Coexistence and corelease of cholinergic and peptidergic transmitters in frog sympathetic ganglia

Both acetylcholine (ACh) and a peptide that resembles luteinizing hormone-releasing hormone (LHRH) serve as transmitters in sympathetic ganglia of the bullfrog. Although ACh is contained and released from both preganglionic B fibers, which form synaptic contacts with only B cells in the ganglia, and preganglionic C fibers, which are in synaptic contact with C cells only, the LHRH-like peptide is contained and released exclusively from preganglionic C fibers. The same preganglionic C fibers appear to supply both ACh and the LHRH-like peptide because the thresholds for the cholinergic fast excitatory postsynaptic potential (EPSP) correlate well with the thresholds for the peptidergic late slow EPSP recorded in the same C cell. Further, anatomical studies showed that almost all nerve terminals on C cells contained the LHRH-like peptide. Some of these same terminals must also contain and release. ACh, mediating the cholinergic fast EPSPs with millisecond synaptic delays. Therefore at least some, if not all, terminals of preganglionic C fibers contain and release both cholinergic and peptidergic transmitters.     

Acetylcholine Synthesis by a Sympathetic Ganglion in the Presence of 2-(4-Phenylpiperidino)cyclohexanol (AH5183) and Picrylsulfonic Acid

The present experiments measured the release and the synthesis of acetylcholine (ACh) by cat sympathetic ganglia in the presence of 2-(4-phenylpiperidino)cyclohexanol (AH5183 or vesamicol) and/or picrylsulfonic acid (TNBS), two compounds known to have the ability to block the uptake of ACh by cholinergic synaptic vesicles in vitro. We confirmed that, in stimulated (5 Hz) perfused (30 min) ganglia, AH5183 depressed ACh release and ACh tissue content increased by 86 +/- 6% compared to contralateral ganglia used as controls. Preganglionic activity increased ACh release by a similar amount in the presence (19.9 +/- 1.0 pmol/min) or absence (20.5 +/- 2.4 pmol/min) of TNBS. The final tissue ACh content was also similar in the presence (1,668 +/- 166 pmol) or absence (1,680 +/- 56 pmol) of TNBS. However, the AH5183-induced increase of tissue ACh content (86 +/- 6%) was abolished completely when AH5183 was perfused with 1.5 mM TNBS (-3.0 +/- 1.0%). This inhibition of ACh synthesis, observed in TNBS-AH5183-perfused ganglia, was not dependent upon further inhibition of ACh release beyond that caused by AH5183 alone, because 14.0 +/- 1.9% of the transmitter store was released by preganglionic nerve stimulation in the presence of TNBS plus AH5183 and this was similar in the presence of AH5183 without TNBS (14.0 +/- 0.6%). Moreover, when ganglia were first treated with TNBS and then stimulated in the presence of AH5183, an increase of 64 +/- 6% of the ganglionic ACh content occurred, and this increase was not statistically different from the increase measured with AH5183 alone (86 +/- 6%).(ABSTRACT TRUNCATED AT 250 WORDS)     

Vagosympathetic interactions in ischemia-induced myocardial norepinephrine and acetylcholine release

To elucidate the pathophysiological roles of vagosympathetic interactions in ischemia-induced myocardial norepinephrine (NE) and acetylcholine (ACh) release, we measured myocardial interstitial NE and ACh levels in response to a left anterior descending coronary occlusion in the following groups of anesthetized cats: intact autonomic innervation (INT, n = 7); vagotomy (VX, n = 6); local administration of atropine (Atro, n = 6); transection of the stellate ganglia (TSG, n = 5); local administration of phentolamine (Phen, n = 6); and combined vagotomy and transection of the stellate ganglia (VX+TSG, n = 5). The maximum NE release was enhanced in the VX group (141 +/- 30 nmol/l, means +/- SE, P < 0.05) compared with the INT group (61 +/- 12 nmol/l). Neither the Atro (50 +/- 24 nmol/l) nor VX+TSG groups (84 +/- 25 nmol/l) showed enhanced NE release. The maximum ACh release was unaltered in the TSG and Phen groups compared with the INT group (19 +/- 4, 18 +/- 4, and 13 +/- 3 nmol/l, respectively). These findings indicate that the cardiac vagal afferent but not efferent activity reduced the ischemia-induced myocardial NE release. In contrast, the cardiac sympathetic afferent and efferent activities played little role in the ischemia-induced myocardial ACh release.     

Electrophysiological effects of GABA on cat pancreatic neurons

In mammalian peripheral sympathetic ganglia GABA acts presynaptically to facilitate cholinergic transmission and postsynaptically to depolarize membrane potential. The GABA effect on parasympathetic pancreatic ganglia is unknown. We aimed to determine the effect of locally applied GABA on cat pancreatic ganglion neurons. Ganglia with attached nerve trunks were isolated from cat pancreata. Conventional intracellular recording techniques were used to record electrical responses from ganglion neurons. GABA pressure microejection depolarized membrane potential with an amplitude of 17.4 +/- 0.7 mV. Electrically evoked fast excitatory postsynaptic potentials were significantly inhibited (5.4 +/- 0.3 to 2.9 +/- 0.2 mV) after GABA application. GABA-evoked depolarizations were mimicked by the GABA(A) receptor agonist muscimol and abolished by the GABA(A) receptor antagonist bicuculline and the Cl(-) channel blocker picrotoxin. GABA was taken up and stored in ganglia during preincubation with 1 mM GABA; beta-aminobutyric acid application after GABA loading significantly (P < 0.05) increased depolarizing response to GABA (15.6 +/- 1.0 vs. 7.8 +/- 0.8 mV without GABA preincubation). Immunolabeling with antibodies to GABA, glial cell fibrillary acidic protein, protein gene product 9.5, and glutamic acid decarboxylase (GAD) immunoreactivity showed that GABA was present in glial cells, but not in neurons, and that glial cells did not contain GAD, whereas islet cells did. The data suggest that endogenous GABA released from ganglionic glial cells acts on pancreatic ganglion neurons through GABA(A) receptors.     

乙酰胆碱对蟾蜍背根神经节神经元膜电位的影响及离子机制

在离体灌流的蟾蜍背根神经节(DRG)标本上,用微电极进行胞内记录。在73个神经元中,依神经纤维的传导速度将神经元分为 A 型及 C 型,其中 A 型细胞67个,C 型6个,静息膜电位为-67.5±1.3mV((?)±SE)。当加4×10~(-4)—6×10~(-4)mol/L 乙酰胆碱(ACh),可观察到如下四种膜电位变化:1.超极化:幅值9.1±3.0mV((?)±SE,n=23);(2)去极化:幅值12.9±2.2mV((?)+SE,n=20);(3)双相反应(n=24):先超极化,后去极化,超极化幅值8.0±2.4mV((?)+SE),去极化幅值10.9±3.1mV((?)±SE);(4)无反应(n=6)。用阿托品(1.3×10~(-5)mol/L,n=23),或同时应用筒箭毒与六甲双铵(浓度均为1.4×10~(-5)mol/L,n=8)灌流,能分别阻断 ACh 引起的膜的超极化或去极化。ACh 引起超极化反应时膜电导平均增加13.8%,翻转电位值大约-96mV。四乙铵(TEA,20mmol/L)能使 ACh 的去极化幅值增加48.2±3.2%((?)±SE,n=6),超极化幅值减小79.4±4.3%((?)±SE,n=8)。MnCl_2(4mmol/L)使 ACh 的去极化及超极化幅值分别减小54.2±7.2%((?)±SE,n=5)及69.2±6.4%((?)±SE,n=14)。以上结果提示:ACh 引起的 DRG 神经细胞膜去极化反应由 N 型乙酰胆碱受体介导,而超极化反应由 Μ 型乙酰胆碱受体介导,前者可能包含了多种离子电导的改变,后者则可能与钾电导增加有关。     

Comparative research on synaptic transmission in the sympathetic ganglia of rabbits and frogs during acetylcholinesterase inhibition

Organophosphorus inhibitor of acetylcholinesterase (AChE) armin (1 x 10(-6) M) induced a variety of pre- and postsynaptic effects resulting from the AChE inhibition and subsequent accumulation of acetylcholine (ACh) in the synaptic cleft. The intensity of postsynaptic effects (level of neuron depolarization, degree of action potential depression) was shown to be different in the ganglia of frog and rabbit. This could be explained by differences in the total amount of ACh released in response to nerve stimulation as well as at rest. Both muscarinic and nicotinic cholinoreceptors were involved in the process of sustained depolarization of the neurons in the rabbit superior cervical ganglion after AChE inhibition. In frog ganglion neurons the nicotinic receptors did not participate in depolarization evidently due to their fast desensitization. The activation of presynaptic muscarinic receptors resulted in decrease of ACh released by nerve stimulation seems to weaken depolarization and blockade of synaptic transmission in sympathetic ganglia treated by AChE inhibitors.     

Substance P-like immunoreactivity in sympathetic ganglion from toad

Substance P-like immunoreactivity cellular in toad sympathetic ganglia was studied in normal and capsaicin-treated ganglia. In the eighth sympathetic ganglion substance P-like immunoreactive are found in mast cells and SIF cells. The effect of substance P (0.001-0.003 mM) caused increase of compound action potential during tetanical stimulation (50 Hz by 40 sec.) and post-tetanic potentiation (0.1 Hz). Our results show that substance P facilitates synaptic transmission in the sympathetic ganglia from Caudiverbera caudiverbera.     

Effect of mesenteric vascular congestion on reflex control of renal blood flow

Portal hypertension initiates a splenorenal reflex, whereby increases in splenic afferent nerve activity and renal sympathetic nerve activity cause a decrease in renal blood flow (RBF). We postulated that mesenteric vascular congestion similarly compromises renal function through an intestinal-renal reflex. The portal vein was partially occluded in anesthetized rats, either rostral or caudal to the junction with the splenic vein. Portal venous pressure increased (6.5 +/- 0.1 to 13.2 +/- 0.1 mmHg; n = 78) and mesenteric venous outflow was equally obstructed in both cases. However, only rostral occlusion increased splenic venous pressure. Rostral occlusion caused a fall in RBF (-1.2 +/- 0.2 ml/min; n = 9) that was attenuated by renal denervation (-0.5 +/- 0.1 ml/min; n = 6), splenic denervation (-0.2 +/- 0.1 ml/min; n = 11), celiac ganglionectomy (-0.3 +/- 0.1 ml/min; n = 9), and splenectomy (-0.5 +/- 0.1 ml/min; n = 6). Caudal occlusion induced a significantly smaller fall in RBF (-0.5 +/- 0.1 ml/min; n = 9), which was not influenced by renal denervation (-0.2 +/- 0.2 ml/min; n = 6), splenic denervation (-0.1 +/- 0.1 ml/min; n = 7), celiac ganglionectomy (-0.1 +/- 0.3 ml/min; n = 8), or splenectomy (-0.3 +/- 0.1 ml/min; n = 7). Renal arterial conductance fell only in intact animals subjected to rostral occlusion (-0.007 +/- 0.002 ml.min(-1).mmHg(-1)). This was accompanied by increases in splenic afferent nerve activity (15.0 +/- 3.5 to 32.6 +/- 6.2 spikes/s; n = 7) and renal efferent nerve activity (32.7 +/- 5.2 to 39.3 +/- 6.0 spikes/s; n = 10). In animals subjected to caudal occlusion, there were no such changes in renal arterial conductance or splenic afferent/renal sympathetic nerve activity. We conclude that the portal hypertension-induced fall in RBF is initiated by increased splenic, but not mesenteric, venous pressure, i.e., we did not find evidence for intestinal-renal reflex control of the kidneys.     

Developmental changes in transmitter sensitivity and synaptic transmission in embryonic chicken sympathetic neurons innervated in vitro.

Dispersed neurons from embryonic chicken sympathetic ganglia were innervated in vitro by explants of spinal cord containing the autonomic preganglionic nucleus or somatic motor nucleus. The maturation of postsynaptic acetylcholine (ACh) sensitivity and synaptic activity was evaluated from ACh and synaptically evoked currents in voltage-clamped neurons at several stages of innervation. All innervated cells are more sensitive to ACh than uninnervated neurons regardless of the source of cholinergic input. Similarly, medium conditioned by either dorsal or ventral explants mimics innervation by enhancing neuronal ACh sensitivity. This increase is due to changes in the rate of appearance of ACh receptors on the cell surface. There are also several changes in the nature of synaptic transmission with development in vitro, including an increased frequency of synaptic events and the appearance of larger amplitude synaptic currents. In addition, the mean amplitude of the unit synaptic current mode increases, as predicted from the observed changes in postsynaptic sensitivity. Although spontaneous synaptic current amplitude histograms with multimodal distributions are seen at all stages of development, histograms from early synapses are typically unimodal. Changes in the synaptic currents and ACh sensitivity between 1 and 4 days of innervation were paralleled by an increase in the number of synaptic events that evoked suprathreshold activity in the postsynaptic neurons. The early pre- and postsynaptic differentiation described here for interneuronal synapses formed in vitro may be responsible for increased efficacy of synaptic transmission during development in vivo.     

Acetylcholine Synthesis and Release by a Sympathetic Ganglion in the Presence of 2-(4-Phenylpiperidino) Cyclohexanol (AH5183)

These experiments measured the release and the synthesis of acetylcholine (ACh) by cat sympathetic ganglia in the presence of 2-(4-phenylpiperidino) cyclohexanol (AH5183), an agent that blocks the uptake of ACh into synaptic vesicles. Evoked transmitter release during short periods of preganglionic nerve stimulation was not affected by AH5183, but release during prolonged stimulation was not maintained in the drug's presence, whereas it was in the drug's absence. The amount of ACh releasable by nerve impulses in the presence of AH5183 was 194 +/- 10 pmol, which represented 14 +/- 1% of the tissue ACh store. The effect of AH5183 on ACh release was not well antagonized by 4-aminopyridine (4-AP), and not associated with inhibition of stimulation-induced calcium accumulation by nerve terminals. It is concluded that AH5183 blocks ACh release indirectly, and that the proportion of stored ACh releasable in the compound's presence represents transmitter in synaptic vesicles available to the release mechanism. The synthesis of ACh during 30 min preganglionic stimulation in the presence of AH5183 was 2,448 +/- 51 pmol and in its absence it was 2,547 +/- 273 pmol. Thus, as the drug decreased ACh release it increased tissue content. The increase in tissue content of ACh in the presence of AH5183 was not evident in resting ganglia; it was evident in stimulated ganglia whether or not tissue cholinesterase was inhibited; it was increased by 4-AP and reduced by divalent cation changes expected to decrease calcium influx during nerve terminal depolarization.(ABSTRACT TRUNCATED AT 250 WORDS)     

Vagal stimulation suppresses ischemia-induced myocardial interstitial norepinephrine release

Although electrical vagal stimulation exerts beneficial effects on the ischemic heart such as an antiarrhythmic effect, whether it modulates norepinephrine (NE) and acetylcholine (ACh) releases in the ischemic myocardium remains unknown. To clarify the neural modulation in the ischemic region during vagal stimulation, we examined ischemia-induced NE and ACh releases in anesthetized and vagotomized cats. In a control group (VX, n = 8), occlusion of the left anterior descending coronary artery increased myocardial interstitial NE level from 0.46+/-0.09 to 83.2+/-17.6 nM at 30-45 min of ischemia (mean+/-SE). Vagal stimulation at 5 Hz (VS, n = 8) decreased heart rate by approximately 80 beats/min during the ischemic period and suppressed the NE release to 24.4+/-10.6 nM (P < 0.05 from the VX group). Fixed-rate ventricular pacing (VSP, n=8) abolished this vagally mediated suppression of ischemia-induced NE release. The vagal stimulation augmented ischemia-induced ACh release at 0-15 min of ischemia (VX: 11.1+/-2.1 vs. VS: 20.7+/-3.9 nM, P < 0.05). In the VSP group, the ACh release was not augmented. In conclusion, vagal stimulation suppressed the ischemia-induced NE release and augmented the initial increase in the ACh level. These modulations of NE and ACh levels in the ischemic myocardium may contribute to the beneficial effects of vagal stimulation on the heart during acute myocardial ischemia.     

Endothelium-dependent vasodilation in different rat hindlimb skeletal muscles.

Few studies have examined potential for endothelium-dependent vasodilation in skeletal muscles of different fiber-type composition. We hypothesized that muscles composed of slow oxidative (SO)- and/or fast oxidative glycolytic (FOG)-type fibers have greater potential for endothelium-dependent vasodilation than muscles composed of fast glycolytic (FG)-type fibers. To test this hypothesis, the isolated perfused rat hindlimb preparation was used with a constant-flow, variable-pressure approach. Perfusion pressure was monitored continuously, and muscle-specific flows were determined by using radiolabeled microspheres at four time points: control, at peak effect of acetylcholine (ACh I; 1-2 x 10(-4) M), at peak effect of ACh after infusion of an endothelial inhibitor (ACh II), and at peak effect of sodium nitroprusside (SNP; 4-5 x 10(-4) M). Conductance was calculated by using pressure and flow data. In the SO-type soleus muscle, conductance increased with ACh and SNP, but the increase in conductance with ACh was partially abolished by the endothelial inhibitor N(G)-nitro-l-arginine methyl ester (control, 0.87 +/- 0.19; ACh I, 2.07 +/- 0.29; ACh II, 1.32 +/- 0.15; SNP, 1.76 +/- 0.19 ml. min(-1). 100 g(-1). mmHg(-1); P < 0.05, ACh I and SNP vs. control). In the FOG-type red gastrocnemius muscle, similar findings were obtained (control, 0.64 +/- 0.11; ACh I, 1.36 +/- 0.21; ACh II, 0.73 +/- 0.16; SNP, 1.30 +/- 0.21 ml. min(-1). 100 g(-1). mmHg; P < 0.05, ACh I and SNP vs. control). In the FG-type white gastrocnemius muscle, neither ACh nor SNP increased conductance. Similar findings were obtained when muscles were combined into high- and low-oxidative muscle groups. Indomethacin had no effect on responses to ACh. These data indicate that endothelium-dependent vasodilation is exhibited by high-oxidative, but not low-oxidative, rat skeletal muscle. Furthermore, endothelium-dependent vasodilation in high-oxidative muscle appears to be primarily mediated by nitric oxide.     

Postsynaptic modulation of cholinergic transmission by endogenous substances

1. Recent concept of postsynaptic modulation is reviewed on the basis of literature data and the results of our investigation using conventional intracellular and voltage-clamp recording methods, in vitro. 2. Experimental evidence provided that the sensitivity of nicotinic ACh receptors endowed on the postsynaptic membrane of the bullfrog sympathetic ganglia and of the frog skeletal muscle end-plate is either facilitated or inhibited by other neurotransmitters or neurohormones. 3. We propose that one neurotransmitter not only initiates its own postsynaptic potential but also regulates the efficacy of synaptic transmission mediated by a distinct neurotransmitter, as an endogenous "antagonist" or "sensitizer".     

Properties of cholinergic receptor-mediated ion channels on type I vestibular hair cells of guinea pigs

To confirm the existence of cholinergic receptors on type I vestibular hair cells (VHCs I) of guinea pigs and to study the properties of the cholinergic receptor-mediated ion channels on VHCs I, electrophysiological responses of isolated VHCs I to external ACh were examined by means of whole-cell patch-clamp recordings. The results showed that 7.5% (21/279) VHCs I were found to be sensitive to ACh (10-1000 mumol/L). ACh generated an outward current in a steady, slow, dose-dependent [EC(50) was (63.78+/-2.31) mumol/L] and voltage-independent manner. In standard extracellular solution, ACh at the concentration of 100 mumol/L triggered a calcium-dependent current of (170+/-15) pA at holding potential of -50 mV, and the current amplitude could be depressed by extracellularly added calcium-dependent potassium channel antagonist TEA. The time interval for the next complete activation of ACh-sensitive current was no less than 1 min. The ion channels did not shut off even when they were exposed to ACh for an extended period of time (8 min). The results suggest that dose-dependent, calcium-dependent and voltage-independent cholinergic receptors were located on a few of the VHCs I investibular epithelium of guinea pigs. The cholinergic receptors did not show desensitization to ACh. This work reveals the existence of efferent neurotransmitter receptors on VHCs I and helps in understanding the function of vestibular efferent nervous system, and may provide some useful information on guiding the clinical rehabilitative treatment of vertigo.     

Metabolic forearm vasodilation is enhanced following Bier block with phentolamine

The extent to which sympathetic nerve activity restrains metabolic vasodilation in skeletal muscle remains unclear. We determined forearm blood flow (FBF; ultrasound/Doppler) and vascular conductance (FVC) responses to 10 min of ischemia [reactive hyperemic blood flow (RHBF)] and 10 min of systemic hypoxia (inspired O(2) fraction = 0.1) before and after regional sympathetic blockade with the alpha-receptor antagonist phentolamine via Bier block in healthy humans. In a control group, we performed sham Bier block with saline. Consistent with alpha- receptor inhibition, post-phentolamine, basal FVC (FBF/mean arterial pressure) increased (pre vs. post: 0.42 +/- 0.05 vs. 1.03 +/- 0.21 units; P < 0.01; n = 12) but did not change in the saline controls (pre vs. post: 0.56 +/- 0.14 vs. 0.53 +/- 0.08 units; P = not significant; n = 5). Post-phentolamine, total RHBF (over 3 min) increased substantially (pre vs. post: 628 +/- 75 vs. 826 +/- 92 ml/min; P < 0.01) but did not change in the controls (pre vs. post: 618 +/- 66 vs. 661 +/- 35 ml/min; P = not significant). In all conditions, compared with peak RHBF, peak skin reactive hyperemia was markedly delayed. Furthermore, post-phentolamine (pre vs. post: 0.43 +/- 0.06 vs. 1.16 +/- 0.17 units; P < 0.01; n = 8) but not post-saline (pre vs. post: 0.93 +/- 0.16 vs. 0.87 +/- 0.19 ml/min; P = not significant; n = 5), the FVC response to hypoxia (arterial O(2) saturation = 77 +/- 1%) was markedly enhanced. These data suggest that sympathetic vasoconstrictor nerve activity markedly restrains skeletal muscle vasodilation induced by local (forearm ischemia) and systemic (hypoxia) vasodilator stimuli.     

Release of non-neuronal acetylcholine from the isolated human placenta is affected by antidepressants

Non-neuronal acetylcholine (ACh) is released from the human placenta into the extracellular space via organic cation transporters (OCTs). The present experiments investigated whether ACh release from epithelial cells is affected by drugs which are substrates of OCTs. The antidepressant drugs amitriptyline and doxepine were tested as both substances are not approved for pregnant women but frequently used. Release of ACh was measured in 10 min intervals over a period of 100 min. Test substances were added from t=50 min of incubation onwards. The effect was calculated by comparing the ACh release of the last three samples (t=70-100 min; B2) with that immediately before the application of the test substances (t=20-50 min; B1). The baseline ACh release amounted to 2.07+/-0.17 nmol/10 min (n=29; villus). Under control conditions a B2/B1 ratio of 0.78+/-0.02 was obtained. The following B2/B1 ratios were found, when therapeutic drugs were added: 0.54+/-0.04 (n=7; P<0.05) in the presence of 10 microM amitriptyline; 0.44+/-0.04 (10; P<0.01) in the presence of 10 microM doxepin; 0.73+/-0.04 (13) in the presence of 10 microM metformin; 0.76+/-0.06 (7) in the presence of 10 microM minoxidil; 0.63+/-0.03 (10) in the presence of 1 microM theophylline. The results demonstrate that antidepressants reduce the release of non-neuronal ACh at least in the human placenta, most likely by intracellular substrate competition at the polyspecific organic cation transporters (OCTs) but only at concentrations roughly 30-fold above the therapeutic range. Theophylline may also interfere with the release of non-neuronal ACh.     

Inhibitory effects of botulinum toxin on pyloric and antral smooth muscle

Botulinum toxin injection into the pylorus is reported to improve gastric emptying in gastroparesis. Classically, botulinum toxin inhibits ACh release from cholinergic nerves in skeletal muscle. The aim of this study was to determine the effects of botulinum toxin on pyloric smooth muscle. Guinea pig pyloric muscle strips were studied in vitro. Botulinum toxin type A was added; electric field stimulation (EFS) was performed every 30 min for 6 h. ACh (100 microM)-induced contractile responses were determined before and after 6 h. Botulinum toxin caused a concentration-dependent decrease of pyloric contractions to EFS. At a low concentration (2 U/ml), botulinum toxin decreased pyloric contractions to EFS by 43 +/- 9% without affecting ACh-induced contractions. At higher concentrations (10 U/ml), botulinum toxin decreased pyloric contraction to EFS by 75 +/- 7% and decreased ACh-induced contraction by 79 +/- 9%. In conclusion, botulinum toxin inhibits pyloric smooth muscle contractility. At a low concentration, botulinum toxin decreases EFS-induced contractile responses without affecting ACh-induced contractions suggesting inhibition of ACh release from cholinergic nerves. At higher concentrations, botulinum toxin directly inhibits smooth muscle contractility as evidenced by the decreased contractile response to ACh.     

Adenosine contributes to hypoxia-induced forearm vasodilation in humans.

In humans, hypoxia leads to increased sympathetic neural outflow to skeletal muscle. However, blood flow increases in the forearm. The mechanism of hypoxia-induced vasodilation is unknown. To test whether hypoxia-induced vasodilation is cholinergically mediated or is due to local release of adenosine, normal subjects were studied before and during acute hypoxia (inspired O(2) 10.5%; approximately 20 min). In experiment I, aminophylline (50-200 microg. min(-1). 100 ml forearm tissue(-1)) was infused into the brachial artery to block adenosine receptors (n = 9). In experiment II, cholinergic vasodilation was blocked by atropine (0.4 mg over 4 min) infused into the brachial artery (n = 8). The responses of forearm blood flow (plethysmography) and forearm vascular resistance to hypoxia in the infused and opposite (control) forearms were compared. During hypoxia (arterial O(2) saturation 77 +/- 2%), minute ventilation and heart rate increased while arterial pressure remained unchanged; forearm blood flow rose by 35 +/- 6% in the control forearm but only by 5 +/- 8% in the aminophylline-treated forearm (P < 0.02). Accordingly, forearm vascular resistance decreased by 29 +/- 5% in the control forearm but only by 9 +/- 6% in the aminophylline-treated forearm (P < 0.02). Atropine did not attenuate forearm vasodilation during hypoxia. These data suggest that adenosine contributes to hypoxia-induced vasodilation, whereas cholinergic vasodilation does not play a role.     

Short-term intermittent hypoxia enhances sympathetic responses to continuous hypoxia in humans.

Short-term intermittent hypoxia leads to sustained sympathetic activation and a small increase in blood pressure in healthy humans. Because obstructive sleep apnea, a condition associated with intermittent hypoxia, is accompanied by elevated sympathetic activity and enhanced sympathetic chemoreflex responses to acute hypoxia, we sought to determine whether intermittent hypoxia also enhances chemoreflex activity in healthy humans. To this end, we measured the responses of muscle sympathetic nerve activity (MSNA, peroneal microneurography) to arterial chemoreflex stimulation and deactivation before and following exposure to a paradigm of repetitive hypoxic apnea (20 s/min for 30 min; O(2) saturation nadir 81.4 +/- 0.9%). Compared with baseline, repetitive hypoxic apnea increased MSNA from 113 +/- 11 to 159 +/- 21 units/min (P = 0.001) and mean blood pressure from 92.1 +/- 2.9 to 95.5 +/- 2.9 mmHg (P = 0.01; n = 19). Furthermore, compared with before, following intermittent hypoxia the MSNA (units/min) responses to acute hypoxia [fraction of inspired O(2) (Fi(O(2))) 0.1, for 5 min] were enhanced (pre- vs. post-intermittent hypoxia: +16 +/- 4 vs. +49 +/- 10%; P = 0.02; n = 11), whereas the responses to hyperoxia (Fi(O(2)) 0.5, for 5 min) were not changed significantly (P = NS; n = 8). Thus 30 min of intermittent hypoxia is capable of increasing sympathetic activity and sensitizing the sympathetic reflex responses to hypoxia in normal humans. Enhanced sympathetic chemoreflex activity induced by intermittent hypoxia may contribute to altered neurocirculatory control and adverse cardiovascular consequences in sleep apnea.     

Strain differences in guinea pigs' bronchial sensitivity to acetylcholine

The bronchial sensitivity to acetylcholine (ACh) of guinea pigs of various strains was investigated to clarify strain differences. Inbred Strain 2, Strain 13 and JY-1 and non-inbred Hartley strain (two colonies) were used in this experiment. (1) Guinea pigs were exposed to 0.08% ACh aerosol and the time needed to produce falling down (TNPFD) was determined. Mean +/- standard error of TNPFD (n = 14 per group) of animals was 182 +/- 28 sec, 148 +/- 22 sec, 210 +/- 30 sec, 342 +/- 24 sec and 406 +/- 36 sec in Strain 2, Strain 13, JY-1, Hartley (Japan SLC) and Hartley (Hitachi), respectively. There was a significant difference in TNPFD between inbred strains and non-inbred strains (P less than 0.05 or P less than 0.01), indicating that inbred strains had higher sensitivity. (2) Guinea pigs were exposed to 20-5000 micrograms/ml ACh for 2 min. The mean dose threshold as determined by transcutaneous oxygen pressure was 524 micrograms/ml, 424 micrograms/ml, 614 micrograms/ml, 1317 micrograms/ml and 1651 micrograms/ml (n = 14 per group) in Strain 2, Strain 13, JY-1, Hartley (Japan SLC) and Hartley (Hitachi), respectively. Inbred strains showed lower dose thresholds than non-inbred strains. (3) Isolated trachea-lungs of 5 guinea pigs were perfused with 10(-9)-10(-5) g/ml ACh to determine strain differences. Dose response curves of animals of inbred strains shifted to the left (lower concentrations), unlike those of non-inbred strains, suggesting that inbred strains had higher sensitivity to ACh than non-inbred strains.(ABSTRACT TRUNCATED AT 250 WORDS)