Modulation of neuronal nicotinic receptor function by the neuropeptides CGRP and substance P on autonomic nerve cells

1. One classical example of how neuropeptides can affect the function of ligand-gated receptors is the modulation of neuronal nicotinic receptors (nAChRs) by substance P. The present review updates current understanding of this action by substance P and compares it with other neuropeptides more recently found to modulate nAChRs in the autonomic nervous system. 2. Calcitonin gene-related peptide (CGRP) and its N-terminal fragments have been shown to exert complex inhibitory as well facilitatory actions on nAChRs. Fragments such as CGRP(1-4), CGRP(1-5) and CGRP(1-6) rapidly and reversibly enhance agonist sensitivity of nAChRs without directly activating those receptors. Longer fragments or the full-length peptide potently inhibit responses mediated by nAChRs via an apparently competitive-type antagonism. This phenomenon differs from the substance P-induced block, which is agonist use-dependent and preferential towards large nicotinic responses. 3. It is argued that the full-length peptides CGRP and substance P might play distinct roles in the activity-dependent modulation of cholinergic neurotransmission, by inhibiting background noise in the case of CGRP or by reducing excessive excitation in the case of substance P. Hence, multiple neuropeptide mechanisms may represent a wide array of fine-tuning processes to regulate nicotinic synaptic transmission. 4. The availability of novel CGRP derivatives with a strong enhancing action on nAChRs may offer new leads for the drug design targeted for potentiation of nAChRs in the autonomic nervous system as well as in the brain, a subject of interest to counteract the deficit of the nAChR function associated with neurodegenerative diseases like Alzheimer's and Parkinson's diseases.

Salivary secretion of immunoglobulin A by submandibular glands in response to autonomimetic infusions in anaesthetised rats

Salivary secretion of immunoglobulin A (lgA) by submandibular glands is increased by stimuli from autonomic nerves. Since it is unclear which specific autonomic receptors transduce such stimuli, we have infused autonomimetics intravenously and compared secretion of fluid, IgA and stored proteins (peroxidase and total protein) with secretory responses during electrical stimulation of the parasympathetic nerve supply in anaesthetized rats. The greatest secretion of IgA was evoked by the alpha-adrenoceptor agonist phenylephrine and this was reduced by the beta-adrenoceptor blocking drug propranolol. The secretion of fluid or proteins but not IgA was increased with frequency of nerve stimulation and dose of methacholine (cholinergic), isoprenaline (beta-adrenergic) or phenylephrine (alpha-adrenergic).

Central 5-HT(3) receptors and water intake in rats

In the present paper, we studied in rats the effect of third ventricle administration of m-chlorophenylbiguanide hydrochloride (1-(3-chlorophenyl)biguanide (m-CPBG), a selective 5-HT(3) agonist, on water intake induced by three different physiological stimuli: water deprivation, acute salt load and hypovolemia. Central acute m-CPBG injections in the doses of 80 and 160 nmol significantly reduced water intake elicited by an acute salt load. Third ventricle injections of m-CPBG in the dose of 160 nmol significantly inhibited water intake in hypovolemic animals, whereas third ventricle injections of m-CPBG in a higher dose (320 nmol) were necessary to decrease water intake in water-deprived rats. Pretreatment with 1-methyl-N-[8-methyl-8-azabicyclo(3.2.1)-oct-3-yl]-1H-indazole-3-carboxamide (LY-278,584), a selective 5-HT(3) antagonist, abolished the inhibitory effect on water intake seen after central administration of m-CPBG in all groups studied. The central administration of m-CPBG was also able to inhibit water intake induced by pharmacological activation of central cholinergic and angiotensinergic pathways. Third ventricle injections of m-CPBG in the highest dose employed in this study (320 nmol) were unable to modify food intake in food-deprived rats. An aversion test has shown that acute third ventricle injections of m-CPBG do not induce illness-like effects that could explain the water intake inhibition here observed. Also, central administration of m-CPBG did not modify the intake of a "dessert" meal consisting of diluted condensed milk. It is concluded that central 5-HT(3) receptor activation exerts a specific inhibitory effect on water intake.

Regulation of feeding behavior, gastric emptying, and sympathetic nerve activity to interscapular brown adipose tissue by galanin and enterostatin: the involvement of vagal-central nervous system interactions

Galanin and enterostatin, which are distributed in both the central nervous system and the gastrointestinal tract, regulate the feeding behavior. In the first set of experiments, we investigated the effects of galanin and enterostatin, injected into the third ventricle, on food intake, gastric emptying, and the sympathetic activity of nerves innervating interscapular brown adipose tissue in rats. Galanin dose-dependently increased the intake of a high-fat diet after overnight starvation, but it did not affect low-fat diet intake. In contrast, enterostatin suppressed the intake of the high-fat diet, while intake of the low-fat diet was not affected. Galanin significantly and dose-dependently suppressed gastric emptying rate. However, gastric emptying showed no response to enterostatin. Galanin produced a dose-dependent suppression of sympathetic firing rate. In rats fed a high-fat diet, the injection of enterostatin showed a dose-dependent increase in firing rate. In contrast, animals fed a chow diet showed almost no response. In the second set of experiments, we investigated the role of the hepatic vagus nerve in modulating the peripheral response to enterostatin in rats. Intraperitoneal (i.p.) enterostatin reduced the intake of a high-fat diet. Immunohistochemical identification indicated that the Fos protein was present in the nucleus tractus solitarius, and parabrachial, paraventricular, and supraoptic nuclei after IP enterostatin. These responses to i.p. enterostatin were blocked by hepatic vagotomy. These results suggest that galanin and enterostatin coordinate to regulate feeding behavior, gastric emptying, and sympathetic activity to interscapular brown adipose tissue via central and peripheral sites of action, one of which was the interaction which was found to exist through the vagal system.

Effects of extrinsic autonomic inputs on expression of c-Fos immunoreactivity in myenteric neurons of the guinea pig distal colon

c-Fos protein is a nuclear protein coded by c-fos proto-oncogene subsequent to synaptic activation of the neurons. We used immunohistochemical methods to visualize the expression of c-Fos protein in myenteric neurons of the guinea pig distal colon and examined the effects of the extrinsic autonomic inputs on the enteric circuits. No c-Fos immunoreactivity was observed in the colonic segments fixed immediately after removal from the animal body. A number of c-Fos-immunoreactive nuclei of myenteric neurons, however, appeared in all preparations that were incubated in Krebs solution in vitro (n=10). Application of tetrodotoxin (0.2 microM) abolished the expression of c-Fos-immunoreactivity (n=6), but hexamethonium (100 microM) failed to decrease the number of c-Fos-positive neurons despite a complete suppression of spontaneous peristaltic movements (n=5). Neither the electrical stimulation (n=8) nor the severing of the pelvic nerves (n=5) changed the number of c-Fos-positive neurons. Application of clonidine, an alpha(2)-agonist, (0.1 microM) abolished the expression of c-Fos protein in all preparations (n=5), while denervation of the sympathetic fibers in the lumbar colonic and hypogastric nerves in vivo increased the number of c-Fos-positive neurons (n=5). The results indicate that the enteric circuit in the distal part of the gastrointestinal tract is under tonic inhibition by the sympathetic nervous system from the lumbar spinal cord. c-Fos immunoreactivity expressed in the colonic preparations in vivo might be the results of enhanced activation of non-nicotinic receptors after removal of the sympathetic inhibition.

Inhibition of autonomic nerve-mediated inotropic responses in guinea pig atrium by bafilomycin A

Neurosecretory vesicles actively accumulate neurotransmitter by consuming proton motive force generated by vacuolar H+-ATPase (V-ATPase). The effects of bafilomycin A, a macrolide antibiotic that inactivates V-ATPase, on nerve stimulation-mediated inotropic responses of the left atrium were studied to explore the role of the enzyme in the cholinergic and adrenergic neurotransmissions. On field stimulation, the contractility of paced atrium exhibited initial atropine-sensitive depression followed by propranolol-sensitive facilitation. Both the negative and positive inotropic effects were abolished by bafilomycin A. The inhibitions were irreversible and followed a similar time course and the inhibitory effects were accelerated by intense nerve stimulation. In contrast, bafilomycin A had no effect on the inotropic responses produced by muscarinic acetylcholine or alpha-adrenergic receptor agonist. Stimulation of neuronal nicotinic acetylcholine receptor also elicited biphasic changes of contractile force, which were depressed by bafilomycin A. Compared with the inhibitory effects on field stimulation, the depressions progressed slowly and incompletely. The results suggest that inhibition of V-ATPase depressed the synaptic transmissions at autonomic nerve-muscle junctions. Furthermore, bafilomycin A preferentially inhibited neurotransmitter release emanating from the immediately releasable pool.

Isoflurane depresses baroreflex control of heart rate in decerebrate rats

BACKGROUND

Isoflurane inhibits baroreflex control of heart rate (HR) by poorly understood mechanisms. The authors examined whether suprapontine central nervous system cardiovascular regulatory sites are required for anesthetic depression.

METHODS

The effects of isoflurane (1 and 2 rat minimum alveolar concentration [MAC]) on the baroreflex control of HR were determined in sham intact and midcollicular-transected decerebrate rats. Intravenous phenylephrine (0.2-12 microg/kg) and nitroprusside (1-60 microg/kg) were used to measure HR responses to peak changes in mean arterial pressure (MAP). Sigmoidal logistic curve fits to HR-MAP data assessed baroreflex sensitivity (HR/MAP), HR range, lower and upper HR plateau, and MAP at half the HR range (BP50). Four groups (two brain intact and two decerebrate) were studied before, during, and after isoflurane. To assess sympathetic and vagal contributions to HR baroreflex, beta-adrenoceptor (1 mg/kg atenolol) or muscarinic (0.5 mg/kg methyl atropine) antagonists were administered systemically.

RESULTS

Decerebration did not alter resting MAP and HR or baroreflex parameters. Isoflurane depressed baroreflex slope and HR range in brain-intact and decerebrate rats. In both groups, 1 MAC reduced HR range by depressing peak reflex tachycardia. Maximal reflex bradycardia during increases in blood pressure was relatively preserved. Atenolol during 1 MAC did not alter maximum reflex tachycardia. In contrast, atropine during 1 MAC fully blocked reflex bradycardia. Therefore, 1 MAC predominantly depresses sympathetic components of HR baroreflex. Isoflurane at 2 MAC depressed both HR plateaus and decreased BP50 in both groups.

CONCLUSIONS

Isoflurane depresses HR baroreflex control by actions that do not require suprapontine central nervous system sites. Isoflurane actions seem to inhibit HR baroreflex primarily by the sympathetic nervous system.

Comparison of the generic neuronal differentiation and neuron subtype specification functions of mammalian achaete-scute and atonal homologs in cultured neural progenitor cells

In the vertebrate peripheral nervous system, the proneural genes neurogenin 1 and neurogenin 2 (Ngn1 and Ngn2), and Mash1 are required for sensory and autonomic neurogenesis, respectively. In cultures of neural tube-derived, primitive PNS progenitors NGNs promote expression of sensory markers and MASH1 that of autonomic markers. These effects do not simply reflect enhanced neuronal differentiation, suggesting that both bHLH factors also specify neuronal identity like their Drosophila counterparts. At high concentrations of BMP2 or in neural crest stem cells (NCSCs), however, NGNs like MASH1 promote only autonomic marker expression. These data suggest that that the identity specification function of NGNs is more sensitive to context than is that of MASH1. In NCSCs, MASH1 is more sensitive to Notch-mediated inhibition of neurogenesis and cell cycle arrest, than are the NGNs. Thus, the two proneural genes differ in other functional properties besides the neuron subtype identities they can promote. These properties may explain cellular differences between MASH1- and NGN-dependent lineages in the timing of neuronal differentiation and cell cycle exit.

Role of tachykininergic and cholinergic pathways in modulating canine gastric tone and compliance in vivo

Acetylcholine and tachykinins act as co-transmitters along excitatory pathways at different gut levels. Since cholinergic pathways are involved in maintaining gastric tone during fasting, our aim was to study the possible role of tachykininergic pathways in modulating canine gastric tone and compliance in vivo by using selective tachykinin receptor antagonists. In four fasting, conscious dogs, we characterized the pressure-volume relationship in the proximal stomach by using a barostat. We increased the pressure of the intragastric bag by 2 mmHg increments every 3 min, starting from a baseline value of 2 up to 12 mmHg. Drug effects were investigated by studying pressure-volume relationships before and 15 min after intravenous (i.v.) administration of SR140333, SR48968, or SR142801 (respectively, NK (1)-, NK (2)-, and NK (3)-receptor antagonist, each at the dose of 1 mg kg (-1)) or atropine (100 microg kg (-1)). Pressure-volume curves were fitted by nonlinear regression analysis. Before drug administration, the curve that best fitted the pressure-volume relationship was exponential. SR140333, SR48968 and SR142801 did not affect baseline gastric tone or the gastric pressure-volume curve at any distension level. At a distending pressure of 6 mmHg, the Delta volumes obtained after administration of SR140333, SR48968 or SR142801 vs control were 65 +/- 28, 27 +/- 26, 14 +/- 20 ml, respectively. The same was true even when all three antagonists were administered together to achieve simultaneous blockade of all three tachykinin receptor subtypes. Atropine increased baseline gastric volume (Delta volume = 237 +/- 15 ml; P< 0.01) and significantly (P< 0.0001) shifted the pressure-volume curve to the left. After atropine, a linear equation best fitted the pressure-volume curve. We conclude that tachykininergic pathways are not involved in modulating canine gastric tone and compliance during fasting, whereas cholinergic pathways play a major role not only in maintaining gastric tone, but also in modulating the compliance of the proximal stomach to a distending stimulus.

Nociceptin inhibits gamma-aminobutyric acidergic inputs to cardiac parasympathetic neurons in the nucleus ambiguus

Studies have shown that nociceptin, the endogenous ligand for the opioid receptor-like receptor (ORL(1)), modulates central control of cardiovascular activity. The nucleus ambiguus, an area containing cardiac parasympathetic neurons, contains both ORL(1) receptors and neurons that contain nociceptin itself. Although previous work has shown that nociceptin acts to increase parasympathetic outflow to the heart, the mechanisms by which this is achieved are unknown. In the present study, the effects of nociceptin on spontaneous gamma-aminobutyric acidergic (GABAergic) input to cardiac parasympathetic neurons (IPSCs) was examined. At 100 microM, nociceptin inhibited both the frequency (-35.6%) and the amplitude (-49.5%) of spontaneous GABAergic IPSCs in cardiac vagal neurons. Nociceptin also caused a novel postsynaptic inhibition of the responses evoked by exogenous application of GABA. These results indicate that nociceptin acts both on neurons precedent to cardiovascular neurons to decrease the activity of GABAergic neurons that synapse upon cardiovascular neurons and directly, inhibiting the postsynaptic currents evoked by GABA. This inhibition by nociceptin would increase parasympathetic outflow to the heart, thus providing a possible mechanism for nociceptin-induced bradycardia.

Dominant anti-vagal effect of pentobarbital on cardiac responses to intracardiac autonomic nerve stimulation in the dog

The isolated canine atrium was perfused by heparinized blood of the donor dog. An adequate dose of pentobarbital that induced a potent hypotension in the donor did not produce any significant change in the atrial rate and developed tension in the isolated atrium perfused with donor's blood. Pentobarbital in doses that modified neither cardiac responses to intracardiac adrenergic nerve stimulation nor exogenously given norepinephrine or acetylcholine significantly inhibited intracardiac vagal responses. From these results, it is concluded that a large dose of pentobarbital has a dominant antivagal effect in the heart.

Acute sarin exposure causes differential regulation of choline acetyltransferase, acetylcholinesterase, and acetylcholine receptors in the central nervous system of the rat

Acute neurotoxic effects of sarin (O:-isopropylmethylphosphonoflouridate) in male Sprague-Dawley rats were studied. The animals were treated with intramuscular (im) injections of either 1 x LD(50) (100 microg/kg), and sacrificed at 0. 5, 1, 3, 6, 15, or 20 h after treatment, or with im injections of either 0.01, 0.1, 0.5, or 1 x LD(50) and sacrificed 15 h after treatment. Plasma butyrylcholinesterase (BChE) and brain regional acetylcholinesterase (AChE) were inhibited (45-55%) by 30 min after the LD(50) dose. BChE in the plasma and AChE in cortex, brainstem, midbrain, and cerebellum remained inhibited for up to 20 h following a single LD(50) treatment. No inhibition in plasma BChE activity was observed 20 h after treatment with doses lower than the LD(50) dose. Midbrain and brainstem seem to be most responsive to sarin treatment at lower doses, as these regions exhibited inhibition (approximately 49% and 10%, respectively) in AChE activity following 0.1 x LD(50) treatment, after 20 h. Choline acetyltransferase (ChAT) activity was increased in cortex, brainstem, and midbrain 6 h after LD(50) treatment, and the elevated enzyme activity persisted up to 20 h after treatment. Cortex ChAT activity was significantly increased following a 0.1 x LD(50) dose, whereas brainstem and midbrain did not show any effect at lower doses. Treatment with an LD(50) dose caused a biphasic response in cortical nicotinic acetylcholine receptor (nAChR) and muscarinic acetylcholine receptor (m2-mAChR) ligand binding, using [(3)H]cytisine and [(3)H]AFDX-384 as ligands for nAChR and mAChR, respectively. Decreases at 1 and 3 h and consistent increases at 6, 15, and 20 h in nAChR and m2-mAChR were observed following a single LD(50) dose. The increase in nAChR ligand binding densities was much more pronounced than in mAChR. These results suggest that a single exposure of sarin, ranging from 0.1 to 1 x LD(50), modulates the cholinergic pathways differently and thereby causes dysregulation in excitatory neurotransmission.

Three-dimensional return map: a new tool for quantification of heart rate variability

BACKGROUND

Several methods are used to study heart rate variability, but they have limitations, which might be overcome by the use of a three-dimensional return map.

OBJECTIVES

To evaluate the performance of three-dimensional return map-derived indices to detect (1) sympathetic and parasympathetic modulation to the sinus node and (2) autonomic dysfunction in diabetic patients.

METHODS

Six healthy subjects underwent partial and total pharmacological autonomic blockade in a protocol that incorporated vagal and sympathetic predominance. Twenty-two patients with type 2 diabetes mellitus and 12 normal controls participated in the subsequent validation experiment. Three-dimensional return maps were constructed by plotting RRn intervals versus the difference between adjacent RR intervals [(RRn+1)-(RRn)] versus the number of counts, and four derived indices (P1, P2, P3, MN) were created for quantification.

RESULTS

Both indices P1 and MN were significantly increased after sympathetic blockade with propranolol, while all indices except P1 were modified after parasympathetic blockade (P < 0.05). During the validation experiments, P1 and MN detected differences between normal controls, and diabetic patients with and without autonomic neuropathy. The overall accuracy of most three-dimensional indices to detect autonomic dysfunction, estimated by the area under the ROC curve, was significantly better than traditional time domain indices. Three-dimensional return map-derived indices also showed adequate reproducibility on two different recording days (intra-class correlation coefficients of 0.69 to 0.82; P < 0.001).

CONCLUSIONS

Three-dimensional return map-derived indices are reproducible, quantify parasympathetic as well as sympathetic modulation to the sinus node, and are capable of detecting autonomic dysfunction in diabetic patients.

Autonomic regulation of cystatin S gene expression in rat submandibular glands

Innervation of rat submandibular and parotid glands by the autonomic nervous system regulates saliva volume, its rate of secretion and its composition. The autonomic nervous system also plays a regulatory role in the differentiation and growth of salivary glands, and in the expression of specific sets of genes. Rat cystatin S, a member of family 2 of the cysteine proteinase inhibitor superfamily, is expressed in submandibular and parotid glands of human and rat. In the rat, cystatin S gene expression is tissue- and cell type-specific, is temporally regulated during postnatal development, and not observed in adult animals. The beta-adrenergic agonist isoproterenol (IPR) induces hypertrophic and hyperplastic enlargements of rat salivary glands and the expression of a number of genes including cystatin S. Sympathectomy reduces, but does not completely block, IPR-induced expression of the cystatin S gene in submandibular glands of adult female rats, indicating the participation of sympathetic factor(s) in its regulation. Bilateral parasympathectomy also reduces IPR-induced cystatin S gene expression, suggesting a role of the parasympathetic nervous system in its regulation. Experiments described in this paper suggest that similar factor(s) arising from both the sympathetic and parasympathetic branches of the autonomic nervous system simultaneously participate in IPR-induced cystatin S gene expression in submandibular glands.

Changes in catecholaminergic pathways innervating paraventricular nucleus and pituitary-adrenal axis response during morphine dependence: implication of alpha(1)- and alpha(2)-adrenoceptors

We have previously shown an enhanced activity of the pituitary-adrenal response in rats dependent on morphine, which occurs concomitantly with an increase in the activity of catecholaminergic terminals in the hypothalamic paraventricular nucleus (PVN). The present study examined the possible role of noradrenergic system in the regulation of opioid withdrawal-induced activation of the hypothalamus-pituitary-adrenocortical (HPA) axis activity. Rats were given morphine by s.c. implantation of morphine pellets for 7 days. On the seventh day, morphine withdrawal was induced by s.c. administration of naloxone (1 mg/kg), rats were sacrificed 30 min later, and changes in noradrenaline (NA) turnover (estimated by the 3-methoxy-4-hydroxyphenylethylen glycol/NA ratio) and in dopamine turnover (estimated by the 3,4-dihydroxyphenylacetic acid/dopamine ratio) in the PVN (HPLC with electrochemical detection) and in plasma corticosterone levels were determined. We found a parallelism between the behavioral signs of withdrawal, an increased activity of noradrenergic and dopaminergic terminals in the PVN, and the hypersecretion of the HPA axis. Pretreatment with alpha(1)- or alpha(2)-adrenoceptor antagonists prazosin or yohimbine, respectively, 15 min before naloxone administration significantly prevented the withdrawal-induced corticosterone hypersecretion and attenuated the behavioral signs of morphine withdrawal. In addition, biochemical analysis indicated that both prazosin and yohimbine completely abolished the withdrawal-induced increase in NA turnover in the PVN. In contrast, neither prazosin nor yohimbine modified the hyperactivity of dopaminergic terminals in the PVN during withdrawal. Collectively, these data suggest that the secretory activity in the HPA axis after morphine withdrawal results from an increase in noradrenergic activity that is dependent on alpha(1)- and alpha(2)-adrenoceptor activation. Activation of dopaminergic pathways might not contribute to the neuroendocrine response during withdrawal.

Activation of an adrenergic and vagally-mediated NANC pathway in surgery-induced fundic relaxation in the rat

The aim of this study was to pharmacologically characterize and investigate the possible contribution of adrenergic and nonadrenergic noncholinergic (NANC) pathways involved in the relaxation of the rat gastric fundus following abdominal surgery. Using an intragastric balloon, the effect of skin incision (SI), laparotomy (LT) and manipulation of the small intestine followed by caecal resection (M + R) on fundic pressure was evaluated. SI resulted in a brief relaxation of the gastric fundus abolished by guanethidine and blocked by hexamethonium and the combination of phentolamine, propranolol and atropine (PPA). LT induced a longer lasting relaxation which was abolished by guanethidine and hexamethonium. It was blocked by PPA and the combination of ganglionectomy and vagotomy, but unaffected by atropine, vagotomy or ganglionectomy. M + R induced a long-lasting relaxation which was only partly blocked by guanethidine or PPA, illustrating an inhibitory NANC component. Vagotomy combined with guanethidine completely abolished the relaxation following M + R, whereas it was significantly blocked by hexamethonium and the combination of ganglionectomy with vagotomy. These results indicate that SI, LT and M + R induce inhibition of fundic motility via an adrenergic mechanism. During M + R, an additional vagally mediated inhibitory NANC pathway is activated. Finally, we suggest that LT and M + R inhibit the gastric fundus via both a splanchnic and a vagal reflex pathway.

Sympathetic inhibition of ascending and descending interneurones during the peristaltic reflex in the isolated guinea-pig distal colon

1. We investigated the effects of sympathetic nerve stimulation within ascending and descending reflex pathways underlying the peristaltic reflex in the guinea-pig distal colon. 2. A three-chambered partitioned bath was used to divide a segment of distal colon into stimulation, recording and intermediate regions. The effects of lumbar colonic nerves (LCN) could be localized to the intermediate region by surgical lesions of the mesentery and by application of guanethidine (3 microM) to the stimulation and recording chambers. 3. Brush stroking the mucosa in the anal and oral stimulation chambers elicited a synchronous contraction of the longitudinal muscle (LM) and circular muscle (CM) oral to, and transient relaxation of the LM and CM anal to, the stimulus, respectively. 4. After N omega-nitro-L-arginine (L-NA; 100 microM) in the oral and intermediate chambers, mucosal stimulation in the oral chamber elicited a prolonged descending inhibitory and excitatory complex in both the LM and CM in the anal recording chamber. This was blocked by hexamethonium (300 microM), which did not affect the transient relaxation response recorded in control conditions. 5. Stimulation of the LCN (1200 pulses, 20 Hz), delivered to the intermediate region, abolished the oral contraction and the L-NA-induced anal complex in both the LM and CM, but was without effect on the transient hexamethonium-resistant anal relaxation. These effects of LCN stimulation were reversed by phentolamine (3 microM) or yohimbine (100 nM), but not propranolol (10 microM), when added to the intermediate chamber. 6. LCN stimuli (2-20 Hz, 600 micros pulses) directed to the recording chamber elicited synchronous relaxations in the LM and CM that were unaffected by hexamethonium (300 microM), but were reduced by yohimbine and usually blocked by the further addition of propranolol (10 microM). 7. In conclusion, sympathetic nerve stimulation inhibits orally and anally projecting cholinergic interneurones underlying the peristaltic reflex in the distal colon. In addition, the LM and CM relax synchronously following release of sympathetic neurotransmitter, over a range of stimulus frequencies.

Lesion of septal-hippocampal neurons with 192 IgG-saporin alters function of M1 muscarinic receptors

Cholinergic neurons projecting from the medial septum to the hippocampus were lesioned with the selective neurotoxin 192 IgG-saporin. Injection of 300 ng of 192 IgG-saporin into the medial septum produced a 60% decrease in choline acetyltransferase activity. M1 muscarinic receptor function was examined by measuring enhancement of evoked release of norepinephrine from rat hippocampal slices by the M1 selective agonist McN-A-343. In hippocampal slices from rats which were lesioned with 192-saporin, the response to McN-A-343 was reduced compared to sham-operated controls. Pirenzepine binding demonstrated no change in M1 receptor number or affinity. However, the curve for displacement of pirenzepine by the muscarinic agonist oxotremorine-M was shifted to the right in hippocampal tissue from lesioned rats. This shift was identical to that produced by addition of the non-hydrolyzable GTP analogue GppNHp, which uncouples the M1 muscarinic receptor/G-protein complex. These results suggest that lesion of septal-hippocampal cholinergic inputs causes uncoupling of the M1 muscarinic receptor, decreasing responsiveness to stimulation. These findings are similar to reports of decreased M1 muscarinic receptor coupling to G-proteins and loss of function in Alzheimer's disease. The 192 IgG-saporin lesion may provide a viable animal model in which to study uncoupling of G-proteins and M1 muscarinic receptors.

Histaminergic influence on vestibular stimulation-induced locus coeruleus inhibition in rats

In previous reports we have shown that caloric stimulation (CS) of the vestibular apparatus inhibits locus coeruleus (LC)-noradrenergic neuronal activity in urethane-anaesthetized rats. The present study examined the effect of neural histamine depletion by alpha-fluoromethylhistidine (alpha-FMH) on CS-induced LC inhibition. In alpha-FMH treated rats, LC neuronal inhibition caused by CS was still observed. This finding indicates that the central histaminergic neuron system does not participate in the CS-induced LC-noradrenergic inhibition. It is suggested that the noradrenergic neuron system is involved in the development of vestibulo-autonomic response, independent of the histaminergic neuron system.

Reflex effects from leptin sensors in the white adipose tissue of the epididymis to the efferent activity of the sympathetic and vagus nerve in the rat

Efferent nerve signals were recorded from the central cut end of the small nerve filament dissected from the sympathetic nerve innervating the white adipose tissue (WAT) of epididymis, inter scapular brown adipose tissue (BAT), pancreas, liver, adrenal medulla, and vagus nerve innnervating the pancreas and liver. Injection of leptin (2 ng, 0.2 ml) into the white adipose tissue of the either side of the epididymis evoked reflex activation of the sympathetic nerve activity and suppression in vagus nerve activity. These observations suggest that leptin sensors in the white adipose tissue of the epididymis play a role in reflex regulation of metabolic functions of the body through the modulatory change in sympathetic and vagal outflow.

Differential effects of neurotoxic destruction of descending noradrenergic pathways on acute and persistent nociceptive processing

Although many pharmacological studies indicate that bulbospinal noradrenergic projections contribute to antinociception, lesions of the major brainstem noradrenergic cell groups have provided conflicting evidence. Here we used a new immunotoxin, anti-dopamine beta-hydroxylase-saporin, to re-examine the contribution of noradrenergic pathways to nociception and to morphine analgesia. We treated rats intrathecally by lumbar puncture with the immunotoxin and examined dopamine beta-hydroxylase (DbetaH) immunoreactivity seven and 14 days after treatment. There was no change in DbetaH staining at 7 days; however, 14 days after treatment we demonstrated significant destruction of noradrenergic neurons in the locus coeruleus and in the A5 and A7 cell groups. There was a concomitant loss of noradrenergic axons in the dorsal and ventral horns of the lumbosacral and cervical cord. Consistent with the lack of anatomical changes, we found no difference in nociceptive responses in the hot-plate, tail-flick or formalin tests one week post-toxin. On day 14 we examined the behavioral response to injection of formalin into the hindpaw and found that responses during the second phase of pain behavior were significantly reduced. There was no change during the first phase. Formalin-evoked fos expression in the spinal cord was also reduced. We also evaluated morphine analgesia in the formalin test and found that toxin-treated animals exhibited enhanced morphine analgesia. These results establish the utility of using this immunotoxin to selectively destroy subpopulations of noradrenergic cell groups and provide evidence that acute and persistent nociception are differentially regulated by descending noradrenergic pathways.

Are cholinergic pathways involved in the anesthetic response to alpha2 agonists

1. We investigated whether change in neuronal activity in cholinergic pathways mediates the anesthetic effect of the alpha2 agonist, dexmedetomidine, by determining whether physostigmine, a cholinesterase inhibitor, could antagonize the hypnotic response to dexmedetomidine in the rat and whether dexmedetomidine decreases the release of acetylcholine (ACh) in the thalamus in vivo. 2. Physostigmine did not significantly change the duration of the hypnotic response to dexmedetomidine. There was no significant change in thalamic ACh release after administration of dexmedetomidine. Therefore, alpha2-adrenergic agonists produce their anesthetic effect through mechanisms which do not involve alteration of the activity of the brainstem cholinergic nuclei.

Comparison of 24-hour blood pressure, heart rate, and autonomic nerve activity in hypertensive patients treated with cilnidipine or nifedipine retard

We compared the effects of cilnidipine and nifedipine retard on 24-h blood pressure (BP), heart rate (HR), and autonomic nerve activity in patients with essential hypertension. Cilnidipine is a novel and unique 1,4-dihydropyridine calcium antagonist that has the L-type and N-type voltage-dependent calcium channel-blocking action. Fourteen hypertensive outpatients (four men and 10 women; aged 64 +/- 2 years, mean +/- SEM) were enrolled in this study. Their ambulatory BP and electrocardiogram were monitored for 24 h at intervals of 30 min with a portable recorder after a 4-week drug-free period, after a 4-week treatment period with cilnidipine (5 or 10 mg once daily), and after a 4-week treatment period with nifedipine retard (10 or 20 mg twice daily). The order of the three periods was randomized. Autonomic nerve activity was evaluated by a power spectral analysis of HR variability, by using the high-frequency (HF) component as an index of parasympathetic nerve activity and the ratio of the low-frequency (LF) component to the HF component (LF/HF) as an index of sympathovagal balance. Cilnidipine and nifedipine retard significantly reduced the 24-h BP of these patients to similar extents (cilnidipine, -11 +/- 3/-6 +/- 1 mm Hg; nifedipine retard, -15 +/- 3/-6 +/- 2 mm Hg). Cilnidipine did not change the 24-h average HR, whereas nifedipine retard significantly increased it (+3.3 +/- 1.4 beats/min; p < 0.05). Nifedipine retard significantly increased the LF/HF ratio in the daytime and the nighttime. Such changes were limited to the daytime in the treatment period with cilnidipine. These results suggest that cilnidipine is effective as a once-daily antihypertensive agent and had less influence on autonomic nervous system and HR than did nifedipine retard.