Destruction by anti-NGF of autonomic, sudomotor neurones and subsequent hyperinnervation of the foot pad by sensory fibres

Topical administration of adrenergic receptor pharmaceutics and nerve growth factor

Topical application of nerve growth factor (NGF) and adrenergic receptor pharmaceutics are currently in use for corneal ulcers and glaucoma. A recent interest in the neuroprotective abilities of NGF has led to a renewed interest in NGF as a therapeutic for retinal and choroidal diseases. NGF can promote cell proliferation through actions of the TrkA receptor or promote apoptosis through receptor p75^NTR. This understanding has led to novel interest in the role of NGF for diseases of the posterior eye. The role of β-adrenergic receptor agonists and antagonists for treatments of glaucoma, diabetic retinopathy, and their potential mechanisms of action, are still under investigation. This review discusses the current knowledge and applications of topical NGF and adrenergic receptor drugs for ocular disease.

Sensory but not parasympathetic nerves are required for ocular vascular remodeling following chronic sympathectomy in rat

Choroidal vascularity increases following chronic sympathetic denervation in rats. The mechanisms of this remodeling are unclear. Since both nitric oxide and substance P/CGRP have been suggested as angiogenic factors in other targets, we hypothesized that sensory or parasympathetic nerves may also participate in ocular vascular remodeling. To test this hypothesis, sympathetic denervation was accomplished by superior cervical ganglionectomy. Sensory denervation was induced by subcutaneous injections of capsaicin on postnatal days 2 and 9, and ocular parasympathetic innervation was ablated by pterygopalatine ganglion excision on postnatal day 60. Eyes were processed and sectioned for light microscopic histomorphometry. Sympathetic denervation for 6 weeks resulted in increased choroidal thickness, vascular luminal area, numbers of large venules and large arterioles, and capillaries in the outer nuclear layer. Capsaicin pretreatment prevented sympathectomy-induced increases in choroidal thickness, vascular luminal area and large venules and large arterioles, whereas pterygopalatine ganglionectomy was without effect. Both sensory and parasympathetic denervation attenuated increases in outer nuclear layer capillaries. These studies indicate that increased choroidal vascularity noted after chronic sympathectomy requires intact sensory innervation.

Nerve growth factor regulates human choroidal, but not retinal, endothelial cell migration and proliferation

We have previously shown that sympathetic denervation results in significant blood vessel growth of the choroid and retina. The mechanism of this growth remains unclear. Since sympathetic denervation can result in increased nerve growth factor (NGF) levels, it was the goal of this study to determine if choroidal and retinal endothelial cells in culture would respond to nerve growth factor and if nerve growth factor promote endothelial cell migration and proliferation, two components of angiogenesis. Western blotting with phospho-specific antibodies, cell migration, and cell proliferation assays were employed to determine NGF effects on both choroidal and retinal cell growth. NGF treatment produced phosphorylation of TrkA in choroidal and retinal endothelial cells. NGF stimulation resulted in activation of ERK1/2, Akt, and Src in choroidal endothelial cells, while little phosphorylation was noted following NGF treatment in retinal endothelial cells. NGF increased choroidal endothelial cell migration by 50% over control and this was inhibited by pretreatment with LY294002 (PI3K inhibitor), Akt inhibitor, and MMP2/9 inhibitor. KT5823, PD98059, and PP2 did not affect choroidal cell migration. NGF also produced a 47% increase in choroidal endothelial cell proliferation, which was blocked by PP2, LY294002, Akt inhibitor, KT5823, and PD98059. NGF stimulation did not alter retinal endothelial cell migration or proliferation. Thus, it appears that increased NGF levels that may be noted after sympathectomy are capable of producing some aspects of vascular remodeling via different signaling cascades in choroidal endothelial cells in culture.

Sympathectomies lead to transient substance P-immunoreactive sensory fibre plasticity in the rat skin

Research using animal models of neuropathic pain has revealed sympathetic sprouting onto dorsal root ganglion cells. More recently, sensory fibre sprouting onto dorsal root ganglion cells has also been observed. Previous work in our laboratory demonstrated persistent sympathetic fibre sprouting in the skin of the rat lower lip following sensory denervation of this region. Therefore, we applied immunocytochemistry to determine the effects of sympathectomies on the terminal fields of sensory fibres. The superior cervical ganglia were removed bilaterally and the effects on the innervation of the skin of the rat lower lip were observed 1, 2, 3, 4, 6 and 8 weeks post-surgery. Substance P and dopamine-beta-hydroxylase immunoreactivities were used to identify a subset of sensory and sympathetic fibres, respectively. We also assessed neurokinin-1 receptor immunoreactivity. Quantitative data was obtained with the aid of an image analysis system. In controls, the epidermis and upper dermis were innervated by substance P-immunoreactive fibres only and upper dermal blood vessels possessed the highest density of neurokinin-1 receptor immunoreactivity. Blood vessels in the lower dermis were innervated by both substance P- and dopamine-beta-hydroxylase-immunoreactive fibres. Following sympathectomies, substance P-immunoreactive fibres in the epidermis and upper dermis were more intensely labelled only 1 and 2 weeks post-surgery when compared to sham controls. The length of substance P-immunoreactive fibres in this region was also increased only on the second week. Neurokinin-1 receptor immunoreactivity in the upper dermis was slightly decreased 1 and 2 weeks post-surgery. In the lower dermis, substance P-immunoreactive fibres associated with blood vessels were more intensely labelled only 1 and 2 weeks post-surgery, and at all post-surgical time points studied, blood vessels in this region were devoid of dopamine-beta-hydroxylase-immunoreactive fibres. The length of substance P-immunoreactive fibres was increased from the first to the third week post-surgery in the lower dermis. These results indicate that sympathectomies lead to transient changes in substance P-immunoreactive fibre innervation and neurokinin-1 receptor expression in rat lower lip skin. The effects are most prominent in the lower dermis probably due to a greater local concentration of nerve growth factor in this region. The plasticity of the interactions between sensory and sympathetic fibres may prove important in the regulation of skin microcirculation and in the generation of painful sensations under normal conditions or following peripheral nerve injuries.

Molecular mechanisms regulating the retrograde axonal transport of neurotrophins

Neurotrophins are released from target tissues following neural innervation and bind to specific receptors situated on the nerve terminal plasma membrane. The neurotrophin-receptor complex undergoes retrograde axonal transport towards the cell soma, where it signals to the nucleus. This process allows neurotrophins to perform their numerous functions, which include the promotion of neuronal survival and the outgrowth of axons towards certain target tissues. The molecular events controlling each of the components of retrograde axonal transport are beginning to become defined. There is good evidence for the participation of phosphatidylinositol 3-kinase, phosphatidylinositol 4-kinase and the actin cytoskeleton in neurotrophin retrograde axonal transport in vivo. It also appears that the retrograde motor protein dynein mediates the retrograde axonal transport in vivo of neurotrophins such as nerve growth factor. This review discusses the role of the neurotrophin receptors in binding and axonal transport, the endocytic processes required for neurotrophin internalization, the targeting and trafficking of neurotrophins, and the propagation of neurotrophin-induced signals along the axon.

Classical and novel directions in neurotrophin transport and research: anterograde transport of brain-derived neurotrophic factor by sensory neurons

After the discovery of nerve growth factor, a classic model of neurotrophin action was developed. In this model, nerve endings compete for limited quantities of neurotrophic factors produced in neuronal target tissues. Neurotrophins are bound with high-affinity receptors expressed on the neuronal membrane and then endocytosed and retrogradely transported back to the cell body of responsive neurons. This classic model of target derived trophic support has been utilized to explain a wide range of trophic actions including effects on neuronal survival, terminal branching, and protein expression. However, a number of recent findings in the field of neurotrophin research cannot be explained using the classic model. In the peripheral nervous system (PNS), sensory neurons have been shown to contain mRNA for a member of the neurotrophin family, brain-derived neurotrophic factor (BDNF). Sensory neurons do not receive synaptic input so neurotrophin production by these cells does not fit into the classic target derived model. In contrast to target derived trophic support, BDNF produced by sensory neurons provides local autocrine and paracrine neurotrophic support in vitro. Furthermore, in vivo, sensory neurons transport BDNF in the anterograde direction away from the cell body, and opposite to the retrograde direction utilized in the classic model. Thus, out of necessity, a new direction for neurotrophin research has developed to study the production and anterograde transport of neurotrophins. The importance of this new mode of neurotrophin action in the PNS is indicated by results that implicate it in the response to pain, inflammation, and nerve injury.

Overexpression of nerve growth factor in epidermis disrupts the distribution and properties of sympathetic innervation in footpads

Sympathetic and sensory neurons form distinct axonal arborizations in several peripheral targets. The developmental mechanisms responsible for partitioning sympathetic and sensory axons between potential target tissues are poorly understood. We have used rodent footpads to study this process because three populations of peripheral axons innervate topographically segregated targets in the footpad; cholinergic sympathetic axons innervate sweat glands, noradrenergic sympathetic axons innervate blood vessels, and sensory axons form a plexus at the epidermal/dermal junction. To examine how nerve growth factor (NGF), a trophic and survival factor for sympathetic and some sensory neurons, may contribute to the generation of the patterned distribution of axons among targets, we studied transgenic mice (K14-NGF mice) in which NGF expression was significantly increased in the epidermis. Whereas the temporal sequence in which sensory and sympathetic fibers arrived in the footpad was not affected, the normal partitioning of axons between target tissues was disrupted. The two sympathetic targets in footpads, sweat glands, and blood vessels lacked substantial innervation and instead a dense plexus of catecholaminergic sympathetic fibers was found commingled with sensory fibers in the dermis. Those sympathetic fibers present in sweat glands expressed an abnormal dual catecholaminergic/cholinergic phenotype. Our findings indicate that overexpression of NGF in skin interferes with the segregation of sensory and sympathetic axonal arbors and suggests a role for target-derived NGF in the establishment of distinct axonal territories. Our data also suggest that by determining where axon arbors form, NGF can indirectly influence the phenotypic properties of sympathetic neurons.

CNTF and LIF are not required for the target-directed acquisition of cholinergic and peptidergic properties by sympathetic neurons in vivo

During development, the sympathetic innervation of two targets, sweat glands and periosteum, changes the neurotransmitters it expresses from noradrenaline to acetylcholine and vasoactive intestinal peptide (VIP). The target-derived molecules that induce, these changes have not been identified. Neuropoietic cytokines, including ciliary neurotrophic factor (CNTF) and leukemia inhibitory factor (LIF), induce the same phenotypic changes in sympathetic neurons in vitro as sweat glands and periosteum do in vivo, raising the possibility that one of these factors mediates induction of cholinergic traits and VIP by these target tissues. Because CNTF and LIF have overlapping functions and signalling pathways, they could act interchangeably or in concert to influence neurotransmitter expression. To determine whether CNTF or CNTF and LIF together are responsible for the induction of cholinergic and peptidergic function in vivo, we analyzed the neurotransmitter properties of sweat gland innervation in mice lacking CNTF or CNTF and LIF. We find that, as in wild-type mice, gland innervation in mice lacking one or both molecules appropriately expresses cholinergic properties and VIP immunoreactivity. Furthermore, footpads of mice lacking one or both genes contain choline acetyltransferase activity comparable to that of wild-type mice, and CNTF- or CNTF/LIF-deficient mice possess the normal complement of active sweat glands. We analyzed the innervation of a second, recently identified cholinergic sympathetic target, the periosteum, which is the connective tissue surrounding bone. Periosteal innervation of mice lacking CNTF, LIF, or both, like that of wild-type mice, is immunoreactive for the vesicular acetylcholine transporter, a recently identified cholinergic marker, and VIP. These results provide evidence that neither CNTF, LIF, nor a combination of the two are required for the developmental change from noradrenergic to cholinergic function that occurs in sympathetic innervation of sweat glands and periosteum.

Long-term sensory hyperinnervation following neonatal skin wounds

Skin innervation during wound healing was investigated using immunocytochemical staining with the panneuronal marker antiprotein gene product (PGP) 9.5, which labels the entire innervation of the skin throughout development and in the adult. Full-thickness skin wounds in the hairy skin of the foot in neonatal rats result in pronounced hyperinnervation of the tissue that persists long after the wound has healed (at least 12 weeks). Quantification of this hyperinnervation by image analysis indicates that skin innervation density in the wounded area can increase up to 300%. The effect is greatest when wounds are performed at postnatal day (P) 0 or 7, declining when performed at P14 and P21 to resemble the weaker and transient effect in the adult. Staining with selective markers for different neuronal populations innervating skin (monoclonal anti-RT97 staining the myelinated axons of large light sensory ganglion cells; anticalcitonin gene-related peptide staining unmyelinated C axons, thinly myelinated A delta axons, and a subpopulation of large A fibres) reveal that both A- and C-fibre sensory axons contribute to this response. Destruction of the majority of the C-fibre population with neonatal capsaicin pretreatment, which leaves large A fibres intact, significantly reduces the hyperinnervation response at 14 days, confirming a major contribution from both A and C fibres. Sympathetic axons, stained with anti-tyrosine hydroxylase, do not sprout into the wounded area. Furthermore, pretreatment of neonates with 6-hydroxydopamine, which destroys the sympathetic innervation, does not significantly reduce the overall sprouting response, as identified by anti-PGP9.5 staining. Behavioural sensory testing revealed a 50% drop in the mechanical threshold in the wounded area after 3 weeks. These remarkably long-term and specific effects on sensory terminal axons following neonatal skin wounding indicate the plasticity of cutaneous innervation density following alterations in the target tissue at a critical stage of development.

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.

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.

Conversion of parasympathetic nerve function from prejunctional inhibition to postjunctional excitation following sympathectomy of rat periorbital smooth muscle

Parasympathetic innervation of rat periorbital smooth muscle normally inhibits excitatory sympathetic neurotransmission but does not directly affect muscle tone. Five weeks after sympathetic denervation, however, parasympathetic stimulation now elicits contractions. These are blocked by atropine, indicating establishment of muscarinic cholinergic neuromuscular transmission. Conversion to excitation is not accompanied by enhanced smooth muscle responsiveness to muscarinic stimulation, indicating that prejunctional alterations are responsible.

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.

Sensory nerves impair sympathetic reinnervation and recovery of smooth muscle function

Neuronal populations projecting to a common target may compete for neurotrophic substances. To determine if competition impairs target reinnervation, we examined the effect of capsaicin-induced sensory denervation on sympathetic nerve ingrowth to the sympathectomized rat superior tarsal smooth muscle. In tarsal muscles with intact sympathetic innervation, capsaicin injection on Day 2 reduced numbers of perimuscular CGRP-ir sensory nerves by 68% at 3-4 months; however, it did not alter dopamine-beta-hydroxylase-ir nerve density, response to nerve stimulation, or tarsal muscle adrenoceptor-mediated contraction. Tarsal muscles denervated by ipsilateral superior cervical ganglionectomy on Postnatal Day 4 were partially reinnervated by fibers from the contralateral ganglion, as noted in previous studies. Sensory denervation by capsaicin improved sympathetic reinnervation, as evidenced by a 174% increase in numbers of DBH-ir nerves and a 62% increase in neurally mediated smooth muscle contraction evoked by electrical stimulation of the contralateral pathway relative to reinnervated muscles of vehicle-injected rats; smooth muscle function was also influenced, as indicated by a decrease toward normal in adrenoceptor sensitivity. Tarsal muscles denervated at 30 days were not reinnervated in either vehicle-injected or capsaicin-treated rats, indicating that sensory denervation does not extend the developmental window during which contralateral reinnervation can occur. Both the vehicle-injected and capsaicin-treated preparations with sustained juvenile sympathectomy showed sensory hyperinnervation as adults; thus, a chronic reduction in competition from sympathetics is a sufficiently powerful stimulus to overcome the decreased nerve density induced by neonatal capsaicin treatment. We conclude that sensory nerves limit the extent of sympathetic reinnervation and functional recovery that can occur following neonatal sympathetic denervation.

Guanethidine sympathectomy increases substance P concentration in the superior sympathetic ganglion of adult rats

Adult rats received intraperitoneal injections of guanethidine or saline for 5 weeks. Six to 8 weeks following completion of treatment, concentrations of substance P and neuropeptide Y (NPY) were measured by radioimmunoassay in the superior cervical ganglion (SCG) and thoracic spinal cord. The SCG was also immunostained for NPY and substance P. No differences were observed in thoracic spinal cord content of either NPY or substance P. We observed depletion of NPY immunoreactive neurons and NPY levels in the SCG, and pharmacologic evidence of postganglionic denervation in guanethidine-treated rats. In guanethidine-treated rats, there was a marked increase of substance P levels in the SCG, where substance P was localized in fibers, but not cell bodies. Thus, sprouting of substance P-containing sensory fibers in the sympathetic ganglia occurs following postganglionic sympathectomy in adult rats.

Developmental regulation of parasympathetic nerve density by sympathetic innervation in the tarsal smooth muscle of the rat

The developmental influence of sympathetic innervation on parasympathetic nerve density was investigated in the tarsal smooth muscle of the rat. Specificity of acetylcholinesterase staining as a marker for parasympathetic innervation was first determined by acute selective denervations. Excision of the ipsilateral superior cervical ganglion caused a 39% reduction in the density of acetylcholinesterase-positive nerves seven days later, indicating that sympathetic nerves contribute to cholinesterase-positive tarsal muscle innervation. Excision of the pterygopalatine ganglion concurrent with superior cervical ganglionectomy caused a virtually complete disappearance of acetylcholinesterase-positive innervation within seven days, indicating that non-sympathetic cholinesterase-positive fibers derive from the pterygopalatine ganglion and are presumed to be parasympathetic. Analysis of the control population indicated that parasympathetic nerve density did not vary significantly between males and females, between the superior and inferior muscles, or in rats studied at four and 12 months of age. The influence of sympathetic innervation on parasympathetic nerve density during postnatal development was examined by conducting surgical sympathectomies on postnatal day 5 and quantifying acetylcholinesterase-positive nerve density at four months of age. Neonatal sympathectomy caused a 46% reduction in cholinesterase-positive nerve density beyond that which occurred in acutely sympathectomized adult controls. It is concluded that sympathetic innervation is required for developing parasympathetic nerves to attain their normal density within the rat tarsal muscle. This finding is consistent with the idea that sympathetic nerves can exert positive effects on parasympathetic nerve outgrowth during development.

Immunohistochemical, morphological and functional changes in the peripheral sudomotor neuro-effector system in elderly people

Age-related changes in the human peripheral sudomotor neuro-effector system have been investigated in six 80-year-olds and six young adults. Histochemical and immunohistochemical studies on forearm skin biopsies showed diminished vasoactive intestinal polypeptide (VIP) and calcitonin gene related peptide (CGRP)-like immunoreactivity and a virtual absence of acetylcholinesterase in the elderly sudomotor nerve endings compared to the young. Reduced size of nerve bundles and decreased density of sympathetic nerve endings adjacent to the sweat glands of old people were shown by the neuronal marker, protein gene product (PGP 9.5), and by electron microscopy. Image analysis techniques were also used to demonstrate a marked regression in secretory coil size with age. Functional decrements accompanying the neurochemical and morphological changes in the neuro-effector system were measured in ten 80-year-olds by local quantitative nicotine axon reflex responses and compared with 12 young adults. These studies demonstrate marked regressive changes in both the nerve endings and target cells in old age and appear to express a significant loss of vigour in trophic interactions.

Increases in NPY in non-sympathetic nerve fibres supplying rat mesenteric vessels after immunosympathectomy

The effect of nerve growth factor (NGF) deprivation on developing peripheral peptide-containing nerves has been examined in Wistar rats. Animals were treated from birth for 7 days with antibodies to NGF (10 microliters/g body weight) and killed at 4 or 8 weeks of age. The nerves of the mesenteric and femoral blood vessels, vas deferns and bladder were viewed with histochemical and immunohistochemical techniques. The effectiveness of anti-NGF treatment was monitored by viewing catecholamine (CA)-containing nerves, which were virtually absent from the blood vessels, but were little affected in the vas deferens and bladder in both age groups. Immunoreactivity for substance P and calcitonin gene-related peptide was slightly reduced in the blood vessels. Immunoreactivity for neuropeptide Y (NPY) was reduced in the femoral blood vessels by 88% at both ages, but reductions in NPY immunoreactivity (NPY-IR) in the mesenteric vessels varied with age. In the mesenteric artery at 4 weeks, NPY-IR was reduced by 96% from control values, but at 8 weeks it was reduced by only 37%. Acute sympathectomy with 6-OHDA treatment reduced NPY-IR in the mesenteric artery by 98% at 4 weeks and 93% at 8 weeks. It is proposed that the increase in NPY-IR but not CA-containing nerves in the mesenteric artery between 4 and 8 weeks after immunosympathectomy is due to compensatory innervation from a non-sympathetic source (probably enteric neurons) that is available to mesenteric, but not to femoral blood vessels.

Acquisition of cholinergic and peptidergic properties by sympathetic innervation of rat sweat glands requires interaction with normal target

The sweat glands, a target of cholinergic sympathetic neurons, were replaced with parotid gland, a target of noradrenergic sympathetic neurons, in neonatal rats. This transplantation paradigm allowed sympathetic neurons that would normally innervate the sweat glands and develop a cholinergic phenotype to innervate the parotid gland instead. The innervation of the transplanted parotid gland did not develop a cholinergic phenotype, as assessed by choline acetyltransferase activity and acetylcholinesterase immunoreactivity, but continued to express intense catecholamine fluorescence. In addition, immunoreactivity for vasoactive intestinal peptide, normally expressed by the sympathetic innervation of the sweat glands but not the parotid, was observed in only a small percentage of the parotid-associated fibers. These results suggest that cellular interactions between neurons and their targets play an important role in the differentiation of mature neurotransmitter and neuropeptide phenotypes in vivo.

Target influences on transmitter choice by sympathetic neurons developing in the anterior chamber of the eye

In contrast to the majority of sympathetic neurons which are noradrenergic, the sympathetic neurons which innervate sweat glands are cholinergic. Previous studies have demonstrated that during development the sweat gland innervation initially contains catecholamines which are lost as cholinergic function appears. The neurotransmitter phenotype of sweat gland neurons further differs from the majority in that they contain vasoactive intestinal peptide (VIP) rather than neuropeptide Y (NPY). In the experiments described here, we addressed the question of whether sympathetic targets influence the neurotransmitter-related properties of the neurons which innervate them; in particular, do sweat glands play a role in reducing the expression of noradrenergic properties and inducing the expression of cholinergic properties and VIP in sympathetic neurons? This was accomplished by cotransplanting to the anterior chamber of the eye of host rats the superior cervical ganglia (SCG) which contains neurons that normally innervate targets other than the sweat glands and differentiate noradrenergically and footpad tissue from neonatal rats. Sweat glands developed in the transplanted footpad tissue and became innervated by the cotransplanted SCG neurons. The transplanted neurons and sweat gland innervation initially exhibited catecholamine histofluorescence which declined with further development in the anterior chamber. After 4 weeks, choline acetyltransferase (ChAT) and VIP immunoreactivities were evident. These observations suggest that as in the neurons which innervate the glands in situ, noradrenergic properties were suppressed and cholinergic function was induced in the neurons which innervated the glands in oculo. To distinguish a specific influence of the sweat glands on transmitter choice, SCG were also cotransplanted with the pineal gland, a normal target of the ganglion. Neurons cotransplanted with the pineal gland continued to exhibit catecholamine histofluorescence and contained NPY immunoreactivity. At least some neurons in SCG/pineal cotransplants, however, developed ChAT immunoreactivity. The target-appropriate expression of catecholamines and peptides in these experiments is consistent with the hypothesis that some transmitter properties are influenced by target tissues. The indiscriminant expression of ChAT, however, suggests that at least in oculo, additional factors can influence transmitter choice.