Increased numbers of substance P-containing sensory neurons in a rat strain with a genetic neurotrophic defect

The GH inbred Wistar rat possesses reduced numbers of sympathetic motor neurons. In the present study, we report that substance P (SP) concentrations in superior cervical ganglion, spinal cord, iris and trachea of GH rats are about two-fold those in normal rats, and that SP-containing sensory neuron numbers are elevated in GH rats. These data suggest increased perinatal survival of SP neurons in the GH strain, due to reduced competition by sympathetic neurons for limited amounts of nerve growth factor. By contrast with the situation in iris and trachea, we found no difference between GH and normal rats in SP content of ear skin, atrium or stomach. This accords with previous findings that only some SP sensory neurons are responsive to nerve growth factor.

Low density, but not high density, C6 glioma cells support dorsal root ganglion and sympathetic ganglion neurite growth

Accumulating evidence suggests that an inhibitory influence of the environment on growth cones plays a crucial role in development and regeneration of neuronal projections. Oligodendrocyte-associated neurite growth inhibiting substance is one of the most extensively studied molecules. Molecular biological studies, however, remain slow in progress. Although finding clonal cells that express such factors would facilitate the analysis of inhibitory influences on neurite growth, few cell lines have been reported to express neurite growth inhibitor. We therefore investigated the possibility of a clonal glial cell line to differentiate and express inhibitory or non-permissive features for neurite outgrowth in culture. We chose the C6 glioblastoma cell line and examined neurite extension from chick dorsal root ganglion (DRG) explants. Neurites from embryonic day 9 DRG extensively grew on C6 cells that were cultured at low cell density, while they failed to grow on C6 cells cultured at high density, even in the presence of nerve growth factor in high concentrations. Membrane extract from high density C6 cells, when used as culture substratum, was less permissive for neurite outgrowth compared to extract from low density cells. Treatment of the membrane extract derived from high density C6 cells with trypsin made it less non-permissive for neurite growth. These results suggest that C6 cells are induced to express a non-permissive property for neurite outgrowth by culturing them at high density.

Nerve growth factor enhances the dendritic arborization of sympathetic ganglion cells undergoing atrophy in aged rats

We have investigated whether dendritic growth can be induced from sympathetic neurons of aged rats by the application of exogenous nerve growth factor to their target tissues. A previous study showed that significant dendritic atrophy (19%) occurs during aging in the sympathetic neurons innervating the middle cerebral artery and that dendritic atrophy correlated with loss of axon collaterals in the same population of neurons. Using retrograde tracing in conjunction with intracellular injection of fixed tissue and confocal microscopy, we now demonstrate that infusion of nerve growth factor over the peripheral processes of the same neurons from aged rats induces significant dendritic (45%) and cell body (60%) growth. However, not all aspects of the dendritic arborization were affected. Primary dendrites and branch points were not altered by nerve growth factor. In contrast, nerve growth factor induced a significant increase in the number of primary dendrites and branch points (100%) of neurons from young adults. Our results demonstrate that sympathetic neurons undergoing dendritic atrophy during aging can exhibit significant dendritic growth in response to the in vivo infusion of nerve growth factor, although the lack of regenerative response displayed by some parts of the dendritic tree leads us to believe that these neurons also show signs of reduced plasticity.

A model of selective synapse formation in sympathetic ganglia

In the sympathetic system, neurons from several spinal segments are mapped onto targets in the periphery in a topographically ordered way by means of selective synaptic connections in the superior cervical ganglion. Experimental evidence points to a crucial role for chemoaffinity in establishing this topographic map. Furthermore, rearrangements of synapses after surgical manipulations indicate that this chemoaffinity is not based on rigid "key-and-lock" markers. Our model is used to study how such nonrigid markers may interact with other regulatory factors, including growth-regulating signals and the growth potential of individual neurons. In the model, these latter factors are limiting, so that an increasing number of synaptic contacts decreases the likelihood of further synapse formation. These factors are combined with chemoaffinity using a linear threshold model. The model is robust to parameter changes and reproduces experimental observations with reasonable detail. Simulation results are used to discuss characteristic experimental results, such as the substantial plasticity of the connections seen after partial denervation. A surprisingly small effect of transient hyperinnervation in the model may help explain why final connectivities are similar in two real situations with high and low degrees of transient hyperinnervation (development and adult reinnervation). It is shown that spatial restrictions on post-synaptic neurons (dendrites) may contribute significantly to the segmentally broad innervation of each ganglion cell. Finally, we discuss potential effects of presynaptic neuronal death in systems with a high degree of plasticity.

Morphometric and neurochemical changes in rat superior cervical ganglion during growth and adulthood

We have previously found in rat superior cervical ganglion that there is a fall in neuron numbers and in cellular neuropeptide Y (NPY) immunoreactivity over the first year of life. In this study, we have used computerized image analysis to quantitate changes in neuron size, numbers and immunoreactivity for neuron-specific enolase (NSE), tyrosine hydroxylase (TH) and NPY in this ganglion between 1 and 85 weeks of age. Neuronal cytoplasmic area increased between 1 and 11 weeks and then remained stable until after 67 weeks, when there was a further increase in size of both NPY-positive and NPY-negative cells. Numbers of NPY-positive cells, but not those of NPY-negative cells, fell between 11 and 30 weeks. Both populations were stable after this time. Neuronal levels of NSE and TH remained constant, but levels of NPY fell between 58 and 67 weeks. These results indicate that changes in adult neuronal size, numbers and neurochemistry are independent phenomena. The increase in cell size and the fall in NPY after 58 weeks correspond to the time of withdrawal of some preganglionic inputs and may be responses to this event. By contrast, the decrease in NPY-positive cell numbers occurs some months before this time.

Neurogenesis and differentiation of sympathetic B and C cells in the bullfrog tadpole

The relation between birthdates of sympathetic neurons and their subsequent differentiation into cutaneous B cells and vasomotor C cells was examined in paravertebral ganglia 9 and 10 of the bullfrog tadpole. Neurons undergoing terminal cell division were identified by injecting tadpoles repeatedly with 5'-bromodeoxyuridine (BRDU) for one to six developmental stages between III and XXI. After allowing the tadpoles to enter late metamorphic stages (XX-XXV), the ganglia were double immunostained for BRDU and neuropeptide Y (NPY). NPY is a marker for mature C-type neurons (Horn et al., 1987). Double-labeled neurons were readily discerned through use of distinct black and brown HRP reaction products and also because immunoreactivity for BRDU was localized in nuclei while that for NPY was localized in perinuclear cytoplasm. Counts of labeled cells showed that neurogenesis occurs throughout limb bud and paddle stages, and that it ceases during early foot stages (XII-XIV), a time coinciding with the onset of NPY expression. By contrast, the labeling of non-neuronal satellite cells with BRDU was most common weeks later during metamorphic stages. Irrespective of their birthdates, about half of the BRDU-labeled neurons were also positive for NPY immunoreactivity. This proportion of NPY-positive cells is indistinguishable from that in the entire adult ganglia (Horn et al., 1987). In addition to establishing that neurogenesis and gliogenesis occurs during tadpole stages, the results indicate that the onset of NPY expression by vasomotor C neurons is unrelated to their time of origin. In other words, the last wave of neurogenesis in sympathetic ganglia does not give rise to a specific subclass of sympathetic neurons.

Neonatal nerve growth factor treatment alters the preganglionic innervation pattern of rat superior cervical ganglion

We treated rat pups with nerve growth factor (10 micrograms/animal/day s.c.) over postnatal days 1-7. Subsequent adult neuron numbers and tyrosine hydroxylase content in superior cervical ganglion were normal, but preganglionic inputs, as gauged from ganglionic choline acetyltransferase, were reduced. In parallel, intraganglionic axon terminals containing calcitonin gene-related peptide, but not those containing substance P, were increased in number. We postulate that neonatal nerve growth factor stimulates sprouting of ingrowing axons that have entered the ganglion soon after birth and that this represses subsequent establishment of cholinergic preganglionic synapses.

Nerve growth cone lamellipodia contain two populations of actin filaments that differ in organization and polarity

The organization and polarity of actin filaments in neuronal growth cones was studied with negative stain and freeze-etch EM using a permeabilization protocol that caused little detectable change in morphology when cultured nerve growth cones were observed by video-enhanced differential interference contrast microscopy. The lamellipodial actin cytoskeleton was composed of two distinct subpopulations: a population of 40-100-nm-wide filament bundles radiated from the leading edge, and a second population of branching short filaments filled the volume between the dorsal and ventral membrane surfaces. Together, the two populations formed the three-dimensional structural network seen within expanding lamellipodia. Interaction of the actin filaments with the ventral membrane surface occurred along the length of the filaments via membrane associated proteins. The long bundled filament population was primarily involved in these interactions. The filament tips of either population appeared to interact with the membrane only at the leading edge; this interaction was mediated by a globular Triton-insoluble material. Actin filament polarity was determined by decoration with myosin S1 or heavy meromyosin. Previous reports have suggested that the polarity of the actin filaments in motile cells is uniform, with the barbed ends toward the leading edge. We observed that the actin filament polarity within growth cone lamellipodia is not uniform; although the predominant orientation was with the barbed end toward the leading edge (47-56%), 22-25% of the filaments had the opposite orientation with their pointed ends toward the leading edge, and 19-31% ran parallel to the leading edge. The two actin filament populations display distinct polarity profiles: the longer filaments appear to be oriented predominantly with their barbed ends toward the leading edge, whereas the short filaments appear to be randomly oriented. The different length, organization and polarity of the two filament populations suggest that they differ in stability and function. The population of bundled long filaments, which appeared to be more ventrally located and in contact with membrane proteins, may be more stable than the population of short branched filaments. The location, organization, and polarity of the long bundled filaments suggest that they may be necessary for the expansion of lamellipodia and for the production of tension mediated by receptors to substrate adhesion molecules.

A monoclonal anti-glycoconjugate antibody defines a stage and position-dependent gradient in the developing sympathoadrenal system

The expression of complex carbohydrate antigens was analysed in developing sympathoadrenal cells of the rat using monoclonal antibodies that react with unique carbohydrate structures. CC1 and CC4 are monoclonal antibodies that react specifically with beta-N-acetylgalactosamine and alpha-galactose/alpha-fucose moieties, respectively. CC1-reactive glycoconjugates are expressed in embryonic superior cervical ganglion (SCG) cells as early as embryonic day 15 (E15). CC4 is expressed in the SCG only for a brief period starting at E18 and then disappearing at P5. During their transient period of expression, CC1 antigens are expressed uniformly throughout the SCG at E15-17, but are then restricted to the rostral portion of the SCG from E18 to P4. CC4 is also concentrated in the rostral portion of the SCG between E21 and P4. In the adrenal medulla, CC1 and CC4 antigens display a post-natal onset of expression commencing approximately at P14 and continue to be expressed on a subset of cells which contain tyrosine hydroxylase (TH). The expression of CC1, however, is restricted to phenylethanolamine-N-methyltransferase-(PNMT)-negative chromaffin cells, whereas CC4 is not. CC1 and CC4-expressing cells appear to be scattered throughout the adrenal medulla without any particular topographic orientation. These findings suggest that the CC1 monoclonal antibody defines a stage-specific differentiation antigen in the sympathoadrenal lineage. Additionally, the CC1 antigen may confer important positional information in the embryonic SCG by distinguishing rostral from caudal neuronal cell bodies.

Distribution and relative density of p75 nerve growth factor receptors in the rat spinal cord as a function of age and treatment with antibodies to nerve growth factor

It has been postulated that nerve growth factor (NGF) binding to the low-affinity fast-dissociating NGF receptor (p75 NGFR) on Schwann cells and growing neurites is involved with the molecular feedback necessary for continued neurite extension during development and regeneration. Since central projections of somatosensory fibers sprout into the spinal cord after daily neonatal injections of antibodies to NGF (ANTI-NGF) for a one month period, it is of interest to determine if the distribution of p75 NGFR correlates with the occurrence of sprouting. Spinal cords from three groups of rats: untreated, preimmune sera treated and ANTI-NGF treated were examined on postnatal days (PD) 0, 14 and 30. The p75 NGFR distribution was determined using the monoclonal antibody 192 with standard immunohistochemical techniques and the optical density of the immunoreaction product was quantified using an Amersham image analysis system. The 192 immunoreaction product was localized to laminae I-IV, the dorsal columns, the dorsolateral funiculus, Lissauer's tract (LT) and the ventral horn on PD 0; to laminae I-III and medial IV and LT on PD 14; and laminae I-II and LT on PD 30. The untreated and preimmune sera treated groups show no difference in distribution. In the ANTI-NGF treated group, the 192 immunoreaction product was localized to laminae I-V and LT on PD 14 and to laminae I-III and medial IV and LT on PD 30. Similarly, the optical density of the ANTI-NGF treated group was significantly greater than same aged untreated and preimmune sera treated groups, but was not statistically different from these two groups examined 14 days earlier. Thus, ANTI-NGF treatment interferes with the postnatal downregulation of p75 NGFR in the dorsal horn and may provide for continued neurite growth.

Transynaptic regulation of low-affinity p75 nerve growth factor receptor mRNA precedes and accompanies lesion-induced collateral neuronal sprouting

The bilateral sympathetic innervation of the rat pineal gland from the two superior cervical ganglia (SCG) is a useful model system to investigate the mechanisms by which intact neurons compensate for neuronal losses. Cutting of the internal carotid nerve (ICN) on one side has been shown to result in the removal of approximately one-half of the innervation to the pineal gland within 2 days. This denervation is followed by the development of collateral neuronal sprouting from the contralateral "intact" SCG, most of which takes place during the next 2 days. Using a solution hybridization protection assay, levels of low-affinity NGF receptor p75NGFR mRNA (pg/microgram total RNA) were found to be increased 25%, with no change in cyclophilin mRNA, in the SCG contralateral to the lesion performed 1 or 3 days earlier. In situ hybridization with a 35S riboprobe complementary to p75NGFR mRNA demonstrated a large increase in this mRNA in some cells of this intact SCG at both 1 and 3 days after a contralateral ICN cut lesion. The clustering of these cells toward the rostral portion of the SCG suggests that they may overlap with the population of sympathetic neurons which provides innervation to bilaterally innervated structures such as the pineal gland. The nature of the signals involved in the regulation of NGF receptor mRNA levels and their role in initiating and maintaining collateral sprouting remain to be fully established. Nevertheless, the time course of the changes in mRNA levels suggests that regulation of the low-affinity NGF receptor gene may be involved in the sequence of events associated with the collateral sprouting response by intact sympathetic nerve cells following partial denervation.

Fine structure of presynaptic axonal terminals in sympathetic autonomic ganglia of aging and diabetic human subjects

The neuropathologic changes that may underlie autonomic nervous system dysfunction in nondiabetic elderly human subjects or as a complication of diabetes have been systematically examined in sympathetic ganglia of a series of autopsied human subjects. As in animal models of aging and diabetes, enormously swollen terminal axons were found closely apposed to the perikarya of principal sympathetic neurons in prevertebral superior mesenteric sympathetic ganglia of aged and diabetic human subjects. Dystrophic axons consisted of two stereotyped forms: the first was composed of large numbers of misaligned aggregates of neurofilaments surrounded by variable numbers of small dense core vesicles; the second was characterized by large numbers of mitochondria, vacuoles, and dense and multivesicular bodies. The fine structural characteristics of neuroaxonal dystrophy, its predilection for prevertebral rather than paravertebral sympathetic ganglia, and the tendency for multiple dystrophic axons to cluster preferentially around selected neurons were identical in aged and diabetic human ganglia and were similar to changes seen in animal models of aging and diabetes. Neither diabetic nor aging ganglia demonstrated evidence of neuronal degeneration. Such structural changes may represent a degenerative influence of diabetes and aging on the normal remodeling of nerve terminals in autonomic ganglia, i.e., the continually ongoing process of turnover and replacement of axonal terminals. Similarity of lesions in human diabetes and aging suggests the possibility of pathogenetic mechanisms that are common to diabetes and the aging process. The substantial parallels between humans and animal models provide support for the validity of testing some proposed pathogenetic mechanisms directly in animal models.

Structural maturation of synapses in the rat superior cervical ganglion continues beyond four weeks of age

We have examined the morphology of preganglionic synapses in the rat superior cervical ganglion (SCG) at 10 days, 4 weeks and 1 year. Between 10 days and 4 weeks the mean thickness of the postsynaptic density (PSD) increased from 45.9 +/- 0.1 nm to 52.1 +/- 1.7 nm (P = 0.017), the mean length of the PSD (0.41 +/- 0.02 microns) did not change, and the distribution of synapses on the neuronal surface changed with a decrease in the proportion of somatic and an increase in the proportion of dendritic spine synapses. Since both synapse elimination and synapse formation are occurring during this period several mechanisms may contribute to these changes. However, between 4 weeks and 1 year, when there is no net change in the number of synapses, the mean length of the PSD increased to 0.53 +/- 0.02 microns (P = 0.001), there was no change in either the mean thickness of the PSD or the distribution of the synapses but the proportion of concave ('smile') synapses increased. A comparison with previous developmental studies of synapses in cerebral cortex of rat and chicken indicate that both the nature and the rate of synapse maturation can vary between different populations of synapses.

Protein kinase C-beta-like immunoreactivity and phosphorylation dependent immunoreactivity of neurofilaments in developing, adult and aged rat peripheral neurons

The localizations of protein kinase C-beta-like immunoreactivity (PKC-beta-LI) and phosphorylated neurofilament-like immunoreactivity (PNF-LI) were studied in developing (E12-P28), adult (3-month-old) and aged (15- and 30-month-old) rat dorsal root (DRG) and superior cervical (SCG) ganglia. A close correlation was found between the localization of PKC-beta-LI and PNF-LI in all age groups. PKC-beta-LI was already present in the rat DRG at the time of the appearance of PNF-LI (E12) and after E15 both PKC-beta-and PNF-LI were found in the same subpopulation of neuronal perikarya. Aging had no effect on the distribution or intensity of either PKC-beta or PNF-LI. In the SCG neurons no association was observed between immunoreactivity and accumulation of lipopigments, but in the DRG neurons, lipopigment accumulation was seen in PKC-beta and PNF-immunoreactive large neurons. The results suggest that PKC-beta may regulate the time of appearance and phosphorylation state of some forms of phosphorylated neurofilaments during development. The results also show that no major change occurs in the amount or distribution of PNFs during normal aging.

Administration or deprivation of nerve growth factor during development permanently alters neuronal geometry

We investigated whether the administration or deprivation of a neuronal growth factor during development can permanently alter the dendritic architecture of sensitive neurons. Nerve growth factor (NGF) or NGF antiserum treatment in the first 2-3 postnatal weeks markedly affected the survival, size, and dendritic arborization of mouse sympathetic ganglion cells acutely. Six months after the completion of treatment, the number of surviving neurons, cell body size, and higher order dendritic branching had changed considerably from their values at 3 weeks, suggesting that these parameters remain malleable throughout postnatal life. However, the number of primary dendrites, a fundamental determinant of organization within sympathetic ganglia, was permanently altered by the neonatal treatment protocol. The idea emerging from this study is that NGF influences the elaboration of primary dendrites by sympathetic ganglion cells only during a critical developmental period. In maturity, NGF acts as a "maintenance" factor necessary for normal neuronal function and survival, but neurons lose the capacity to respond with wholesale rearrangements of dendritic architecture.

Immunohistochemical localization of GAP-43 in rat and human sympathetic nervous system--effects of aging and diabetes

The neuronal 43 kDa growth associated peptide (GAP-43) is expressed in conditions of embryonic growth, axonal regeneration, and, to a limited degree, within the central nervous system as an indicator of synaptic plasticity. Although much is known about the expression of GAP-43 in cultured sympathetic neurons, information concerning the existence, immunolocalization and response of GAP-43 to experimental injury is not available for intact sympathetic ganglia in vivo. In this study we have characterized the in situ distribution and identity of GAP-43 in adult rat and human prevertebral and paravertebral sympathetic ganglia using immunohistochemical and biochemical methods. Antisera to GAP-43 intensely labeled intraganglionic presynaptic axons and synapses terminating on neurons of normal adult rat and human sympathetic ganglia in situ. There was minimal GAP-43 immunoreactivity of principal sympathetic neuron perikarya, proximal dendrites and initial axonal segments. The immunohistologic appearance of GAP-43 was unchanged in the ganglia of aged and diabetic rats and elderly humans, conditions in which presynaptic terminal axons and synapses show evidence of chronic degeneration, regeneration and neuroaxonal dystrophy, an unusual ultrastructural alteration which may represent disordered synaptic plasticity. Radioimmunoassay of ganglionic GAP-43 is comparable in young adult, aged and diabetic rat prevertebral or paravertebral sympathetic ganglia. Double immunolocalization of NPY (which labeled markedly swollen dystrophic axons) and GAP-43 in human sympathetic ganglia using a sequential immunogold-silver/fluorescence technique demonstrated that typical dystrophic axons contain little GAP-43.

Development and migration of avian sympathetic preganglionic neurons

Modern neuronanatomical techniques were used to investigate the development of the avian sympathetic preganglionic cell column in the spinal cord of the chick embryo. [3H]thymidine autoradiography indicated that the majority of these preganglionic, or "Terni column" neurons are generated between stages 18 and 24 (days 2-4). This coincides with the genesis of the somatic motoneurons in the thoracic levels of the cord, and therefore differences in the time of origin cannot explain the divergent fates of these two neuronal populations. Data obtained from short-survival autoradiographic experiments indicated that many early born cells remain close to the ventral region of the ventricular epithelium until day 5 of incubation. Ventral root injections used to label retrogradely neurons projecting an axon into the ventral root (Terni cells and somatic motoneurons) have labeled neurons next to the ventricular epithelium at the same early stages. Thus, it seems likely that some Terni cells, if not all, maintain medial positions and do not migrate laterally to join a common motor column before initiating a dorsal migration. Analysis of a closely staged series of embryos, whose Terni column neurons were retrogradely labeled with wheat germ agglutinin-horseradish peroxidase (WGA-HRP), revealed that between days 5 and 8 of incubation, Terni column neurons migrated dorsally to attain their adult position adjacent to the central canal. These changes in position were reflected in the changing morphology of the Terni column neurons, visualized by the Golgi-like HRP labeling. The positions of the migrating Terni cells differed from those of commissural cells, indicating that these fibers are not the substrate for the dorsal migration. The dorsal migration of Terni column cells was not disrupted by the surgical removal of the sympathetic ganglia, the synaptic targets of these neurons, nor by disruption of spinal afferents. Taken together, these results suggest that the migratory behavior of Terni cells in distinctive when compared to that of somatic motoneurons, and that local and/or intrinsic cues within the spinal cord guide the dorsal migration of Terni column cells.

Histochemistry of sympathetic neurons allotransplanted from young and aged mice to the submandibular gland

Sympathetic ganglion tissue of young (3 months) and aged (24 months) NMRI mice was allotransplanted into the submandibular gland to study the influence of aging on the survival of grafted neurons. The submandibular gland (SMG) was chosen as a host tissue because of its high concentration of NGF and good blood supply. Four weeks postgrafting the viability of transplants was evaluated using the formaldehyde-induced fluorescence technique, tyrosine hydroxylase (TH) immunohistochemistry, and morphometry. The density of neurons, catecholamine fluorescence and TH immunoreactivity (TH-IR) appeared to be almost unchanged when the transplant was completely surrounded by the SMG tissue, whereas transplants located within the interlobular septum and capsule, or even outside the capsule, showed significantly reduced neuronal survival. The shape of most of the transplanted neurons was not different from those in the intact ganglia. The average diameter of the transplanted young neurons was significantly decreased; this was not the case with the aged neurons. The histograms of grouped diameter values showed a shift to smaller cells in ganglion transplants in both age groups. The transplants in mice treated with 6-OH-dopamine showed considerable regrowth of adrenergic nerve fibers. There seemed to be no marked difference in the survival of transplanted neurons between aged and young animals. The results indicate that the sympathetic neurons from both young adult and aged animals survive the allotransplantation procedure. The neurotrophic factors together with dense vascularization present in the mouse submandibular gland may be beneficial for the restoration of the integrity of mature and aged adrenergic neurons.

Development of fast synaptic transmission in bullfrog sympathetic ganglia

Extracellular recordings were made of postsynaptic responses originating in sympathetic ganglia 9 and 10 of bullfrog tadpoles and adults. At stage III, when the length and diameter of the developing hindlimb bud are equal, preganglionic stimulation elicits postganglionic action potentials in spinal nerves 9 and 10 near the sciatic plexus. Although they fluctuate in amplitude, these responses follow short trains of repetitive stimuli at 20 Hz. Their mediation by nicotinic synapses was demonstrated by reversible blockade in low Ca2+, high Mg2+ Ringer and in nicotine. Parallel sympathetic B and C systems are clearly defined by stage III. They can be selectively activated by appropriate segmental stimulation of the sympathetic chain and are characterized by distinct conduction velocities which both lie in the C fiber range (less than 1 m/s). Throughout subsequent tadpole stages, the conduction velocities of the developing B and C systems gradually double while the magnitudes of their compound action potentials grow exponentially by 100-fold. Conduction velocities reach adult values after completion of metamorphosis. These results provide physiological evidence that synapse formation in sympathetic ganglia supplying the hindlimbs begins by the earliest stages of limb bud development, is selective, and progresses over a protracted period of months, prior to myelination.

Gender differences in neurotransmitter expression in the rat superior cervical ganglion

Sexual dimorphism of neuron number has been observed in several areas in the central and peripheral nervous system. In many of these areas enhanced neuron survival exists in males during the period of naturally occurring cell death. This has been attributed to high levels of circulating testosterone in the perinatal period. The superior cervical ganglion (SCG) of the rat exhibits this sexual dimorphism. The difference in neuron numbers is established by two weeks postnatally and precedes the differences in body weight and sympathetic target mass between the sexes. At this two week time point, fewer SCG neurons in the female rat must supply neurotransmitter to the same mass of sympathetic target as in the male. The present study examined some of the mechanisms used by neurons in the SCGs of male and female rats to compensate in supplying neurotransmitter to their targets. At birth, the SCGs of male and female rats contain equal numbers of neurons. There is also no sex difference at this time in the content of norepinephrine (NE) in these neurons or in the enzyme activity of tyrosine hydroxylase (TH). However, a sex difference does exist in the expression of TH-mRNA, with SCG neurons in female expressing more TH-mRNA than males. At this time, there is no sex difference in either the total body weight of males and females or in the mass of sympathetic target organs. During the first two postnatal weeks, natural neuron death in the SCG results in the loss of significantly more neurons in females than in males. At the end of the period of cell death, neurons in females continue to express more TH-mRNA, and at this time both TH enzyme activity and NE content per neuron are also higher in females. Since the adult sex difference in body weight and sympathetic target mass has not yet been established, the same amount of target mass is innervated by fewer neurons in females. In the adult, the sex difference in SCG neuron number is maintained. However, both overall body weight and sympathetic target mass are significantly greater in males. At this time expression of TH-mRNA is greater in SCG neurons of males, while both TH enzyme activity and NE content per neuron are equal in males and females. One of the challenges presented to the developing nervous system is to match a population of neurons with its targets.(ABSTRACT TRUNCATED AT 400 WORDS)

Reorganization of cranial sympathetic pathways following neonatal ganglionectomy in the rat

Postganglionic sympathetic innervation normally is distributed ipsilaterally to lateral cranial targets. However, contralateral outgrowth occurs following unilateral ganglionectomy in neonatal rats. This study was conducted to determine the prevalence, morphological features, ganglionic derivations, and temporal sequence of sympathetic reinnervation of denervated cranial targets. Unilateral superior cervical ganglionectomy of mature rats revealed exclusively ipsilateral distributions of catecholaminergic histofluorescent fibers to orbital targets (Meibomian gland, tarsal muscle, orbital muscle, iris, ciliary body, vasculature) and the circle of Willis, with the exception of the anterior cerebral artery. In mature rats following neonatal unilateral ganglionectomy, all targets were reinnervated by fibers displaying morphologies and target relationships similar to normal innervation, but with lower densities. Acute excision of the remaining superior cervical ganglion eliminated all fibers in 7 of 8 preparations. In adult rats receiving neonatal bilateral superior cervical ganglionectomies, cerebral vasculature was reinnervated consistently, and orbital targets contained fluorescent fibers in 6 of 16 cases, indicating that reinnervation can derive from other sources when superior ganglion outgrowth is prevented. Observations in developing rats revealed fibers along the cranial portion of the contralateral optic nerve sheath at 2-3 days postganglionectomy, and within the orbit at later ages, reaching the most distal targets by 14 days. It is concluded that widespread sympathetic reinnervation of orbital and cerebrovascular targets derives primarily from the contralateral superior ganglion. Orbital ingrowth apparently originates intracranially and enters the orbit by an atypical pathway within the optic foramen.

Age-related decrease in sympathetic sprouting is primarily due to decreased target receptivity: implications for understanding brain aging

Aging of the nervous system is characterized by reduced anatomical plasticity. The cause of this decreased plasticity is not known because it is usually not possible to distinguish between extrinsic and intrinsic factors that affect neuronal growth. One example of age-related reduced neuronal plasticity that is amendable to such analysis is the growth of sympathetic axons into the rat hippocampal formation following septal denervation. This sprouting response can be elicited throughout the lifespan of the rat but is drastically reduced in aged animals. The age-related reduction in ingrowth could theoretically be due to decreased receptivity of the target (reduced trophic support or increased inhibition of growth), decreased responsivity of the sympathetic neurons or a combination of both factors. In order to test the relative contributions of the age of the target tissue and the age of the sympathetic neurons to the reduced growth observed in aged animals, superior cervical ganglia were transplanted from young animals into old animals (y/o) and from old animals into young animals (o/y) as well as autologously within the same animals (y/y and o/o). The extent of sympathetic ingrowth and the survival of transplanted neurons were assessed with fluorescence histochemical methods. The extent of ingrowth was significantly greater in young hosts compared with old hosts regardless of the age of the donor. In addition, the survival of transplanted neurons was greater in younger hosts than in aged hosts regardless of donor age. These results indicate that sympathetic ingrowth is reduced in aging primarily because of decreased receptivity of the hippocampal target tissue.

Increased numbers of extra-adrenal chromaffin cells in the abdominal paraganglia of senescent F344 rats: a possible role for the glucocorticoid receptor

The increase in numbers of extra-adrenal chromaffin cells of abdominal paraganglia in senescent F344 rats was investigated by 5-bromo-2'-deoxyuridine immunocytochemistry. A monoclonal antibody raised against 5-bromo-2'-deoxyuridine was used to react with tissue-sections of paraganglia taken from 28-month-old animals given weekly injections of the thymidine analog over a 14-week period. No immunoreactivity was detected in the extra-adrenal chromaffin cells, whereas control sections of intestinal epithelium showed abundant immunoreactivity. Also, the profile for immunoreactivity of the glucocorticoid receptor in relation to age was compared between extra-adrenal and adrenal chromaffin cells, which share cytological characteristics, but not the increase associated with senescence. In the extra-adrenal chromaffin cells, the intensity of receptor immunostaining was unchanged, while in the adrenal chromaffin cells it decreased with age. These results indicate that hypertrophy of the paraganglia in aged F344 rats is not due to the proliferation of extra-adrenal chromaffin cells. Instead, they suggest that the chromaffin cell phenotype may be induced in pre-existing cells and that the expression of the glucocorticoid receptor has an intrinsic role in this change.

Afferent regulation of neurotransmitter metabolism in perikarya and terminals of developing sympathetic neurons

Steady-state levels and turnover of the neurotransmitter, norepinephrine (NE), were measured in sympathetic perikarya and in two sympathetic target organs in the rat at various times during postnatal development. NE content in sympathetic perikarya in the superior cervical ganglion (SCG) increases 15-fold from birth to reach adult levels by 60 days. This increase in NE content parallels the increase in total protein in the ganglion. The rate of turnover of NE in the sympathetic perikarya increases slightly from birth to adulthood. Since the perikarya in the SCG project to a variety of different targets in the head and neck, NE metabolism was also examined in two terminal sympathetic plexuses, in the iris and in the submandibular gland (SMG). The terminal noradrenergic plexuses within these target organs do not mature with the same time course. In the iris, levels of NE increase 24-fold from birth until 90 days postnatally. Turnover of NE in sympathetic terminals in the iris at the time of birth is equivalent to that in the adult. In contrast, both the content and turnover of NE in sympathetic terminals in the SMG are very low at birth, and increase dramatically in the first month postnatally. Deafferentation of the SCG at birth impairs the development of normal levels of NE in sympathetic perikarya by approximately 40%, and total ganglionic protein is similarly affected. NE turnover in sympathetic perikarya deafferented at birth is only slight reduced from normal. The response to neonatal deafferentation differs in the two terminal sympathetic plexuses. In neurons that project to the iris, no detectable NE turnover could be measured, although the content of transmitter attains 64% of control values after deafferentation.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth cone-growth cone interactions in cultures of rat sympathetic neurons

Growth cones of sympathetic neurons from the superior cervical ganglia of neonatal rats were studied using video-microscopy to determine events following contact between growth cones and other cell surfaces, including other growth cones and neurites. A variety of behaviors were observed to occur upon contact between growth cones. Most commonly, one growth cone would collapse and subsequently retract upon establishing filopodial contact with the growth cone of another sympathetic neuron. Contacts resulting in collapse and retraction were often accompanied by a rapid and transient burst of lamellipodial activity along the neurite 30-50 microns proximal to the retracting growth cone. In no instances did interactions between growth cones and either fibroblasts or red blood cells result in the growth cone collapsing, suggesting that a specific recognition event was involved. On several occasions, growth cones were seen to track other growth cones, although fasciculation was rare. In some cases, there was no obvious response between contacting growth cones. Growth cone-growth cone contact was almost four times more likely to result in collapse and retraction than was growth cone-neurite contact (45% vs 12%, respectively). These observations suggest that the superior cervical ganglion may be composed of neurons with different cell surface determinants and that these determinants are more concentrated on the surface of growth cones than on neurites. These results further suggest that contact-mediated inhibition of growth cone locomotion may play an important role in growth cone guidance.