Neuroprotective effect of the ethanol extract of Artemisia capillaris on transient forebrain ischemia in mice via nicotinic cholinergic receptor / 中国天然药物

Artemisia capillaris Thunberg is a medicinal plant used as a traditional medicine in many cultures. It is an effective remedy for liver problems including hepatitis. Recent pharmacological reports have indicated that Artemisia species can exert various neurological effects. Previously, we reported a memory-enhancing effect of Artemisia species. However, the mechanisms underlying the neuroprotective effect of A. capillaris (AC) are still unknown. In the present study, we investigated the effect of an ethanol extract of AC on ischemic brain injury in a mouse model of transient forebrain ischemia. The mice were treated with AC for seven days, beginning one day before induction of transient forebrain ischemia. Behavioral deficits were investigated using the Y-maze. Nissl and Fluoro-jade B staining were used to indicate the site of injury. To determine the underlying mechanisms for the drug, we measured acetylcholinesterase activity. AC (200 mg·kg) treatment reduced transient forebrain ischemia-induced neuronal cell death in the hippocampal CA1 region. The AC-treated group also showed significant amelioration in the spontaneous alternation of the Y-maze test performance, compared to that in the untreated transient forebrain ischemia group. Moreover, AC treatment showed a concentration-dependent inhibitory effect on acetylcholinesterase activity in vitro. Finally, the effect of AC on forebrain ischemia was blocked by mecamylamine, a nonselective nicotinic acetylcholine receptor antagonist. Our results suggested that in a model of forebrain ischemia, AC protected against neuronal death through the activation of nicotinic acetylcholine receptors.

Neuroprotective effect of the ethanol extract of Artemisia capillaris on transient forebrain ischemia in mice via nicotinic cholinergic receptor / 中国天然药物

Artemisia capillaris Thunberg is a medicinal plant used as a traditional medicine in many cultures. It is an effective remedy for liver problems including hepatitis. Recent pharmacological reports have indicated that Artemisia species can exert various neurological effects. Previously, we reported a memory-enhancing effect of Artemisia species. However, the mechanisms underlying the neuroprotective effect of A. capillaris (AC) are still unknown. In the present study, we investigated the effect of an ethanol extract of AC on ischemic brain injury in a mouse model of transient forebrain ischemia. The mice were treated with AC for seven days, beginning one day before induction of transient forebrain ischemia. Behavioral deficits were investigated using the Y-maze. Nissl and Fluoro-jade B staining were used to indicate the site of injury. To determine the underlying mechanisms for the drug, we measured acetylcholinesterase activity. AC (200 mg·kg) treatment reduced transient forebrain ischemia-induced neuronal cell death in the hippocampal CA1 region. The AC-treated group also showed significant amelioration in the spontaneous alternation of the Y-maze test performance, compared to that in the untreated transient forebrain ischemia group. Moreover, AC treatment showed a concentration-dependent inhibitory effect on acetylcholinesterase activity in vitro. Finally, the effect of AC on forebrain ischemia was blocked by mecamylamine, a nonselective nicotinic acetylcholine receptor antagonist. Our results suggested that in a model of forebrain ischemia, AC protected against neuronal death through the activation of nicotinic acetylcholine receptors.

The role of spinal adrenergic receptors on the antinociception of ginsenosides in a rat postoperative pain model / 대한마취과학회지

BACKGROUND: The effect of spinal adrenergic and cholinergic receptors on the anti-nociceptive effect of intrathecal ginsenosides was determined in a rat postoperative pain model. METHODS: Catheters were placed into the intrathecal space of male Sprague-Dawley rats. Postoperative pain was evoked by an incision to the plantar surface of a hind paw. Withdrawal thresholds was used as a nociceptive parameter and was measured with a von Frey filament. After observing the effect of intrathecal ginsenosides, an alpha-1 adrenergic receptor antagonist (prazosin), an alpha-2 adrenergic receptor antagonist (yohimbine), a muscarinic acetylcholine receptor antagonist (atropine), and a nicotinic acetylcholine receptor antagonist (mecamylamine) were given 10 min before administration of the ginsenosides to analyze the contribution of spinal adrenergic and cholinergic receptors on the antinociceptive effect of ginsenosides. RESULTS: Paw incision decreased withdrawal threshold in incised site of paw, but no change of withdrawal threshold was not seen in non-incised site. The intrathecal ginsenosides increased withdrawal threshold of the incised paw in a dose-dependent manner. Pre-treatment with both prazosin and intrathecal yohimbine antagonized the anti-nociceptive effect of the ginsenosides. However, pre-treatments with atropine or mecamylamine had any effect on the antinociceptive activity of ginsenosides. CONCLUSIONS: Intrathecal ginsenosides are effective in attenuation of postoperative pain induced in the rat model. Anti-nociceptive action of ginsenosides is partially mediated by spinal adrenergic receptors, but does not appear to be related to spinal cholinergic receptors.

Glycine- and GABA-mimetic Actions of Shilajit on the Substantia Gelatinosa Neurons of the Trigeminal Subnucleus Caudalis in Mice

Shilajit, a medicine herb commonly used in Ayurveda, has been reported to contain at least 85 minerals in ionic form that act on a variety of chemical, biological, and physical stressors. The substantia gelatinosa (SG) neurons of the trigeminal subnucleus caudalis (Vc) are involved in orofacial nociceptive processing. Shilajit has been reported to be an injury and muscular pain reliever but there have been few functional studies of the effect of Shilajit on the SG neurons of the Vc. Therefore, whole cell and gramicidin-perfotrated patch clamp studies were performed to examine the action mechanism of Shilajit on the SG neurons of Vc from mouse brainstem slices. In the whole cell patch clamp mode, Shilajit induced short-lived and repeatable inward currents under the condition of a high chloride pipette solution on all the SG neurons tested. The Shilajit-induced inward currents were concentration dependent and maintained in the presence of tetrodotoxin (TTX), a voltage gated Na+ channel blocker, CNQX, a non-NMDA glutamate receptor antagonist, and AP5, an NMDA receptor antagonist. The Shilajit-induced responses were partially suppressed by picrotoxin, a GABAA receptor antagonist, and totally blocked in the presence of strychnine, a glycine receptor antagonist, however not affected by mecamylamine hydrochloride (MCH), a nicotinic acetylcholine receptor antagonist. Under the potassium gluconate pipette solution at holding potential 0 mV, Shilajit induced repeatable outward current. These results show that Shilajit has inhibitory effects on the SG neurons of Vc through chloride ion channels by activation of the glycine receptor and GABAA receptor, indicating that Shilajit contains sedating ingredients for the central nervous system. These results also suggest that Shilajit may be a potential target for modulating orofacial pain processing.

The Role of Adrenergic and Cholinergic Receptors on the Antinociception of Korean Red Ginseng in the Spinal Cord of Rats / 대한통증학회지

BACKGROUND: Experimental evidence indicates that ginseng modulate the nociceptive transmission. Authors examined the role of adrenergic and cholinergic receptors on the antinociceptive action of Korean red ginseng against the formalin-induced pain at the spinal level. METHODS: Catheters were inserted into the intrathecal space of male Sprague-Dawley rats. Fifty microl of 5% formalin solution was injected to the hindpaw for induction of pain and formalin-induced pain (flinching response) was observed. The role of spinal adrenergic and cholinergic receptors on the effect of Korean red ginseng was assessed by antagonists (prazosin, yohimbine, atropine and mecamylamine). RESULTS: Intrathecal Korean red ginseng produced a dose-dependent suppression of the flinching response in the rat formalin test. All of prazosin, yohimbine, atropine and mecamylamine antagonized the antinociception of Korean red ginseng. CONCLUSIONS: Spinal Korean red ginseng is effective against acute pain and facilitated pain state evoked by formalin injection. All of alpha 1, alpha 2, muscarinic and nicotinic receptors may play an important role in the antinociceptive action of Korean red ginseng at the spinal level.

The Role of Adrenergic and Cholinergic Receptors on the Antinociception of Intrathecal Zaprinast in the Formalin Test of Rats / 대한마취과학회지

BACKGROUND: Spinal zaprinast, phospodiesterase inhibitor, has been shown to have an antinociception through an increase of cGMP. The aim of this study was to examine the role of spinal adrenergic and cholinergic receptors on the antinociceptive action of intrathecal zaprinast. METHODS: Rats were implanted with lumbar intrathecal catheters. After formalin injection, formalin-induced nociceptive behavior (flinching response) was observed for 60 min. After observing the effect of intrathecal zaprinast, antagonism of intrathecal prazosin, yohimbine, atropine and mecamylamine for the effect of zaprinast were evaluated. RESULTS: Intrathecal zaprinast produced a dose-dependent suppression of formalin-induced flinches in both phases of the formalin test. Intrathecal prazosin reversed the antinociception of zaprinast in phase 2, but not phase 1. Intrathecal yohimbine reversed the antinociception of zaprinast in both phases. Neither atropine nor mecamylamine reversed the antinocicetive action of zaprinast. CONCLUSIONS: Intrathecal zaprinast is against the nociceptive state evoked by formalin stimulus. Alpha 2 or alpha 1 adrenergic receptor, but not cholinergic receptors, may be related to the action of zaprinast in the spinal cord.

Association of nicotinic acetylcholine receptors with central respiratory control in isolated brainstem-spinal cord preparation of neonatal rats

Nicotine exposure is a risk factor in several breathing disorders Nicotinic acetylcholine receptors (nAChRs) exist in the ventrolateral medulla, an important site for respiratory control. We examined the effects of nicotinic acetylcholine neurotransmission on central respiratory control by addition of a nAChR agonist or one of various antagonists into superfusion medium in the isolated brainstem-spinal cord from neonatal rats. Ventral C4 neuronal activity was monitored as central respiratory output, and activities of respiratory neurons in the ventrolateral medulla were recorded in whole-cell configuration. RJR-2403 (0.1-10mM), a4b2 nAChR agonist induced dose-dependent increases in respiratory frequency. Non-selective nAChR antagonist mecamylamine (0.1-100mM), a4b2 antagonist dihydro-b-erythroidine (0.1-100mM), a7 antagonist methyllycaconitine (0.1-100mM), and a-bungarotoxin (0.01-10mM) all induced dose-dependent reductions in C4 respiratory rate. We next examined effects of 20mM dihydro-b-erythroidine and 20mM methyllycaconitine on respiratory neurons. Dihydro-b-erythroidine induces hyperpolarization and decreases intraburst firing frequency of inspiratory and preinspiratory neurons. In contrast, methyllycaconitine has no effect on the membrane potential of inspiratory neurons, but does decrease their intraburst firing frequency while inducing hyperpolarization and decreasing intraburst firing frequency in preinspiratory neurons. These findings indicate that a4b2 nAChR is involved in both inspiratory and preinspiratory neurons, whereas a7 nAChR functions only in preinspiratory neurons to modulate C4 respiratory rate.

Characterization of Acetylcholine-induced Currents in Male Rat Pelvic Ganglion Neurons

The pelvic ganglia provide autonomic innervations to the various urogenital organs, such as the urinary bladder, prostate, and penis. It is well established that both sympathetic and parasympathetic synaptic transmissions in autonomic ganglia are mediated mainly by acetylcholine (ACh). Until now, however, the properties of ACh-induced currents and its receptors in pelvic ganglia have not clearly been elucidated. In the present study, biophysical characteristics and molecular nature of nicotinic acetylcholine receptors (nAChRs) were studied in sympathetic and parasympathetic major pelvic ganglion (MPG) neurons. MPG neurons isolated from male rat were enzymatically dissociated, and ionic currents were recorded by using the whole cell variant patch clamp technique. Total RNA from MPG neuron was prepared, and RT-PCR analysis was performed with specific primers for subunits of nAChRs. ACh dose-dependently elicited fast inward currents in both sympathetic and parasympathetic MPG neurons (EC50; 41.4microliterM and 64.0microliterM, respectively). ACh-induced currents showed a strong inward rectification with a reversal potential near 0 mV in current-voltage relationship. Pharmacologically, mecamylamine as a selective antagonist for alpha3beta4 nAChR potently inhibited the ACh-induced currents in sympathetic and parasympathetic neurons (IC50; 0.53micrometer and 0.22micrometer, respectively). Conversely, alpha- bungarotoxin, alpha-methyllycaconitine, and dihydro-beta-erythroidine, which are known as potent and sensitive blockers for alpha7 or alpha4beta2 nAChRs, below micromolar concentrations showed negligible effect. RT-PCR analysis revealed that alpha3 and beta4 subunits were predominantly expressed in MPG neurons. We suggest that MPG neurons have nAChRs containing alpha3 and beta4 subunits, and that their activation induces fast inward currents, possibly mediating the excitatory synaptic transmission in pelvic autonomic ganglia.

Spinal Gabapentin and Antinociception: Mechanisms of Action

Spinal gabapentin has been known to show the antinociceptive effect. Although several assumptions have been suggested, mechanisms of action of gabapentin have not been clearly established. The present study was undertaken to examine the action mechanisms of gabapentin at the spinal level. Male SD rats were prepared for intrathecal catheterization. The effect of gabapentin was assessed in the formalin test. After pretreatment with many classes of drugs, changes of effect of gabapentin were examined. General behaviors were also observed. Intrathecal gabapentin produced a suppression of the phase 2 flinching, but not phase 1 in the formalin test. The antinociceptive action of intrathecal gabapentin was reversed by intrathecal NMDA, AMPA, D-serine, CGS 15943, atropine, and naloxone. No antagonism was seen following administration of bicuculline, saclofen, prazosin, yohimbine, mecamylamine, L-leucine, dihydroergocristine, or thapsigargin. Taken together, intrathecal gabapentin attenuated only the facilitated state. At the spinal level, NMDA receptor, AMPA receptor, nonstrychnine site of NMDA receptor, adenosine receptor, muscarinic receptor, and opioid receptor may be involved in the antinociception of gabapentin, but GABA receptor, L-amino acid transporter, adrenergic receptor, nicotinic receptor, serotonin receptor, or calcium may not be involved.

Effect of Spinal Adrenergic and Cholinergic Antagonists for Antinociception of Intrathecal Gabapentin / 대한마취과학회지

BACKGROUND: Intrathecal gabapentin is effective on nociceptive states evoked by tissue injury. In addition, gabapentin interacts synergistically with clonidine at the spinal level, suggesting that a mechanism of gabapentin may be related to spinal adrenoceptors. However, it has not been established whether this drug is associated with cholinergic receptors. The aim of this study was to examine the role of spinal adrenergic and cholinergic receptors on the antinociceptive action of intrathecal gabapentin. METHODS: Rats were implanted with lumbar intrathecal catheters. For a nociceptive test, 50nl of 5% formalin solution was injected into the hindpaw. The effect of intrathecal gabapentin, administered 10 min before the formalin injection, was assessed. Next, antagonistic effects of intrathecal prazosin, yohimbine, atropine and mecamylamine for the action of intrathecal gabapentin were evaluated. RESULTS: Formalin injection caused a biphasic incidence of flinching of the injected paw. Intrathecal gabapentin produced a dose-dependent suppression of only the phase 2 flinching response in the formalin test. Intrathecal atropine, but not prazosin, yohimbine nor mecamylamine, reversed the antinociception of intrathecal gabapentin. CONCLUSIONS: The antinociceptive effect of intrathecal gabapentin on facilitated states may be mediated through the muscarinic receptor but by neither the nicotinic receptor nor the adrenergic receptor at the spinal level.

Difference in action sites between mecamylamine and hexamethonium on nicotinic receptors of sympathetic neurons / 生理学报

To compare the difference in action sites between mecamylamine (MEC) and hexamethonium (HEX) on nicotinic receptors of sympathetic neurons, we investigated the effects of MEC and HEX on the nicotine-induced currents in cultured superior cervical ganglion neurons by whole-cell patch clamp technique. The IC(50) of MEC and HEX for antagonizing the effect of 0.08 mmol/L nicotine was 0.0012 and 0.0095 mmol/L, respectively. Both MEC and HEX accelerated the desensitization of nicotinic receptors. Furthermore, by comparing their effects at holding potentials 30, 70 and 110 mV, it was indicated that their suppressing effect on the nicotine-induced currents was voltage-dependent. However, different from that of HEX, the inhibitory effect of MEC increased with administering the mixture of MEC and nicotine at intervals of 3 min, indicating a use-dependent effect of MEC. It is concluded that the action site of MEC on nicotinic receptors of sympathetic neurons is different from that of HEX.

Antinociception induced by stimulating amygdaloid nuclei in rats: changes produced by systemically administered antagonists

The antinociceptive effects of stimulating the medial (ME) and central (CE) nuclei of the amygdala in rats were evaluated by the changes in the latency for the tail withdrawal reflex to noxious heating of the skin. A 30-s period of sine-wave stimulation of the ME or CE produced a significant and short increase in the duration of tail flick latency. A 15-s period of stimulation was ineffective. Repeated stimulation of these nuclei at 48-h intervals produced progressively smaller effects. The antinociception evoked from the ME was significantly reduced by the previous systemic administration of naloxone, methysergide, atropine, phenoxybenzamine, and propranolol, but not by mecamylamine, all given at the dose of 1.0 mg/kg. Previous systemic administration of naloxone, atropine, and propranolol, but not methysergide, phenoxy-benzamine, or mecamylamine, was effective against the effects of stimulating the CE. We conclude that the antinociceptive effects of stimulating the ME involve at least opioid, serotonergic, adrenergic, and muscarinic cholinergic descending mechanisms. The effects of stimulating the CE involve at least opioid, beta-adrenergic, and muscarinic cholinergic descending mechanisms.

The Effect of Selective Muscarinic Receptor Antagonists on Antiallodynic Action in a Rat Model of Neuropathic Pain / 대한마취과학회지

BACKGROUND: Peripheral nerve injury may produce a syndrome consisting of spontaneous pain, allodynia and hyperpathia. In previous study, we examined the antiallodynic action produced by intrathecal (i.t.) cholinesterase inhibitors (ChEi) in a neuropathic pain rat model and the reversal of antiallodynic state by i.t. atropine, muscarinic antagonist, but not by nicotinic antagonist mecamylamine. The purpose of this study was to determine the selective antagonistic action of four subtypes of muscarinic receptor on antiallodynic state by i.t. ChEi in a rat model of neuropathic pain. METHODS: Sprague Dawley rats were prepared with tight ligation of left L5/L6 spinal nerves with 6-0 black silk and chronic lumbar intrathecal catheters. After obtaining the baseline hindpaw withdrawal scores, edrophonium (100 microgram) or neostigmine (10 microgram) was administered intrathecally. Tactile allodynia was measured using von Frey filaments and allodynic threshold was calculated by the up-down method. Allodynic changes were tested at 15, 30, 45, 60, 90, 120 and 180 minutes. To examine the reversal of antiallodynia and to compare the antagonizing action of antiallodynic state produced by i.t. administration of ChEi, non-selective muscarinic receptor antagonists atropine (10 microgram), M1 antagonist pirenzepine (3 microgram), M2 antagonist methoctramine (3 microgram), M3 antagonist 4-DAMP (3 microgram) and M4 antagonist tropicamide (3 microgram) were injected intrathecally respectively 5 minutes prior to the injection of edrophonium or neostigmine. RESULTS: Antiallodynia produced by i.t. edrophonium was reversed by pretreatment with i.t. methoctramine, 4-DAMP, tropicamide and pirenzepine (P<0.05). On the contrary, antiallodynic state made by i.t. neostigmine was not antagonized by methoctramine, 4-DAMP and tropicamide. M1 antagonist pirenzepine had a moderate, statistically significant (P<0.05) effect on reversal of increased allodynic threshold while atropine showed a complete antagonism. CONCLUSION: These experiments suggest that antialllodynic action of cholinesterase inhibitors is likely due to mediation of spinal muscarinic system and M1 receptor subtype is more likely involved in this mechanism.

The Antiallodynic Effect of Edrophonium and Neostigmine in a Neuropathic Pain Model / 대한마취과학회지

BACKGROUND: Peripheral nerve injury may produce a syndrome consisting of spontaneous pain, allodynia and hyperpathia. Cholinesterase inhibitors are known to have an antinociceptive effect in hot plate and tail flick tests and to be mediated by spinal muscarinic system. The purpose of the current study was to determine the effect of intrathecally (i.t.) administered edrophonium and neostigmine on the touch-evoked allodynia and to identify the antagonism of antiallodynia in a rat model of neuropathic pain. METHODS: Sprague Dawley rats were prepared with tight ligation of left L5/L6 spinal nerves with 6~0 black silk and chronic lumbar intrathecal catheters. After obtaining the baseline hindpaw withdrawal scores, edrophonium (3~100ug) or neostigmine (0.3~10ug) was administered intrathecally. Tactile allodynia was measured using von Frey filaments and allodynic threshold was calculated by updown method. Motor dysfunction was assessed by observing righting/stepping reflex responses and abnormal weight bearing. To examine the reversal of antiallod ynia, muscarinic receptor antagonist atropine (10ug) or nicotinic receptor antagonist mecamylamine (10ug) was injected intrathecally 5 min. prior to injection of edrophonium or neostigmine. RESULTS: I.t. edrophonium and i.t. neostigmine produced a dose dependent antagonism of allodynic state but had moderate to severe effect on motor weakness at doses of 3 and 10 g of neostigmine. Pretreatment with i.t. atropine yielded a complete antagonism of antiallodynia in both drugs, but i.t. mecamylamine did not significantly reverse incresed allodynic threshold. CONCLUSIONS: These experiments suggest that i.t. edrophonium or i.t. neostigmine produces a dose dependent antagonism on touch-evoked allodynia at the spinal level and this antagonism is likely due to spinal muscarinic system.

Antinociceptive effects of stimulation of discrete sites in the rat hypothalamus: evidence for the participation of the lateral hypothalamus area in descending pain suppression mechanisms

The sites in the rat hypothalamus where microinjection of morphine 5 mug/0.5 mul) or electrical stimulation depresses the tail withdrawal reflex to noxious heating of the skin were examined. Among other hypothalamic sites found to be sensitive to morphine or to an electrical stimulus, the posterior part of the lateral hypothalamic area (LHA) was the only portion of the hypothalamus that was strongly sensitive to both manipulations. A 15-sec period of 35-muA sine-wave stimulation of the LHA significantly increased the latency of the tail reflex for periods up to 30 min. The effects of intraperitoneal administration of antagonists to opioids (naloxone), 5-hydroxytryptamine (methysergide), noradrenaline (phenoxybenzarnine), dopamine (haloperidol and acetylcholine (atropine and mecamylamine) on the antinociceptive effects of LHA stimulation were also examined. Naloxone, methysergide, and atropine (all given at doses of 0.5 and 1.0 mg/kg attenuated the effects of LHA stimulation in a dose-dependent manner. Phenoxybenzamine, but not haloperidol (both at the dose of 1.0 mg/kg), was also effective but dose-dependent curves could not be constructed. Mecamylamine (1.0 mg/kg) reduced the duration but no the peak effect of stimulating the LHA. We conclude that antagonism at the level of opioid, serotonergic, adrenergic, and muscarinic cholinergic receptors, but not dopamine or nicotinic cholinergic receptors reduces the antinociceptive effects of LHA stimulation. This may imply that antinociception evoked from the LHA depends on the activation of descending pathways that relay in the mesencephalic periaqueductal gray matter and then in the nucleus raphe magnus and/or nucleus reticularis paragigantocellularis.

Influence of GABAergic Receptors on Catecholamine Secretion in the Isolated Rat Adrenal Glands

BACKGROUND: The influence of gamma-aminobutyric acid(GABA), which is well-known as a major inhibitory neurotransmitter in central nervous system, on secretion of catecholamines(CA) was investigated in the isolated perfused rat adrenal gland. METHODS: Mature male Sprague-Dawley rats were anesthetized with ether. Ther adrenal gland was isolated by the methods f Wakade. A cannula used for perfusion of the adrenal gladn was inserted into the distal end of the renal vein. The adrenal gland, along with ligated blood vessels and the cannula, was carefully removed from the animal and placed on a platform of a leucite chamber. RESULTS: GABA given into an adrenal vein of the rat produced markedly secretion of CA from the adrenal gland. Tachyphylaxis to the relesing effect of CA evoked by GABA was observed. The secretory effect of CA evoked by GABA was attenuated singnificantly by pretreatment with mecamylamine or atropine. Ouabain inhibited greatly the secretory response of GABA. When omitting the external potassium ion, the basal release of CA was increased. During this period GABA no longer revealed the increase in CA release. CA secretion evoked by GABA was blocked significantly by perfusion of calcium-free Krebs solution containing 5mMEGTA for 30-min. Pretreatment with bicuculline or picrotoxin inhibited CA secretion evoked by GABA as well as ACh. ACh-evoked CA release was potentiated by GABA infusion(400ug/30min). CONCLUSION: The experimental findings suggest that GABA causes the secretory effect of CA in a fashion of external calcium and potassium iosn-dependence, and that this releasing effect of CA induced by GABA may be exterted by stimulation of GABAergic A-reccptors located on adrenomedullary chromaffine cell, which is likely associated with cholinergic receptor activation evoked CA secretion.

Studies on the Interactions of M1-, M2- Receptors with Nicotinic Receptors in Rabbit Sympathetic Ganglia

Effects of a M1 receptor antagonist, pirenzepine, a M2 receptor antagonist, AF-DX116, and a nicotinic receptor antagonist, mecamylamine on the pressor responses to preganglionic sympathetic nerve stimulation(PNS) and McN-A-343 and DMPP in spinal(pithed) rabbits were investigated in order to elucidate a functional role of M1, M2 and nicotinic receptors in ganglionic transmission. Pirenzepine and AF-DX116 selectively inhibited the McN-A-343-induced pressor reponse in chlorisondamine-treated rabbit and the BCh-induced bradycardia, respectively. Electrical stimulations of preganglionic sympathetic outflow at T8 level produced increases in blood pressure. Pirenzepine(3 microgram/kg) significantly inhibited the PNS-induced pressor response and the degree of inhibition was not changed by increasing the doses to 100 microgram/kg. AF-DX116(100 microgram/kg) had no effect on the PNS-induced pressor response. Mecamylamine inhibited the PNS-induced pressor response in a dose-dependent manner. The inhibitory action of mecamylamine was significantly augmented by combined-treatment with pirenzepine(30 microgram/kg) but AF-DX116(100 microgram/kg) did not affect the inhibitory action of mecamylamine. McN-A-343 and DMPP elicited pressor response in the spinal rabbit. Pirenzepine and AF-DX116 dose-dependently inhibited the McN-A-343-induced pressor response but they did not affect DMPP-induced pressor response. Mecamylamine inhibited both pressor responses induced by Mc-N-343- and DMPP. These results suggest that not only nicotinic receptors but also M1 receptors play a facilitatory role in ganglionic transmission but M2 receptors do not contribute the transmission in spinal(pithed) rabbits.

Influence of sympathetic tone on the reactivity to indorenate in the external carotid vascular bed of the dog

The present study was designed to analyze the effects of drugs th at interfere with sympathetic transmission on the external carotid vasodilator response induced by the 5-HT1A receptor agonist, indorenate, in pentobarbital-anesthetized dogs. Intracarotid (i.c.) infusions of indorenate (1000 µg/lmin) produced an increase in external carotid blood flow (external C.B.F.) without modifying mean arterial blood pressure or heart rate. This effect of indorenate was dose-dependently antagonized by intravenous (i.v.) administration of the Ó1-adrenoceptor antagonist, prazosin (1, 3.1, 10, 31 and 100 µg/kg), the ganglionic blocking agent, mecamylamine (0.31, 0.1, 0.31, 1, 3.1 and 10 mg/kg) or the 5-HT2 receptor and Ó1-adrenoceptor antagonist, ketanserin (10, 31 and 100 µ/kg). It is concluded that indorenate.induced increase in canine external C.B.F. is dependent on the vascular neurogenic tone

Effects of nicotine on pain and aggressivity and antagonism of these effects by mecamylamine

Nicotine caused a dose-dependent decrease [1.25 and 2.5 mg/kg] on writhing score of the mice, made painful by intraperitoneal [i.p.] acetic acid injection. At the dose of 0.75 mg/kg i.p. nicotine lowered attack score and time of the mice but there wasn't a significant change at 0.5 mg/kg dosage. These effect of nicotine were blocked by 2.5 mg/kg mecamlamine which was given 15 minutes before nicotine administration

Sudies About the Pressor Response to Intracerebroventricular Infusion of Hypertonic NaCl in Rabbits

Changes of blood pressure, heart rate, ECG, respiration rate and pupil size by intracerebroventricular(ICV) infusion of hypertonic NaCl with 0.04 ml/min for 5 min(total 0.2ml) were observed in urethane-anesthetized rabbits. ICV infusion of 0.75M NaCl produced slight pressor effect (11mmHg) and did not affect other parameters. ICV infusion of 1.5M NaCl began to increase blood pressure from 2~3 min after the infusion and produced maximal increase(24mmHg) at 5~10 min. Then the pressor effect was recovered to the original level at 30~60 min. Change of heart rate by the infusion was not clear, but ST-segment of ECG was markedly depressed. Respiration rate increased about 1.5 times than the control in accordance with the pressor effect and the state was continued even after the recover of the pressor effect. Both pupils dilated markedly and light-reflex was lost. Changes of parameters by ICV infusion of 3.0M NaCl were similar to those by 1.5M NaCl and some rabbits caused severe arrhythmias and died. The purpose of present study is to investigate the mechansim(s) of the pressor effect induced by the ICV infusion of 1.5M NaCl. The pressor effect of 1.5M NaCl was attenuated by the continuous infusion of vasopressin antagonist(20microm/kg/min) but not affected by intravenous treatment with 2mg/kg phentolamine, 2mg/kg propranolol and 1mg/kg chlorisondamine. The pressor effect was not altered with ICV 0.12mg/kg phenoxybenzamine, 0.4mg diltiazem, 0.1mg/kg mecamylamine and 0.2mg/kg atropine. After ICV infusion of 25microg/kg/min of diazepam, however, the pressor effect was completely abolished and restored 3~4 hours after stopping diazepam infusion. The pressor effect was rather potentiated than inhibited in bilateral adrenalectomized or nephrectomized rabbits. Infusion of 2microg/kg/min of saralasin for 10 min in the bliateral adrenalectomized rabbit did not affect the pressor effect at all. These results suggest that hypertensive effect induced by ICV infusion of hypertonic NaCl is mediated by the increase of vasopressin secretion.