Postganglionic sympathetic neurons, but not locus coeruleus optostimulation, activates neuromuscular transmission in the adult mouse in vivo.

Recent work demonstrated that sympathetic neurons innervate the skeletal muscle near the neuromuscular junction (NMJ), and muscle sympathectomy and sympathomimetic agents strongly influence motoneuron synaptic vesicle release ex vivo. Moreover, reports attest that the pontine nucleus locus coeruleus (LC) projects to preganglionic sympathetic neurons and regulates human mobility and skeletal muscle physiology. Thus, we hypothesized that peripheral and central sympathetic neurons projecting directly or indirectly to the skeletal muscle regulate NMJ transmission. The aim of this study was to define the specific neuronal groups in the peripheral and central nervous systems that account for such regulation in adult mice in vivo by using optogenetics and NMJ transmission recordings in 3-5-month-old, male and female ChR2(H134R/EYFP)/TH-Cre mice. After detecting ChR2(H134R)/EYFP fluorescence in the paravertebral ganglia and LC neurons, we tested whether optostimulating the plantar nerve near the lumbricalis muscle or LC neurons effectively modulates motor nerve terminal synaptic vesicle release in living mice. Nerve optostimulation increased motor synaptic vesicle release in vitro and in vivo, while the presynaptic adrenoceptor blockers propranolol (ß1/ß2) and atenolol (ß1) prevented this outcome. The effect is primarily presynaptic since miniature end-plate potential (MEPP) kinetics remained statistically unmodified after stimulation. In contrast, optostimulation of LC neurons did not regulate NMJ transmission. In summary, we conclude that postganglionic sympathetic neurons, but not LC neurons, increased NMJ transmission by acting on presynaptic ß1-adrenergic receptors in vivo.

Human epicardium-derived cells reinforce cardiac sympathetic innervation.

RATIONALE: After cardiac damage, excessive neurite outgrowth (sympathetic hyperinnervation) can occur, which is related to ventricular arrhythmias/sudden cardiac death. Post-damage reactivation of epicardium causes epicardium-derived cells (EPDCs) to acquire a mesenchymal character, contributing to cardiac regeneration. Whether EPDCs also contribute to cardiac re/hyperinnervation, is unknown. AIM: To investigate whether mesenchymal EPDCs influence cardiac sympathetic innervation. METHODS AND RESULTS: Sympathetic ganglia were co-cultured with mesenchymal EPDCs and/or myocardium, and neurite outgrowth and sprouting density were assessed. Results showed a significant increase in neurite density and directional (i.e. towards myocardium) outgrowth when ganglia were co-cultured with a combination of EPDCs and myocardium, as compared to cultures with EPDCs or myocardium alone. In absence of myocardium, this outgrowth was not directional. Neurite differentiation of PC12 cells in conditioned medium confirmed these results via a paracrine effect, in accordance with expression of neurotrophic factors in myocardial explants co-cultured with EPDCs. Of interest, EPDCs increased the expression of nerve growth factor (NGF) in cultured, but not in fresh myocardium, possibly due to an "ischemic state" of cultured myocardium, supported by TUNEL and Hif1α expression. Cardiac tissues after myocardial infarction showed robust NGF expression in the infarcted, but not remote area. CONCLUSION: Neurite outgrowth and density increases significantly in the presence of EPDCs by a paracrine effect, indicating a new role for EPDCs in the occurrence of sympathetic re/hyperinnervation after cardiac damage.

The actions of hyperthermia on the autonomic nervous system: central and peripheral mechanisms and clinical implications.

Hyperthermia is defined as an elevated body temperature due to failed thermoregulation. It can occur under physiological conditions such as intense exercise or due to pathology such as malignant hyperthermia and heat stroke. It has also been implicated as a cause for sudden infant death syndrome. High temperatures are also used in medical interventions - hyperthermic chemotherapy or radiofrequency ablation, for example, which have serious side effects. The effect of hyperthermia on the central nervous system has not been fully researched, but even less is known on the effects of hyperthermia on the peripheral autonomic nervous system. In this review we discuss how conditions such as malignant or therapeutic hyperthermia affect the central and peripheral components of the autonomic nervous system, smooth muscle, skeletal muscle and cardiac muscle. We conclude that there is sufficient evidence for the detrimental effect of hyperthermia on central nerves, and that these effects are long lasting, although the major mechanism for this remains unknown. Similarly, the direct damage of hyperthermia to the enteric nerves also seems to be long lasting. In contrast, the reduced contractility of cardiac muscle and gastrointestinal smooth muscle when exposed to hyperthermia is short-lived. The consensus is that inadequate calcium handling is the mechanism of heat damage to cardiac and skeletal muscle. There is no such consensus when dealing with smooth muscle. The mechanism of hyperthermic damage to autonomic end organs such as the gastrointestinal tract has yet to be elucidated and further research into both central and peripheral hyperthermia is necessary.

Role of adenosine A2A receptor signaling in the nicotine-evoked attenuation of reflex cardiac sympathetic control.

Baroreflex dysfunction contributes to increased cardiovascular risk in cigarette smokers. Given the importance of adenosinergic pathways in baroreflex control, the hypothesis was tested that defective central adenosinergic modulation of cardiac autonomic activity mediates the nicotine-baroreflex interaction. Baroreflex curves relating changes in heart rate (HR) to increases or decreases in blood pressure (BP) evoked by i.v. doses (1-16µg/kg) of phenylephrine (PE) and sodium nitroprusside (SNP), respectively, were constructed in conscious rats; slopes of the curves were taken as measures of baroreflex sensitivity (BRS). Nicotine (25 and 100µg/kg i.v.) dose-dependently reduced BRS(SNP) in contrast to no effect on BRS(PE). BRS(SNP) was also attenuated after intracisternal (i.c.) administration of nicotine. Similar reductions in BRS(SNP) were observed in rats pretreated with atropine or propranolol. The combined treatment with nicotine and atropine produced additive inhibitory effects on BRS, an effect that was not demonstrated upon concurrent exposure to nicotine and propranolol. BRS(SNP) was reduced in preparations treated with i.c. 8-phenyltheophylline (8-PT, nonselective adenosine receptor antagonist), 8-(3-Chlorostyryl) caffeine (CSC, A(2A) antagonist), or VUF5574 (A(3) antagonist). In contrast, BRS(SNP) was preserved after blockade of A(1) (DPCPX) or A(2B) (alloxazine) receptors or inhibition of adenosine uptake by dipyridamole. CSC or 8-PT abrogated the BRS(SNP) depressant effect of nicotine whereas other adenosinergic antagonists were without effect. Together, nicotine preferentially impairs reflex tachycardia via disruption of adenosine A(2A) receptor-mediated facilitation of reflex cardiac sympathoexcitation. Clinically, the attenuation by nicotine of compensatory sympathoexcitation may be detrimental in conditions such as hypothalamic defense response, posture changes, and ventricular rhythms.

The melanocortin system is involved in regulating autonomic nerve activity through central pituitary adenylate cyclase-activating polypeptide.

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a peptidergic neurotransmitter that is highly expressed in the nervous system. We have previously reported that a central injection of PACAP leads to changes in the autonomic nervous system tones including sympathetic excitation and parasympathetic inhibition. An anatomical study revealed that melanocortin and PACAP are colocalized in some hypothalamic nuclei. Here, we investigated the possible role of the melanocortin system in autonomic control by PACAP using SHU9119, an antagonist of the melanocortin receptors (MC3-R/MC4-R). Pretreatment with SHU-9119 did not affect the activating neural responses of adrenal, renal, and lumbar sympathetic nerves following a PACAP injection However, SHU9119 significantly eliminated the suppressing effect of a PACAP injection on gastric vagal nerve activity and excitation effects on liver and brown adipose tissue sympathetic nerve activities. These results suggest that the brain melanocortin system might play a key role in the control of thermogenic sympathetic outflows and digestive parasympathetic outflow by PACAP, but this system does not participate in the central effects of PACAP on cardiovascular function and neural activities of renal, adrenal, and lumbar sympathetic nerves.

Mechanisms of adaptive supersensitivity in vas deferens.

Adaptive supersensitivity is a phenomenon characteristic of excitable tissues and discloses as a compensatory adjustment of tissue's response to unrelated stimulatory endogenous and exogenous substances after chronic interruption of excitatory neurotransmission. The mechanisms underlying such higher postjunctional sensitivity have been postulated for a variety of cell types. In smooth muscles, especially the vas deferens with its rich sympathetic innervation, the mechanisms responsible for supersensitivity are partly understood and appear to be different from one species to another. The present review provides a general understanding of adaptive supersensitivity and emphasizes early and recent information about the putative mechanisms involved in this phenomenon in rodent vas deferens.

Melatonin and the immune system in aging.

Aging is associated with a decline in immune function (immunosenescence), a condition known to correlate with increased incidence of cancer as well as infectious and degenerative diseases. Innate, cellular and humoral immunity all exhibit increased deterioration with age. Circulating melatonin decreases with age, and in recent years much interest has been focused on its immunomodulatory effect. Melatonin stimulates the production of progenitor cells for granulocytes and macrophages. It also stimulates the production of natural killer cells and CD4+ cells and inhibits CD8+ cells. The production and release of various cytokines from natural killer cells and T helper lymphocytes are enhanced by melatonin. Melatonin has the potential therapeutic value to enhance immune function in aged individuals.

Sympathicotomy affects cutaneous blood flow, temperature, and sympathicus-mediated reflexes.

OBJECTIVE: To study the sympathetically mediated effects of transthoracic endoscopic sympathicotomy (TES) in the treatment of severe primary palmar hyperhidrosis. MATERIALS AND METHODS: The effects of TES, on sympathetic ganglia at the thoracic level of 2-3, finger blood flow, temperature, and on heat and cold provocation were investigated. Middle cerebral artery (MCA) blood flow velocities were studied by transcranial Doppler. RESULTS: The finger blood flow increased by about 700% after TES and finger temperature by 7.0 +/- 0.5 degrees C. Several autonomic reflexes were dramatically affected. A finger pulp-shrinking test showed a major decrease after surgery. MCA mean blood flow velocities were not affected by TES. CONCLUSIONS: Besides the high success rate of good clinical effect of TES on palmar hyperhidrosis, major effects on local blood flow and temperature are elicited by TES. Complex autonomic reflexes are also affected. The patient should be completely informed before surgery of the side effects elicited by TES.

Olfactory stimulation with scent of grapefruit oil affects autonomic nerves, lipolysis and appetite in rats.

In a previous study, we found that olfactory stimulation with scent of grapefruit oil (SGFO) excites the sympathetic nerve innervating the white adipose tissue in rats. Here we further examined the effects of SGFO in rats and observed that olfactory stimulation with SGFO excited the sympathetic nerves innervating the brown adipose tissue and adrenal gland and inhibited the parasympathetic gastric nerve. Local anesthesia of the nasal mucosa with xylocaine or anosmic treatment using ZnSO4 eliminated the autonomic changes caused by SGFO. Moreover, stimulation with SGFO elevated the plasma glycerol level, and treatment with either ZnSO4 or an intraperitoneal injection of diphenhydramine, a histamine H1 receptor-antagonist, abolished the glycerol elevation by SGFO. Furthermore, a 15-min exposure to SGFO three times a week reduced food intake and body weight. Finally, limonene, a component of grapefruit oil, induced responses similar to those caused by SGFO, and diphenhydramine eliminated the glycerol response to limonene. Thus, the scent of grapefruit oil, and particularly its primary component limonene, affects autonomic nerves, enhances lipolysis through a histaminergic response, and reduces appetite and body weight.

IL-1 alpha and TNF-alpha expression in rat periapical lesions and dental pulp after unilateral sympathectomy.

OBJECTIVES: Apical periodontitis is an inflammatory disease characterized by bone resorption, and sympathetic nerves are known to modulate bone resorption and bone remodeling. Higher numbers of osteoclasts and larger periapical lesions have been observed after sympathectomy in rats, but the mechanisms underlying the inhibitory effect of sympathetic nerves on osteoclasts are unknown. This study aimed to test the hypothesis that sympathetic nerves inhibit the production of the bone-resorbing pro-inflammatory cytokines IL-1 alpha and TNF-alpha in rat periapical lesions. METHODS: Rats were unilaterally sympathectomized and apical lesions were induced by exposing the dental pulp of molar teeth to the oral microflora. We quantified the cytokines IL-1 alpha and TNF-alpha by enzyme-linked immunosorbent assay, and immunohistochemical analysis was done for qualitative localization. Pulp from intact incisor teeth was tested as a control. RESULTS: We showed that IL-1 alpha was increased, but not TNF-alpha, in the periapical lesions on the sympathectomized side. Both IL-1 alpha and TNF-alpha were expressed in unexposed pulp. TNF-alpha was significantly decreased in the denervated incisor pulp, whereas the level of IL-1 alpha remained unchanged. CONCLUSIONS: This study suggests that sympathetic nerves have an inhibitory effect on IL-1 alpha in periapical lesions and a stimulatory effect on TNF-alpha in the intact rat pulp.

Increased O2*- production and upregulation of ETB receptors by sympathetic neurons in DOCA-salt hypertensive rats.

Superoxide anion (O2*-) production is elevated in the vasculature of hypertensive animals but it is not known if O2*- production is also elevated in the sympathetic nervous system. We measured O2*- levels in prevertebral sympathetic ganglia of deoxycorticosterone acetate (DOCA)-salt hypertensive rats using the dihydroethidine (DHE) fluorescence method. O2*- was elevated in ganglia from DOCA-salt rats compared with normotensive sham rats. Treatment of ganglia with endothelin (ET)-1 (3x10(-8) mol/L) resulted in a 200% increase in fluorescence intensity in neurons, which was attenuated by the ET(B) receptor antagonist BQ788 (10(-7) mol/L). ET-1 also increased the O2*- induced fluorescence in dissociated sympathetic neurons and PC-12 cells via activation of ET(B) receptors, but not ET(A) receptors. To evaluate whether elevated ET-1 levels in the ganglia might contribute to the elevated O2*- found in ganglia we measured the amount of ET-1 using an ELISA assay. ET-1 levels in sham rat celiac ganglia were 695.6+/-40.9 picogram per gram; they were not different than ET-1 levels in ganglia from DOCA-salt rats. We then compared ET(B) receptor levels in ganglia from sham and DOCA-salt animals. ET(B) receptor mRNA levels were 32% higher and ET(B) receptor protein levels were 20% higher in celiac ganglia from DOCA-salt rats than from sham rats separately. In conclusion, O2*- is elevated in prevertebral sympathetic ganglia in DOCA-salt hypertension, and ET-1 is a potent stimulus for the elevation of O2*- levels in sympathetic ganglia, an effect that may be mediated by the upregulation of ET(B) receptors.

Kinetic properties of voltage-gated Na+ currents in rat muscular sympathetic neurons with and without adenosine triphosphate and guanosine triphosphate in intracellular solution.

Voltage-gated Na+ currents were recorded from anatomically identified postganglionic muscular sympathetic neurons without and with ATP and GTP in the intracellular solution. The main findings of the study were that cells without ATP and GTP in the intracellular solution express a higher amplitude and greater density of voltage-gated Na+ current, and their Na+ current activates faster and also inactivates faster time dependently. The current is also steady-state inactivated to a lesser degree and recovers from inactivation more slowly in cells without added ATP and GTP. These findings suggest that the presence of ATP and GTP, substrates for channel phosphorylation, changes the kinetic properties of Na+ currents.

Splenic denervation suppresses mRNA gene expression and protein production of IL-1beta and IL-6 by peritoneal macrophages in both Trypanosoma brucei brucei-infected and non-infected rats.

OBJECTIVE: To test the hypothesis that the nervous system participates in modulating the immune response during experimental African trypanosomiasis caused by Trypanosoma brucei brucei. METHODS AND RESULTS: Using in situ hybridization and immunochemistry, we studied the effects of splenic sympathectomy on mRNA gene expression and protein production of IL-1beta and IL-6 in splenic and peritoneal macrophages (PMPhi) of Sprague-Dawley rats infected with T. brucei brucei and non-infected rats. The enhancements of mRNA gene expression and production of IL-1beta and IL-6 by peritoneal macrophages were significantly suppressed by the splenic sympathectomy in both infected and non-infected rats. CONCLUSIONS: Our data indicate a probably stimulatory role of the sympathetic nervous system during the host immune response in both normal and T. brucei brucei-infected rats.

Intrinsic choroidal neurons in the human eye: projections, targets, and basic electrophysiological data.

PURPOSE: The chemical coding of intrinsic choroidal neurons (ICNs) has features in common with extrinsic fibers (e.g., from the pterygopalatine ganglion) making it impossible to assess whether a neuronal nitric oxide synthase (nNOS)/vasoactive intestinal polypeptide (VIP)-immunoreactive nerve fiber is of intrinsic or extrinsic origin. Neurobiotin injections into single neurons allow the visualization of projections of these cells and the determination of the origin of target innervation. Thus, this technique was used in the present study to help characterize the organization of the ICN in the human eye. METHODS: ICNs were visualized with the fluorescent vital dye 4-Di-2-ASP. Electrophysiological properties were determined by means of intracellular recordings. The impaled neurons were iontophoretically filled with neurobiotin. After fixation, immunohistochemistry for neuronal nitric oxide synthase (nNOS), alpha-smooth muscle actin, and calcitonin gene-related peptide (CGRP) was conducted. RESULTS: ICN processes were traced over distances of up to 2.612 micro m. They were found in the immediate vicinity of other nNOS-positive or -negative ICNs and were also found apposed to smooth muscle fibers (vascular and stromal nonvascular). CGRP-positive fibers forming boutons were observed closely associated with ICNs. Electrophysiological recording showed phasic firing without slow afterhyperpolarization, no spontaneous activity, an input resistance of 136 +/-73 MOmega, and a membrane time constant of 7 +/- 1 ms. CONCLUSIONS: Apart from the first functional characterization of ICNs, this study provided more precise evidence of reciprocal ICN-to-ICN contacts and innervation of both choroidal nonvascular and vascular smooth muscle. The presented technique offers promising perspectives to further investigate the function of ICNs in ocular homeostasis.

Cardiac nociception in rats: neuronal pathways and the influence of dermal neurostimulation on conveyance to the central nervous system.

Neurostimulation for refractory angina pectoris is often advocated for its clinical efficacy. However, the recruited pathways to induce electroanalgesia are partially unknown. Therefore, we sought to study the effect of neurostimulation on experimentally induced cardiac nociception, using capsaicin as nociception-induced substance. Four different groups of male Wistar rats were pericardially infused with either saline or capsaicin with or without neurostimulation. Group StimCap was infused with capsaicin, and group StimVeh was infused with saline. Both groups were treated with neurostimulation. Group ShamCap was only infused with capsaicin without stimulation, whereas group ShamVeh was only infused with saline. Neuronal activation differences were assessed with cytochemical staining, revealing the cellular expression of c-fos. Pain behavior was registered on video and was quantitatively analyzed. In the StimCap and ShamCap groups, all animals exerted typical pain behavior, whereas in the StimVeh group only moderate changes in behavior were observed. Group ShamVeh animals were unaffected by the procedure. The upper thoracic spinal cord showed high numbers of c-fos-positive cells, predominantly in laminae III and IV in both StimCap and StimVeh groups. Almost no c-fos expression was noticed in groups ShamCap and ShamVeh in these sections of the spinal cord. In groups StimCap and ShamCap a significantly higher number of c-fos-positive cells in comparison with groups StimVeh and ShamVeh were noticed in the periambigus region, the nucleus tractus solitarius, and the paraventricular hypothalamus. In the paraventricular thalamus, periaqueductal gray, and central amygdala, no significant differences were noticed among the first three groups, and the c-fos concentration in these three groups was significantly higher than in group ShamVeh. It is concluded that neurostimulation does not influence capsaicin-induced cardiac nociceptive pain pulses to the central nervous system. Furthermore, capsaicin-induced cardiac pain and neurostimulation may utilize two different pathways.

Syncopal attack alters the burst properties of muscle sympathetic nerve activity in humans.

This study aimed at examining whether the properties of microneurographically recorded muscle sympathetic nerve activity (MSNA) were altered during hypotensive attacks. A retrospective study was performed on 74 subjects who participated in tilt studies when vasodepressive syncope was induced incidentally in six subjects. The specific features of MSNA that distinguish this activity from skin sympathetic nerve activity are (1) rhythmic pulse synchronous burst discharge, (2) a duration of approximately 150-300 ms, and (3) no response to arousal stimuli were abolished during the syncopal attack. The altered features observed during the syncopal attack in these six subjects were (1) scattered reflex latencies of MSNA peak from the ECG R-wave, (2) elongated burst duration twice to five times as long as that in conscious state, and (3) response to arousal stimuli. The reduced input from the baroreceptors due to suppression on the central sympathetic volley proximal to the nucleus tractus solitarius might be attributed to the lost features characteristic of MSNA.

Transdermal estrogen replacement therapy decreases sympathetic activity in postmenopausal women.

BACKGROUND: Menopause heralds a dramatic increase in incident hypertension, suggesting a protective effect of estrogen on blood pressure (BP). In female rats, estrogen has been shown to decrease sympathetic nerve discharge (SND) and BP. SND, however, has not been recorded during estrogen replacement therapy (ERT) in humans. Methods and Results-In 12 normotensive postmenopausal women, we conducted a randomized crossover placebo-controlled study to test whether chronic ERT caused a sustained decrease in SND and BP. Twenty-four-hour ambulatory BP, SND, and arterial baroreflex sensitivity were measured before and after 8 weeks of transdermal estradiol (200 microgram/d), oral conjugated estrogens (0.625 mg/d), or placebo. To test the acute effects of estrogen on SND, additional studies were performed in the same women receiving intravenous conjugated estrogens or sublingual estradiol. After 8 weeks of transdermal ERT, the basal rate of SND decreased by 30% (from 40+/-4 to 27+/-4 bursts per minute, P=0.0001) and ambulatory diastolic BP fell by 5+/-2 mm Hg (P=0.0003). In contrast, SND and BP were unaffected either by 8 weeks of oral ERT or by acute estrogen administration. Neither transdermal nor oral ERT had any effects on baroreflex sensitivity. CONCLUSIONS: In normotensive postmenopausal women, chronic transdermal ERT decreases SND without augmenting arterial baroreflexes and causes a small but statistically significant decrease in ambulatory BP. Sympathetic inhibition is evident only with chronic rather than acute estrogen administration, implying a genomic mechanism of action. Because the effects of transdermal ERT are larger than those of oral ERT, the route of administration may be an important consideration in optimizing the beneficial effects of ERT on BP and overall cardiovascular health.

Differential regulation of the oscillations in sympathetic nerve activity and renal blood flow following volume expansion.

Renal sympathetic nerve activity (RSNA) and renal blood flow (RBF) both show oscillations at various frequencies but the functional significance and regulation of these oscillations is not well understood. To establish whether the strength of these oscillations is under differential control we measured the frequency spectrum of RSNA and RBF following volume expansion in conscious rabbits. Seven days prior to experiment animals underwent surgery to implant an electrode for recording renal nerve activity and a flow probe for recording RBF. Volume expansion (Haemaccel, 1.5 ml min(-1) kg(-1) for 15 min) resulted in a 25 +/- 5% decrease in mean RSNA, paralleled by an increase in RBF to 60 +/- 12 ml min(-1) from resting levels of 51 +/- 11 ml min(-1). Renal denervated rabbits did not show an increase in RBF with volume expansion. Arterial baroreflexes were unaltered by volume expansion. Spectral analysis of the different frequencies in RSNA showed oscillations in RSNA between 0.2 and 0.4 Hz were selectively decreased following volume expansion (14 +/- 3 to 6 +/- 1% of total power in RSNA at < 3 Hz). A corresponding decrease in the strength of oscillations in RBF at this frequency was also seen (20 +/- 6 to 8 +/- 2%). In contrast, the strength of respiratory (0.8-2.0 Hz) and cardiac (3-6 Hz) related rhythms did not change with volume expansion. These results show that selective changes in the different frequency components of RSNA can occur. We suggest that input from cardiopulmonary receptors and/or other vascular beds, and/or altered vascular resistance after volume expansion can reduce the strength of the 0.3 Hz oscillation independent of changes in arterial baroreflex control of RSNA.

Evaluation of direct and axon reflex sweating in the mouse.

The nicotinic axon reflex-mediated sudomotor response was studied in mice and rats by recording the impressions of sweat droplets made in silicone molds after local injection of nicotine, and compared with sweating induced by acetylcholine and pilocarpine. Nicotine failed to activate mouse plantar sweat glands at any of the concentrations used (from 3 x 10(-6) to 3 x 10(-1) M). On the contrary, both acetylcholine and pilocarpine produced a dose-dependent increase in the number of secreting sweat glands. The location of sweat glands reactive to pilocarpine and acetylcholine was similar and restricted to the pads near the site of injection. We conclude that the sudomotor axon reflex response mediated by nicotinic receptors is not present in the mouse and the rat.

Calcium transients evoked by action potentials in the somata of chick ciliary neurons.

The effect of action potentials on the calcium concentration in the somata of chick ciliary neurons ([Ca2+]s) was determined by loading these with the calcium indicator calcium green-1. Following trains of 1-10 impulses (30 Hz) to the postganglionic nerve, the [Ca2+]s increased rapidly and then declined along a single exponential with a time constant of 0.70 +/- 0.04 s (fast phase). After trains of 20 or 50 impulses, the elevated [Ca2+]s declined as the sum of two exponentials, with time constants of 0.78 +/- 0.12 s (fast phase) and 4.0 +/- 0.4 s (moderate phase). After a 600-impulse postganglionic train of impulses, the elevated [Ca2+]s declined quickly over about 1 s, and then as the sum of two exponentials: that of the moderate phase and a slower component with a time constant of 109 +/- 16 s (slow phase). Similar time courses were observed following stimuli to the preganglionic nerve. Caffeine (3 mM) and ryanodine (20 microM) both sped the fast phase and slowed the moderate phase of [Ca2+]s decline. Carbonyl cyanide m-chlorophenyl hydrazone (CCCP, 2 microM) slowed the slow phase, without affecting the other phases of decline. These results are discussed in relation to identifying the mechanisms responsible for these different phases of Ca2+ removal.