Rat Sympathetic Preganglionic Neurons Research Articles

Potentiation of NMDA-Mediated Responses by Amyloid-β Peptide 1-40 in Rat Sympathetic Preganglionic Neurons.

The abnormal accumulation of amyloid-β peptides (Aβ) is one of the main characteristics of Alzheimer's disease (AD). Cerebro- and cardiovascular diseases may be the risk factors for developing AD. The effect of Aβ on central sympathetic control of cardiovascular function remains unclear. The present study examines the acute effects of Aβ oligomers on the function of NMDA receptors, a subtype of ionotropic glutamate receptors, in rat sympathetic preganglionic neurons (SPNs). In the in vitro electrophysiological study, Aβ1-40 but not Aβ1-42 applied by superfusion for 5 min significantly potentiated NMDA-induced depolarizations in SPNs of neonatal rat spinal cord slice preparation. Application of Aβ1-40 had little effects on AMPA-induced depolarizations or GABA-induced hyperpolarizations. Treatment with a selective protein kinase C (PKC) inhibitor applied together with Aβ1-40 blocked the augmentation by Aβ1-40 of NMDA-induced depolarizations. Western blot analysis showed an increase in the levels of phosphoserine 896, selectively regulated by PKC, without significant changes in phosphoserine 897 on GluN1 subunits in lateral horn areas of spinal cord slices following treatment with Aβ1-40. In the in vivo study, intrathecal injection of Aβ1-40 (0.2 nmol) potentiated the pressor effects induced by NMDA (2 nmol) injected intrathecally in urethane-anesthetized rats. These results suggest that different fragments of Aβ may have differential effects on the NMDA receptor function and the selective augmentation of NMDA receptor function by Aβ1-40 may involve PKC-dependent mechanisms in sympathetic preganglionic neurons.

Mapping the cellular electrophysiology of rat sympathetic preganglionic neurones to their roles in cardiorespiratory reflex integration: a whole cell recording study in situ

Sympathetic preganglionic neurones (SPNs) convey sympathetic activity flowing from the CNS to the periphery to reach the target organs. Although previous in vivo and in vitro cell recording studies have explored their electrophysiological characteristics, it has not been possible to relate these characteristics to their roles in cardiorespiratory reflex integration. We used the working heart–brainstem preparation to make whole cell patch clamp recordings from T3–4 SPNs (n = 98). These SPNs were classified by their distinct responses to activation of the peripheral chemoreflex, diving response and arterial baroreflex, allowing the discrimination of muscle vasoconstrictor-like (MVClike, 39%) from cutaneous vasoconstrictor-like (CVClike, 28%) SPNs. The MVClike SPNs have higher baseline firing frequencies (2.52 ± 0.33 Hz vs. CVClike 1.34 ± 0.17 Hz, P = 0.007). The CVClike have longer after-hyperpolarisations (314 ± 36 ms vs. MVClike 191 ± 13 ms, P < 0.001) and lower input resistance (346 ± 49 MΩ vs. MVClike 496 ± 41 MΩ, P < 0.05). MVClike firing was respiratory-modulated with peak discharge in the late inspiratory/early expiratory phase and this activity was generated by both a tonic and respiratory-modulated barrage of synaptic events that were blocked by intrathecal kynurenate. In contrast, the activity of CVClike SPNs was underpinned by rhythmical membrane potential oscillations suggestive of gap junctional coupling. Thus, we have related the intrinsic electrophysiological properties of two classes of SPNs in situ to their roles in cardiorespiratory reflex integration and have shown that they deploy different cellular mechanisms that are likely to influence how they integrate and shape the distinctive sympathetic outputs.

Neurochemically coding functional subpopulations of rat sympathetic preganglionic neurons activated after glucoprivation

Neurochemically coding functional subpopulations of rat sympathetic preganglionic neurons activated after glucoprivation

Electrophysiological, pharmacological and molecular profile of the transient outward rectifying conductance in rat sympathetic preganglionic neurons in vitro

Transient outward rectifying conductances or A-like conductances in sympathetic preganglionic neurons (SPN) are prolonged, lasting for hundreds of milliseconds to seconds and are thought to play a key role in the regulation of SPN firing frequency. Here, a multidisciplinary electrophysiological, pharmacological and molecular single-cell rt-PCR approach was used to investigate the kinetics, pharmacological profile and putative K + channel subunits underlying the transient outward rectifying conductance expressed in SPN. SPN expressed a 4-aminopyridine (4-AP) sensitive transient outward rectification with significantly longer decay kinetics than reported for many other central neurons. The conductance and corresponding current in voltage-clamp conditions was also sensitive to the Kv4.2 and Kv4.3 blocker phrixotoxin-2 (1–10 μM) and the blocker of rapidly inactivating Kv channels, pandinotoxin-Kα (50 nM). The conductance and corresponding current was only weakly sensitive to the Kv1 channel blocker tityustoxin-Kα and insensitive to dendrotoxin I (200 nM) and the Kv3.4 channel blocker BDS-II (1 μM). Single-cell RT-PCR revealed mRNA expression for the α-subunits Kv4.1 and Kv4.3 in the majority and Kv1.5 in less than half of SPN. mRNA for accessory β-subunits was detected for Kvβ2 in all SPN with differential expression of mRNA for KChIP1, Kvβ1 and Kvβ3 and the peptidase homologue DPP6. These data together suggest that the transient outwardly rectifying conductance in SPN is mediated by members of the Kv4 subfamily (Kv4.1 and Kv4.3) in association with the β-subunit Kvβ2. Differential expression of the accessory β subunits, which may act to modulate channel density and kinetics in SPN, may underlie the prolonged and variable time-course of this conductance in these neurons.

Variability in the occurrence of nitric oxide synthase immunoreactivity in different populations of rat sympathetic preganglionic neurons

The proportion of sympathetic preganglionic neurons (SPN) showing nitric oxide synthase (NOS) immunoreactivity appears to vary with innervation target and blood pressure level. For normotensive Sprague-Dawley rats (SD), we evaluated peroxidase immunolabelling for choline acetyltransferase (ChAT) plus NOS in spinal cord segments T1-L2 and assessed NOS immunofluorescence in SPN retrogradely labelled with cholera toxin B subunit from the adrenal medulla (AM) or superior cervical (SCG), coeliac (CG), or major pelvic (MPG) ganglia. We also compared the distributions and numbers of NOS-positive and NOS-negative/ChAT-positive lateral horn neurons in SD with those in normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). In SD, WKY, and SHR, rostrocaudal, dorsoventral, and mediolateral differences occurred in the distributions of NOS-positive and NOS-negative/ChAT-positive neurons in the intermediolateral cell column (IML), whereas the two groups were similarly distributed throughout the central autonomic area (CAA). Among the four retrogradely labelled populations of SPN, the percentages showing NOS immunoreactivity differed (CG-projecting, 54.8% +/- 0.7%; SCG-projecting, 75.3% +/- 1.2%; MPG-projecting, 89% +/- 1.1% and AM-projecting, 98.6% +/- 0.2%). Within each retrogradely labelled group of SPN, the NOS-positive proportion also varied with subnuclear location (e.g., 25.5% +/- 4.0% of CG-projecting SPN in the CAA vs. 82.7% +/- 7.6% of CG-projecting SPN in the dorsolateral funiculus). The numbers of NOS-positive and NOS-negative/ChAT-positive neurons in T9-T11 were the same in SD and SHR but differed in WKY. Our results show that the expression of NOS within SPN varies depending on the target that they innervate and also on their subnuclear location. Our data indicate that there are no anatomical differences between nitric oxide-synthesizing SPN in normotensive SD and hypertensive SHR.

Comparison of the electrophysiological properties of neonatal mouse and rat sympathetic preganglionic neurones in vitro

Comparison of the electrophysiological properties of neonatal mouse and rat sympathetic preganglionic neurones in vitro

Immunoreactivity for cocaine‐ and amphetamine‐regulated transcript in rat sympathetic preganglionic neurons projecting to sympathetic ganglia and the adrenal medulla

Many sympathetic preganglionic neurons (SPN) in the intermediolateral cell column (IML) contain cocaine- and amphetamine-regulated transcript (CART), but the function of these CART-immunoreactive (IR) neurons is unknown. To test the possibility that CART might mark SPN involved in cardiovascular regulation, we first established whether all CART neurons in the spinal cord were SPN by double-immunofluorescent labelling for CART and choline acetyltransferase (ChAT). All autonomic subnuclei contained SPN immunoreactive for ChAT plus CART. Occasional ChAT-negative, CART-positive neurons occurred adjacent to the IML, indicating the existence of CART-IR interneurons. We then retrogradely labelled SPN with cholera toxin subunit B (CTB) from a variety of targets and used double immunofluorescence to detect CTB and CART. Among SPN in the IML, 43% projecting to the coeliac ganglion, 34% projecting to the major pelvic ganglion, and about 15% projecting to the superior cervical ganglion or adrenal medulla contained CART. CART also occurred in most SPN projecting to the major pelvic ganglion from either the central autonomic area (63%) or the intercalated nucleus (58%). Finally, we used drug-induced hypotension in conscious rats to evoke Fos immunoreactivity in barosensitive SPN and immunostained to reveal Fos and CART. CART immunoreactivity was present in 41% of the Fos-IR barosensitive neurons, which were concentrated in the IML of segments T5-T13. CART-positive, Fos-negative neurons also occurred in the same segments. These results indicate that CART occurs in barosensitive SPN, nonbarosensitive SPN, and interneurons. Thus, CART is not an exclusive marker for cardiovascular SPN but is likely to influence many autonomic activities.

Mid-year progress report 2004

EDITORIALSMid-year progress report 2004Pontus PerssonPontus PerssonPublished Online:01 Oct 2004https://doi.org/10.1152/ajpregu.00422.2004MoreSectionsPDF (57 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat now that this editorial team has completed its first term, it is with great pleasure that I briefly update our readers regarding the journal's progress. Various statistics from 2003 have been trickling in, and although they are uniformly encouraging, it is perhaps the feedback that we are receiving from our readers and contributors that is the most satisfying and reassuring.First for the hard numbers. For better or worse, the Impact Factor remains one of the most widely quoted methods of rating journals. Although we do not like to place too much importance on these numbers, that fact that our Impact Factor has been steadily rising since 2001 can only be taken as a promising result. From a level of 2.4 in 2001, we have risen to 3.627 according to the ISI Journal Citation reports for 2003, an increase of 50%. Although an imperfect and incomplete way of assessing the performance of a journal, we are always pleased to see improvements wherever they may be.Our submission numbers are perhaps a more pertinent indication of whether our journal has remained relevant and is still considered a valuable publishing venue for scientists. Here too we feel encouraged by our results. Whereas there was a certain amount of fluctuation in submissions in 2003, 2004 has by far been one of our strongest years in recent memory (Fig. 1).We strive to offer our authors the most appropriate and responsive forum in which to present their work. We also hope to provide the greatest service and most rapid methods of publication. Barely 1 wk is required before an accepted manuscript is published and citable as an Article in PresS. The prompt publication process provides our authors the benefit of rapid dissemination of their research and results.One method of enticing scientists is our attempt to offer a wide variety of types of manuscripts that the authors can use to best present their findings. Whether it is in a Letter to the Editor, Invited Review, a Call for Papers manuscript, or an Original Article, we hope to provide authors with the greatest number of publication options. As can be seen from our Invited Review series and the overwhelming response we often have to our Calls for Papers, I am hopeful that we are accomplishing this goal. We had an extremely enthusiastic response to our Call for Papers for Fetal Physiological Programming and are looking forward to publishing an issue devoted to this topic as a result of our call. Although that call has expired, we hope that we have opened the door to receiving an even greater number of manuscripts on this topic. To see all the topics for which we are currently soliciting papers, please refer to our journal homepage at http://ajpregu.physiology.org/.Currently, we have an acceptance rate for manuscripts submitted from the beginning of 2003 until the present of 48%, which is adjusted to 38% when only the Original Articles are taken into account. A regional breakdown of the acceptance rate (Fig. 2) shows that, as with the submission rate, North America accounts for the greater portion of accepted articles, with Europe, Asia, and the South Pacific holding their ground proportional to submission rates.Because the people most responsible for the progress and reputation of the journal are all those scientists who contribute their best and most innovative studies, we would like to single out the five contributors who, in terms of citations in the past year, were most popular (Table 1). These articles mirror the broad field of research published in the American Journal of Physiology-Regulatory, Integrative and Comparative Physiology.Finally, I would like to take this opportunity to thank all the contributors, referees, editors, and editorial staff who work to make this a truly leading journal in its field. Fig. 1.Submission of manuscripts for the months January through May for the years 2003 and 2004.Download figureDownload PowerPoint Fig. 2.Percentage of published original articles by region.Download figureDownload PowerPoint Table 1. Five most referenced articles in 2003ArticleShort TitleTypeCountryVolume:PageNagaya et al.Ghrelin administration in humansOAJapan280:R1483Morrison et al.Differential control of sympathetic outflowREVUSA281:R683Brown et al.TGF in A1-deficient miceOASweden281:R1362Antunes et al.Orexins/hypocretins excite rat sympathetic preganglionic neurons in vivo and in vitroOAUSA281:R1801Schnackenberg et al.Physiological and pathophysiological roles of oxygen radicals in the renal microvasculatureREVUSA282:R335OA, original article; REV, review.This article has no references to display. Download PDF Back to Top Next FiguresReferencesRelatedInformation More from this issue > Volume 287Issue 4October 2004Pages R697-R697 Copyright & PermissionsCopyright © 2004 the American Physiological Societyhttps://doi.org/10.1152/ajpregu.00422.2004History Published online 1 October 2004 Published in print 1 October 2004 Metrics

2003 was a good year for the American Journal of Physiology-Regulatory, Integrative and Comparative Physiology

EDITORIALS2003 was a good year for the American Journal of Physiology-Regulatory, Integrative and Comparative PhysiologyPontus B. PerssonPontus B. PerssonPublished Online:01 Apr 2004https://doi.org/10.1152/ajpregu.00015.2004MoreSectionsPDF (59 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations The beginning of new life in spring often causes reflection on the year that passed and prompts optimism for the year to come. Determined to keep the American Journal of Physiology-Regulatory, Integrative and Comparative Physiology a leader in its field, we are encouraged by last year's outcome. The team of editors and I have been overseeing the progress of the journal for two and a half years, and we are confident that this journal is becoming increasingly valuable to the scientific community committed to regulatory, integrative, and comparative physiology.The international mixture of our editorial team is generally reflected in the variety of regions that supply the bulk of our manuscripts (Fig. 1). The United States supplies the largest portion of manuscripts, but we also have a healthy flow coming from Canada, Europe, Asia, and the South Pacific, as well as the Middle East and South America. We have a broad scope of regional sources for manuscripts submitted to the journal and further encourage international scholars interested in submitting their works to us. Fig. 1.Breakdown of the number of submitted manuscripts by regions.Download figureDownload PowerPoint An overview of rapidly developing fields was provided by 16 Invited Reviews that appeared in 2003. More than a dozen Invited Reviews are currently in production to help our readers keep up with this year's trends. In addition to the Invited Reviews, we are launching an increasing amount of Special Calls for Papers. With the topics for which we are currently soliciting papers, we hope to encourage the advance of a wide range of important studies. For details, please refer to our journal homepage at http://ajpregu.physiology.org/.Currently, we have an acceptance rate for 2003 manuscripts of 42%, which is adjusted to 38% when only the original articles are taken into account. A regional breakdown of the acceptance rate (Fig. 2) shows that, as with the submission rate, North America accounts for the greater portion of accepted articles, with Europe, Asia, and the South Pacific holding their ground proportional to submission rates. Fig. 2.Percentage of published original articles by region.Download figureDownload PowerPoint Although we recognize the equivocal scientific value of the impact factor, we are nonetheless encouraged by our recent upward trend. In the past year and a half, we have seen it rise by over 30% to the 2002 impact factor of 3.16. Moreover, our calculations for 2003 indicate yet another marked increase. More importantly, the reviewing times for manuscripts have become very rapid. The time an author must wait for a first decision on a submitted manuscript is on average only 28 days. Barely a week is required before an accepted manuscript is published and citable as an Article in Press. The prompt publication process provides our authors the benefit of rapid dissemination of their research and results.Because the people most responsible for the progress and reputation of the journal are all those scientists who contribute their best and most innovative studies, we would like to single out the five contributors who, in terms of citations in the past year, were most popular (Table 1). Their articles mirror the broad field of research published in the American Journal of Physiology-Regulatory, Integrative and Comparative Physiology. Table 1. The 5 most referenced articles in 2003 Article Short Title Type Country Volume: Page Nagaya et al. Ghrelin administration in humans OA Japan 280: R1483 Morrison et al. Differential control of sympathetic outflow Rev USA 281: R683 Brown et al. TGF in A1-deficient mice OA Sweden 281: R1362 Antunes et al. Orexins/hypocretins excite rat sympathetic preganglionic neurons in vivo and in vitro OA USA 281: R1801 Schnackenberg et al. Physiological and pathophysiological roles of oxygen radicals in the renal microvasculature Rev USA 282: R335 OA, original article; Rev, review. Finally, I would like to take this opportunity to thank all the contributors, referees, editors, and editorial staff who work to make this a truly leading journal in its field.FOOTNOTESApril 2004, Volume 286This article has no references to display. Download PDF Back to Top Next FiguresReferencesRelatedInformation Cited ByGlobal metabolic profiling of hemorrhagic shock and resuscitation12 January 2021 | Biomedical Chromatography, Vol. 35, No. 4Arginine vasopressin infusion is sufficient to model clinical features of preeclampsia in mice4 October 2018 | JCI Insight, Vol. 3, No. 19 More from this issue > Volume 286Issue 4April 2004Pages R607-R607 Copyright & PermissionsCopyright © 2004 the American Physiological Societyhttps://doi.org/10.1152/ajpregu.00015.2004PubMed15003940History Published online 1 April 2004 Published in print 1 April 2004 Metrics

Independent inputs by VGLUT2- and VGLUT3-positive glutamatergic terminals onto rat sympathetic preganglionic neurons.

To characterize glutamatergic axon terminals onto sympathetic preganglionic neurons (SPNs), we visualized immunohistochemically three vesicular glutamate transporters (VGLUTs) in the intermediolateral cell column (IML) of rat thoracic spinal cord. VGLUT2 and VGLUT3 immunoreactivities but not VGLUT1 immunoreactivity were distributed in the IML and found in terminals making asymmetric synapses and apposed to dendrites immunopositive for choline acetyltransferase, an SPN marker. VGLUT2 and VGLUT3 immunoreactivities were not co-localized with each other. A population of VGLUT2-immunoreactive but not VGLUT3-immunoreactive terminals were adrenergic or noradrenergic. Some of VGLUT3-immunoreactive but not VGLUT2-immunoreactive terminals contained serotonin. These results indicate at least two independent glutamatergic terminal populations, which include a distinct monoaminergic subpopulation, making excitatory inputs onto SPNs.

Hydrogen peroxide increases the activity of rat sympathetic preganglionic neurons in vivo and in vitro

Reactive oxygen species (ROS) have been shown to modulate neuronal synaptic transmission and have also been implicated in cardiovascular diseases such as hypertension. The hypothesis that H 2O 2 acting on sympathetic preganglionic neurons (SPNs) affects spinal sympathetic outflow was tested in the present study. H 2O 2 was applied intrathecally via an implanted cannula to the T7–T9 segments of urethane-anesthetized rats. Blood pressure and heart rate were used as indices to evaluate the spinal sympathetic effects of H 2O 2 in vivo. Intrathecal H 2O 2 (100–1000 nmol) dose-dependently increased both the mean arterial pressure and heart rate. Reproducible pressor effects of H 2O 2 (1000 nmol) applied consecutively at intervals of 30 min were observed. The pressor effects of intrathecal H 2O 2 (1000 nmol) were attenuated by pretreatment with intrathecal administration of catalase (500 units), or N-acetyl-cysteine (1000 nmol). The pressor effects of intrathecal H 2O 2 (1000 nmol) were also antagonized dose-dependently by prior intrathecal injection of AP-5 ( dl-2-amino-5- phosphonovaleric acid, 10 and 30 nmol), or 6-cyano-7- nitroquinoxaline-2,3-dione, 10 and 30 nmol. In vitro electrophysiological study in spinal cord slices showed that superfusion of 1 mM H 2O 2 for 3 min, which had no effect on membrane potential, caused an increase in amplitude of excitatory postsynaptic potentials in SPNs, but had little effect on that of inhibitory postsynaptic potentials. Taken together, these results demonstrated that oxidative stress in spinal cord may cause an increase in spinal sympathetic tone by acting on SPNs, which may contribute to ROS-induced cardiovascular dysfunction.

Orexins induce increased excitability and synchronisation of rat sympathetic preganglionic neurones.

The neuropeptides orexin A and B are synthesised by perifornical and lateral hypothalamic (LH) neurones and exert a profound influence on autonomic sympathetic processes. LH neurones project to spinal areas containing sympathetic preganglionic neurones (SPNs) and therefore may directly modulate sympathetic output. In the present study we examined the possibility that orexinergic inputs from the LH influence SPN activity. Orexin-positive neurones in the LH were labelled with pseudorabies virus injected into the liver of parasympathetically denervated animals and orexin fibres were found adjacent to the soma and dendrites of SPNs. Orexin A or B (10-1000 nM) directly and reversibly depolarised SPNs in spinal cord slices. The response to orexin A was significantly reduced in the presence of the orexin receptor 1 (OX1R) antagonist SB334867A at concentrations of 1-10 micro M. Single cell reverse transcriptase-polymerase chain reaction revealed expression of mRNA for both OX1R and OX2R in the majority of orexin-sensitive SPNs. The orexin-induced depolarisation involved activation of pertussis toxin-sensitive G-proteins and closure of a K+ conductance via a protein kinase A (PKA)-dependent pathway that did not require an increase in intracellular Ca2+. Orexins also induced biphasic subthreshold membrane potential oscillations and synchronised activity between pairs of electrically coupled SPNs. Coupling coefficients and estimated junctional conductances between SPNs were not altered indicating synchronisation is due to activation of previously silent coupled neurones rather than modulation of gap junctions. These findings are consistent with a direct excitation and synchronisation of SPNs by orexinergic neurones that in vivo could increase the frequency and coherence of sympathetic nerve discharges and mediate LH effects on sympathetic components of energy homeostasis and cardiovascular control.

Excitatory action of lead on rat sympathetic preganglionic neurons in vitro and in vivo

Lead exposure elicited an increase in blood pressure and was considered to be a cardiovascular risk factor. The involvements of sympathetic nervous system and circulating catecholamines have been implicated in lead-induced hypertension. This study examined the effects of PbCl 2 on sympathetic preganglionic neurons (SPNs) in vitro and in vivo. In vitro electrophysiological study showed that superfusion of a low concentration (5 μM) of PbCl 2, which had no effects on membrane potential and spontaneous discharge rate, enhanced excitatory postsynaptic potentials (EPSPs) in some of the SPNs examined but inhibited inhibitory postsynaptic potentials (IPSPs) in other SPNs tested. A higher concentration (50 μM) of PbCl 2 inhibited both EPSPs and IPSPs in all SPNs examined. In vivo study showed that intrathecal injection of PbCl 2 (10 and 100 nmol) via an implanted cannula to the T7–T9 segments of urethane-anesthetized rats increased both the heart rate and mean arterial pressure. The pressor and tachycardic responses of intrathecal PbCl 2 (100 nmol) were attenuated by pretreatment with intravenous administration of hexamethonium (10 mg/kg) or intrathecal AP-5 (DL-2-amino-5-phosphonovaleric acid, 100 nmol), but were not significantly antagonized by prior intrathecal administration of CNQX (6-cyano-7-nitroquinoxaline-2,3-dione, 100 nmol). Taken together, these results demonstrated that lead may exert a stimulatory effect on SPNs, which may result from the enhancement of EPSPs and inhibition of IPSPs by low concentrations of lead.

Nociceptin inhibits rat sympathetic preganglionic neurons in situ and in vitro.

In vitro and in situ experiments were conducted to evaluate the hypothesis that the nonclassical opioid peptide nociceptin acting on sympathetic preganglionic neurons (SPNs) inhibits spinal sympathetic outflow. First, whole cell patch recordings were made from antidromically identified SPNs from immature (12-16 day old) rat spinal cord slices. Nociceptin (0.1, 0.3, and 1 microM) concentration dependently suppressed the excitatory postsynaptic potentials (EPSPs) evoked by focal stimulation and hyperpolarized a population of SPNs; these effects were naloxone insensitive. L-Glutamate-induced depolarizations were not significantly changed by nociceptin. Results from this series of experiments indicate that nociceptin inhibits the activity of SPNs by either a presynaptic or postsynaptic site of action, whereby the peptide reduces, respectively, the amplitude of EPSPs or the excitability of SPNs. Second, intrathecal injection of nociceptin (3, 10, and 30 nmol) to urethan-anesthetized rats dose dependently reduced the mean arterial pressure and heart rate; these effects were not prevented by prior intravenous administration of naloxone (1 mg/kg). Physiological saline given intrathecally was without appreciable effects. These results, together with earlier observations of the detection of nociceptin-immunoreactive nerve fibers and nociceptin receptor immunoreactivity in the rat intermediolateral cell column, raise the possibility that the opioid peptide, which may be released endogenously, reduces spinal sympathetic outflow by depressing the activity of SPNs.

Electrophysiological properties of electrical synapses between rat sympathetic preganglionic neurones in vitro.

1. The electrophysiological properties of electrical synaptic transmission between sympathetic preganglionic neurones (SPNs) in slices of rat spinal cord were investigated using simultaneous dual-electrode patch-clamp recordings. Electrotonic coupling was directly demonstrated between 21 pairs of SPNs. 2. Coupling coefficients determined from the steady-state response of both neurones to current steps injected into either neurone ranged from 0. 02 to 0.48 (0.18 +/- 0.02, mean +/- s.e.m.). Synapses were bidirectional and symmetrical for the majority of connections with coupling coefficients similar in either direction. Asymmetrical coupling between a minority of cell pairs was due to differences in passive neuronal properties rather than rectification of the synaptic conductances. 3. Action potentials were manifest in adjoining cells as biphasic electrical postsynaptic potentials (ePSPs), composed of a rapid depolarising component followed by a more prolonged hyperpolarisation with amplitudes of 1.2 +/- 0.2 and 2.1 +/- 0.6 mV, respectively. 4. Postsynaptic potentials resembled low-pass filtered presynaptic spikes with frequency dependence determined by the junctional conductance and postsynaptic membrane properties. Increases in presynaptic action potential frequency caused attenuation of the hyperpolarising component of the ePSP that was attributed to shorter duration presynaptic spikes being more markedly filtered. 5. Synchronisation of spontaneous action potentials between electrotonically coupled neurones was driven by subthreshold membrane potential activity resembling repetitive ePSPs. Synchronous spike firing in previously silent neurones could be driven by suprathreshold ePSPs induced by suprathreshold depolarisation of a single adjoining neurone. 6. These data characterise reliable communication of sub- and suprathreshold activity by electrical synapses enabling synchronised SPN firing which may contribute to generation of coherent sympathetic rhythms and promote summation of inputs to postganglionic neurones.

Fast excitatory post synaptic potentials and their response to catecholaminergic antagonists in rat sympathetic preganglionic neurones in vitro

In an in vitro slice preparation from neonatal rats intracellular recordings were made from electrophysiologically identified sympathetic preganglionic neurones. Electrical stimulation in the lateral funiculus (>500 μm) from the recording site elicited a mono- or polysynaptic excitatory post synaptic potential. The latter potential was blocked with the dopamine D 2 antagonist haloperidol but not with the dopamine D 1 antagonist SCH 23390. We therefore report the first showing of a functional descending pathway in an in vitro slice preparation describing both the transmitter and the receptor subtype involved and physiologically show that dopamine may exert an indirect excitatory influence on sympathetic preganglionic neurones possibly via interneurones present in the spinal cord.

Glutamate receptor subunits associated with rat sympathetic preganglionic neurons

The purpose of this study was to determine what subunits of the glutamate ( α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)) receptor are expressed by sympathetic preganglionic neurons in the spinal cord of adult rats. Preganglionic neurons were retrogradely labelled with Fluorogold, double-labelled with choline acetyltransferase immunofluorescence, and examined with confocal microscopy for evidence of immunoreactivity for GluR1, GluR2, GluR2/3 and GluR4 subunits. Quantitative analysis revealed that 92, 63 and 85% of preganglionic cells in the T8 segment express GluR1, GluR2 and GluR2/3 subunits, respectively. Cells were not immunoreactive for the GluR4 subunit. This evidence is consistent with the idea that most sympathetic preganglionic neurons form heteromeric AMPA receptors. Cells with GluR2 subunits will assemble receptors which are impermeable to calcium ions and may be resistant to excitotoxic cell death.

GABA- and glutamate-immunoreactive synapses on sympathetic preganglionic neurons projecting to the superior cervical ganglion

Our previous work suggests that virtually all of the synapses on sympathetic preganglionic neurons projecting to the rat adrenal medulla are immunoreactive for either the inhibitory amino acid, γ-aminobutyric acid (GABA) or the excitatory amino acid, l-glutamate. To investigate whether or not this is true for other groups of sympathetic preganglionic neurons, and to determine whether or not the proportion of inputs containing each type of amino acid neurotransmitter is the same for different groups of sympathetic preganglionic neurons, we retrogradely labelled rat and rabbit sympathetic preganglionic neurons projecting to the superior cervical ganglion and used post-embedding immunogold on ultrathin sections to localise GABA- and glutamate-immunoreactivity. The cell bodies and dendrites of both rat and rabbit sympathetic preganglionic neurons projecting to the superior cervical ganglion received synapses and direct contacts from nerve fibres immunoreactive for GABA and from nerve fibres immunoreactive for glutamate. In the rat, GABA was present in 48.9% of the inputs to sympathetic preganglionic neurons projecting to the superior cervical ganglion, and glutamate was present in 51.7% of inputs. Double immunogold labelling for glutamate and GABA on the same section, as well as labelling of consecutive serial sections for the two antigens, indicated that GABA and glutamate occur in separate populations of nerve fibres that provide input to rat sympathetic preganglionic neurons projecting to the superior cervical ganglion. We now have shown that GABA or glutamate is present in virtually all of the inputs to sympathetic preganglionic neurons projecting to the superior cervical ganglion and in essentially all of the inputs to sympathetic preganglionic neurons supplying the adrenal medulla. These findings are consistent with the hypothesis that all fast synaptic transmission in central autonomic pathways may be mediated by either excitatory or inhibitory amino acids. Furthermore, we showed a statistically significant difference in the proportion of glutamate-immunoreactive inputs between sympathetic preganglionic neurons projecting to the superior cervical ganglion and sympathoadrenal neurons (data from Llewellyn-Smith et al. [Llewellyn-Smith, I.J., Phend, K.D., Minson, J.B., Pilowsky, P.M., Chalmers, J.P., 1992. Glutamate immunoreactive synapses on retrogradely labelled sympathetic neurons in rat thoracic spinal cord. Brain Res. 581, 67–80]), with preganglionics supplying the adrenal medulla receiving more excitatory inputs than those supplying the superior cervical ganglion. This increased excitatory input to sympathoadrenal neurons may explain the predominant activation of these neurons following baroreceptor unloading.

Bilaterally evoked monosynaptic EPSPs, NMDA receptors and potentiation in rat sympathetic preganglionic neurones in vitro.

1. Whole-cell patch clamp and intracellular recordings were obtained from 190 sympathetic preganglionic neurones (SPNs) in spinal cord slices of neonatal rats. Fifty-two of these SPNs were identified histologically as innervating the superior cervical ganglion (SCG) by the presence of Lucifer Yellow introduced from the patch pipette and the appearance of retrograde labelling following the injection of rhodamine-dextran-lysine into the SCG. 2. Electrical stimulation of the ipsilateral (n = 71) or contralateral (n = 32) lateral funiculi (iLF and cLF, respectively), contralateral intermediolateral nucleus (cIML, n = 41) or ipsilateral dorsal horn (DH, n = 34) evoked EPSPs or EPSCs that showed a constant latency and rise time, graded response to increased stimulus intensity, and no failures, suggesting a monosynaptic origin. 3. In all neurones tested (n = 60), fast rising and decaying components of EPSPs or EPSCs evoked from the iLF, cLF, cIML and DH in response to low-frequency stimulation (0.03-0.1 Hz) were sensitive to non-NMDA receptor antagonists. 4. In approximately 50 % of neurones tested (n = 29 of 60), EPSPs and EPSCs evoked from the iLF, cLF, cIML and DH during low-frequency stimulation were reduced by NMDA receptor antagonists. In the remaining neurones, an NMDA receptor antagonist-sensitive EPSP or EPSC was revealed only in magnesium-free bathing medium, or following high-frequency stimulation. 5. EPSPs evoked by stimulation of the iLF exhibited a sustained potentiation of the peak amplitude (25.3 +/- 11.4 %) in six of fourteen SPNs tested following a brief high-frequency stimulus (10-20 Hz, 0.1-2 s). 6. These results indicate that SPNs, including SPNs innervating the SCG, receive monosynaptic connections from both sides of the spinal cord. The neurotransmitter mediating transmission in some of the pathways activated by stimulation of iLF, cLF, cIML and DH is glutamate acting via both NMDA and non-NMDA receptors. Synaptic plasticity is a feature of glutamatergic transmission in some SPNs where EPSPs are potentiated following a brief high-frequency stimulus. Our data also suggest a differential expression of NMDA receptors by these neurones.

Presynaptic inhibition by noradrenaline of the EPSC evoked in neonatal rat sympathetic preganglionic neurons

Visually identified and electrophysiologically characterized sympathetic preganglionic neurons (SPNs) were recorded using the whole-cell voltage clamp technique in slices of neonatal rat spinal cord. Monosynaptic excitatory postsynaptic currents (EPSCs) were evoked by electrical stimulation of the nucleus intercalatus in the presence of strychnine (5 μM) and bicuculline (10 μM). These EPSCs were abolished by the antagonist of AMPA-type glutamate receptors, 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX; 10 μM). Bath applied noradrenaline (NA; 0.5–50 μM) dose-dependently and reversibly decreased by up to around 60% the amplitude of the EPSC, without affecting the holding current. The EPSC depression by NA was not accompanied by a change in EPSC reversal potential (around +5 mV), nor were inward currents generated by pressure application of glutamate affected by NA application. A comparable degree of EPSC depression was also seen with the α 2-adrenoceptor agonist clonidine (5 μM), and the α 2A-agonist oxymetazoline (5 μM), while the α 1-agonist phenylephrine (100 μM) caused only a 22% depression. The EPSC depression caused by NA (10 μM) was completely antagonized by either the α-antagonist phentolamine (10 μM) or the α 2-antagonist idazoxan (2 μM). Conversely, the β-adrenoceptor antagonist popranolol (5 μM), and the α 1-, α 2B- and α 2C-antagonist prazosin (2 μM) were without effect. These results indicate that activation of presynaptic α 2A-adrenoceptors on inputs to SPNs decreases glutamate release.