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J D Wood

Publications and source records attributed to J D Wood.

At least 19 recordsLinked to original sources
PubMed1992

Suppression of nicotinic synaptic transmission by adenosine in myenteric ganglia of the guinea-pig gastric antrum.

Conventional intracellular recording techniques were used to investigate actions of adenosine on nicotinic cholinergic transmission in myenteric neurons of the gastric antrum. Adenosine or the more potent derivatives, 5'-N-ethylcarboxamidoadenosine (NECA), 5'-N-cyclopropylcarboxamidoadenosine, 1-deaza-2-chloro-N6-cyclopentyladenosine or N6-cyclopentyladenosine reversibly and dose dependently inhibited the fast excitatory postsynaptic potentials (fast EPSPs) in 60% of the gastric neurons. Neither adenosine nor NECA affected excitatory responses to the nicotinic agonist 1,1-dimethyl-4-phenyl-piperazinium iodine. The EC50 concentration for inhibition of the fast excitatory postsynaptic potential (EPSP) by adenosine was 55 microM NECA was a more potent inhibitor than adenosine. The specific adenosine receptor antagonists 1,3-dipropyl-8-p-sulfophenyl xanthine or 1,3-dipropyl-8-(cyclopentyl) xanthine blocked the inhibitory effects of adenosine or NECA. Fast EPSPs were enhanced by superfusion of the antagonists alone, suggestive of ongoing inhibition of nicotinic transmission by endogenous adenosine. The antagonists had no effect on resting membrane properties, excitability or antidromic action potentials. In neurons with suppression of fast EPSPs, adenosine did not suppress all cholinergic inputs to the same neuron. The results suggest that adenosine inhibits nicotinic transmission by interacting with presynaptic P1 adenosine receptors located at cholinergic release sites.

Action Potentials↗
PubMed1992

Evidence that cellobiose:quinone oxidoreductase from Phanerochaete chrysosporium is a breakdown product of cellobiose oxidase.

Phanerochaete chrysosporium releases two enzymes that oxidize cellobiose and higher cellodextrins: the flavohaemoprotein cellobiose oxidase and the flavoprotein cellobiose:quinone oxidoreductase (CBQase). Partial digestion of these enzymes with Staphylococcal V8 proteinase or cyanogen bromide yielded many identical bands on SDS-polyacrylamide gels. A polyclonal antibody to either purified protein gave cross-reaction. The purification procedure also yielded a haem protein that ran on dodecyl sulphate gels at Mr 31,000, as compared with 91,000 for cellobiose oxidase and 63,000 for CBQase. The 31 kDa haem protein cross-reacted with polyclonal antibody to cellobiose oxidase, but not with antibody to CBQase. Sulphite bleached the flavin of cellobiose oxidase, but gave no reaction with the 31 kDa haem protein, suggesting an absence of flavin. It is proposed that CBQase and the 31 kDa haem protein are formed from cellobiose oxidase by proteolytic cleavage.

Agaricales↗
PubMed1992

Corticotropin-releasing hormone excites myenteric neurons in the guinea-pig small intestine.

The electrophysiological actions of corticotropin-releasing hormone (CRH) on myenteric neurons from the guinea-pig ileum were studied by intracellular microelectrode recording. CRH, when applied by micropressure ejection or in the medium (0.2-20 nM) evoked prolonged depolarization in 21 of 42 S/type 1 neurons and in 28 of 40 AH/type 2 neurons. These responses were associated with increased input resistance and augmented excitability. The post-spike hyperpolarization in AH/type 2 cells was suppressed during the CRH-evoked responses. The reversal potential of the response to CRH was about -90 mV, consistent with the closure of potassium channels by the peptide. The CRH-induced depolarization was prevented by incubation in 10 microM 5'-N-ethylcarboxamidoadenosine (NECA, an adenosine analog) suggesting that the response was mediated by stimulation of adenylate cyclase and elevation of cAMP. CRH reduced the amplitude of fast nicotinic excitatory postsynaptic potentials. This appeared to be a postsynaptic action because the peptide also reduced the responses to exogenously applied acetylcholine. These results suggest that CRH can directly influence intestinal function by acting on myenteric neurons.

Animals↗
PubMed1992

Effects of brain-gut related peptides on cAMP levels in myenteric ganglia of guinea-pig small intestine.

This study was designed to test the hypothesis that stimulation of adenylate cyclase and elevation of cAMP is involved in the signal transduction process for substance P, calcitonin gene-related peptide, vasoactive intestinal peptide, cholecystokinin or gastrin releasing peptide in myenteric ganglia. Enzymatically dissociated ganglia from the myenteric plexus of the guinea-pig small intestine were used to study changes in levels of cAMP in response to application of the brain-gut peptides in the presence and absence of forskolin. Application of substance P and calcitonin gene-related peptide were found to increase intraganglionic cAMP in a dose-dependent fashion when a phosphodiesterase inhibitor was present. The ED50 values for substance P and calcitonin gene-related peptide were 5 microM and 0.75 microM, respectively. The presence of forskolin in the incubation medium resulted in significant upward shifts of the dose-response curves for both peptides. Neither vasoactive intestinal peptide, cholecystokinin nor gastrin releasing peptide stimulated increases in intraganglionic cAMP under the same experimental conditions used for substance P and calcitonin gene-related peptide.

1-Methyl-3-isobutylxanthine↗
PubMed1992

Effects of prolonged exposure to histamine on guinea pig intestinal neurons.

Intracellular microelectrodes were used to study the effects of prolonged exposure to histamine on the electrophysiological behavior of AH/type-2 neurons in the myenteric plexus of the guinea pig small intestine. Application of histamine activated H2 receptors to convert the neurons to a heightened state of excitability. Heightened excitability was evident as repetitive spike discharge made possible, in part, by suppression of postspike after-hyperpolarization. The hyperexcitable state persisted unchanged for prolonged periods of 4.5 hr in the continued presence of histamine, suggesting that desensitization may never occur in vivo. The results are interpreted as a neural correlate for the pathophysiology associated with microscopic colitis and other inflammatory conditions involving mast cell hyperplasia.

Animals↗
PubMed1992

Actions of noradrenaline on myenteric neurons in the guinea pig gastric antrum.

We used intracellular electrophysiological recording to study the actions of noradrenaline on myenteric neurons in the guinea pig gastric antrum. Noradrenaline caused a dose-dependent inhibition of the stimulus-evoked cholinergic fast excitatory postsynaptic potentials (EPSPs). Noradrenaline had no effect on the postsynaptic response to acetylcholine, suggesting a presynaptic site of action. The slow EPSP was also presynaptically inhibited by noradrenaline. In only 5% of the neurons, noradrenaline caused a postsynaptic depolarization, accompanied by increased input resistance and enhanced excitability. Studies with adrenergic antagonists and agonists revealed that the presynaptic inhibitory effect was mediated by an alpha 2-receptor, while the postsynaptic excitatory effect seemed to be mediated by an alpha 1 receptor. We conclude that noradrenaline inhibits neurotransmitter release from cholinergic and non-cholinergic nerve terminals in the myenteric plexus of the antrum and that it excites a subpopulation of antral neurons. Both mechanisms may contribute to the neurally mediated inhibitory action of noradrenaline on gastric contractility.

Acetylcholine↗
PubMed1992

Synaptic behaviour in the myenteric plexus of the guinea-pig gastric antrum.

1. Intracellular recording methods were used to study the synaptic behaviour of neurones in the myenteric plexus of the guinea-pig gastric antrum. Synaptic potentials occurred spontaneously or were evoked by focal electrical stimulation of interganglionic fibre tracts. Synaptic events consisted of fast and slow excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs). 2. Fast EPSPs with durations less than 20 ms were evoked in every antral neurone in a population sample of 370 cells. Most of the ganglion cells received multiple inputs from axons entering the individual ganglia in several different interganglionic fibre tracts. Many of the neurones also received input from multiple axons projecting in individual fibre tracts. The fast EPSPs behaved like nicotinic cholinergic EPSPs. They were evoked at stimulus frequencies up to 60 Hz without evidence of the run-down characteristic of fast EPSPs in the intestine. 3. Slow EPSPs were evoked by repetitive stimulation of the interganglionic connectives. They consisted of a slowly activating depolarization which persisted for several seconds after termination of the stimulus. The depolarizing responses were associated with an increase in the input resistance, with enhanced excitability and with suppression of hyperpolarizing after-potentials in AH/type 2 neurones. They were observed in 14.4% of the neurones of which 89% were AH/type 2 neurones. AH/type 2 neurones, unlike other myenteric neurones, were identified by action potentials with long lasting after-hyperpolarization. 4. IPSPs were hyperpolarizing potentials evoked by repetitive stimulation of interganglionic fibre tracts. The hyperpolarizing responses were associated with decreased input resistance. They occurred in 1.4% of the antral neurones. 5. Application of acetylcholine (ACh) by micro-ejection mimicked the fast EPSPs in all neurones. This fast nicotinic response to ACh was followed by a slowly activating, long-lasting muscarinic depolarization in 32% of the neurones. The slow muscarinic response was associated with increased input resistance, suppression of hyperpolarizing after-potentials and enhanced excitability. 6. Fast EPSPs were not suppressed by accumulation of ACh at presynaptic transmitter release sites. Unlike the intestine, presynaptic muscarinic autoreceptors appeared to be absent from the microcircuits in the antrum. 7. Synaptic behaviour in the local circuits of the gastric antrum differed from the gastric corpus. This may be a reflection of specialization of the circuits for organization of the distinctive patterns of digestive behaviour found in this region of the stomach.

Action Potentials↗
PubMed1992

Electrical behaviour of myenteric neurones in the gastric antrum of the guinea-pig.

1. Intracellular microelectrodes were used to study the electrical behaviour of ganglion cells in the myenteric plexus of the antrum of the guinea-pig stomach. In the absence of any information on antral myenteric neurones, the aim was to characterize the electrical behaviour and identify biophysical properties of the neurones that could be related to specialized organization of the neural microcircuits in this physiologically important division of the stomach. 2. Myenteric neurones in the gastric antrum were classified into four subtypes based on electrophysiological properties. These were gastric I, II, III and AH/type 2 neurones. Gastric I neurones were characterized by repetitive spike discharge during intraneuronal injection of depolarizing current, by higher input resistances and by lower resting membrane potentials than the other cell types. Gastric II neurones did not discharge repetitively. They discharged one or two spikes only at the beginning of depolarizing current pulses. Gastric III neurones did not discharge action potentials in response to depolarizing pulses. These neurones had higher membrane potentials and lower input resistances than the other types. A fourth type of neurone discharged one or more spikes during depolarizing current pulses and had long-lasting hyperpolarizing after-potentials associated with the spikes. The behaviour of these neurones was like AH/type 2 neurones found elsewhere in the enteric nervous system. 3. Action potentials in gastric I and II neurones were abolished by tetrodotoxin. Spikes of the AH/type 2 cells were not abolished by tetrodotoxin due to a calcium component of the inward current. Application of tetraethylammonium broadened the spikes. This was reversed by removal of Ca2+ from the bathing medium. 4. The hyperpolarizing after-potentials of AH/type 2 neurones were suppressed by removal of Ca2+ from the bathing medium. Treatment with 4-aminopyridine decreased the amplitude and duration of the after-hyperpolarization, whereas tetraethylammonium increased the duration and amplitude of the after-potentials. The hyperpolarizing after-potentials were unaffected by apamin. 5. Elevation of cyclic 3',5'-adenosine monophosphate by forskolin resulted in excitation of all AH/type 2 neurones and some of the gastric III cells. Gastric I and II neurones were unaffected. 6. The electrophysiological behaviour of myenteric neurones in the antrum was similar in some respects and different in others from neurones in the gastric corpus and the small and large intestine of the same animal. The differences may reflect distinct organization of the microcircuits for the specialized neural control of the effector functions which characterize the gastric antrum.

4-Aminopyridine↗
PubMed1992

Patch-clamp recording in myenteric neurons of guinea pig small intestine.

The results of our research established the feasibility of applying patch-clamp methods in the study of the cellular neurophysiology of myenteric neurons enzymatically dissociated from adult guinea pig small intestine. Recording in current-clamp mode revealed two populations of neurons. One population discharged repetitively during depolarizing current pulses and displayed anodal-break excitation reminiscent of S/type 1 myenteric neurons. In the second population, spike discharge was limited to one or two spikes at the onset of depolarizing pulses and was similar to the behavior of AH/type 2 neurons. Recording in voltage-clamp mode revealed a complex of overlapping inward and outward whole cell currents. Fast and slow components of inward current were interpreted as sodium and calcium currents, respectively. Outward currents were blocked by cesium and consisted of components with properties of delayed rectifier current and A-type potassium current.

Animals↗
PubMed1992

Submucosal reflexes: distension-evoked ion transport in the guinea pig distal colon.

Muscle-stripped segments of distal colon from guinea pigs were mounted in modified flux chambers to determine the effect of distension on mucosal secretion. Ion secretion was monitored as changes in short-circuit current (Isc). Distending forces were pressure gradients established by controlled reduction in liquid volume of the submucosal compartment of the chamber. Volume removal for 10 s or 5 min evoked a monophasic or biphasic increase in Isc, which returned to baseline within 5-20 min. The amplitude of the response correlated with the volume removed and was reduced by bumetanide and Cl-free solutions but not by tetraethylammonium or amiloride. Tetrodotoxin and atropine also suppressed the response. Neither the nicotinic receptor antagonist mecamylamine, the 5-hydroxytryptamine3 (5-HT3) receptor antagonist ICS 205-930, or the prostaglandin synthesis inhibitor piroxicam altered the response. Addition of prostaglandin D2 to the submucosal bath significantly enhanced the response. The results suggest that distension of the colon evokes anion secretion by activation of reflex circuits with cholinergic neurons and muscarinic synapses. Prostaglandins and 5-hydroxytryptamine acting at 5-HT3 receptors appear not to be signal substances in the reflex pathway, which evokes the secretory response to distension.

Animals↗
PubMed1992

Actions of 5-hydroxytryptamine on myenteric neurons in guinea pig gastric antrum.

Intracellular recording methods were used to study the actions of 5-hydroxytryptamine (5-HT) on 257 myenteric neurons in the guinea pig gastric antrum. Application of 5-HT caused three types of postsynaptic responses. A fast-activating depolarizing response was accompanied by a decreased input resistance and desensitized quickly to repeated applications. It was mediated by a 5-HT3 receptor. A slowly activating depolarization, accompanied by an increase in the input resistance and enhancement of the excitability, was mainly observed in after hyperpolarizing/type 2 neurons. It was suppressed by the prokinetic benzamide compound renzapride, while classical 5-HT1-4 receptor antagonists had no effect, suggesting the involvement of a 5-HT1p receptor as described in small intestinal neurons. A long-lasting hyperpolarizing response, accompanied by a decreased input resistance, was observed in a small subset of neurons. This response seemed to be mediated by a 5-HT1a receptor. Superfusion of 5-HT caused a dose-dependent inhibition of the stimulus-evoked nicotinic cholinergic fast excitatory postsynaptic potential (EPSP), which was mediated by a presynaptic 5-HT1a receptor. 5-HT also presynaptically inhibited the slow EPSP.

Animals↗
PubMed1991

Thyrotropin-releasing hormone excites submucous neurons in guinea-pig ileum.

Actions of thyrotropin-releasing hormone (TRH) on submucous neurons of the guinea-pig ileum were examined with intracellular electrophysiological methods. TRH evoked excitatory responses in S/type 1 and AH/type 2 neurons. The responses consisted of slowly activating membrane depolarization, augmented excitability and an increase in input resistance that resulted from a decrease in potassium conductance. The results suggest a neuromodulatory/neurotransmitter function for TRH.

Animals↗
PubMed1991

Neuropharmacology of the muscarinic antagonist telenzepine in myenteric ganglia of the guinea-pig small intestine.

Intracellular recording methods were used to investigate the actions of the putative M1 muscarinic receptor antagonist telenzepine on the electrical and synaptic behavior of myenteric neurons. Telenzepine had no effect on resting membrane potential, input resistance, excitability and antidromic potentials in both AH/type 2 and S/type 1 neurons, when applied in concentrations of 0.1-2000 nM, although higher concentrations (10-100 microM) did have a significant non-specific effect on the postsynaptic membrane. Micromolar concentrations of telenpzepine (1-2 microM) had no effect on excitatory responses to substance P, vasoactive intestinal peptide, the nicotinic agonist 1,1-dimethyl-4-phenylpiperazinium or the nicotinic action of acetylcholine. Nicotinic fast excitatory postsynaptic potentials were also unaffected by 2 microM telenzepine. In contrast, at submicromolar concentrations (100 nM), telenzepine abolished responses to either muscarine or the muscarinic component of the acetylcholine response. The excitatory effect of muscarine at postsynaptic M1 receptors was dose dependently inhibited by telenzepine (0.1-1000 nM) at concentrations which had no effect on the electrical properties of the cells. This effect was slowly reversible, usually requiring more than 60 min for significant recovery. The threshold dose of telenzepine as an antagonist of the muscarinic depolarization in AH/type 2 neurons was in the range of 0.1-1 nM. The IC50 concentration of telenzepine needed to abolish the response was 8.5 nM. A small proportion of stimulus-evoked slow excitatory postsynaptic potentials in both AH/type 2 and S/type 1 cells were abolished by 1 microM telenzepine, while the majority of them remained unaffected, indicating that some slow excitatory postsynaptic potentials are mediated by the muscarinic action of released acetylcholine.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Determination of levels of cyclic AMP in the myenteric plexus of guinea-pig small intestine.

Enzymatically dissociated ganglia from the myenteric plexus of the guinea-pig small intestine were used to investigate changes in levels of cyclic 3',5'-adenosine monophosphate (cAMP) in response to stimulation of adenylate cyclase by forskolin and inhibition of phosphodiesterase by 3-isobutyl-1-methylxanthine (IBMX). A linear relation with a positive correlation coefficient greater than 0.98 was found between: (1) amount of cAMP and number of ganglia; (2) amount of protein and number of ganglia; (3) amount of DNA and amount of protein; (4) amount of DNA and number of ganglia. Basal levels of cAMP were 2.25 +/- 0.21 fmol per ganglion for 900 ganglia. Forskolin stimulated a dose-dependent increase in cAMP over a concentration range of 0.05 to 50 microM, with a level of 18.6 +/- 4.9 fmol/ganglion at 50 microM forskolin. The inactive forskolin analog 1,9-dideoxyforskolin did not elevate cAMP. Addition of IBMX to the incubation medium stimulated a dose-dependent increase in cAMP over a concentration range of 0.1-1000 microM, with a level of 17.58 +/- 3.38 fmol/ganglion at 1000 microM IBMX. Application of 1 mM IBMX strongly potentiated the stimulating action of forskolin on cAMP levels. Our results derived from direct determination of cAMP changes in small intestinal myenteric ganglia are consistent with existing electrophysiological evidence for second messenger function of cAMP in slow synaptic modulation of excitability in AH/Type 2 neurons of the enteric nervous system.

1-Methyl-3-isobutylxanthine↗
PubMed1991

Regulation of the GABAA receptor/ion channel complex by intracellular GABA levels.

Synaptosomes and synaptoneurosomes were prepared from the cerebral cortex of control rats and of rats treated with gabaculine, gamma-vinylGABA (GVG), hydrazine and isonicotinic acid hydrazide (INH). An inverse relationship was observed between the GABA content of the synaptoneurosomes and the muscimol-stimulated chloride ion uptake by the organelles. The relationship held over an extensive range of experimental conditions including different drugs, different dosage levels of the same drug, different time intervals after administration of the same drug, and both single and multiple injections of drugs. The results indicated that the phenomenon was associated with the neurosome component of the preparation, and raised the possibility that GABA levels within the postsynaptic cell might regulate the functioning of the GABAA receptor complex.

Aminocaproates↗