to find none in postnatal TH-null pups. Despite the fact that the TH-null pups lack TH and have not been supplemented with catecholamine precursers, catecholamines are readily detected in our pigmented line of TH-null mice by glyoxylic acid-induced histofluorescence at postnatal day 7 (P7) and P15 and quantitatively at P15 in sympathetically innervated peripheral organs, in sympathetic ganglia, in adrenal glands, and in brains. Between 2 and 22% of wild-type catecholamine concentrations are found in these tissues in mutant pigmented mice. To ascertain the source of the catecholamine, we examined postnatal TH-null albino mice that lack tyrosinase, another enzyme that converts tyrosine to L-Dopa but does so during melanin synthesis. In contrast to the pigmented TH-null mice, catecholamine histofluorescence is undetectable in postnatal albino mutants, and the catecholamine content of TH-null pups lacking tyrosinase is 18% or less than that of TH-null mice with tyrosinase. Thus, these extraordinary circumstances reveal that tyrosinase serves as an alternative pathway to supply catecholamines.

Development of the innervation and airway smooth muscle in human fetal lung

Human and porcine fetal airways have been shown to contract spontaneously from the first trimester, the latter also contracting in response to neural stimulation. Our object was to map immunohistochemically the innervation and its relationship to the airway smooth muscle (ASM) in the human fetal lung from early gestation to the postnatal period. Whole mounts of the bronchial tree were stained with antibodies to the pan-neuronal marker protein gene product 9.5, the Schwann cell marker S-100, and the ASM contractile protein alpha-actin, and imaged using confocal microscopy. By the end of the embryonic period (53 d gestation), the branching epithelial tubules in the primordial lung were covered with ASM to the base of the terminal sacs. An extensive plexus of nerve trunks containing nerve bundles, forming ganglia, and Schwann cells ensheathed the ASM. By 16 wk (canalicular stage), maturation of the innervation was advanced with two major nerve trunks running the length of the bronchial tree, giving rise to varicosed fibers lying on the ASM. An extensive nerve plexus in the mucosa was also present. The distal airways of infants who had died of Sudden Infant Death Syndrome were also covered with smooth muscle and were well innervated. Thus, an essentially complete coat of ASM and an abundant neural plexus ensheathing the airways are an integral part of the branching epithelial tubules from early in lung development.

Recombinant human amyloid precursor-like protein 2 (APLP2) expressed in the yeast Pichia pastoris can stimulate neurite outgrowth

The human amyloid precursor-like protein 2 (APLP2) is a member of the Alzheimer's disease amyloid precursor protein (APP) gene family. The human APLP2 ectodomain (sAPLP2) was expressed in the yeast Pichia pastoris and the recombinant sAPLP2 was purified from the culture medium in a single step by metal-chelating Sepharose chromatography. The neuritotrophic activity of APLP2 was compared to the APP isoforms sAPP695 and sAPP751 on chick sympathetic neurones. APLP2 had neurite outgrowth-promoting activity similar to that of the APP isoforms. This suggests that APP and APLP2 have a similar or related role and supports the idea of a redundancy in function between the APP-gene family proteins.

Diurnal rhythms in norepinephrine and acetylcholine synthesis of sympathetic ganglia, heart and adrenals of aging rats: effect of melatonin

The effect of aging and melatonin on 24-h rhythms in tyrosine hydroxylase activity and 3H - choline conversion into 3H - acetylcholine were examined in cervical, stellate, coeliac-mesenteric and hypogastric ganglia, and in the adrenal medulla and heart of rats. Young (50 days old) and old (18 months old) rats received evening injections of 10 or 100 microg of melatonin or its vehicle for 17 days. In superior cervical, stellate and coeliac-superior mesenteric ganglia, as well as in the adrenal medulla, norepinephrine and acetylcholine synthesis attained maximal values at night (c.a. 2030-0100 h). In the hypogastric ganglion, maximal tyrosine hydroxylase activity occurred at night at both studied ages. Two maxima in acetylcholine synthesis were detected in hypogastric ganglion of young rats (c.a. 1300 h and 0100 h, respectively) while in old rats a single maximum was observed at noon. Cardiac tyrosine hydroxylase activity peaked at early night (c.a. 2200-2300 h) while cardiac acetylcholine synthesis peaked at the afternoon (c.a. 1700-1900 h). Old rats exhibited a significant decrease of rhythm amplitude and increase of mean values in tyrosine hydroxylase activity in autonomic ganglia and adrenal medulla, and abolition of tyrosine hydroxylase rhythm in the heart. Twenty-four hour rhythmicity in acetylcholine synthesis was impaired or abolished in aged rats. Treatment of old rats with 10 or 100 microg melatonin generally augmented amplitude of rhythms and reinduced the nocturnal peak of acetylcholine synthesis in the hypogastric ganglion. Only the high melatonin dose significantly augmented rhythm amplitude of tyrosine hydroxylase activity (superior cervical and coeliac-superior mesenteric ganglia) and acetylcholine synthesis (superior cervical, stellate and coeliac-superior mesenteric ganglia) in young rats. The results indicate that the activity of the central oscillator, driven to the organs in part via the autonomic nervous system, deteriorates significantly with aging and that melatonin may restore partially such a deterioration.

Complementary and overlapping expression of Y1, Y2 and Y5 receptors in the developing and adult mouse nervous system

Neuropeptide Y, a 36 amino acid peptide, mediates its biological effects by activating the Y1, Y2, Y5 and Y6 receptors, which are also receptors for the structurally related peptide YY. Different classes of receptors have been suggested to be involved in different neuropeptide Y functions. In this report, we have characterized the developmental regulation and compared the cellular localization of these receptors in the developing and in the adult central and peripheral nervous systems of the mouse. RNase protection assays revealed that Y1, Y2 and Y5 messenger RNAs were expressed very early in spinal cord, brain, cerebellum and dorsal root ganglion development and were often down-regulated at times corresponding to their acquirement of the adult function in neurotransmission. In situ hybridization of the adult brain showed that Y1 was widely expressed, Y2 displayed a more restricted pattern, Y5 was expressed at very low levels and only in a few brain nuclei and Y6 was not expressed. Virtually all areas containing neurons positive for Y5 also expressed Y1, whereas many Y1-positive cells clearly did not express Y5. In contrast, Y2 was not expressed by the neurons expressing Y1 or Y5. These findings suggest that neuropeptide Y signaling in the brain could be mediated by simultaneous Y1 and Y5 activation. Similar results were also obtained in peripheral sensory neurons. Furthermore, our results suggest that neuropeptide Y/peptide YY receptors play an important role in nervous system development and that selective receptor combinations are responsible for signaling the different effects of neuropeptide Y in the peripheral and central nervous systems.

Neurotrophin sensitivity of prevertebral and paravertebral rat sympathetic autonomic ganglia

Prevertebral and paravertebral sympathetic autonomic ganglia respond differently to a large number of experimental and clinical insults. The selective involvement of subpopulations of sympathetic neurons may reflect differences in their response to neurotrophic substances. To test this hypothesis, we investigated the response of prevertebral and paravertebral rat sympathetic ganglia to selected neurotrophic substances in vivo and in vitro and identified the ganglionic distribution of neurons expressing high affinity neurotrophin receptor mRNAs. Dissociated cultures of embryonic prevertebral and paravertebral ganglionic neurons showed comparable responses to NGF deprivation and only small differences in their response to rescue with other trophic substances. In situ hybridization studies of adult rat sympathetic ganglia using probes specific for the high-affinity neurotrophin receptor transcripts trks A, B, and C demonstrated that neurons in both prevertebral and paravertebral sympathetic ganglia express predominantly trkA receptors in vivo. In addition, increased tyrosine hydroxylase (TOH) activity was induced only by doses of neurotrophic substances that activate trkA and showed only small differences between neonatal prevertebral and paravertebral ganglia. Although small differences in the sensitivity of pre- and paravertebral sympathetic neurons to various neurotrophins have been identified in our studies, they are unlikely, in isolation, to explain major differences in the sensitivity of these ganglia to neuropathologic processes.

Central regulation of sympathetic ganglia development: heterogeneous response of paravertebral, prevertebral, and terminal ganglia

These studies expand previous observations regarding the central control of neuronal maturation and indicate that paravertebral, prevertebral, and terminal ganglia are all under central influences, but in varying degrees. These variations are probably related to the relative contributions that central pathways exert on specific peripheral neuronal populations during growth and development as well as the various roles of more peripheral developmental modulators such as target organs and hormones, especially in the case of the HG. It is apparent, therefore, that during development central injury may result in heterogeneous deficits depending on the unique intrinsic and extrinsic environment that each ganglion population shares.

VIP -- a 'very important peptide' in the sympathetic nervous system?

Vasoactive intestinal peptide (VIP) is involved in the control of smooth muscle activity, blood flow and exo- as well as endocrine secretion. More recent work has elucidated the effects of this peptide on central and peripheral neurons. These studies suggest that VIP is an important modulator of cell growth, differentiation and neuronal survival during development of the sympathetic nervous system. VIP is also expressed in a subset of adult postganglionic sympathetic neurons. Furthermore, VIP is induced in an additional neuronal subpopulation of the rat superior cervical ganglion after axotomy. The mechanisms leading to increased VIP expression and its possible role during sympathetic nerve regeneration are currently being elucidated. This review summarizes the distribution, regulation and functions of VIP in cervical sympathetic ganglia of higher vertebrates.

Nerve growth factor stimulates the accumulation of beta1 integrin at the tips of filopodia in the growth cones of sympathetic neurons

Addition of nerve growth factor (NGF) to sympathetic neurons that have been starved of it causes a rapid induction of growth cone motility and the resumption of neurite growth. Using immunofluorescence staining, we show that within 10 min, NGF stimulated the accumulation of dense aggregates of beta1 integrin [a receptor for extracellular matrix (ECM) proteins] at most of the tips of either newly extended or preexisting filopodia. This effect occurred in the absence of ECM proteins and in the presence of 1 mg/ml Arg-Gly-Asp-Ser peptide, which blocks ECM binding to integrin, indicating that occupation of the integrin receptor is not necessary for tip localization. In fact, addition of either laminin or fibronectin caused a rapid withdrawal of beta1 integrin aggregates from filopodial tips at a rate comparable to that of the rearward flow of actin filaments in the periphery of the growth cone. Surface labeling of the extracellular domain of beta1 integrin while aggregated at the tips of filopodia or withdrawing in response to ECM proteins showed that the receptor is positioned within the membrane. The drug butanedione monoxime, an inhibitor of myosins, blocked the accumulation of beta1 integrin at the tips of filopodia without inhibiting the formation of filo-podia, suggesting the involvement of a myosin motor in beta1 integrin transport. These results provide the first evidence of NGF-mediated accumulation of ECM receptors to sensory elements of the growth cone and suggest one mechanism whereby soluble and substrate-bound cues coordinate to produce directed neurite growth.

A family of rat CRMP genes is differentially expressed in the nervous system

Members of the collapsin/semaphorin family play an important role in creating the complex pattern of neuronal connectivity. Inhibition of growth cone motility by chick collapsin is mediated by the intraneuronal protein CRMP-62. We have now isolated four rat sequences that are highly related to chick CRMP-62. All four genes are expressed exclusively in the nervous system and primarily during development. Rat CRMP-2/TOAD-64 is most closely related to chick CRMP-62 and is the most widely expressed CRMP within the nervous system. Rat CRMP-1 and CRMP-4/rUlip are expressed during discrete periods of neuronal development and are not found in the adult nervous system. Rat CRMP-3 has a distinct distribution, being expressed transiently in developing spinal cord and selectively in the postnatal cerebellum. The differential expression of these genes suggests that CRMPs may transduce signals from different semaphorins and that semaphorins may regulate the plasticity of the adult nervous system.

Autonomic nervous system as a model of neuronal aging: the role of target tissues and neurotrophic factors

The aim of this study was to determine the role of target tissues and neurotrophic factors in the growth and atrophy of autonomic neurons during development and aging. Using quantitative neuroanatomical techniques, it is shown that, although axonal and dendritic growth is apparent throughout postnatal development, different patterns of growth are found in autonomic neurons innervating different target tissues. For example, sympathetic neurons innervating the submandibular gland continue to grow well into maturity, but those innervating the iris cease net growth early in postnatal development. Similarly, although neuronal atrophy was observed in aged autonomic ganglia, this was not a general phenomenon but was specific to neurons innervating particular target tissues. Sympathetic neurons innervating the middle cerebral artery showed significant axonal and dendritic atrophy in old age, whereas neurons innervating the iris were morphologically unchanged. The trophic influence of peripheral target tissues on their innervating neurons has been shown to decline in old age possibly as a result of decreased availability of target-derived neurotrophic factors such as nerve growth factor (NGF) [Gavazzi et al. (1992) Neuroreport, 3:717-720]. Therefore, in an attempt to reverse neuronal atrophy where it occurred, NGF was infused via miniosmotic pumps over the peripheral axons of aged neurons. NGF induced increases in soma size, dendritic length and axonal arborization. However, in contrast to young adult neurons, no increase in the number of dendritic branch points or primary dendrites was observed, suggesting that some aspects of neuronal plasticity are impaired in old age. In sum, these results show a range of age- and target-specific differences in the axonal and dendritic morphology of autonomic neurons that may result from differing trophic interactions with their target tissues.

Phenotype of intraadrenal ganglion neurons during postnatal development in rat

The postnatal development of intraadrenal ganglion neurons was studied in rat by using indirect immunohistochemistry and in situ hybridization. The large neuropeptide tyrosine (NPY)-expressing ganglion neurons (type I ganglion neurons) matured postnatally, with marked increases in acetylcholinesterase (AChE)-, neurofilament 10 (NF10)-, and tyrosine hydroxylase (TH)-like immunoreactivities (LIs) paralleled by increasing levels of mRNAs encoding NPY, low-affinity neurotrophin receptor (LANR), and tropomyosin kinase receptor (trk). The smaller vasoactive intestinal polypeptide (VIP)-immunoreactive (IR) ganglion neurons (type II ganglion neurons) expressed increasing levels of VIP mRNA postnatally and also contained immunoreactive nitric oxide synthase (NOS) and its mRNA. These type II ganglion neurons appeared to be relatively mature already at postnatal day (P2) and did not express detectable levels of LANR or trk mRNAs. The cell size of both the type I and type II ganglion neurons increased about 2.5-fold postnatally. The type I ganglion neurons formed more densely packed clusters with increasing age, whereas the type II ganglion neurons were spread out in small groups or individually, mainly in the peripheral parts of the medulla, and appeared to fulfill their migration into the medulla and/or to the inner regions of the cortex early postnatally, possibly after establishing contact with their cortical targets. We suggest that the type I ganglion neurons represent sympathetic ganglion neurons of the same origin as the chromaffin cells and that they mature mainly postnatally. The development of the type II (VIP/NOS) ganglion neurons takes place earlier; however, their phenotype remains more uncertain.

Region- and stage-specific patterns of melanocortin receptor ontogeny in rat central nervous system, cranial nerve ganglia and sympathetic ganglia

Observations on developmental actions of melanotropic peptides in nervous system have been difficult to interpret in the absence of data on receptor ontogeny. We investigated binding of [125I]Nle4,D-Phe7-alpha-MSH ([125I]NDP) in developing Long Evans rats from gestational day (E) 13 by quantitative autoradiography. Regional [125I]NDP binding characteristics were assessed by competition experiments in early postnatal brain. The study revealed region- and stage-specific, often transient ontogenetic patterns. Sympathetic ganglia exhibit high [125I]NDP binding from E13, with a peak in superior cervical ganglion at E16-E18. The first central [125I]NDP binding sites transiently appear in parts of thalamus between E13 and E15. The early fetal period is characterized by prominent peaks of receptor density in somatosensory and viscerosensory nuclei (trigeminal sensory nuclei, solitary tract nucleus), paralleled by receptor expression in 5th, 7th, 9th and 10th cranial nerve ganglia. During late fetal life, receptor density peaks in dorsal motor nucleus of vagus and inferior olive; binding sites transiently appear in cerebellum. Caudate-putamen, nucleus accumbens, olfactory tubercle and septohippocampal nucleus show a high perinatal maximum. Starting with late fetal piriform cortex, [125I]NDP binding peaks sequentially in cerebral cortical areas, with highest levels in entorhinal cortex. Preoptic, septal, hypothalamic and amygdaloid areas known for elevated receptor densities in adulthood, exhibit a slow, peri- and postnatal receptor ontogeny. Temporal relations to regional developmental processes support the idea of a role of melanocortins during ontogeny.