Release of acetylcholine by syringin, an active principle of Eleutherococcus senticosus, to raise insulin secretion in Wistar rats

The present study is designed to screen the effect of syringin, an active principle purified from the rhizome and root parts of Eleutherococcus senticosus (Araliaceae), on the plasma glucose and investigate the possible mechanisms. Plasma glucose decreased in a dose-dependent manner 60 min after intravenous injection of syringin into fasting Wistar rats. In parallel to the decrease of plasma glucose, increases of plasma insulin level as well as the plasma C-peptide was also observed in rats receiving same treatment. Both the plasma glucose lowering action and the raised plasma levels of insulin and C-peptide induced by syringin were also inhibited by 4-diphenylacetoxy-N-methylpiperdine methiodide (4-DAMP), the antagonist of the muscarinic M3 receptors, but not affected by the ganglionic nicotinic antagonist, pentolinium or hexamethonium. Moreover, disruption of synaptic available acetylcholine (ACh) using an inhibitor of choline uptake, hemicholinium-3, or vesicular acetylcholine transport, vesamicol, abolished these actions of syringin. Also, physostigmine at concentration sufficient to inhibit acetylcholinesterase enhanced the actions of syringin. Mediation of ACh release from the nerve terminals to enhance insulin secretion by syringin can thus be considered. The results suggest that syringin has an ability to raise the release of ACh from nerve terminals, which in turn to stimulate muscarinic M3 receptors in pancreatic cells and augment the insulin release to result in plasma glucose lowering action.     

Release of acetylcholine by Hon-Chi to raise insulin secretion in Wistar rats

The mandarin Hon-Chi is the red yeast rice fermented with Monascus pilous and Monascus purpureus. The present study is designed to screen the effect of Hon-Chi on plasma glucose and investigate the possible mechanisms. After oral administration into fasting Wistar rats for 90min, Hon-Chi decreased the plasma glucose in a dose-dependent manner. In parallel to the reduction of plasma glucose, an increase of plasma level of insulin or C-peptide was also observed in rats receiving same treatment. Moreover, disruption of synaptic available acetylcholine (ACh) using an inhibitor of choline uptake, hemicholinium-3, or vesicular acetylcholine transport, vesamicol, abolished these actions of Hon-Chi. Also, physostigmine at concentration sufficient to inhibit acetylcholinesterase enhanced the actions of Hon-Chi. Mediation of ACh release from the nerve terminals to enhance insulin secretion by Hon-Chi can thus be considered. Both the plasma glucose lowering action and the raised plasma levels of insulin and C-peptide induced by Hon-Chi were also inhibited by 4-diphenylacetoxy-N-methylpiperdine methiodide (4-DAMP), but not affected by the ganglionic nicotinic antagonist, pentolinium or hexamethonium, indicating the mediation of muscarinic M(3) receptors. The results suggest that Hon-Chi has an ability to raise the release of ACh from nerve terminals, which in turn to stimulate muscarinic M(3) receptors in pancreatic cells and augment the insulin release to result in plasma glucose lowering action. Thus, Hon-Chi seems suitable to employ as the health food for increase of insulin secretion in the prevention of type-2 diabetes.     

Release of acetylcholine to raise insulin secretion in Wistar rats by oleanolic acid, one of the active principles contained in Cornus officinalis

The plasma glucose lowering action of fruits of cornus (Cornus officinalis), the major active constituent of Die-Huang-Wan, has been documented to mediate acetylcholine (ACh) release, which in turn to stimulate muscarinic M(3) receptors resulting in the enhancement of insulin secretion in rats with functional pancreatic beta-cells. The present study was conducted to investigate the effect of oleanolic acid, one of the active principles of cornus fruit, on the release of insulin in rats. After an intraperitoneal injection into the fasting Wistar rats for 90 min, oleanolic acid decreased the plasma glucose in a dose-dependent manner in parallel to an increase of plasma levels of insulin as well as C-peptide. Moreover, disruption of synaptic ACh using an inhibitor of choline uptake, hemicholinium-3, or vesicular acetylcholine transport, vesamicol, abolished these actions of oleanolic acid. Also, physostigmine at concentration sufficient to inhibit acetylcholinesterase enhanced the actions of oleanolic acid. Both the plasma glucose lowering action and the raised plasma levels of insulin and C-peptide induced by oleanolic acid were also inhibited by 4-diphenylacetoxy-N-methylpiperdine methiodide (4-DAMP), but not affected by the ganglionic nicotinic antagonist, pentolinium or hexamethonium. The results suggest that oleanolic acid has an ability to raise the release of ACh from nerve terminals, which in turn to stimulate muscarinic M(3) receptors in the pancreatic cells and augment the insulin release to result in plasma glucose lowering action. Thus, oleanolic acid is one of the active principles responsible for the increase of plasma insulin produced by cornus fruit in rats.     

Activation of muscarinic M-3 receptor may decrease glucose uptake and lipolysis in adipose tissue of rats

Role of muscarinic receptor in the regulation of glucose uptake or lipolysis in adipose tissue remained unclear. In epididymal white adipose tissue (WAT) isolated from Wistar rats, we observed that acetylcholine (ACh) attenuated the insulin-stimulated glucose uptake and the release of glycerol from WAT in a concentration-dependent manner. Using the blockade of specific antagonists, both actions of ACh were characterized mainly due to an activation of M3 receptors. In the presence of various inhibitors for PLC–PKC pathway, ACh-decreased glucose uptake was also reversed. Taken together, these results suggest that muscarinic M3 receptor is involved in the regulation of glucose uptake and/or lipolysis in adipose tissue.     

Autonomic regulation of insulin secretion is changed by pentobarbital in mice

It has been established that insulin secretion is regulated by autonomic nervous homeostasis. In the screen of plasma glucose level, anesthetized animals were widely used. However, effects of anesthetics on blood glucose remain unclear. In the present study, we compared the hypoglycemic action of ginseng that was induced by insulin secretion in mice between conscious and under anesthesia with pentobarbital. The hypoglycemic effect of ginseng was only produced in anesthetized BALB/c mice but not in the conscious mice. Similar results were also observed in C57BL/6 mice. However, the hypoglycemic action of ginseng failed to produce in anesthetized BALB/c mice received streptozotocin to induce type-1 like diabetes showing an insulin-dependent manner. The plasma insulin level in anesthetized BALB/c mice was markedly raised by ginseng but this effect was not observed in conscious mice. Blockade of muscarinic receptors by atropine inhibited ginseng-induced insulin secretion in anesthetized mice. Otherwise, the hypoglycemic action of ginseng was restored in conscious mice treated guanethidine at a sufficient dose to block sympathetic tone. In conclusion, the obtained results suggest that insulin secretion regulated by autonomic nervous homeostasis can be changed by pentobarbital through decrement in sympathetic tone to increase the insulin secretion induced by agent(s) via higher of parasympathetic tone. This finding is suitable to explain the critical hypoglycemia was not observed in subjects received ginseng.     

The role of muscarinic receptor subtypes in acetylcholine release from urinary bladder obtained from muscarinic receptor knockout mouse

We investigated the subtype of prejunctional muscarinic receptors associated with inhibition of acetylcholine (ACh) released from the mouse bladder. We measured endogenous ACh release in the bladder obtained from the wild-type mice and muscarinic 1-5 (M1-M5) receptor knockout (KO) mice. Electrical field stimulation increased ACh release in all bladder preparations obtained from wild-type and M1-M5 receptor KO mice. The amount of ACh released from M1-M3 and M5 receptor KO mice was equal to that in the wild-type mice. In contrast, the amount of electrical field stimulation-induced ACh release in M4 receptor KO mice was significantly larger than that in the wild-type mice, but the extent of increase was small. Atropine increased electrical field stimulation-induced ACh release to levels found in wild-type mice in all M1-M5 receptor KO mice. In M2/M4 receptor double KO mice, the amount of electrical field stimulation-induced ACh release was equivalent to that in the M4 receptor KO mice. The cholinergic component of electrical field stimulation-induced contraction (in the presence of alpha,beta-methylene ATP) in the detrusor of M4 receptor KO mice was no different from that in the detrusor of wild-type mice. M4 receptor immunoreactivity was located between smooth muscle cells, colocalized with choline acetyltransferase immunoreactivity. These results indicate that the prejunctional inhibitory muscarinic receptors are of the M4 and non-M2 receptor subtypes. The nature of the non-M2 receptors remains unknown.     

Coupling of presynaptic muscarinic autoreceptors to serine kinases in low and high release conditions on the rat motor nerve terminal

We used intracellular recording to investigate how muscarinic acetylcholine receptors and the serine kinase signal transduction cascade are involved in regulating transmitter release in the neuromuscular synapses of the levator auris longus muscle from adult rats. Experiments with M1 and M2 selective blockers show that these subtypes of muscarinic receptors were involved in enhancing and inhibiting acetylcholine (ACh) release, respectively. Because the unselective muscarinic blocker atropine considerably increased release, the overall presynaptic muscarinic mechanism seemed to moderate ACh secretion in normal conditions. This muscarinic function did not change when more ACh was released (high external Ca2+) or when there was more ACh in the cleft (fasciculin II). However, when release was low (high external Mg2+ or low external Ca2+) or when there was less ACh in the cleft (when acetylcholinesterase was added, AChE), the response of M1 and M2 receptors to endogenously released ACh shifted to optimize release, thus producing a net potentiation of the Mg2+-depressed level. Protein kinase A (PKA) (but not protein kinase C, PKC) has a constitutive role in promoting a component of normal release because when it is inhibited with N-[2-((p-bromocinnamyl)amino)ethyl]-5-isoquinolinesulfonamide, 2 HCl, release diminishes. The imbalance of the muscarinic acetylcholine receptors (mAChRs) (with the selective block of M1 or M2) inverts the kinase function. PKC can then tonically stimulate transmitter release, whereas PKA is uncoupled. The muscarinic function can be explained by an increased M1-mediated PKC activity-dependent release and a decreased M2-mediated PKA activity-dependent release. In the presence of high external Mg2+ or low Ca2+, or when AChE is added, both mAChRs may potentiate release through an M2-mediated PKC mechanism and an M1-mediated mechanism downstream of the PKC.     

Activation of I2-imidazoline receptors by agmatine improved insulin sensitivity through two mechanisms in type-2 diabetic rats

In an attempt to clarify the role of endogenous opioid in peripheral I₂-imidazoline receptors activation for improvement of insulin action, bilateral adrenalectomy was carried out in rats with insulin resistance induced by 4-week fructose-rich chow feeding. Single intravenous (i.v.) injection of agmatine (1 mg/kg) for 30 min increased the plasma β-endorphin-like immunoreactivity (BER) in a way parallel to the reduction of plasma glucose in sham-operated fructose chow-fed rats; this action of agmatine was totally abolished by BU224 at sufficient dosage (1 mg/kg, i.v.) to block I₂-imidazoline receptors. The plasma glucose lowering effect of agmatine was markedly reduced but not totally deleted by adrenalectomy in fructose chow-fed rats. A direct effect of agmatine on glucose homeostasis can thus be considered. The hyperinsulinemic-euglycemic clamp technique was performed to evaluate insulin sensitivity. The effect of agmatine on elevation of the average rate of glucose infusion at the glucose clamp steady state in sham-operated fructose chow-fed rats was lessen in adrenalectomized fructose chow-fed rats, but was completely abolished by BU224. The obtained results suggest that the improvement of insulin sensitivity by agmatine is produced by two mechanisms, stimulation of adrenal gland to enhance β-endorphin secretion and a direct activation of peripheral I₂-imidazoline receptor in tissues, for the amelioration of insulin action.     

Antihyperglycemic Effects of Separate and Composite Extract of Root of Musa Paradisiaca and Leaf of Coccinia Indica in Streptozotocin-Induced Diabetic Male Albino Rat

We evaluated the antihyperglycaemic properties of aqueous-methanolic (40:60) extract of root of Musa paradisiaca and leaf of Coccinia indica in separate as well as in composite manner by conducting experiment on streptozotocin-induced diabetic rats. We measured food and water intake ability, the fasting blood glucose level, glucose tolerance, activities of important carbohydrate metabolic enzymes like glucose-6-phosphatase, glucose-6-phosphate dehydrogenase, hexokinase in liver along with quantification of glycogen in liver and in skeletal muscle and serum insulin level. We noted that after treatment of aqueous methanolic extract of above plant parts in separate as well as in composite manner at a concentration of 80mg/100g body weight/day to streptozotocin-induced diabetic rat resulted in a significant remedial effect on blood glucose level as well as carbohydrate metabolic enzymes and the quantity of liver and skeletal muscle glycogen. Serum insulin level that was diminished in streptozotocin-induced diabetic rat recovered significantly after the co-administration of extract of above plant parts. All the above parameters showed a more potent remedial effect after composite extract treatment with respect to separate treatment and none of the extract has any general metabolic toxicity induction.     

Negative crosstalk between M1 and M2 muscarinic autoreceptors involves endogenous adenosine activating A1 receptors at the rat motor endplate

At the rat motor nerve terminals, activation of muscarinic M₁ receptors negatively modulates the activity of inhibitory muscarinic M₂ receptors. The present work was designed to investigate if the negative crosstalk between muscarinic M₁ and M₂ autoreceptors involved endogenous adenosine tonically activating A₁ receptors on phrenic motor nerve terminals. The experiments were performed on rat phrenic nerve-hemidiaphragm preparations loaded with [³H]-choline (2.5 μCi/ml). Selective activation of muscarinic M₁ and adenosine A₁ receptors with 4-(N-[3-clorophenyl]-carbamoyloxy)-2-butyryltrimethylammonium (McN-A-343, 3 μM) and R-N⁶-phenylisopropyladenosine (R-PIA, 100 nM), respectively, significantly attenuated inhibition of evoked [³H]-ACh release induced by muscarinic M₂ receptor activation with oxotremorine (10 μM). Attenuation of the inhibitory effect of oxotremorine (10 μM) by R-PIA (100 nM) was detected even in the presence of pirenzepine (1 nM) blocking M₁ autoreceptors, suggesting that suppression of M₂-inhibiton by A₁ receptor activation is independent on muscarinic M₁ receptor activity. Conversely, the negative crosstalk between M₁ and M₂ autoreceptors seems to involve endogenous adenosine tonically activating A₁ receptors. This was suggested, since attenuation of the inhibitory effect of oxotremorine (10 μM) by McN-A-343 (3 μM) was suppressed by the A₁ receptor antagonist, 1,3-dipropyl-8-cyclopentylxanthine (2.5 nM), and by reducing extracellular adenosine with adenosine deaminase (0.5 U/mL) or with the adenosine transport blocker, S-(p-nitrobenzyl)-6-thioinosine (NBTI, 10 μM). The results suggest that the negative crosstalk between muscarinic M₁ and M₂ autoreceptors involves endogenous adenosine outflow via NBTI-sensitive (es) nucleoside transport system channelling to the activation of presynaptic inhibitory A₁ receptors at the rat motor endplate.     

Presynaptic inhibition of acetylcholine release

High potassium (51 mM) has been shown to evoke release of acetylcholine ([3H]ACh and endogenous ACh) from cholinergic nerves in rat bronchial smooth muscle. The release of [3H]ACh was reduced by 85% when the Ca2+ concentration was changed from 2 to 0.1 mM. The veratridine-induced release was completely inhibited by tetrodotoxin, but tetrodotoxin did not reduce the potassium-evoked release. The muscarinic agonist, oxotremorine, reduced the potassium stimulated release of [3H]ACh, without affecting the basal release. In contrast, scopolamine substantially potentiated the potassium-evoked release. Adenosine had a dual effect in the rat bronchi. Adenosine inhibited the potassium-evoked release of [3H]ACh and this presynaptic effect of adenosine was antagonized by 8-phenyltheophylline. Adenosine also induced contraction of the bronchial smooth muscle and there was potentiation by adenosine of the ACh-induced contraction. The results indicate that cholinergic nerve terminals in the rat bronchi possess muscarinic receptors which inhibit the release of ACh. Adenosine may have analogous effects, e.g. presynaptic inhibition of transmitter release in addition to postsynaptic enhancement of bronchial smooth muscle contraction.     

High spatial resolution studies of muscarinic neuroeffector junctions in mouse isolated vas deferens

It is acknowledged that neurotransmission in the mouse vas deferens is predominantly mediated by ATP and noradrenaline (NA) released from sympathetic nerves while cholinergic transmission in the rodent vas deferens is often overlooked despite early literature. Recently we have characterized a cholinergic component of neurogenic contraction of mouse isolated vas deferens. In the present paper, by confocal imaging of Ca²⁺ dynamics we detected acetylcholine (ACh) action at muscarinic cholinergic neuroeffector junctions at high-resolution. Experiments were carried out in the presence of prazosin (100 nM) and α,β methylene ATP (α,β-MeATP) (1 μM) to inhibit responses to NA and ATP respectively. Exogenous ACh (10 μM) elicited Ca²⁺ transients, an effect blocked by the muscarinic receptor antagonist, cyclopentolate (1 μM). Ca²⁺ transients were evoked by electrical stimulation of intrinsic nerves in the presence of the cholinesterase inhibitor neostigmine (10 μM). Stimulation produced a marked increase in the frequency and number of Ca²⁺ transients. Cyclopentolate reduced the frequency of occurrence of spontaneous and evoked events to control levels. The α₂-adrenoceptor antagonist yohimbine (300 nM) did not affect the spontaneous Ca²⁺ transients, but increased the frequency of occurrence of evoked transients, an effect inhibited by cyclopentolate. The postjunctional effects of neuronally-released ACh are limited by the action of cholinesterase. Release of ACh appears to be tonically inhibited by NA released from sympathetic nerve terminals through action at prejunctional α₂-adrenoceptors. Tetrodotoxin (TTX, 300 nM) abolished the nerve-evoked Ca²⁺ events, with no effect on Ca²⁺ transients elicited by exogenous ACh. In conclusion, the presence of spontaneous and evoked cholinergic Ca²⁺ transients in smooth muscle cells of the mouse isolated vas deferens has been revealed. These events are mediated by ACh acting at M₃ muscarinic receptors. This action stands in marked contrast to the lack of effect of neuronally-released NA on smooth muscle Ca²⁺ dynamics in this tissue.     

Role of sympathetic tone in the loss of syringin-induced plasma glucose lowering action in conscious Wistar rats

Syringin is an active principle purified from the rhizome and root parts of Eleutherococcus senticosus (Araliaceae). The present study is designed to clarify the role of sympathetic activation in the insulinotropic effect of syringin. Plasma glucose lowering effect accompanying with the increase of plasma insulin and C-peptide were obtained in pentobarbital anesthetized Wistar rats 60min after an intravenous (i.v.) injection of syringin (100 microg/kg). However, neither the plasma glucose lowering action, nor the raised plasma levels of insulin and C-peptide can be obtained in conscious rats received same syringin treatment. Otherwise, the insulin-releasing and plasma glucose lowering actions of syringin (100 microg/kg, i.v.) were appeared in conscious rats under chemical sympathectomy using an intraperitoneal injection of guanethidine. In addition, plasma glucose lowering action of syringin (100 microg/kg, i.v.) was observed in conscious rats with alpha1-adrenoceptor blockade by prazosin. The stimulatory actions of syringin on the secretion of plasma insulin and C-peptide were also obtained in prazosin-treated conscious rats. The obtained results suggest that insulinotropic effect of syringin on the plasma glucose regulation is impaired in conscious rats with a regular sympathetic tone; decrease of sympathetic tone as observed in anesthetized animal might be helpful in the therapeutic benefit of syringin.     

Inhibitory M2 muscarinic receptors are upregulated in both axotomized and intact small diameter dorsal root ganglion cells after peripheral nerve injury

Acetylcholine reduces nociceptive input in part by activating inhibitory M2 muscarinic receptors on primary sensory neurons, and acetylcholinesterase inhibitors and muscarinic agonists produce analgesia in humans and animals. M2 muscarinic receptors are upregulated in animals with diabetic neuropathy, but their level of expression and function after peripheral nerve injury has not been previously examined. This study tested, using intracellular Ca(2+) response to membrane depolarization, the effect of the M2 muscarinic receptor agonist bethanechol on individual dorsal root ganglion cells from normal and L5-6 spinal nerve-ligated rats, followed by M2 muscarinic receptor immunostaining. We also examined functional transient receptor potential for vanilloids-1 activity by determining intracellular Ca(2+) response evoked by capsaicin in M2 muscarinic receptor immunoreactive cells. In normal dorsal root ganglion cells, bethanechol inhibited the Ca(2+) response in a concentration-related fashion, and this inhibition was blocked by the M2 muscarinic receptor antagonist gallamine. Cells expressing M2 muscarinic receptors by immunostaining were significantly inhibited by bethanechol, whereas those lacking positive staining were not. The proportion of studied dorsal root ganglion neurons with positive M2 muscarinic receptor staining increased significantly in the injured ipsilateral L5-6 and the uninjured ipsilateral L4 ganglia, but not in the contralateral dorsal root ganglion neurons compared with normals. In contrast, the proportion of neurons responding to capsaicin significantly decreased in the injured ipsilateral L5-6 dorsal root ganglion cells. These results suggest that inhibitory M2 muscarinic receptors are upregulated in small- and medium-sized axotomized dorsal root ganglion neurons and their uninjured neighbors following nerve injury, and may represent an appropriate target for analgesia in this setting.     

Purine P2Y receptors in ATP-mediated regulation of non-quantal acetylcholine release from motor nerve endings of rat diaphragm

We established the effect of ATP, which is released together with acetylcholine (ACh), on the non-quantal ACh release (NQR) in rat diaphragm endplates and checked what kind of purine receptors are involved. NQR was estimated by the amplitude of endplate hyperpolarization (the H-effect) following the blockade of postsynaptic nicotinic receptors and cholinesterase. 100 μM ATP reduced the H-effect to 66% of the control. The action of ATP remained unchanged after the inhibition of ionotropic P2X receptors by Evans blue and PPADS, but disappeared after the application of the broad spectrum P2 receptor antagonist suramin, metabotropic P2Y receptor blocker reactive blue 2 and U73122, an inhibitor of phospholipase C. P2Y-mediated regulation is not coupled to presynaptic voltage-dependent Ca²⁺ channels. During the simultaneous application of ATP and glutamate (which is another ACh cotransmitter reducing non-quantal release), the additive depressant effect led to a disappearance of the H-effect. This can be explained by the independence of the action of ATP and glutamate. Unlike the effects of purines on the spontaneous quantal secretion of ACh, its non-quantal release is regulated via P2Y receptors coupled to G_q/11 and PLC. ATP thus regulates the neuromuscular synapse by two different pathways.     

The modulatory effect of substance P on rat pineal norepinephrine release and melatonin secretion

Secretion of melatonin by the mammalian pineal gland is primarily regulated by the release of norepinephrine (NE) from sympathetic nerve terminals that originate from the superior cervical ganglia. Peptidergic nerves that originate in the perikarya located in the sensory trigeminal ganglia also innervate the pineal gland. Some of these peptidergic nerve fibers contain substance P. Previously, we have characterized neurokinin 1 type substance P receptors in the pineal gland. However, the function of this receptor in the pineal gland remains unclear. Here, we examined the modulatory effect of substance P on rat pineal NE transmission. We show that at the presynaptic level, substance P stimulates the KCl-induced [³H]NE release from the pineal nerve ending. However, we found that substance P did not affect the basal levels of either arylalkylamine-N-acetyltransferase (AANAT) activity or melatonin secretion in rat pineal organ cultures. However, in the presence of NE, substance P inhibited the NE-induced increase in AANAT activity and melatonin secretion. This is the first time that a function for substance P in the mammalian pineal gland has been demonstrated.     

Presynaptic M1 muscarinic receptor modulates spontaneous release of acetylcholine from rat basal forebrain slices

Spontaneous release of acetylcholine (ACh) from rat basal forebrain slices in the presence of cholinesterase inhibitor was directly determined using a specific radioimmunoassay for ACh. The release was calcium dependent. A consistent amount of ACh release was observed throughout the experiment. Atropine (10(-8) to 10(-5) M) and pirenzepine (10(-7) to 10(-5) M) enhanced spontaneous ACh release. These findings indicate the presence of an M1 muscarinic autoreceptor that modulates spontaneous release of ACh in the rat basal forebrain.     

Postsynaptic muscarinic M1 receptors activate prefrontal cortical EEG of C57BL/6J mouse

Recent pharmacological studies exploring the functional roles of muscarinic cholinergic receptor (mAChR) subtypes in prefrontal cortex of C57BL/6J (B6) mouse have provided evidence for a presynaptic M2 autoreceptor. The B6 mouse was chosen for these studies because it is a genetically well-characterized model that also provides the genomic background for many genetically modified mice. In addition to increasing ACh release, one functional consequence of pharmacologically blocking the cortical M2 autoreceptor is activation of the contralateral prefrontal cortical EEG. To date, the mechanisms through which M2 autoreceptor antagonism causes cortical EEG activation have not been investigated. The present study tested the hypothesis that, in the B6 mouse, prefrontal cortical ACh activates the contralateral prefrontal EEG via postsynaptic M1 receptors. This hypothesis was tested in 15 mice using in vivo microdialysis delivery of muscarinic antagonists with simultaneous quantification of ACh release, number of 7- to 14-Hz EEG spindles, and fast Fourier transformation analysis of prefrontal EEG. Dialysis delivery of the nonsubtype selective muscarinic antagonist scopolamine (10 nM) significantly (P = 0.01) increased ACh release. Quantitative EEG analysis showed that scopolamine did not alter contralateral prefrontal cortical EEG. To differentiate mAChR subtypes mediating pre- versus postsynaptic responses, additional experiments used muscarinic antagonists with different affinities for the five mAChR subtypes. Microdialysis delivery of 3 nM AF-DX 116, a muscarinic antagonist with relatively high affinity for the M2 and M4 subtypes, significantly (P < 0.01) increased prefrontal cortical ACh release and activated EEG in the contralateral prefrontal cortex. EEG activation was characterized by a significant decrease in number of 7- to 14-Hz EEG spindles (P < 0.0001) and power (Vrms) of EEG slow waves (P < 0.05). Microdialysis delivery of 3 nM AF-DX 116 plus 3 nM pirenzepine, a relatively selective M1 and M4 muscarinic antagonist, also significantly (P < 0.01) increased ACh release but did not decrease the number of EEG spindles and did not change EEG slow waves. The differential EEG and ACh responses to dialysis delivery of the muscarinic antagonists support the conclusion that, in B6 mouse, postsynaptic muscarinic receptors of the M1 subtype are a primary site by which ACh activates the EEG.     

中枢胆碱能M受体在烫伤应激后的改变

用放射配基结合分析法对烫伤应激后大鼠脑皮质、海马区M受体、胞内环磷酸腺苷和环磷酸鸟苷以及M受体激动剂乙酰胆碱进行测定。发现烫伤应激后中枢胆碱能神经系统有如下改变:(1)胆碱能递质ACh释放,作用于M受体后使其出现下行调节。(2)M受体介导cAMP和cGMP增高而调节神经元的兴奋性。(3)ACh释放后很快被乙酰胆碱酯酶水解。(4)应激后ACh、M受体及cAMP和cGMP逐渐恢复至正常水平。     

Chlorophytum borivilianum Root Extract Maintains near Normal Blood Glucose,Insulin and Lipid Profile Levels and Prevents Oxidative Stress in the Pancreas of Streptozotocin-Induced Adult Male Diabetic Rats

The effect of C. borivilianum root on blood glucose, glycated hemoglobin (HbAIc), insulin and lipid profile levels in diabetes mellitus are not fully understood. This study therefore investigated the effect of C. borivilianum root on the above parameters and oxidative stress of the pancreas in diabetes. Methods: C. borivilianum root aqueous extract (250 and 500 mg/kg/day) was administered to streptozotocin (STZ)-induced male diabetic rats for 28 days. Body weight, blood glucose, HbA1c, insulin, lipid profile levels and glucose homeostasis indices were determined. Histopathological changes and oxidative stress parameters i.e. lipid peroxidation (LPO) and antioxidant enzymes activity levels of the pancreas were investigated. Results: C. borivilianum root extract treatment to diabetic rats maintained near normal body weight, blood glucose, HbA1c, lipid profile and insulin levels with higher HOMA-β cell functioning index, number of Islets/pancreas, number of β-cells/Islets however with lower HOMA-insulin resistance (IR) index as compared to non-treated diabetic rats. Negative correlations between serum insulin and blood glucose, HbA1c, triglyceride (TG) and total cholesterol (TC) levels were observed. C. borivilianum root extract administration prevented the increase in lipid peroxidation and the decrease in activity levels of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) with mild histopathological changes in the pancreas of diabetic rats. Conclusions: C. borivilianum root maintains near normal levels of these metabolites and prevented oxidative stress-induced damage to the pancreas in diabetes.