Autonomic neurogenesis and apoptosis are alternative fates of progenitor cell communities induced by TGFbeta

The question of how appropriate cell types are generated in correct numbers during development of the peripheral nervous system has become particularly intriguing with the identification of multipotent progenitor cells in postmigratory targets of the neural crest. Recently, we have provided evidence that community effects in response to factors of the TGFbeta family might represent a mechanism to suppress inappropriate nonneural fates from multipotent progenitors in developing peripheral ganglia. In culture, BMP2 and TGFbeta promote neurogenesis at the expense of a smooth-muscle-like fate in clusters of neural-crest-derived multipotent progenitor cells. We now show that the neurons generated by TGFbeta factors belong to the autonomic lineage and that cells within the developing sympathetic ganglia express TGFbeta-type II receptor. In addition to its neurogenic activity, TGFbeta but not BMP2 also induces apoptosis as an alternative fate in cultured progenitor communities. Interestingly, these fate decisions are controlled by graded changes in TGFbeta concentrations: lower doses of TGFbeta promote neurogenesis while slightly higher doses induce predominantly apoptosis. These effects of TGFbeta are specific for an early developmental stage since progenitor cells lose their competence to respond to the proapoptotic activity of TGFbeta upon neuronal differentiation. In vivo, the expression of TGFbeta3 in differentiated neurons suggests that the signal concentration gradually increases with the number of neurons formed in the autonomic ganglia. We propose that TGFbeta functions in a biphasic manner during autonomic gangliogenesis to control both neurogenesis and subsequently the number of neurons generated from progenitor cells.

Actions of histamine on muscle and ganglia of the guinea pig gallbladder

Histamine is an inflammatory mediator present in mast cells, which are abundant in the wall of the gallbladder. We examined the electrical properties of gallbladder smooth muscle and nerve associated with histamine-induced changes in gallbladder tone. Recordings were made from gallbladder smooth muscle and neurons, and responses to histamine and receptor subtype-specific compounds were tested. Histamine application to intact smooth muscle produced a concentration-dependent membrane depolarization and increased excitability. In the presence of the H(2) antagonist ranitidine, the response to histamine was potentiated. Activation of H(2) receptors caused membrane hyperpolarization and elimination of spontaneous action potentials. The H(2) response was attenuated by the ATP-sensitive K(+) (K(ATP)) channel blocker glibenclamide in intact and isolated smooth muscle. Histamine had no effect on the resting membrane potential or excitability of gallbladder neurons. Furthermore, neither histamine nor the H(3) agonist R-alpha-methylhistamine altered the amplitude of the fast excitatory postsynaptic potential in gallbladder ganglia. The mast cell degranulator compound 48/80 caused a smooth muscle depolarization that was inhibited by the H(1) antagonist mepyramine, indicating that histamine released from mast cells can activate gallbladder smooth muscle. In conclusion, histamine released from mast cells can act on gallbladder smooth muscle, but not in ganglia. The depolarization and associated contraction of gallbladder smooth muscle represent the net effect of activation of both H(1) (excitatory) and H(2) (inhibitory) receptors, with the H(2) receptor-mediated response involving the activation of K(ATP) channels.

Paraldehyde and methylpentynol and ganglionic transmission

Paraldehyde and methylpentynol blocked transmission of nerve impulses through the superior cervical ganglion of the cat when the drugs were administered intra-arterially to the ganglion or intravenously using the nictitating membrane as an indicator. Electrical studies showed that concentrations of methylpentynol and paraldehyde which blocked transmission in the isolated rat superior cervical ganglion were without action on the preganglionic nerve fibre. In amounts which blocked transmission in the isolated rat ganglion, paraldehyde had no depolarizing activity directly on the ganglion cells and did not interfere with the depolarizing activity of added acetylcholine. The results suggest that the block in transmission of the impulse could be accounted for by a decrease in the release of acetylcholine from the preganglionic nerve terminals. In both species the block was reversible.

Effect of histamine on ganglionic transmission

Histamine has been shown to depress transmission through the perfused superior cervical ganglion of the cat when doses of 150 mug. or more were administered. The intensity of the ganglionic block was related to the dose of histamine employed. In one-third of the experiments, a slow contracture of the nictitating membrane occurred after histamine had been injected; the contracture lasted up to 10 min., and subsequent injections of histamine gave rise to progressively smaller responses. The blocking action of histamine was evident in all experiments and was the most prominent feature observed. Histamine in a sub-depressant dose enhanced the action of the competitive blocking agents tetraethylammonium and hexamethonium, and also the depolarizing blocking agents tetramethylammonium and nicotine. The possible physiological rôle of histamine in the autonomic nervous system is discussed.

The effect of methylpentynol and methylpentynol carbamate on the perfused superior cervical ganglion of the cat

The action of methylpentynol and methylpentynol carbamate on the perfused superior cervical ganglion of the cat was analysed. Both drugs, in doses of 1 to 5 mg., depressed the output of acetylcholine. If the acetylcholine output was reduced by more than about 50%, transmission failed. Both drugs also reduced the response of the ganglion to injected acetylcholine. The carbamate, but not methylpentynol itself, had a transient stimulant action on the ganglion, unaccompanied by acetylcholine release.

Endogenous tachykinins cause bradycardia by stimulating cholinergic neurons in the isolated guinea pig heart

The purpose of this study was to determine if endogenous tachykinins can cause bradycardia in the isolated perfused guinea pig heart through stimulation of cholinergic neurons. Capsaicin was used to stimulate release of tachykinins and calcitonin gene-related peptide (CGRP) from cardiac afferents. A bolus injection of 100 nmol capsaicin increased heart rate by 26 +/- 7% from a baseline of 257 +/- 14 beats/min (n = 6, P < 0.01). This positive chronotropic response was converted to a minor bradycardic effect in hearts with 1 microM CGRP-(8-37) present to block CGRP receptors. The negative chronotropic response to capsaicin was markedly potentiated in another group of hearts with the further addition of 0.5 microM neostigmine to inhibit cholinesterases. In this group, capsaicin decreased heart rate by 30 +/- 10% from a baseline of 214 +/- 6 beats/min (n = 8, P < 0.05). This large bradycardic response to capsaicin was inhibited by 1) infusion of neurokinin A to desensitize tachykinin receptors or 2) treatment with 1 microM atropine to block muscarinic receptors. The latter observations implicate tachykinins and acetylcholine, respectively, as mediators of the bradycardia. These findings support the hypothesis that endogenous tachykinins could mediate axon reflexes to stimulate cholinergic neurons of the intrinsic cardiac ganglia.

Trophic actions of neurotrophin-3 on postnatal rat myenteric neurons in vitro

A number of neurotrophic factors have been implicated in the prenatal development of the enteric nervous system. Although several of these factors continue to be expressed in the gut during postnatal life, their actions on postnatal enteric neurons are not understood. One such factor is the neurotrophin, NT-3. Both NT-3 and its high affinity receptor, trk C, are expressed in the postnatal gut at a time when changes in the density of intestinal innervation are occurring. We have therefore examined the effects of NT-3 on postnatal myenteric neurons, using dissociated cell cultures of ganglia isolated from 6-8 day postnatal rat small intestine. Effects of NT-3 on neurite outgrowth and neuronal and glial cell numbers were measured after 2 days in vitro. The proportion of neurons was increased in NT-3 treated cultures, as was the proportion of neurons that extended processes. NT-3 treatment, at concentrations of between 0.1 ng and 10 ng/ml, also resulted in a significant increase in mean total neurite length. These results indicate that NT-3 may play a role in the postnatal development of the enteric nervous system.

Interleukin-1beta causes a biphasic response in neurons of rat major pelvic ganglia

The effect of interleukin-1beta (IL-1beta) on peripheral autonomic neurons was examined with intracellular microelectrodes, in vitro. Recombinant human IL-1beta (6-300 pM) produced a depolarization, associated with decrease in input resistance, followed by a hyperpolarization, associated with increase in input resistance, in neurons of rat major pelvic ganglia (MPG). IL-1beta 163-171 (10-100 pM), the active domain of human IL-1beta, also produced a biphasic response. The IL-1beta-induced responses reversed polarity at the equilibrium potential for Cl-. The IL-1beta-induced responses were blocked by picrotoxin (100 microM) but not by bicuculline (20 microM). Imidazole-4-acetic acid (14AA, 100 microM), a GABA(C) receptor antagonist, reduced the IL-1beta-induced responses. The results suggest that the IL-1beta-induced biphasic response is mediated through GABA(C) receptors in rat MPG neurons.

Androgen-sensitive preganglionic neurons innervate the male rat pelvic ganglion

In adult male rats many pelvic autonomic ganglion cells change in structure and function after androgen deprivation. In this study we have investigated whether preganglionic neurons in the lumbar and sacral spinal cord that innervate these ganglion cells are also androgen-sensitive. Numerous spinal neurons retrogradely labelled from the pelvic ganglion possessed androgen receptor immunoreactivity and this was diminished by castration or enhanced by additional testosterone exposure. These comprised 27-77% of all preganglionic neurons innervating the pelvic ganglion, depending on the spinal level and whether animals were administered testosterone prior to sacrifice or not. When adult animals were castrated, no change occurred in the soma size or number of primary dendrites in these lumbar or sacral preganglionic neurons. Mean dendrite length was also determined in lumbar preganglionic neurons supplying the pelvic ganglion, but was not affected by castration. However, the total volume of lumbar preganglionic terminal varicosities supplying each noradrenergic pelvic ganglion cell decreased in parallel with the volume of the target neuron. These studies show that many preganglionic autonomic neurons involved in pelvic reflexes are androgen-sensitive, but that androgens selectively influence particular neuronal compartments. The prevalence of androgen receptors in these neurons suggests that testosterone may directly influence gene expression of preganglionic neurons. Together these studies suggest that testosterone (or a metabolite) has widespread actions on pelvic reflex circuits during adulthood and that under conditions of diminished circulating androgens a variety of reflex activities may not function optimally.

Serotonin receptor subtypes that depolarize guinea pig inferior mesenteric ganglion neurons

Our previous studies indicated that serotonin (5-HT) depolarized a majority of guinea pig inferior mesenteric ganglion (IMG) neurons and may be another transmitter for the noncholinergic late slow excitatory postsynaptic potential (ls-EPSP) in the IMG. However, the subtypes of 5-HT receptor mediating these responses have not yet been identified. Using intracellular recording, we examined the effect of 5-HT receptor antagonists with specificity to various 5-HT receptor subtypes on the 5-HT-mediated depolarization and ls-EPSP in IMG neurons in vitro. Cyproheptadine, a 5-HT(1/2) receptor antagonist, reversibly inhibited the slow, but not the fast, depolarization and ls-EPSP in the 5-HT-sensitive neurons. Both mianserin and spiperone, 5-HT(2) and 5-HT(1A) receptor antagonists, did not significantly alter either the fast or slow depolarizing responses or the ls-EPSP. The 5-HT(3) receptor antagonist MDL 72222 (Bemesetron) completely inhibited the fast depolarization with little diminution of the slow depolarization and ls-EPSP. Superfusion of putative 5-HT(1P) receptor antagonist, BRL 24924 (Renzapride), reversibly attenuated both the depolarization and ls-EPSP. However, 5-HT-insensitive neurons with ls-EPSP were found to be insensitive to both cyproheptadine and BRL 24924. In most 5-HT-sensitive neurons, the 5-HT(3) receptor agonist, 2-methyl-5-HT, and the selective 5-HT(1P) agonist, MCPP or 5-OHIP, evoked a fast and a slow depolarization in 55.6 and 71.4% of the neurons, respectively, without a significant effect on the membrane potential in 85.7 and 100% of the 5-HT-insensitive neurons. In 5-HT-sensitive neurons, MDL 72222 reversibly abolished the fast depolarization induced by 2-methyl-5-HT; BRL 24924 significantly inhibited the slow depolarization induced by MCPP or 5-OHIP, but not by SP. Prolonged superfusion of 5-HT-sensitive neurons with MCPP abolished the evoked ls-EPSP without inhibition of action potential. These results suggest that the fast and slow depolarizations in these neurons are mediated by 5-HT(3) and 5-HT(1P) receptor subtypes, respectively. The latter may also mediate the ls-EPSP in 5-HT-sensitive neurons.

Immediate-early gene expression in the inferior mesenteric ganglion and colonic myenteric plexus of the guinea pig

Activation of neurons in the inferior mesenteric ganglion (IMG) was assessed using c-fos, JunB, and c-Jun expression in the guinea pig IMG and colonic myenteric plexus during mechanosensory stimulation and acute colitis in normal and capsaicin-treated animals. Intracolonic saline or 2% acetic acid was administered, and mechanosensory stimulation was performed by passage of a small (0.5 cm) balloon either 4 or 24 hr later. Lower doses of capsaicin or vehicle were used to activate primary afferent fibers during balloon passage. c-Jun did not respond to any of the stimuli in the study. c-fos and JunB were absent from the IMG and myenteric plexus of untreated and saline-treated animals. Acetic acid induced acute colitis by 4 hr, which persisted for 24 hr, but c-fos was found only in enteric glia in the myenteric plexus and was absent from the IMG. Balloon passage induced c-fos and JunB in only a small subset of IMG neurons and no myenteric neurons. However, balloon passage induced c-fos and JunB in IMG neurons (notably those containing somatostatin) and the myenteric plexus of acetic acid-treated animals. After capsaicin treatment, c-fos and JunB induction by balloon passage was inhibited in the IMG, but there was enhanced c-fos expression in the myenteric plexus. c-fos and JunB induction by balloon stimulation was also mimicked by acute activation of capsaicin-sensitive nerves. These data suggest that colitis enhances reflex activity of the IMG by a mechanism that involves activation of both primary afferent fibers and the myenteric plexus.

Leptin modulates fast synaptic transmission in dog pancreatic ganglia

The aim of this study was to determine whether leptin modulates neuronal activity in intrapancreatic ganglion neurons. Intracellular recordings were made in dog pancreatic neurons. Recombinant mouse leptin (313 nM) was added by superfusion. When leptin was present, fast EPSPs which were subthreshold in normal Krebs solution reached threshold for firing action potentials. However, leptin had no significant (P > 0.05, n = 18) effect on either the resting membrane potential or on membrane input resistance. To determine whether leptin increased the postsynaptic sensitivity to acetylcholine, the response was tested by pressure ejection of acetylcholine. Acetylcholine evoked a 9.4+/-2.2 mV (mean +/- SEM, n = 5) depolarization in normal Krebs solution. In the presence of leptin, the response was not significantly different (9.6+/-2.4 mV, P > 0.05). The results suggest that leptin modulates fast synaptic transmission in pancreatic ganglion neurons by acting on presynaptic nerve terminals.

Cardiovascular activity of 14-deoxy-11,12-didehydroandrographolide in the anaesthetised rat and isolated right atria

The cardiovascular activity of 14-deoxy-11,12-didehydroandrographolide (DDA) from Andrographis paniculata (Burm.f.) Nees (Acanthaceae) was elucidated in anaesthetised Sprague-Dawley (SD) rats and isolated rat right atria. In anaesthetised rats, DDA produced significant falls in mean arterial blood pressure (MAP) and heart rate in a dose-dependent manner with the maximum decrease of 37.6 +/- 2.6% and 18.1 +/- 4.8%, respectively. The ED50 value for MAP was 3.43 mmol kg-1. Pharmacological antagonist studies were done using this dose. The hypotensive action of DDA was not mediated through effects on the alpha-adrenoceptor, muscarinic cholinergic and histaminergic receptors, for it was not affected by phentolamine, atropine as well as pyrilamine and cimetidine. However, it seems to work via adrenoceptors, autonomic ganglia receptor and angiotensin-converting enzyme, since the hypotensive effect of DDA was negated or attenuated in the presence of propranolol, hexamethonium and captopril. In the isolated right atria, DDA caused negative chronotropic action and antagonised isoproterenol-induced positive chronotropic actions in a non-competitive and dose-dependent manner. These results further supported the bradycardia-inducing and beta-adrenoceptor antagonistic properties of DDA in vivo.

Central somatostatin diminished inhibitory action of central CGRP on pancreatic basal secretion in conscious rats

We examined whether central somatostatin prevents an inhibitory effect of central calcitonin-gene related peptide (CGRP) on pancreatic secretion in conscious male Wistar rats (330-330 g). Rats were prepared with separate cannulas for draining bile and pancreatic juice and with a duodenal cannula and an extrajugular vein cannula. In addition, another cannula was stereotactically implanted into the left lateral cerebral ventricle. Rats were placed in restraint cages and experiments were conducted 4 days after the operation without anesthesia. An injection of CGRP (0.1, 1.0 nmol/10 microl) into the left lateral cerebral ventricle (i.c.v.) inhibited pancreatic secretion dose-dependently. To confirm the inhibitory effect of CGRP (i.c.v.) was mediated via sympathetic nerves, phentolamine was injected intravenously (i.v.) bolus (0.5 mg kg(-1)) 0.5-h before CGRP (i.c.v.), followed by continuous infusion of 0.2 mg kg(-1) h(-1). Phentolamine (i.v.) reversed the inhibition produced by CGRP (i.c.v.). An injection of 4 nmol/10 microl somatostatin (i.c.v.) 5 min prior to CGRP injection diminished the inhibitory effect of CGRP (i.c.v.). It is concluded that centrally administered somatostatin diminished the inhibitory action of CGRP (i.c.v.) on pancreatic secretion, probably via inhibiting autonomic (sympathetic) nerve excitation at the central site.

Regulation of excitatory neural input to longitudinal intestinal muscle by myenteric interneurons

The circuit of myenteric interneurons that regulate excitatory input to longitudinal colonic muscle was identified using dispersed ganglia and longitudinal muscle strips with adherent myenteric plexus from rat distal colon. The preparations enabled measurement of neurotransmitter release from interneurons and/or excitatory motoneurons innervating longitudinal muscle. 1, 1-Dimethyl-4-phenylpiperizinium (DMPP) and somatostatin were used to activate myenteric neurons in dispersed ganglia and muscle strips, respectively. DMPP-stimulated vasoactive intestinal peptide (VIP) release in dispersed ganglia was inhibited by [Met]enkephalin and bicuculline and augmented by naloxone and GABA, implying that inhibitory opioid and stimulatory GABA neurons regulate the activity of VIP interneurons. In muscle strips, VIP stimulated basal and augmented somatostatin-induced substance P (SP) release; the somatostatin-induced increase in SP release was inhibited by VIP-(10-28) and NG-nitro-L-arginine, implying that excitatory VIP neurons regulate tachykinin motoneurons innervating longitudinal muscle. Somatostatin inhibited [Met]enkephalin and stimulated VIP release; basal and somatostatin-stimulated VIP release were inhibited by [Met]enkephalin and bicuculline and augmented by naloxone and GABA, implying that inhibitory pathways linking somatostatin, opioid, and GABA neurons regulate VIP interneurons, which in turn regulate tachykinin and probably cholinergic motoneurons.

Organization of intrinsic cholinergic neurons projecting within submucosal plexus of guinea pig ileum

Electrophysiological techniques were employed to examine the organization of the projections of submucosal neurons in the submucosal plexus of guinea pig ileum. These neurons were activated by focal pressure-pulse application of 5-hydroxytryptamine (5-HT) to single ganglia in submucosal preparations in vitro, and resulting fast excitatory postsynaptic potentials (EPSPs) were recorded intracellularly in S-type neurons. 5-HT-evoked fast EPSPs were blocked by TTX, hexamethonium, and ICS-205-930 (tropisetron). 5-HT was applied either directly to the ganglion containing the neuron recorded intracellularly or to adjacent ganglia positioned at increasing distances on either side of the impaled cell in circumferential or longitudinal orientations. All S-type neurons recorded in this study (n = 103) received nicotinic fast EPSPs from cholinergic neurons when 5-HT was applied directly to the ganglion containing the impaled neuron. Stimulation of adjacent ganglia also evoked nicotinic fast EPSPs, but the number of neurons that received this input decreased as the distance between the stimulus and the impaled cell increased. Maximal projections were 3 mm in the circumferential and orad-to-aborad orientations. There were no significant projections in the aborad-to-orad direction. These findings suggest that S-type neurons in the submucosal plexus are innervated by intrinsic cholinergic neurons that project over relatively short distances and have a distinct orad-to-aborad polarity.

Activation of alpha- and beta-adrenoceptors by sympathetic nerve stimulation in the large intestine of the rat

1. The effects of sympathetic nerve stimulation on the motility of the circular and longitudinal muscle of the large intestine were investigated in vitro, and the involvement of various adrenoceptor subtypes determined. A comparison between the sympathetic supply arising from the prevertebral and pelvic ganglia was also made. 2. In the longitudinal muscle of the distal colon, sympathetic nerve stimulation caused responses which were contractile (0.1-2 Hz), biphasic (5-10 Hz) or purely inhibitory (20-30 Hz). All contractile responses were removed with phentolamine (3 microM), whereas the inhibitory responses were significantly diminished by propranolol (0.1 microM) and completely abolished by alprenolol (3 microM) or nadolol (300 microM). 3. In the longitudinal muscle of the proximal colon, the effects of sympathetic nerve stimulation were predominantly inhibitory. Some of this inhibition was removed by propranolol (0.1 microM), but was largely unaffected by alprenolol (3 microM). The remainder of the inhibitory response was probably non-noradrenergic as it was not removed by a combination of phentolamine (3 microM) and alprenolol (3 microM). 4. In the circular muscle of both the proximal and distal colon, sympathetic stimulation caused a strong contractile response which was completely removed by phentolamine (3 microM) to reveal an inhibitory response. This inhibitory response was unchanged by propranolol (0.1 microM) but was removed by alprenolol (3 microM), following which a weak non-noradrenergic contractile response was unmasked. 5. Stimulation of the hypogastric nerve to activate pelvic sympathetic pathways had no effect on the motility of the longitudinal muscle, but caused a contractile response in the circular muscle which was completely removed by phentolamine (3 microM). 6. We conclude that sympathetic nerves innervate adrenoceptors of different types in the various muscle layers and regions of the colon. They innervate a mixture of alpha-, and beta(3)-adrenoceptors in the longitudinal muscle of the proximal colon, alpha-, classical beta- and beta(3)-adrenoceptors in the distal colon, and primarily alpha-adrenoceptors with a few beta(3)-adrenoceptors in the circular muscle. In addition, the pelvic sympathetic innervation of the rectum differs from the prevertebral supply by innervating only excitatory alpha-adrenoceptors.

Systemic hemodynamic responses to chronic angiotensin II infusion into the renal artery of dogs

Chronic intrarenal infusion of angiotensin II (0.5 ng.kg-1.min-1) in dogs increases arterial pressure. In the present study we determined whether this was associated with changes in cardiac output or in total peripheral resistance. Mean arterial pressure did not change initially but was significantly increased over days 14-28 of the infusion period (+6 +/- 2 mmHg), as was total peripheral resistance (+4 +/- 2 mmHg.min.l-1). Neither cardiac output, renal blood flow, nor glomerular filtration rate was significantly changed over this period. To determine the influence of the autonomic nervous system on the developing hypertension, periodic acute autonomic ganglion blockade was performed. Before angiotensin II infusion ganglion blockade reduced total peripheral resistance and increased cardiac output, and this effect was similar across the 4 wk of angiotensin II infusion. Systemic hemodynamics were not affected by intravenous angiotensin II infusion (0.5 ng.kg-1.min-1). Thus intrarenal infusion of low-dose angiotensin II produced a chronic increase in arterial pressure due to an action within the kidney. The hypertension was associated with increased total peripheral resistance but not with marked changes in cardiac output or renal function or in the influence of the autonomic nervous system on systemic hemodynamics.

Effects of inhalation anesthetics on parasympathetic reflex vasodilation in the lower lip and palate of the cat

The present experiments were designed to examine the effects of inhalation anesthetics (isoflurane, halothane, and sevoflurane) on the parasympathetic reflex vasodilation in the lower lip and palate elicited by electrical stimulation of the central cut end of the lingual nerve in vagosympathectomized cats. Isoflurane (1.5%), halothane (1.0%), and sevoflurane (2.5%), each at a concentration of 1.0 minimum alveolar concentration, markedly suppressed the evoked blood flow increases in the lower lip, whereas nitrous oxide (70% in 30% oxygen) and morphine (2 mg/kg iv) did not. Prior administration of picrotoxin, a gamma-aminobutyric acid (GABA) antagonist (2 mg/kg iv), reversed the inhibitory effect of isoflurane on the parasympathetic reflex response. Decerebration had no significant effect on the isoflurane-induced inhibition. These findings suggest that there is a GABA-mediated suppressive mechanism acting on this parasympathetic reflex response; the sites at which inhalation anesthetics exert such an inhibitory action could be in the midbrain, pons, or medulla, but not in the hypothalamus or higher structure.

Myocardial protection by brief ischemia in noncardiac tissue

BACKGROUND

Brief coronary artery occlusions (CAOs) protect both the artery's own perfusion territory ("myocardial preconditioning") and adjacent "virgin" myocardium. Whether ischemia in remote organs protects myocardium is unknown. We examined whether brief occlusion of the anterior mesenteric artery (MAO) or left renal artery (RAO) protects against myocardial infarction.

METHODS AND RESULTS

Area at risk (AR) and infarcted area (IA) were determined in anesthetized rats after 180 minutes of reperfusion following a 60-minute CAO. At normothermia (body temperature, 36.5 degrees C to 37.5 degrees C), IA/AR was 68 +/- 2% (mean +/- SEM, n = 11) in control rats and 50 +/- 3% (n = 9, P < .001) in rats preconditioned by 15-minute CAO 10 minutes before 60-minute CAO. A 15-minute MAO was equally protective (IA/AR = 50 +/- 3%, n = 10, P < .001), whereas 15-minute RAO failed to limit IA/AR (72 +/- 5%, n = 8). Hypothermia (body temperature, 30 degrees C to 31 degrees C) did not affect IA/AR (67 +/- 3%, n = 11) in control animals but enhanced protection by 15-minute CAO (IA/AR = 22 +/- 3%, n = 8), whereas protection by 15-minute MAO (IA/AR = 44 +/- 5%, n = 11, P < .001) was minimally enhanced. Hypothermia unmasked protection by 15-minute RAO (IA/AR = 46 +/- 6%, n = 9, P < .01). Hexamethonium (20 mg/kg IV) did not alter protection by 15-minute CAO, but it abolished protection by 15-minute MAO. When MAO was sustained throughout the study, cardioprotection was absent.

CONCLUSIONS

Brief ischemia in "remote" organs protects myocardium against infarction as effectively as myocardial preconditioning. The mechanism of protection by MAO differs from that of CAO, because ganglion blockade abolished protection by MAO but not by CAO. The neurogenic pathway is activated during reperfusion after 15-minute MAO, because sustained MAO failed to produce cardioprotection.

Actions of calcitonin gene-related peptide in guinea pig gallbladder ganglia

The actions of calcitonin gene-related peptide (CGRP) have been determined from intracellular recordings obtained from gallbladder neurons in intact whole mount preparations. In most cells, pressure microejection of CGRP elicited a slow, monophasic depolarization, 4 mV in amplitude, that was associated with a decrease in input resistance and increased excitability. The CGRP-induced depolarization was attenuated in a low-Na+ solution and had a reversal potential of -8 mV. In 10% of the cells, microejection of CGRP elicited a biphasic response that was composed of a rapid transient depolarization followed by a slow depolarization that was similar to the monophasic response. Addition of CGRP (1-10 nM) to the bathing solution elicited a monophasic depolarization and desensitized the cells to applications of CGRP by microejection. Forskolin, applied either by microejection or bath application, also depolarized gallbladder neurons and produced cross-desensitization to CGRP. Responses to substance P were not enhanced by CGRP, and CGRP did not affect fast synaptic responses. It is concluded that CGRP may contribute to a local axon reflex response in gallbladder ganglia.

Autonomic mediation of glucagon secretion during insulin-induced hypoglycemia in rhesus monkeys

Autonomic activation mediates the majority of the increase of glucagon secretion during insulin-induced hypoglycemia in several species including dogs, mice, and rats. However, the role of the autonomic nervous system to increase glucagon during hypoglycemia in humans remains controversial, and investigations in nonhuman primates have not been previously conducted. The autonomic contribution to glucagon secretion during hypoglycemia in a nonhuman primate was examined by two independent pharmacological approaches. Glucagon responses to clamped insulin-induced hypoglycemia were compared in conscious rhesus monkeys in the presence or absence of ganglionic blockade with trimethaphan, or during combined muscarinic and adrenergic receptor blockade with atropine, propranolol, and tolazoline. Insulin-induced hypoglycemia (plasma glucose = 1.9 +/- 0.1 mmol/l) activated parasympathetic nerves to the pancreas as assessed by increased plasma pancreatic polypeptide (PP) levels (delta = 135.0 +/- 36.8 pmol/l, P < 0.01), produced sympathoadrenal activation as assessed by elevations of plasma epinephrine (EPI) (delta = 22.3 +/- 2.95 nmol/l, P < 0.0005) and norepinephrine (NE) (delta = 3.72 +/- 0.77 mmol/l, P < 0.0025) and increased plasma immunoreactive glucagon (IRG) (delta = 920 +/- 294 ng/l, P < 0.025). Nicotinic ganglionic blockade with trimethaphan prevented parasympathetic (deltaPP = 16.5 +/- 16.3 pmol/l, P < 0.01 vs. control) and sympathoadrenal (deltaEPI = 1.52 +/- 0.98 nmol/l; deltaNE = -0.62 +/- 0.24 mmol/l, both P < 0.0025 vs. control) activation during hypoglycemia and inhibited the IRG response by 70% (delta = 278 +/- 67 ng/l, P < 0.025 vs. control). Combined muscarinic and adrenergic receptor blockade reduced parasympathetic activation (deltaPP = 48.3 +/- 16.3 pmol/l, P < 0.01 vs. control) and inhibited the IRG response by a similar degree to ganglionic blockade (deltaIRG = 284 +/- 60 ng/l, P < 0.025 vs. control). These results demonstrate by two independent pharmacological approaches that autonomic activation makes a substantial contribution to increased glucagon secretion during hypoglycemia of approximately 2.0 mmol/l in a species of nonhuman primate.

Functional, biochemical and anatomical changes in the rat urinary bladder induced by perigangliar injection of colchicine

The aim of this study was to assess the effect of blocking the axonal transport of sensory neuropeptides, by local injection of colchicine at pelvic ganglia level, on the sensory and efferent functions mediated by capsaicin-sensitive primary afferent neurons innervating the rat urinary bladder. Bilateral injection of colchicine in the prostatic tissue underneath the pelvic ganglia of male rats induced a time-dependent reduction (maximal at 72 h, 100% reduction) of the in vitro contraction of the bladder strips induced by capsaicin (1 microM). The response to electrical field stimulation was also reduced, although to a lesser extent. The direct contractions induced by substance P (100 nM) or KCl (80 mM) were not affected by colchicine pretreatment. In vivo, perigangliar injection of colchicine (72 h before) greatly increased bladder capacity, and reduced the amplitude of micturition contractions and micturition frequency. Capsaicin-induced plasma protein extravasation was abolished in the urinary bladder and reduced in the distal, but not the proximal ureter of colchicine-treated rats. Topical application of capsaicin onto the urinary bladder or onto the stomach induced a cardiovascular pressor reflex in urethane-anaesthetized, spinalized rats. Colchicine pretreatment reduced (by about 50%) the pressor response elicited by chemonociceptive stimulation of the bladder but not that arising from the stomach. Colchicine pretreatment did not produce overt changes of nerve profiles immunoreactive for calcitonin gene-related peptide- or tachykinin-like material in the rat urinary bladder. A more intense staining of nerve fibres positive for calcitonin-gene related peptide-like immunoreactivity and tachykinin-like immunoreactivity was observed in pelvic ganglia of colchicine-pretreated rats. No changes were detected in the dorsal horns of spinal cord segments where pelvic bladder afferents project (L6-S1). Colchicine pretreatment reduced, but did not abolish, bladder levels of substance P-, neurokinin A-, calcitonin gene-related peptide- and neuropeptide Y-like immunoreactivity. However, vasoactive intestinal peptide-like immunoreactivity levels were not changed. The capsaicin-evoked (1 microM) release of calcitonin gene-related peptide was abolished in capsaicin as well as in colchicine-pretreated animals. The present findings demonstrate that local treatment of pelvic ganglia with colchicine totally eliminates the "efferent" functions of capsaicin-sensitive afferent nerves in the urinary bladder. Although reduced, tissue levels of sensory neuropeptides are not completely depleted, thus indicating the existence of a releasable versus non-releasable pool. The chemically induced blockade of axoplasmic transport also induces a limited impairment of the sensory function of capsaicin-sensitive afferents, and of the parasympathetic efferent system.

[Multinuclear neurons in the ganglia of the gastrointestinal tract]

Findings of light optical and electron microscopy studies on formation of multinuclear neurons in gastrointestinal tract myenteric plexus in mammals affected by extreme factors (vagotomy, modelling of portal hypertension. Hyperbaric oxygenation and hypergravitation) were presented. A model for original transformation of multinuclear neuron as a mechanism of new nerve cells formation in the course of the organism compensatory-adaptive reaction to extreme action was obtained.