Functional properties of postganglionic sympathetic neurones supplying the submandibular gland in the anaesthetized rat

Responses of the Human Submandibular Artery to ACh and VIP

Endothelial vasodilatory substances may play a central role in the local regulation of vascular tone. We hypothesized that these substances can mediate endothelium-dependent vasodilatory responses to acetylcholine (ACh) and vasoactive intestinal peptide (VIP) in the human submandibular artery. We evaluated the contributions of endothelial vasodilatory substances to vessel relaxation in response to ACh and VIP, using different inhibitors of endothelial vasodilation, the nitric oxide synthase inhibitor, the cyclo-oxygenase inhibitor, indomethacin, the potassium channel blocker, and 4-aminopyridine. ACh and VIP caused an endothelium- and concentration-dependent relaxation in this artery. ACh relaxation was completely blocked after the concomitant addition of NG-nitro-L-arginine and indomethacin. The vasorelaxant effect of ACh was not influenced by 4-aminopyridine. VIP relaxation was almost completely abolished by 4-aminopyridine, and was partly inhibited by NG-nitro-L-arginine, but was not affected by indomethacin. Thus, in the human submandibular artery, ACh and VIP produced endothelium-dependent vasodilation with different underlying mechanisms: release of nitric oxide (NO) and cyclo-oxygenase products for ACh, and release of NO and endothelium-derived hyperpolarizing factor for VIP.

Baroreceptor-mediated activation of sympathetic nerve activity to salivary glands

Salivary gland function is regulated by both the sympathetic and parasympathetic nervous systems. Previously we showed that the basal sympathetic outflow to the salivary glands (SNA(SG)) was higher in hypertensive compared to normotensive rats and that diabetes reduced SNA(SG) discharge at both strains. In the present study we sought to investigate how SNA(SG) might be modulated by acute changes in the arterial pressure and whether baroreceptors play a functional role upon this modulation. To this end, we measured blood pressure and SNA(SG) discharge in Wistar-Kyoto rats (WKY-intact) and in WKY submitted to sinoaortic denervation (WKY-SAD). We made the following three major observations: (i) in WKY-intact rats, baroreceptor loading in response to intravenous infusion of the phenylephrine evoked an increase in SNA(SG) spike frequency (81%, p<0.01) accompanying the increase mean arterial pressure (ΔMAP: +77 ± 14 mmHg); (ii) baroreceptor unloading with sodium nitroprusside infusion elicited a decrease in SNA(SG) spike frequency (17%, p<0.01) in parallel with the fall in arterial blood pressure (ΔMAP: -30 ± 3 mmHg) in WKY-intact rats; iii) in the WKY-SAD rats, phenylephrine-evoked rises in the arterial pressure (ΔMAP: +56 ± 6 mmHg) failed to produce significant changes in the SNA(SG) spike frequency. Taken together, these data show that SNA(SG) increases in parallel with pharmacological-induced pressor response in a baroreceptor dependent way in anaesthetised rats. Considering the key role of SNA(SG) in salivary secretion, this mechanism, which differs from the classic cardiac baroreflex feedback loop, strongly suggests that baroreceptor signalling plays a decisive role in the regulation of salivary gland function.

SGLT1 protein expression in plasma membrane of acinar cells correlates with the sympathetic outflow to salivary glands in diabetic and hypertensive rats

Salivary gland dysfunction is a feature in diabetes and hypertension. We hypothesized that sodium-glucose cotransporter 1 (SGLT1) participates in salivary dysfunctions through a sympathetic- and protein kinase A (PKA)-mediated pathway. In Wistar-Kyoto (WKY), diabetic WKY (WKY-D), spontaneously hypertensive (SHR), and diabetic SHR (SHR-D) rats, PKA/SGLT1 proteins were analyzed in parotid and submandibular glands, and the sympathetic nerve activity (SNA) to the glands was monitored. Basal SNA was threefold higher in SHR (P < 0.001 vs. WKY), and diabetes decreased this activity (∼50%, P < 0.05) in both WKY and SHR. The catalytic subunit of PKA and the plasma membrane SGLT1 content in acinar cells were regulated in parallel to the SNA. Electrical stimulation of the sympathetic branch to salivary glands increased (∼30%, P < 0.05) PKA and SGLT1 expression. Immunohistochemical analysis confirmed the observed regulations of SGLT1, revealing its location in basolateral membrane of acinar cells. Taken together, our results show highly coordinated regulation of sympathetic activity upon PKA activity and plasma membrane SGLT1 content in salivary glands. Furthermore, the present findings show that diabetic- and/or hypertensive-induced changes in the sympathetic activity correlate with changes in SGLT1 expression in basolateral membrane of acinar cells, which can participate in the salivary glands dysfunctions reported by patients with these pathologies.

Fluorescence-based monitoring of in vivo neural activity using a circuit-tracing pseudorabies virus

The study of coordinated activity in neuronal circuits has been challenging without a method to simultaneously report activity and connectivity. Here we present the first use of pseudorabies virus (PRV), which spreads through synaptically connected neurons, to express a fluorescent calcium indicator protein and monitor neuronal activity in a living animal. Fluorescence signals were proportional to action potential number and could reliably detect single action potentials in vitro. With two-photon imaging in vivo, we observed both spontaneous and stimulated activity in neurons of infected murine peripheral autonomic submandibular ganglia (SMG). We optically recorded the SMG response in the salivary circuit to direct electrical stimulation of the presynaptic axons and to physiologically relevant sensory stimulation of the oral cavity. During a time window of 48 hours after inoculation, few spontaneous transients occurred. By 72 hours, we identified more frequent and prolonged spontaneous calcium transients, suggestive of neuronal or tissue responses to infection that influence calcium signaling. Our work establishes in vivo investigation of physiological neuronal circuit activity and subsequent effects of infection with single cell resolution.

Effects of ATP and GTP on voltage-gated K+ currents in glandular and muscular sympathetic neurons

This study assesses the effects of ATP and GTP on the kinetic properties of voltage-gated K+ currents in anatomically identified postganglionic sympathetic neurons innervating the submandibular gland and the masseter muscle in rats. Three types of K+ currents were isolated: the I(Af) steady-state inactivating at more hyperpolarized potentials, I(As) steady-state inactivating at less hyperpolarized potentials than I(Af) and the I(K) current independent of membrane potential. The kinetic properties of these currents were tested in neurons with ATP (4 mM) and GTP (0.5 mM) or without ATP and GTP in the intracellular solution. In glandular and muscular neurons in the absence of ATP and GTP in the intracellular solution, the current density of I(Af) was significantly larger (142 pA/pF and 166 pA/pF, respectively) comparing to cells with ATP and GTP (96 pA/pF and 100 pA/pF, respectively). The I(As) was larger only in glandular neurons (52 pA/pF vs. 37 pA/pF).Conversely, I(K) current density was smaller in glandular and muscular neurons without ATP and GTP (17 pA/pF and 31 pA/pF, respectively) comparing to cells with ATP and GTP (57 pA/pF and 58 pA/pF, respectively). In glandular (15.5 nA/ms vs. 6.9 nA/ms) and muscular (10.9 nA/ms vs. 7.5 nA/ms) neurons, the I(Af) activated faster in the absence of ATP and GTP. Half inactivation voltage of I(Af) in glandular (-110.0 mV vs. -119.7 mV) and muscular (-108.4 vs. -117.3 mV) neurons was shifted towards depolarization in the absence of ATP and GTP. We suggest that the kinetic properties of K+ currents in glandular and muscular sympathetic neurons change markedly in the absence of ATP and GTP in the cytoplasm. Effectiveness of steady-state inactivated currents (I(Af) and I(AS)) increased, while effectiveness of steady-state noninactivated currents decreased in the absence of ATP and GTP. The effects were more pronounced in glandular than in muscular neurons.

Suppression of inferior alveolar nerve-induced vasoconstrictor response by ongoing cervical sympathetic nerve activity in cat

We examined the effects of ongoing cervical sympathetic trunk (CST) stimulation on the vasoconstrictor responses in the lower lip elicited by electrical stimulation (ES) of the inferior alveolar nerve (IAN) or CST in anaesthetised cats to determine whether (i) the previously reported suppressive effect of ongoing CST activity on IAN-induced vasoconstriction occurs during not only ipsilateral, but also contralateral CST stimulation; and (ii) a vasoconstriction can be elicited by brief CST stimulation during ongoing stimulation of the contralateral CST. The central lower lip blood vessels are innervated by both left and right CST. The fall in central lip blood flow (LBF) elicited by IAN stimulation alone was reduced in a frequency-dependent manner during concurrent CST stimulation at 0.2-2 Hz, and at the high end of this frequency range was transformed to a rise regardless of whether the CST stimulation was ipsilateral or contralateral to the IAN stimulation. The fall in central LBF elicited by stimulation of one CST was not transformed to a rise by ongoing stimulation of the contralateral CST. Possibly, IAN-evoked orofacial vasoconstriction does not occur under physiological conditions (unlike IAN-evoked vasodilatation) because it is suppressed by the spontaneous sympathetic discharge in CST.

Postdecentralization plasticity of voltage-gated K+ currents in glandular sympathetic neurons in rats

This paper presents the kinetic and pharmacological properties of voltage-gated K(+) currents in anatomically identified glandular postganglionic sympathetic neurons isolated from the superior cervical ganglia in rats. The neurons were labelled by injecting the fluorescent tracer Fast Blue into the submandibular gland. The first group of neurons remained intact, i.e. innervated by the preganglionic axons until the day of current recordings (control neurons). The second group of neurons was denervated by severing the superior cervical trunk 4-6 weeks prior to current recordings (decentralized neurons). In every control and decentralized neuron three categories of voltage-dependent K(+) currents were found. (i) The I(Af) K(+) current, steady state, inactivated at hyperpolarized membrane potentials. This current was fast activated and fast time-dependently inactivated, insensitive to TEA and partially depressed by 4-AP. (ii) The I(As) K(+) current, which was steady-state inactivated at less hyperpolarized membrane potentials than I(Af). The current activation and time-dependent inactivation kinetics were slower than those of I(Af). I(As) was blocked by TEA and partially inhibited by 4-AP. (iii) The IK K(+) current did not undergo steady-state inactivation. In decentralized compared to control neurons the maximum I(Af) K(+) current density (at +50 mV) increased from 116.9 +/- 8.2 to 189.0 +/- 11.5 pA/pF, the 10-90% current rise time decreased from 2.3 to 0.7 ms and the recovery from inactivation was faster. Similarly, in decentralized compared to control neurons the maximum I(As) K(+) current density (at +50 mV) increased from 49.9 +/- 3.5 to 74.3 +/- 5.0 pA/pF, the 10-90% current rise time shortened from 29 to 16 ms and the recovery from inactivation of the current was also faster. The maximum density (at +50 mV) of I(K) in decentralized compared to control neurons decreased from 76.6 +/- 3.9 to 60.7 +/- 6.3 pA/pF. We suggest that the upregulation of voltage-gated time-dependently-inactivated K(+) currents and their faster recovery from inactivation serve to restrain the activity of glandular sympathetic neurons after decentralization.

Neurophysiological analysis of target-related sympathetic pathways--from animal to human: similarities and differences

The sympathetic nervous system regulates many different target tissues in the somatic and visceral domains of the body in a differentiated manner, indicating that there exist separate sympathetic pathways that are functionally defined by their target cells. Signals generated by central integration and channelled through the preganglionic neurons into the final sympathetic pathways are precisely transmitted through the para- and prevertebral ganglia and at the neuroeffector junctions to the effector cells. Neurophysiological recordings of activity in postganglionic neurons in skin and muscle nerves using microneurography in human subjects and in skin, muscle and visceral nerves, using conventional recording techniques in anaesthetized animals, clearly show that each type of sympathetic neuron exhibits a discharge pattern that is characteristic for its target cells and, therefore, its function. These findings justify labelling the neurons as muscle vasoconstrictor, cutaneous vasoconstrictor, sudomotor, lipomotor, cardiomotor, secretomotor neurons, etc. The discharge patterns monitor aspects of the central organization of the respective sympathetic system in the neuraxis and forebrain. They can be dissected into several distinct reflexes (initiated by peripheral and central afferent inputs) and reactions connected to central signals (related to respiration, circadian and other rhythms, command signals generated in the forebrain, etc). They are functional markers for the sympathetic final pathways. These neurophysiological recordings of the discharge patterns from functionally identified neurons of sympathetic pathways in the human and in animals are the ultimate reference for all experimental investigations that aim to unravel the central organization of the sympathetic systems. The similarities of the results obtained in the in vivo studies in the human and in animals justify concluding that the principles of the central organization of sympathetic systems are similar, if not identical, at least in the neuraxis, in both species. Future progress in the analysis of the central neuronal circuits that are associated with the different final sympathetic pathways will very much depend on whether we are able to align the human models and the animal models. Human models using microneurography have the advantage to work under awake conditions. The activity in the postganglionic neurons can be correlated with various other (afferent, centrally generated) signals, effector responses, perceptions, central changes monitored by imaging methods, etc. However, human models have considerable limitations. Animal models can be divided into in vivo models and various types of reduced in vitro models. Animal models allow using various methodological approaches (e.g., neurophysiological, pharmacological, modern anatomical tracing methods; behavioural animal models; transgenic animals), which cannot be used in the human. Interaction of the research performed in the human and animals will allow to design animal models that are relevant for diseases in which the sympathetic nervous systems is involved and to trace down the underlying pathophysiological mechanisms. The scientific questions to be asked are formulated on the basis of clinical observations resulting in testable hypotheses that are investigated in the in vivo human and animal models. Results obtained in the in vivo models lead to the formulation of hypotheses that are testable in reduced in vivo and particularly in vitro animal models. Microneurographic recordings from sympathetic postganglionic fibres in the human will keep its place in the analysis of the sympathetic nervous system in health and disease although only relatively few laboratories in the world will be able to keep the standards and expertise to use this approach. Experimental investigation of the organization of the sympathetic nervous system in animal models has changed dramatically in the last 15 years. The number of in vitro models and the methodological diversity have increased. In vivo experimentation on larger animals has almost disappeared and has been replaced by experimentation on rats, which became the species for practically all types of studies on the central organization of the sympathetic nervous system.

Reflex patterns in preganglionic sympathetic neurons projecting to the superior cervical ganglion in the rat

Reflex patterns in preganglionic neurons projecting in the cervical sympathetic trunk (CST) were analyzed in response to stimulation of various afferent systems. We focused on the question whether these preganglionic neurons can be classified into functionally distinct subpopulations. Reflex responses were elicited by stimulation of trigeminal and spinal nociceptive, thermoreceptive as well as baroreceptor and chemoreceptor afferents. Multi- and single fiber preparations were studied in baroreceptor intact and sino-aortically denervated animals. Spontaneous activity of 36 preganglionic single neurons ranged from 0.2 to 3.5 imp/s (median= 1.11 imp/s). The degree of cardiac rhythmicity (CR) in the activity of sympathetic neurons was 69.5+/-13% (mean+/-S.D.; N=52; range=39-95%). Noxious stimulation of acral skin activated the majority (67%) of sympathetic preparations by 37+/-25% (N=35) above pre-stimulus activity; 15% were inhibited. In these neurons the response to noxious stimulation of acral skin was significantly correlated with the degree of CR (P<0.001, N=52) in that neurons showing the strongest excitation to noxious stimulation displayed the strongest CR. Noxious mechanical stimulation of body trunk skin (N=60) inhibited the majority (80%) of fiber preparations tested (by 34+/-18% of pre-stimulus activity, N=48); an activation was not observed. Cold stimulation of acral (N=9) and body trunk skin (N=42) activated most fiber preparations. Trigeminal stimulation evoked a uniform reflex activation of preganglionic neurons (+79+/-73% of pre-stimulus activity, N=32). Chemoreceptor stimulation by systemic hypercapnia elicited inhibitory (-31+/-19%, N=8) as well as excitatory (+59+/-5%, N=4) responses. These results show that preganglionic sympathetic neurons projecting to target organs in the head exhibit distinct reflex patterns to stimulation of various afferent systems; however, a clear classification into different functional subgroups did not emerge. Furthermore, reflex patterns showed a segmental organization to noxious cutaneous stimulation of acral parts and body trunk reflecting a differential central integration of spinal afferent input. Compared with the cat the reflex organization of sympathetic neurons projecting to the head seems to be less differentiated in the anesthetized rat.

Functional roles played by the sympathetic supply to lip blood vessels in the cat

In the anesthetized cat we used laser-Doppler flowmetry to investigate the part played by cervical superior sympathetic trunk (CST) fibers in the control of blood vessels in an orofacial area (the lower lip). The blood flow increase (antidromic vasodilatation) elicited by inferior alveolar nerve (IAN) stimulation was not affected by ongoing repetitive CST stimulation over the frequency range examined (0.2-10 Hz), although reflex parasympathetic vasodilatation was attenuated. The vasoconstrictor responses elicited by IAN stimulation in some preparations were reduced in a frequency-dependent manner (at 0.2-1 Hz) during ongoing CST stimulation (and replaced by vasodilator responses). The vasoconstrictor response evoked directly by brief CST stimulation was attenuated, but not transformed to a vasodilator response, by ongoing CST stimulation. Thus in the cat lower lip 1) sympathetic stimulation attenuated one type of vasodilator response (parasympathetic-mediated vasodilatation), but not another (antidromic vasodilatation), and 2) ongoing sympathetic (CST) stimulation at low frequencies (<1 Hz) prevented further sympathetic-mediated vasoconstriction.

Hypoventilation recruits preganglionic sympathetic fibers with inspiration-related activity in the superior cervical trunk of the rat

Activity in preganglionic sympathetic neurons projecting in the cervical sympathetic trunk (CST) of rats was analysed with respect to changes in the pattern of the respiratory modulation during a long lasting hypoventilation. Under normal acid-base status (pH: 7.36+/-0.04, pCO2: 42.1+/-6.1 mm Hg, pO2: 135.8+/-43 mm Hg) a maximum of activity during expiration (expiration-related activity) was observed in all nerve recordings (n = 27). No other pattern of respiratory modulation was observed under this condition. Under a hypoventilation a dissociation between the duration of phrenic nerve activity and that of the inspiratory inhibition in neurons with expiration-related activity was observed as the inhibition was significantly prolonged by 49+/-24.9% and outlasted inspiration in 5/7 multifibers. When acid-base status was systematically changed (pH: 7.15+/-0.05, pCO2: 80.4+/-11.8 mm Hg, pO2: 62.8+/-17.5 mm Hg [n = 7]) by a hypoventilation lasting for several hours activity with a maximum peak during central inspiration (inspiration-related activity) emerged and disappeared when control conditions were reestablished. Neurons with expiration-related activity showed a cardiac rhythmicity (CR) of 62.5+/-14.6% (n = 27) and were inhibited to baroreceptor stimulation whereas neurons with inspiration-related activity showed no discernible CR (23.1+/-5.1%; n = 7) and were not inhibited to baroreceptor stimulation. Furthermore, expiration-related neurons were inhibited by 32.5+/-18.3% (n = 27) during noxious cutaneous stimulation while neurons with inspiration-related activity were activated by 21.5+/-12.1% (n = 7). These findings suggest that the respiratory modulation of preganglionic sympathetic activity in the CST consists of expiration-related activity in normal acid-base status. During hypoventilation neurons with inspiration-related activity are recruited. These neurons show reflex patterns distinct from expiration-related neurons and probably constitute a subgroup of sympathetic neurons which is activated under increased respiratory drive.

Rhythmicity in single fiber postganglionic activity supplying the rat tail

Rhythmicity in single fiber postganglionic activity supplying the rat tail. The temporal pattern of ongoing sympathetic vasoconstrictor activity may play an important role for neurovascular transmission. Here we analyzed the activity of postganglionic fibers projecting into the ventral collector nerve of anesthetized and artificially ventilated vagotomized Wistar rats with respect to the presence of rhythmic firing under normocapnic conditions. Most of the fibers studied were likely vasoconstrictor and involved in thermoregulation. Accumulated histograms of sympathetic activity were produced synchronized with the electrocardiogram to detect cardiac rhythmicity, with phrenic nerve activity to detect modulation with the central respiratory cycle, and with tracheal pressure to uncover a reflex modulation associated with artificial ventilation. Sympathetic activity, phrenic activity, and tracheal pressure also were examined by spectral analysis and autocorrelation to detect rhythmicities distinct from respiration. Twenty-seven filaments containing two to seven fibers with spontaneous activity and 51 single fibers were analyzed. Ongoing activity was 1.12 +/- 0.65 imp/s (mean +/- SD, n = 51); conduction velocity was 0.62 +/- 0.06 m/s (n = 30). Cardiac rhythmicity in sympathetic activity was weak (46.2 +/- 16.4%). The dominant rhythm in the activity of 19/27 few-fiber preparations and 37/51 single fibers corresponded to the central respiratory cycle. The pattern consisted of an inhibition during inspiration and an activation in expiration. In 10/19 few-fiber preparations and 21/37 single fibers of this group, there was also a concomitant, less prominent rhythm related to artificial ventilation. By contrast, 8/27 few-fiber preparations and 11/51 single fibers exhibited a dominant pump-related modulation, whereas phrenic-related rhythmicity was subordinate. The dominant rhythm in the activity of two single fibers was related to neither central respiration nor artificial ventilation. We conclude that the ongoing activity of most postganglionic neurons supplying the rat tail is modulated by the central respiratory rhythm generator, suggesting that changes in respiratory drive may alter perfusion of the tail and therefore heat dissipation. Reflex modulation in parallel with artificial ventilation, independent of vagal afferents and possibly due to ventilatory changes of baroreceptor activity, is also an important source of rhythmicity in these neurons.

Nervous control of blood flow in the orofacial region

The blood vessels of orofacial tissues are innervated by cranial parasympathetic, superior cervical sympathetic, and trigeminal nerves, a situation somewhat different from that seen in body skin. This review summarizes our current knowledge of the nervous control of blood flow in the orofacial region, and focuses on what we know of the respective roles of sympathetic, parasympathetic, and trigeminal sensory nerves in the regulation of blood flow in this region, with particular attention being paid to the mutual interaction between them.

Analysis of the periodicity of synaptic events in neurones in the superior cervical ganglion of anaesthetized rats

1. The patterns of on-going synaptic events recorded intracellularly in neurones of superior cervical ganglia (SCG)of anaesthetized female rats were analysed by constructing inter-event interval histograms, autocorrelograms, ln-survivor curves and histograms triggered by the arterial pulse wave and by the intercostal EMG. 2. In 11/12 cells with on-going frequencies > 0.5 Hz, one or two inputs were strong (i.e. always suprathreshold). In five cells, action potentials also arose from synaptic potentials with amplitudes close to threshold. 3. Synaptic events in 5/11 neurones tested were phase-related to the arterial pressure wave (i.e. had cardiac rhythmicity, CR). 4. Synaptic events in 9/10 neurones tested (including all with CR) were phase-related to the intercostal EMG and/or their autocorrelograms showed peaks at multiples of the respiratory interval (i.e. had respiratory rhythmicity, RR). 5. The intervals between all synaptic events were exponentially distributed in 8/12 neurones although intervals between single strong events showed peaks related to the respiratory cycle. Bursts occurred only by chance. 6. Event patterns could be simulated by combining events from several respiration-modulated inputs with their timing distributed over nearly half the cycle. From the simulations, the mean number of active preganglionic inputs was estimated to be approximately 6 with mean discharge frequency approximately 0.4 Hz. 7. We conclude that, in the spontaneously breathing anaesthetized rat, most preganglionic neurones to the SCG fire with relatively low probability in relation to the respiratory cycle. Rhythms in a postganglionic neurone reflect the activity of its suprathreshold preganglionic inputs.

Sympathetic attenuation of parasympathetic vasodilatation in oro-facial areas in the cat

1. The present study was designed to examine the interaction between sympathetic and parasympathetic influences on blood flow in oro-facial areas such as lower lip, palate and submandibular gland (SMG) and in the common carotid artery (CCA) in anaesthetized cats. 2. Section of the ipsilateral superior cervical sympathetic trunk (CST) increased the basal CCA blood flow significantly. The control level with the nerve intact was comparable with that seen at 0.5-1 Hz CST stimulation, suggesting a spontaneous discharge of around 0. 5-1 Hz in the CST fibres innervating the beds supplied by the CCA. The basal blood flow at all sites examined was reduced by CST stimulation in a frequency-dependent manner. 3. Electrical stimulation of the central end of the lingual nerve (LN) evoked blood flow increases in the lower lip and palate. These blood flow increases were markedly reduced by concurrent CST stimulation in a manner that was frequency dependent, but not simply related to the vasoconstrictor effect of CST stimulation. This effect of CST stimulation was not observed in tongue or SMG, even though CST stimulation evoked vasoconstriction in these tissues. A significant reduction in the level of CCA blood flow attained during LN stimulation was observed on repetitive CST stimulation only at 10 Hz, indicating that this response behaved in a fashion different from that seen in the lower lip, palate, tongue and SMG. 4. The present study suggests that concurrent repetitive CST stimulation reduces parasympathetically mediated blood flow increases in certain oro-facial areas (such as the lower lip and palate), but not in the tongue and SMG. This inhibitory action was not a simple additive effect (between vasoconstriction and vasodilatation) and it disappeared rapidly after the cessation of CST stimulation.

Properties of Na+ currents in putative submandibular and cardiac sympathetic postganglionic neurones

This study was performed to compare the kinetic properties of Na+ currents in putative salivary and cardiac postganglionic sympathetic neurones isolated from the superior cervical and stellate ganglia, respectively. Neurones were labelled with a fluorescent tracer-Fast Blue, injected into the submandibular gland (in the case of salivary neurones) and into the pericardial cavity or left ventricular wall (in the case of cardiac neurones). Voltage-dependent Na+ current was then isolated and recorded from labelled cells. The major findings of this study were: (1) Peak Na+ current was larger in salivary than in cardiac neurones (5.7 nA vs. 2.4 nA; for 30 mM Na+ in extra- and 15 mM in the intracellular solution). (2) The somata of salivary neurones were twice as large as those of cardiac neurones, as indicated by the values of their membrane capacitance (36 pF vs. 18 pF). (3) There was a greater Na+ current density (169 pA/pF vs. 128 pA/pF) in salivary than in cardiac neurones. (4) Recovery from inactivation was faster in salivary neurones with 90% recovery time being 93 ms for salivary and 144 ms in cardiac neurones. (5) Half-activation times were voltage-dependent and consistently longer for salivary than for cardiac neurones. (6) Remaining parameters, such as current threshold, maximum current voltage and kinetics of steady-state inactivation did not significantly differ in salivary compared to cardiac neurones.

On-going and reflex synaptic events in rat superior cervical ganglion cells

1. Synaptic events evoked by brief noxious cutaneous stimuli were recorded in sympathetic neurones in the superior cervical ganglion of anaesthetized rats. 2. On-going excitatory synaptic potentials (ESPs) and/or action potentials (APs) were recorded in 69% of neurones at mean frequencies that varied from 0.01 to 6.3 Hz in different cells. From histograms of ESP amplitude during membrane hyperpolarization, it appears that most cells received one (52%), or two or more (36%), suprathreshold inputs and several subthreshold inputs with overlapping amplitudes. 3. Pinching the skin for 1-3 s evoked either a brief burst of synaptic events (lasting about 300 ms) preceding a few seconds of inhibition (burst-inhibitory (BI) neurones), or simply an excitation (excitatory (E) neurones), or no response (O neurones). In 60% of BI neurones, a second burst occurred after the end of the pinch. 4. BI neurones had a higher frequency of on-going synaptic activity (2.9 +/- 0.5 Hz, n = 15) than E neurones (0.2 +/- 0.1 Hz, n = 5) or O (0.2 +/- 0.1 Hz, n = 5) neurones. Most neurones with two or more suprathreshold inputs were BI neurones. In 20% of neurones (all BI with high rates of synaptic activity), several other inputs had ESPs with amplitudes close to threshold. 5. Subthreshold and suprathreshold inputs responded in the same way in only 45% of neurones, but suprathreshold inputs were excited in 73% of BI and all E neurones. The order of recruitment of different inputs varied from trial to trial. If classification was based only on suprathreshold responses, there were 36% BI, 32% E and 32% O neurones. 6. In the majority of neurones, postganglionic discharge was initiated exclusively by suprathreshold inputs, even during reflex excitation. 7. Qualitatively similar, but smaller, responses were evoked by a puff of air on the abdomen in 71% of cells tested. 8. The data suggest that the natural discharge of SCG neurones is largely determined by the activity of one or two preganglionic inputs with high quantal contents. BI neurones may include vasoconstrictor neurones, whereas the other types include secretomotor, pilomotor and other neurones projecting to targets in the head.