The effect of taget organ removal on the development of sympathetic neurons

Distribution of alpha-synuclein in rat salivary glands

Expression of alpha-synuclein (Syn), a presynaptic neuronal protein, was immunohistochemically examined in intact rat submandibular, sublingual, and lingual glands. The submandibular gland contained abundant periductal Syn-immunoreactive (-ir) nerve fibers. Abundant Syn-ir varicosities were present in acini of the sublingual and serous lingual glands. By confocal laser scanning microscopy, Syn-ir nerve fibers around smooth muscle actin (SMA)-ir cells alone were infrequent; however, those around aquaporin-5 (AQP5)-ir cells alone and both SMA- and AQP5-ir cells were abundant in the sublingual and serous lingual glands. SMA-ir cells were occasionally immunoreactive for toll-like receptor 4, a Syn receptor. Syn-ir nerve fibers contained tyrosine hydroxylase (TH) in the submandibular gland and choline acetyltransferase (ChAT) in all examined salivary glands. In the superior cervical (SCG), submandibular, and intralingual ganglia, sympathetic and parasympathetic neurons co-expressed Syn with TH and ChAT, respectively. SCG neurons innervating the submandibular gland contained mostly Syn. In the thoracic spinal cord, 14.7% of ChAT-ir preganglionic sympathetic neurons co-expressed Syn. In the superior salivatory nucleus, preganglionic parasympathetic neurons projecting to the lingual nerve co-expressed Syn and ChAT. The present findings indicate that released Syn acts on myoepithelial cells. Syn in pre- and post-ganglionic neurons may regulate neurotransmitter release and salivary volume and composition.

Transmitter phenotypic expression in the embryo

The initial appearance and development of noradrenergic and adrenergic phenotypic characters was studied in the rat embryo by immunocytochemical methods. Tyrosine hydroxylase and dopamine-beta-hydroxylase (noradrenergic enzymes) appeared at 11.5 days of gestation (Day E 11.5; 27-30 somites) in sympathetic ganglion primordia and in cells of the gut. While tyrosine hydroxylase and dopamine beta-hydroxylase immunoreactivity increased progressively in ganglion primordia, the enzymes disappeared in the gut cells after E 13.5. However, the gut cells themselves persisted, as indicated by the high-affinity uptake of noradrenaline (norepinephrine). Consequently, initial appearance of noradrenergic characters does not ensure persistence and subsequent development, indicating that early phenotypic expression is a mutable process. This contention was supported by the observations that pharmacological stress of pregnant rats in the form of reserpine, or treatment with glucocorticoids, prolonged the appearance of catecholamines in the gut cells. Thus, maternal-embryonic relations in general, and maternal glucocorticoids in particular, may influence embryonic phenotypic expression. Treatment of embryos with nerve growth factor also prolonged the appearance of noradrenergic characters in the gut cells. Expression of the adrenergic phenotype was apparently regulated differently from noradrenergic expression, since phenylethanolamine-N-methyltransferase (PNMT), the adrenaline-(epinephrine)-synthesizing enzyme, was undetectable in ganglion primordia and gut cells. PNMT initially appeared at E 17.5 in cells which had migrated to be adrenal anlage. Extensive studies suggest that the initial appearance of PNMT occurs independently of glucocorticoid regulation, while subsequent development is dependent on corticoids.

Use of the herpes amplicon system as a vehicle for somatic gene transfer

The study of herpes virus biology has produced two vector delivery strategies which exploit the highly evolved neuronal tropism and life cycle regulation exhibited by this class of viruses. Amplicon and recombinant herpes simplex virus systems show promise for use in gene transfer to the nervous system and although neither vector has been used in clinical trials to date, their application to gene delivery and perturbation of neuronal physiology have been well established. We will review the properties of the herpes amplicon system, and demonstrate its utility in neuroscience applications.

Transfer of the nerve growth factor gene into cell lines and cultured neurons using a defective herpes simplex virus vector. Transfer of the NGF gene into cells by a HSV-1 vector

Nerve growth factor (NGF) can be expressed in cells by gene transfer using a defective Herpes Simplex virus type 1 (HSV-1) vector. In this report, the defective HSV-1 vector, pHSVngf, is used to infect established cell lines and cultured neurons. Infection of cell lines with pHSVngf results in gene transcription, correct RNA processing, and production of biologically active NGF. Infection of the PC12 neuronal cell line results in the production of biologically active NGF and infection of NGF-dependent neonatal sympathetic neurons in primary culture with pHSVngf leads to neuronal survival in the absence of exogenously-added NGF. NGF expressed by pHSVngf-infected cells does not appear to work through an autocrine intracellular pathway since NGF antibody added to culture media of infected cells could block NGF action. Infection with pHSVngf of cholinergic striatal or septal neurons in dissociated cell culture resulted in an increase in choline acetyltransferase activity. These studies demonstrate the efficacy of defective HSV-1 vectors for delivery and expression of neurotrophin genes in cultured neural cells.

Target determination of neurotransmitter phenotype in sympathetic neurons

While the majority of sympathetic neurons are noradrenergic, a minority population are cholinergic. At least one population of cholinergic sympathetic neurons arises during development by a target-dependent conversion from an initial noradrenergic phenotype. Evidence for retrograde specification has been obtained from transplantation studies in which sympathetic neurons that normally express a noradrenergic phenotype throughout life were induced to innervate sweat glands, a target normally innervated by cholinergic sympathetic neurons. This was accomplished by transplanting footpad skin containing sweat gland primordia from early postnatal donor rats to the hairy skin region of host rats. The sympathetic neurons innervating the novel target decreased their expression of noradrenergic traits and developed choline acetyltransferase (ChAT) activity. In addition, many sweat gland-associated fibers acquired acetylcholinesterase (AChE) staining and VIP immunoreactivity. These studies indicate that sympathetic neurons in vivo alter their neurotransmitter phenotype in response to novel environmental signals and that sweat glands play a critical role in the cholinergic and peptidergic differentiation of the sympathetic neurons that innervate them. The sweat gland-derived cholinergic differentiation factor is distinct from leukemia inhibitory factor and ciliary neurotrophic factor, two well-characterized cytokines that alter the neurotransmitter properties of cultured sympathetic neurons in a similar fashion. Recent studies indicate that anterograde signalling is also important for the establishment of functional synapses in this system. We have found that the production of cholinergic differentiation activity by sweat glands requires sympathetic innervation, and the acquisition and maintenance of secretory competence by sweat glands depends upon functional cholinergic innervation.

Expression of nerve growth factor in vivo from a defective herpes simplex virus 1 vector prevents effects of axotomy on sympathetic ganglia

Sympathetic neurons in the superior cervical ganglion (SCG) of adult rats depend on target-derived nerve growth factor (NGF) for maintenance of tyrosine hydroxylase (TH) levels and the noradrenergic neurotransmitter system. Axotomy of a SCG results in NGF deprivation, causing a decline in TH activity; continuous local application of NGF can prevent this decline in TH activity. We now report that injection of a defective herpes simplex virus 1 vector that expresses NGF (pHSVngf) into a SCG can prevent the decline in TH activity that follows axotomy. SCG of adult rats were injected with either pHSVngf virus or pNFlac virus, which expresses Escherichia coli beta-galactosidase. Analysis of RNA from pHSVngf-infected SCG indicated that the NGF gene was efficiently transcribed and processed. Furthermore, 4 days after pHSVngf injection animals underwent axotomy of the virus-injected SCG. After another 10 days, animals were sacrificed and both the injected-axotomized and contralateral control ganglia were assayed for TH activity. Axotomy of SCG injected with pNFlac virus produced a 50% decline in TH activity relative to control ganglia (P = 0.02). In contrast, SCG injected with pHSVngf virus did not show a decline in TH activity following axotomy; instead, these ganglia manifested an 18% increase in TH levels relative to control ganglia. These data demonstrate that herpes simplex virus 1 vectors can be used to modify neuronal physiology in vivo; specifically, expression of a critical gene product by neural cells that do not normally produce it has potential applications for gene therapy.

Nerve growth factor receptor immunoreactivity in the rat septohippocampal pathway: a light and electron microscope investigation

Nerve growth factor receptor immunoreactivity in the septohippocampal pathway of adult Fischer 344 rats was assessed at the light and electron microscope level. The medial septum possesses immunoreactive somata, dendrites, axons, and terminals. Immunostained somata are either bipolar or multipolar in appearance. Dendritic processes of immunoreactive septal neurons are categorized into two groups: proximal dendrites with smooth plasma membranes and distal dendrites with numerous swellings. Immunoreactive axons within the septum are long and slender and do not possess varicosities. At the electron microscope level, immunoreactivity is confined predominantly to the plasma membrane of cell bodies and dendrites of septal neurons, as well as to the plasma membrane of axons and terminals. Both immunoreactive and nonimmunoreactive terminals that contain clear, spherical vesicles are observed contacting immunoreactive dendrites and somata. Although accumulations of vesicles are evident within these terminals at sites of contact, distinct synaptic specializations are difficult to distinguish due to the localization of reaction product on the apposing plasma membranes. Axons possessing immunoreactivity are also observed in the fimbria-fornix pathway, a major source of afferent inputs to the hippocampus. Immunoreactive axons and terminals are topographically organized in the hippocampal dentate gyrus. The density of immunostained axons and terminals is highest immediately adjacent to the granular layer. In comparison, a moderate density of immunoreactive axons is found in the outer molecular layer and a weak density in the inner molecular, granular, and polymorphic layers. Immunoreactivity is found on the plasma membrane of small unmyelinated axons and terminals aggregated into clusters throughout the dentate gyrus. Definitive examples of axosomatic and axodendritic synapses possessing immunoreactivity presynaptically are not observed. Immunoreactive profiles within the medial septum and hippocampus also circumfuse a small number of intracerebral vessels. Ultrastructural examination reveals that immunoreactivity is present within a narrowed extension of the subarachnoid space and appears to be closely associated with the plasma membrane of leptomeningeal cell processes. The present study provides direct evidence for the cellular distribution of nerve growth factor receptor immunoreactivity in the medial septum and dentate gyrus in the adult rat and offers new insight into the ultrastructural localization of nerve growth factor receptor among septal cholinergic neurons and their efferent projections to the hippocampus.

Transneuronal regulation of neuronal specific gene expression in the mouse olfactory bulb

Peripheral afferent denervation (deafferentation) of the rodent main olfactory bulb produces a marked decrease in tyrosine hydroxylase (TH) activity and immunoreactivity in a population of juxtaglomerular dopaminergic neurons. Preservation of activity and immunostaining for aromatic L-amino acid decarboxylase implies that these cells do not die, but change phenotype. We now report that the steady-state level of TH mRNA markedly decreases in the adult mouse olfactory bulb in response to deafferentation. This reduction is permanent following intranasal irrigation with 0.17 M zinc sulphate (ZnSO4) but reversible following deafferentation produced by intranasal irrigation with 0.7% Triton X-100. The initial declines in TH activity, protein and mRNA of dopaminergic juxtaglomerular neurons observed after Triton X-100 treatment are all reversible as the steady-state level of TH mRNA gradually returns to control levels. Steady-state levels of mRNA for olfactory marker protein (OMP), a protein found in high concentrations in olfactory receptor neurons and their processes which innervate the olfactory bulb, were also monitored following deafferentation. Following treatment with either ZnSO4 or Triton X-100, the pattern of changes in steady-state levels of OMP mRNA was similar to that observed for TH. The steady-state level of PEP19 mRNA, a peptide previously localized to granule cells in the olfactory bulb, was not altered by deafferentation. These data indicate selective and parallel regulation of TH and OMP message and protein levels following deafferentation.

Neurotrophic molecules

Neurotrophic molecules have a profound influence on developmental events such as naturally occurring cell death, differentiation, and process outgrowth. Despite their striking effects on developing neurons, a role for these molecules in the pathogenesis or therapy of neurological disease has not yet been defined. However, a variety of recent advances promise to provide the techniques necessary to assess the potential relevance of neurotrophic molecules to clinical neurology. In this article we review recent investigations into the biological effects, regulation of production, and mechanisms of action of the best characterized trophic molecule, nerve growth factor. In addition we review studies characterizing brain-derived neurotrophic factor and other putative neurotrophic molecules. Finally, we discuss how pharmacological effects of these molecules may be relevant to the therapy of disease states as well as neural regeneration.

Influence of olfactory bulb on dendritic knob density of rat olfactory receptor neurons in vitro

The maturation of olfactory receptor cells is facilitated by the presence of their target tissue, the olfactory bulb. Organ cultures of embryonic rat olfactory mucosa (OM) maintained in the presence of the presumptive olfactory bulb (POB) had a significantly higher (1.6 X) density of ciliated dendritic knobs than those without the POB. No significant difference was found in the density of non-ciliated dendritic knobs and total knob density in these two groups of cultures. A control group of explants in which the OM and POB had been separated and recombined also showed an increased ciliated dendritic knob density. The area of the olfactory epithelium was the same whether or not the POB was present. In addition, scanning electron microscopy observations revealed a high degree of heterogeneity in the surface morphology of the olfactory epithelium.

Neurotrophic stimulation of fetal rat retinal explant neurite outgrowth and cell survival: age-dependent relationships

Serum-free tissue culture conditions have been defined where stimulation of neurite outgrowth from fetal rat retinal explants occurred only in the presence of an active fraction (BE) prepared from a pig brain extract purification procedure. Under these conditions, 18-20-day fetal retinal explants survived and continued to extend long radial neurites for at least 3 weeks in the presence of BE. However, if fibronectin was not equilibrated onto the basic collagen/poly-L-lysine substrate the neurite outgrowth was restricted to a short halo about the circumference of the explant. In addition, a dose-response relationship was demonstrated in the presence of increasing concentrations of BE with respect to the neurite growth index. The half-maximal response for BE was estimated to be between 5 and 10 micrograms/ml. In addition a number of important age-dependent relationships were observed with respect to BE stimulation of retinal neurite outgrowth and cell survival. An inverse relationship was demonstrated between increased developmental age and responsiveness to BE. After 1 week in culture, there was a 3-fold reduction in retinal neurite length measured from the 2-day neonatal explant when compared to that of the 18-day fetus. There was also a significant inverse relationship demonstrated between the length of time before BE was added to the culture medium and the ability of 20-day fetal explants to extend neurites onto the culture substrate. If BE was added as late as 2 weeks after initial explant culture, the various neurite outgrowth indices were significantly lower than in those situations where BE was added at the time of culture or 1 week later. These results imply that BE not only is required for stimulating neurite outgrowth from fetal rat retinal explants, but may be important in survival and maturation of developing retinal neurons. This hypothesis was confirmed when morphometric analysis was performed on 16- and 20-day explants cultured for a week in the presence or absence of BE. The number of necrotic cells in the developing retinal ganglion plexiform-cell layer of 20-day fetal explants was significantly lower when treated with BE. Conversely, the density of identifiable differentiating retinal ganglion-like cells was significantly greater in response to BE treatment in both 16- and 20-day retinal explants.

Hormonal regulation of adult sympathetic neurons: the effects of castration on tyrosine hydroxylase activity

The effects of the hormone testosterone on neurotransmitter synthesis in peripheral sympathetic ganglia were examined in adult male Sprague-Dawley rats. Tyrosine hydroxylase (T-OH), the rate limiting enzyme in catecholamine biosynthesis was examined in the hypogastric (HG), coeliac (CG), and superior cervical ganglion (SCG) subsequent to castration. Initial studies indicated that 2 weeks after surgery, HG T-OH activity fell to approximately 30% of control. In order to more clearly define the pattern of testosterone effects, HG was examined 1, 2 and 4 weeks after surgery. T-OH activity was 67%, 50% and 11% of control at these 3 respective time points, and the observed alteration in T-OH activity appeared to parallel changes in the size of pelvic target organs. Similar hormonal effects did not occur in other peripheral sympathetic ganglia; T-OH activity was unchanged in SCG and CG when examined 1 month after castration. Enzyme activity was restored following replacement therapy with testosterone, whereas the neural metabolite 17-beta estradiol was without effect. The recovery in T-OH activity was associated with partial recovery of target organ size. These studies suggest that hormonal factors regulate neurotransmitter synthesizing enzymes in adult sympathetic neurons and may do so via consequences of alterations in target organs. These observations parallel similar events in the developing nervous system.

Target organ regulation of substance P in sympathetic neurons in culture

Target organ regulation of the putative, peptide neurotransmitter, substance P (SP) was examined in explants and dissociated cell cultures of the neonatal rat sympathetic superior cervical ganglion (SCG). SP levels increased dramatically in explants, rising more than 30-fold after 72 hr in culture. By contrast, peptide levels did not increase in dissociated ganglion cultures. However, SP increased almost 10-fold in cell cultures grown on a monolayer of cells derived from the pineal or salivary gland, targets of the SCG. By contrast, SP content did not increase in cultures grown on a substrate of cells derived from heart or intestine. Peptide identity in the SCG-target cocultures was authenticated by means of combined high-pressure liquid chromatography (HPLC)-radioimmunoassay. Moreover, immunohistochemical examination localized the peptide virtually exclusively to sympathetic neurons and nerve processes. Mechanisms mediating the sympathetic-target interaction were examined in SCG-pineal cocultures. The increase in peptide required interactions with living tissue, since substrates of killed target cells did not elevate SP levels. The target influences were not mediated by nerve growth factor or indoleamines, potential secretory products of pineal in culture. Veratridine treatment prevented the increase in SP in the cocultures, and tetrodotoxin blocked the veratridine effect, suggesting that sodium influx and membrane depolarization prevent SP elevation. Our observations suggest that sympathetic neuron interactions with target organs influence peptidergic expression, and that this interaction may be restricted to certain appropriate target structures.

Reserpine induction of tyrosine hydroxylase in paraplegia

Reserpine induction of tyrosine hydroxylase (TH) activity reflects the biochemical adaptability of sympathetic neurons. Midthoracic spinal cord transection in adult animals precludes TH induction in the sixth lumbar (L6) ganglion, a ganglion innervated by spinal segments caudal to the lesion. However, in animals receiving lesions as neonates, an elevation in L6 ganglion TH activity occurred after reserpine. This retained biochemical adaptability indicates an increased recuperative capacity of developing neurons.

Hormonal regulation of sympathetic neuron development. The effects of neonatal castration

The effects of neonatal castration on neuronal ontogeny were examined in peripheral sympathetic ganglia in male Sprague-Dawley rats. Tyrosine hydroxylase (T-OH) activity, the rate-limiting enzyme in catecholamine biosynthesis and a marker of noradrenergic maturation, was examined in the hypogastric (HG) and superior cervical ganglion (SCG). Initial studies characterized the normal development of T-OH activity in HG ganglia. Neonatal castration at 10-11 days of age prevented the normal ontogeny of HG T-OH activity: T-OH activity failed to develop normally and was 17% of sham-operated littermate controls when examined at 8 weeks of age, and less than 5% when studied 10 weeks after surgery. In contrast to the effects in HG, there was no change in enzyme activity in the SCG. Replacement therapy with testosterone decanoate completely reversed the developmental alteration in enzyme activity. These observations suggest that hormonal factors modulate noradrenergic ontogeny in peripheral sympathetic ganglia but these effects appear restricted to ganglia whose targets include hormonally dependent sex organs.

Long-term effects of spinal transection on the development and function of sympathetic ganglia

The long-term effect of interruption of descending central pathways on the biochemical development and function of sympathetic neurons was examined in the sixth lumbar (L6) sympathetic ganglia of the rat. Previous investigations had defined the normal maturation of presynaptic choline acetyltransferase (CAT) activity, postsynaptic tyrosine hydroxylase (T-OH) activity and total protein in L6 ganglia. Neonatal spinal cord transection prevented the normal ontogeny of CAT activity: enzyme activity was 40% of control one week and one year after surgery. Similarly, T-OH activity failed to develop normally after transection and was 22% of control one year postoperatively. Spinal transection at 30 days of age did not alter baseline CAT or T-OH activities in L6 ganglia when examined up to 6 months after surgery. Apparently during the first month of life descending central pathways exert critical facilitatory influences on sympathetic ganglia maturation; interruption of these influences results in long-lasting biochemical deficits. We also examined the role of central mechanisms in adult sympathetic function. Stressful stimuli, including reserpine treatment, normally induce adult T-OH through reflex sympathetic activation. This biochemical adaptability was studied by treating rats with reserpine after spinal transection. After motor and autonomic spinal reflexes returned in paraplegic animals, reserpine treatment was initiated. Spinal animals did not exhibit T-OH induction. These observations indicate that central rather than spinal mechanisms govern this biochemical adaptability of mature sympathetic neurons.

Developmental changes of the hypogastric ganglion associated with the differentiation of the reproductive tracts in the mouse

Prenatal exposure of male or female mice to diethylstilbestrol (DES) or testosterone propionate (TP) from days 9 to 16 of gestation produces pseudohermaphrodites with dual reproductive tracts. In these animals, the hypogastric ganglion which is thought to innervate the internal genitalia was examined at birth. The number of ganglion cells was significantly larger in prenatally DES-exposed male and TP-exposed female mice than that of controls. These results suggest that the number of hypogastric ganglion cells is dependent on the number of the target organs for innervation.

Glucose utilization in sympathetic ganglia of male Fischer-344 rats at different ages

The relation of glucose utilization to age was studied with the [14C]2-deoxy-D-glucose method in 3 peripheral sympathetic ganglia of conscious male Fischer-344 rats. The hypogastric ganglion, coeliac-mesenteric ganglion complex and superior cervical ganglion were examined in 3-, 12-, 24- and 30-33-month-old animals. Glucose utilization increased significantly between 12 and 30-33 months in the superior cervical ganglion and between 3 and 24 months in the coeliac-mesenteric ganglion complex. No significant, age-related changes were observed in the hypogastric ganglion. In addition, neuron density decreased significantly between 3 and 12 months in the hypogastric ganglion and between 3 and 30-33 months in the coeliac-mesenteric ganglion complex, but no changes were observed in the superior cervical ganglion. Despite the increased glucose utilization in the superior cervical ganglion, heart rate decreased between 12 and 24 months, and mean arterial blood pressure decreased between 24 and 30-33 months. The results suggest that functional activity of some sympathetic ganglia increases in older rats, although end organ effects may be reduced.

Antiserum to a new neuronal growth factor: effects on neurite outgrowth

A new neuronal growth factor (CMF) isolated from mouse heart-cell-conditioned medium stimulates morphologic and biochemical development of mouse embryo sympathetic neurons [Coughlin et al, 1981]. Further analysis of CMF by chromatographic and electrophoretic procedures has shown that under nondissociating conditions, CMF activity is associated with very high molecular weight material. All biological activity eluted within the included volume of a Sepharose CL-2B column in a molecular weight range corresponding to approximately 5 X 10(6) daltons. Similarly, electrophoresis showed no activity and very little protein entering 3% polyacrylamide gels, whereas both protein and activity migrated through 0.6% agarose-1.2% acrylamide composite gels. To further characterize the biological effects of CMF on normal neuronal development, antibodies to CMF were employed. Rabbits immunized against CMF developed high titres of antibodies with activity specifically directed against CMF (anti-CMF). Although anti-CMF inhibited nerve growth factor (NGF)-stimulated neurite outgrowth from the neonatal superior cervical ganglion, it did not inhibit the NGF-stimulated increase in tyrosine hydroxylase activity. Moreover, ganglia incubated for 3 days in the presence of anti-CMF were subsequently capable of producing neurites when washed and cultured in medium free of antiserum. Thus, anti-CMF specifically blocked neurite extension without causing cell death or irreversible damage in ganglionic explants. Our observations suggest, therefore, that CMF or antigenically similar material is a requirement for neurite extension.

Similarities in development of substance P and somatostatin in peripheral sensory neurons: effects of capsaicin and nerve growth factor

Development of the two putative peptide neurotransmitters, substance P (SP) and somatostatin (SS), were compared in rat dorsal root ganglion (DRG) and spinal cord in vivo. The content of SS in the sixth cervical DRG increased 5-fold during the first 5 weeks of life, rising from 24 pg per ganglion at birth. SP content increased 4.5-fold during the first 5 weeks, from 56 pg per ganglion at birth. The developmental profiles for these two peptides were virtually parallel, suggesting that their respective neuronal populations developed in synchrony. Treatment with nerve growth factor (NGF) significantly increased the content of both SP and SS in the DRG and dorsal spinal cord. Conversely, treatment with capsaicin significantly decreased both SP and SS in the DRG and dorsal spinal cord. Consequently, experiments involving NGF or capsaicin treatment of sensory neurons must be interpreted with extreme care, because specificity is not limited to a single peptide phenotype. Although the mechanisms of action of NGF and capsaicin on SP and SS have not been defined, the similarity of the responses of the two peptides suggests that their development may be regulated by similar processes.

Differentiation of alpha-adrenergic responsiveness in the neonatal rat iris after decentralization or extirpation of the superior cervical ganglion

The effects of stimulating alpha-adrenergic receptors in the iris of neonatal rats (up to 30 days of age) whose superior cervical ganglion (SCG) has been decentralized or extirpated 3 days after birth were investigated by measuring changes in pupil diameter. The responses of these experimental animals were compared with those of normal animals of similar age. Alpha-adrenergic stimulation was effected by topical application of noradrenaline (NA) after blockade of beta-adrenoceptors with dichlorisoproterenol and cholinoceptors with atropine. The results reveal that although decentralization of the SCG depletes the NA content of the ipsilateral iris as demonstrated by radio-chemical assay and formaldehyde-induced fluorescence, it does not affect the development of alpha-adrenoceptor responsiveness. Even the more severe disruption of the innervation caused by extirpation of the SCG did not affect the responsiveness of the ipsilateral iris.

Pineal cells enhance choline acetyltransferase activity in sympathetic neurons

Cells derived from the neonatal rat pineal gland were cocultured with cells derived from neonatal rat superior cervical ganglia (SCG) in an attempt to determine whether a sympathetic target organ with only adrenergic properties could enhance the development of adrenergic transmitter properties in sympathetic neurons in tissue culture. Choline acetyltransferase was measured as an index of cholinergic differentiation, and tyrosine hydroxylase was measured as an index of adrenergic differentiation. As indices of total cell number and cellular volume, DNA and protein, respectively, were also measured. We found that the pineal-SCG cocultures contained ten times greater choline acetyltransferase activity than sister neuronal cultures cultured without pineal cells, thus indicating that the pineal cells enhanced cholinergic properties in the sympathetic neurons. This cholinergic enhancement was dependent upon the presence of nerve growth factor and could not be obtained with pineal-conditioned medium. Tyrosine hydroxylase activity, measured on cultures sister to those mentioned above, was low in all cultures and decreased somewhat in SCGs cultured alone. TH activity in the pineal-SCG cocultures, however, increased slightly. Some tyrosine hydroxylating activity developed in pineals cultured alone, however, and may have been responsible for the small increase in tyrosine hydroxylase activity noted in the pineal-SCG cocultures. The implications of these results for a determination of the role that target organ plays in the development of the transmitter properties of sympathetic neurons are discussed.

Regeneration and myelination in autonomic ganglia transplanted to intact brain surfaces

Fragments of superior cervical ganglia (SCG) from donor rats between newborn and three months of age were transplanted either into the fourth ventricle, onto the dorsal surface of the medulla or in contact with the area postrema of recipient rats aged 6--14 days (allografts) and 3--4 weeks (autografts). Except for the meninges, the entire brain surface and parenchyma was undisturbed. The regenerative capacity of the transplanted ganglia and its interaction with the brain surfaces was followed for post-operative periods between 1 h and six months. Both ependymal and glial cells reacted to the transplant even though there was no mechanical damage to the brain. Ependymal cells developed luminal fronds that projected into the ventricle and the subpial glia displayed a very subtle gliosis in the form of thin multi-laminated processes. Schwann cells from the transplant tended to cover the free surfaces of the brain. The transplants, often incorporated into the stroma of the choroid plexus, received an extensive vascular supply of both fenestrated and non-fenestrated vessels. In contrast to SCG in tissue culture, the perinatal explants quickly degenerated while all those from older donors, at least 3--4 weeks of age, regenerated briskly in the ambient cerebrospinal fluid. Thriving SCG neurons, which diminished in number over time, sprouted numerous neurites as early as one week; growth cones and synaptic contacts between cell processes were still evident at six months. The trasplanted mature SCG fragment underwent a redevelopment after an initial period of degeneration. It seems likely that the survival of the allografted ganglion cells depends on their acquisition of a target site in their new environment. By four to six months many axons became enclosed by myelin produced by SCG Schwann cells that normally do not form myelin in situ. Other Schwann cells appeared reactive in that they had a great increase in cytoplasmic filaments and formed gap junctions, two characteristics of C.N.S. astrocytes. It is possible that the proximity to the C.N.S. changes the character of certain Schwann cells or, alternatively, resulted in the migration of glial cells out of the brain. If the glial cells have migrated into the transplant, they may support alien neural tissue. This system in which the transplantation site is easily accessible with a minimum of trauma could lend itself to the study of some underlying mechanisms of the growth and regulation of both central and autonomic neurons and their supporting cells.

Decentralization of the superior cervical ganglion in neonates impairs the development of the innervation of the iris. A quantitative ultrastructural study

The superior cervical sympathetic ganglion was decentralized unilaterally by section of the preganglionic chain in 2- or 4-day-old rats. Twenty-one days post-operatively the dilator muscle of the iris was examined electron microscopically. Quantitative estimates demonstrated that there was a reduction both in the numbers of axon bundles and of individual axons in the iris innervated by the deafferented ganglion as compared with its fellow of the contralateral control side.

L-Glutamate decarboxylase

Much progress has been made in recent years regarding enzymological aspects of mammalian brain GAD, such as its purification and characterization, but some uncertainty still remains concerning its molecular weight and forms, and its subunit structure. The availability of antibodies to this enzyme has allowed immunocytochemical studies which have provided important information on the intrinsic organization of GABA-ergic neurones in the CNS, particularly in the cerebellum and nigrostriatal pathway. With the increased understanding of the enzymology of GAD and the distribution of central GABA-ergic neurones, it is becoming feasible to study the regulatory biochemistry of GAD in terms of control and adaptive mechanisms at the cellular level. In our own laboratory, as well as in others, initial approaches have already begun. Obviously, cellular regulation of this phenotypic enzyme is an important issue for the understanding of GABA-ergic neurones and their functions.

Enhanced sympathetic activity in young spontaneously hypertensive rats is not the trigger mechanism for genetic hypertension

In young, spontaneously hypertensive rats (SHR), a preganglionic, nerve-dependent, elevation of choline acetyltransferase (ChAc) and tyrosine hydroxylase (TH) activities was found in celiac ganglia as compared with those in young, normotensive Kyoto Wistar rats, that was not present in superior cervical ganglia, stellate ganglia and adrenal glands. The rise in both enzyme activities in the celiac ganglion disappeared in adult SHR. An elevation of plasma norepinephrine and dopamine beta-hydroxylase levels found in prehypertensive SHR, a probable indication of peripheral sympathetic activation, disappeared after the bilateral removal of the celiac ganglion. However, ganglionectomy did not change the subsequent development of hypertension. These results indicate that the faster maturation of the celiac ganglion and the end organs it innervates in yount SHR are causally related to the activation of the peripheral sympathetic nervous system. The peripheral sympathetic activation in young SHR is regarded as a warning sign but this does not trigger the development of hypertension.

Target organ regulation of sympathetic neuron development

The role of target organs in the morphological and biochemical development of sympathetic neurons was examined in the neonatal rat. The superior cervical ganglion (SCG) and its end organs, the salivary glands and iris were employed as a model system. Unilateral sialectomy and iridectomy prevented the normal developmental increase in ipsilateral ganglion tyrosine hydroxylase (T-OH) activity, a marker for adrenergic maturation. Enzyme activity remained depressed by approximately 30% for at least 6 months, the longest time tested. Ganglion morphometry was performed to investigate the basis of the abnormal biochemical ontogeny. Target organ removal significantly decreased the number of adrenergic neurons in the Scg by approximately 30%. Total ganglion volume was reduced in a parallel fashion. Thus, end organ extirpation may prevent the biochemical maturation of the SCG by decreasing adrenergic neuron survival. Sialectomy without iridectomy prevented the normal postnatal increase in ganglion T-OH activity, but did not alter iris activity. These observations suggest that target removal prevents the development of only those neurons destined to innervate that organ. In addition to preventing normal adrenergic neuron ontogeny, target extirpation also prevented the normal development of presynaptic choline acetyltransferase activity. Presynaptic ganglion terminal may have failed to mature normally secondary to adrenergic destruction, or may have responded in some other manner to target organ extirpation.