Effects Of Bicuculline Research Articles

The pharmacodynamics of anticonvulsant and subconvulsant effects of ethanol in CBA and C57BL/6 mice

A method of determination of minimal effective doses (MEDs) of bicuculline causing clonic–tonic convulsions (CTC) and tonic extension (TE) was used to investigate ethanol pharmacodynamics in C57BL/6 and CBA mice, differing in levels of alcohol predisposition. It is observed that ethanol produces a powerful anticonvulsant action antagonizing convulsant effects of bicuculline. On a long-term scale, the pharmacological action of alcohol had two phases in both strains of mice: anticonvulsant (in the interval 5 min to 4 h after ethanol administration) and subconvulsant (4–24 h after ethanol administration). C57BL/6 mice were characterized by a more rapid development of the anticonvulsant effect and its faster decay in comparison to CBA strain. A possibility of correct quantitative evaluation of data allows using the method of MED determination as an express model of an acute alcohol abstinence syndrome, as well as for screening of new antialcohol drugs.

Effects of bicuculline on direction-sensitive relay cells in the dorsal lateral geniculate nucleus (LGNd) of cats

The direction sensitivity of relay cells in the cat’s dorsal lateral geniculate (LGNd) was measured using sinusoidal grating stimuli before and during local bicuculline administration. One hundred and twenty-eight LGNd relay cells were recorded in laminae A and A1, of which 44 relay cells (34%) were found to be sensitive to direction of stimulus movement. The direction-sensitive LGNd relay cells could be differentiated into two subgroups based on different measures of their response amplitude. Type I cells exhibited their direction sensitivity when the fundamental Fourier component (FFC) of the poststimulus time histograms (PSTHs) was used as response measure, but did not show significant direction sensitivity when mean firing rate was used. Type II cells exhibited their direction sensitivity, no matter whether the FFC or mean firing rate was used as the measure. Of 35 cells analyzed, 27 cells remained direction sensitive during bicuculline administration. At the population level, the direction bias of type I cells did not change systematically, while the direction bias of type II cells decreased significantly during bicuculline administration. These results suggest that the direction bias of these two types of relay cells are mediated by different neural mechanisms. The direction bias of type I cells may involve multiple inputs from spatio-temporally separate subunits within retinal ganglion cells receptive fields. The direction bias of type II cells may involve GABAergic neuronal circuits within the LGNd.

Neuronal Activity and Brain-Derived Neurotrophic Factor Regulate the Density of Inhibitory Synapses in Organotypic Slice Cultures of Postnatal Hippocampus

Hippocampal interneurons inhibit pyramidal neurons through the release of the neurotransmitter GABA. Given the importance of this inhibition for the proper functioning of the hippocampus, the development of inhibitory synapses must be tightly regulated. In this study, the possibility that neuronal activity and neurotrophins regulate the density of GABAergic inhibitory synapses was investigated in organotypic slice cultures taken from postnatal day 7 rats. In hippocampal slices cultured for 13 d in the presence of the GABA(A) receptor antagonist bicuculline, the density of glutamic acid decarboxylase (GAD) 65-immunoreactive terminals was increased in the CA1 area when compared with control slices. Treatment with the glutamate receptor antagonist 6,7-dinitroquinoxaline-2,3-dione decreased the density of GAD65-immunoreactive terminals in the stratum oriens of CA1. These treatments had parallel effects on the density of GABA-immunoreactive processes. Electron microscopic analysis after postembedding immunogold labeling with antibodies against GABA indicated that bicuculline treatment increased the density of inhibitory but not excitatory synapses. Application of exogenous BDNF partly mimicked the stimulatory effect of bicuculline on GAD65-immunoreactive terminals. Finally, antibodies against BDNF, but not antibodies against nerve growth factor, decrease the density of GAD65-immunoreactive terminals in bicuculline-treated slices. Thus, neuronal activity regulates the density of inhibitory synapses made by postnatal hippocampal interneurons, and BDNF could mediate part of this regulation. This regulation of the density of inhibitory synapses could represent a feedback mechanism aimed at maintaining an appropriate level of activity in the developing hippocampal networks.

Local GABAergic modulation of acetylcholine release from the cortex of freely moving rats.

Cortical perfusion with GABA agonists and antagonists modulates the spontaneous release of cortical acetylcholine and GABA in freely moving rats. Twenty-four hours after implantation of a dialysis fibre, cerebral cortex spontaneously released acetylcholine (3.8 +/- 0.2 pmol/10 min) and GABA (6.6 +/- 0.4 pmol/10 min) at a stable rate. Local administration of GABA (1 or 5 mM) or the GABAA agonist muscimol (25 or 50 microM) had no effect on the spontaneous release of acetylcholine. However, bicuculline (1-25 microM), a GABAA antagonist, added to the dialysis perfusate, elicited a concentration-dependent increase of acetylcholine release to approximately double that of control. This effect of bicuculline (25 microM) was completely prevented by coperfusion with muscimol (50 microM). Local administration of the GABAB receptor agonist baclofen (10 or 50 microM) elicited a concentration-dependent increase in spontaneous acetylcholine release with a maximal increase of about 60%. Intracortical administration of baclofen also decreased the spontaneous release of GABA. The GABAB receptor antagonist CGP 35348 (1 mM), administered alone for 20 min through the dialysis fibre, was without effect on spontaneous acetylcholine release; however, it completely blocked both the baclofen-induced increase in acetylcholine release and the decrease in GABA release. These results suggest that cortically released GABA exerts a tonic influence on cholinergic activity.

Effect of bicuculline on K+ currents in rat medial preoptic neurons

Effect of bicuculline on K+ currents in rat medial preoptic neurons

Rapid activation of GABAergic interneurons and possible calcium independent GABA release in the mormyrid electrosensory lobe.

The primary afferent fibers from the electroreceptors of mormyrid electric fish terminate centrally in the granular layer of the electrosensory lobe (ELL). This study examines the excitatory and inhibitory processes that take place in this layer using an in vitro slice preparation and field potentials evoked by stimulation of primary afferent fibers in the deep fiber layer of ELL. The postsynaptic response to stimulation of the afferent fibers was still present after blocking chemical transmission in three different ways: by adding glutamate receptor antagonists to the medium, by substituting a nominally calcium-free medium for normal medium, and by blocking calcium channels with cadmium. Blockade of chemical transmission was demonstrated by disappearance of control responses to parallel fiber stimulation. The continued presence of a postsynaptic response in the absence of chemical excitation is consistent with previous anatomic and physiological evidence for electrical synapses between afferent fibers and granular cells in ELL. Granular cell activation by primary afferent fibers was followed by a powerful, short-latency inhibition mediated by GABA and GABA(A) receptors, as indicated by a large increase in the postsynaptic response to afferent fiber stimulation following application of the GABA(A) receptor antagonist, bicuculline. Bicuculline caused a marked increase of the postsynaptic response even after chemical synaptic excitation had been blocked by glutamate receptor antagonists, by a calcium-free medium, or by cadmium. Thus activation of the inhibitory interneurons responsible for GABA release did not require chemical excitation. Nonchemical excitation of the inhibitory interneurons could be mediated either by electrical synapses between afferent fibers and inhibitory interneurons, or by nonsynaptic activation of the large GABAergic terminals that are known to be present on granular cells. The marked increase of the postsynaptic response caused by bicuculline in a calcium-free medium or in the presence of cadmium suggests that the release of GABA by inhibitory terminals was not entirely dependent on calcium influx. This effect of bicuculline on the postsynaptic response in a calcium-free medium or in the presence of cadmium was markedly reduced by prior addition of the GABA transporter antagonist, nipecotic acid. Thus calcium-independent release of GABA may occur in ELL and may be partly dependent on reversal of a GABA transporter. Rapid and powerful inhibition at the first stage in the processing of electrosensory information could serve to enhance the small differences in latency among afferent fibers that appear to encode small differences in stimulus intensity.

Bidirectional modulation of nociception by GABA neurons in the dorsolateral pontine tegmentum that tonically inhibit spinally projecting noradrenergic A7 neurons

The A7 catecholamine cell group in the dorsolateral pontine tegmentum constitutes an important part of the descending pathways that modulate nociception. Evidence from immunocytochemical studies demonstrate that noradrenergic A7 neurons are densely innervated by GABA terminals arising from GABA neurons that are located in the dorsolateral pontine tegmentum medial to the A7 cell group. GABA A receptors are also located on the somata and dendrites of noradrenergic A7 neurons. These findings suggest that noradrenergic neurons in the A7 cell group may be under tonic inhibitory control by GABA neurons. To test this hypothesis, the GABA A antagonist bicuculline methiodide in doses of 0.2 or 1.0 nmol was microinjected into sites located dorsal to the A7 cell group and the resulting effects on tail flick and nociceptive foot withdrawal responses were measured. Both doses of bicuculline produced significant increases in tail flick latencies and small, but significant, increases in foot withdrawal latencies. Intrathecal injection of the alpha 2-adrenoceptor antagonist yohimbine, in a dose of 76.7 nmol (30 μg), attenuated the antinociceptive effect of bicuculline on both the tail and the feet. In contrast, the alpha 1-adrenoceptor antagonist WB4101, in a nearly equimolar dose of 78.6 nmol (30 μg), increased the antinociceptive effect of bicuculline on both the tail and the feet. Intrathecal injection of the antagonists alone did not consistently alter nociceptive responses of either the feet or the tail. These findings suggest that noradrenergic neurons in the A7 cell group are tonically inhibited by local GABA neurons. Furthermore, these findings suggest that inhibition of GABA A receptors located on spinally-projecting A7 noradrenergic neurons disinhibits, or activates, two populations of A7 neurons that have opposing effects on nociception. One of these populations facilitates nociception by an action mediated by alpha 1-adrenoceptors in the spinal cord dorsal horn and the other population inhibits nociception by an action mediated by alpha 2-adrenoceptors.

Bicuculline antagonizes 5-HT 3A and α2 glycine receptors expressed in Xenopus oocytes

The present study examined the effects of bicuculline on the mouse 5-hydroxytryptamine 3A receptor (5-HT 3A receptor and the human α2 subunit of the glycine receptor. Bicuculline antagonized both the 5-HT 3A receptor (IC 50=20.12±0.39 μM) and the α2 glycine receptor (IC 50=169.40±1.73 μM). A competitive form of antagonism by bicuculline was suggested by experiments in which the EC 50s for 5-HT and glycine were increased in the 5-HT 3A and α2 glycine receptors, respectively, as bicuculline concentrations were increased. A competitive nature of antagonism by bicuculline at the 5-HT 3A receptor was also suggested by displacement of the competitive antagonist, [ 3H]GR65630 in SF21 insect cells expressing the 5-HT 3A receptor ( K i =19.01±0.71 μ M). Our data and that of others reveal that bicuculline, a purported selective antagonist of the GABA A receptor, antagonizes at least one receptor subclass in every member of the superfamily of ligand-gated ion channels.

Effects of bicuculline and different glutamate receptor antagonists on 4-aminopyridine-induced epileptiform discharges in rat hippocampal-entorhinal cortex slices

Application of 4-aminopyridine has previously been reported to produce different patterns of epileptiform discharges in entorhinal cortex-hippocampal-slices. We describe two types of discharges: seizure-like events and negative-going potentials in the medial entorhinal cortex. Using recordings of field potentials, we investigated the pharmacological effects of the GABAA-receptor antagonist bicuculline and blockers of NMDA and non-NMDA glutamate receptors (APV as well as NBQX) on 4-aminopyridine-induced epileptiform activity. Using K+-sensitive microelectrodes we measured changes in extracellular K+ concentrations associated with the discharges. The different discharge patterns could be distinguished by their different pharmacological sensitivity to the different receptor antagonists. We propose that the study of the different activities induced by 4-aminopyridine may provide an in vitro model for the development of new drugs against difficult-to-treat focal epilepsies.

Effects of bicuculline and different glutamate receptor antagonists on 4-aminopyridine-induced epileptiform discharges in rat hippocampal-entorhinal cortex slices

Effects of bicuculline and different glutamate receptor antagonists on 4-aminopyridine-induced epileptiform discharges in rat hippocampal-entorhinal cortex slices

Effects of treatment with GABA A receptor subunit antisense oligodeoxynucleotides on GABA-stimulated 36Cl − influx in the rat cerebral cortex

GABA A receptor function was studied in cerebral cortical vesicles prepared from rats after intracerebroventricular microinjections of antisense oligodeoxynucleotides (aODNs) for α1, γ2, β1, β2 subunits. GABA A receptor α1 subunit aODNs decreased α1 subunit mRNA by 59±10%. Specific [ 3H]GABA binding was decreased by α1 or β2 subunit aODNs (to 63±3% and 64±9%, respectively) but not changed by γ2 subunit aODNs (94±5%). Specific [ 3H]flunitrazepam binding was increased by α1 or β2 subunit aODNs (122±8% and 126±11%, respectively) and decreased by γ2 subunit aODNs (50±13%). The “knockdown” of specific subunits of the GABA A receptor significantly influenced GABA-stimulated 36Cl − influx. Injection of α1 subunit aODNs decreased basal 36Cl − influx and the GABA E max; enhanced GABA modulation by diazepam; and decreased antagonism of GABA activity by bicuculline. Injection of γ2 subunit aODNs increased the GABA E max; reversed the modulatory efficacy of diazepam from enhancement to inhibition of GABA-stimulation; and reduced the antagonist effect of bicuculline. Injection of β2 subunit aODNs reduced the effect of diazepam whereas treatment with β1 subunit aODNs had no effect on the drugs studied. Conclusions from our studies are: (1) α1 subunits promote, β2 subunits maintain, and γ2 subunits suppress GABA stimulation of 36Cl − influx; (2) α1 subunits suppress, whereas β2, and γ2 subunits promote allosteric modulation by benzodiazepines; (3) diazepam can act as an agonist or inverse agonist depending on the relative composition of the receptor subunits; and (4) the mixed competitive/non-competitive effects of bicuculline result from activity at α1 and γ2 subunits and the lack of activity at β1 and β2 subunits.

BDNF and NT-4 differentiate two pathways in the modulation of neuropeptide protein levels in postnatal hippocampal interneurons.

Neuropeptide protein levels in hippocampal interneurons exhibit a considerable maturation in postnatal animals. This study characterizes the role of neuronal activity in determining neuropeptide protein levels in postnatal hippocampal interneurons, and the involvement of neurotrophins. In hippocampal slices from 7-day-old rats cultured for 2 weeks, treatment with the gamma-aminobutyric acidA (GABAA) receptor antagonist bicuculline increased the staining intensity and the number of neurons immunoreactive for neuropeptide Y (NPY). An opposite effect was observed when non-N-methyl-d-aspartate (non-NMDA) excitatory transmission was blocked. The effects of either treatment were reversed after return to control medium. These findings were similar to those previously obtained on the effects of activity on somatostatin immunostaining. Blockade of endogenous tyrosine kinase neurotrophin receptors using K252a prevented the effects of bicuculline on NPY- and somatostatin-immunoreactive neurons. Application of exogenous neurotrophin-3 (NT-3) increased NPY and somatostatin protein levels in long-term but not short-term cultures, while nerve growth factor (NGF) had no effect. In contrast, brain-derived neurotrophic factor (BDNF) or neurotrophin-4 (NT-4) did not affect equally NPY and somatostatin immunoreactivity: they mimicked the effects of bicuculline treatment on NPY-immunoreactive neurons, but exerted no conspicuous effect on somatostatin immunostaining. These results indicate that although neuronal activity plays a major role in determining neuropeptide protein levels in postnatal hippocampal interneurons, its effects on different neuropeptides might be exerted through different mechanisms, with or without the mediation of BDNF or NT-4.

A threonine residue in the M2 region of the β 1 subunit is needed for expression of functional α 1β 1 GABA A receptors

Although there is a high degree of homology in the M2 transmembrane segments of α 1 and β 1 subunits, subunit-specific effects were observed in α 1β 1 GABA A receptors expressed in Spodoptera frugipedra ( Sf9) cells when the conserved 13′ threonine residue in the M2 transmembrane region was mutated to alanine. When threonine 263 (13′) was mutated to alanine in the β 1 subunit, high-affinity muscimol binding and the response to GABA were abolished. This did not occur when the threonine 263 (13′) was mutated to alanine in the α 1 subunit, but the rate of desensitisation increased and the effect of bicuculline, a competitive inhibitor, was reduced. The results show differential effects of subunits on receptor function and support a role for M2 in desensitisation.

Cardiovascular effects of intracerebroventricular bicuculline in rats with absence seizures.

Gamma-aminobutyric acid (GABA) plays an important role in both central cardiovascular homeostasis and pathogenesis of epileptic seizures. Previous studies have indicated a critical role of the amygdala in the spread of seizures from brainstem to forebrain and in the regulation of autonomic responses such as blood pressure and heart rate. The purpose of the present study was to examine blood pressure and heart rate effects of bicuculline, a GABA(A) antagonist, and the effect of lesions of the central or the basolateral nuclei of the amygdala on bicuculline-induced cardiovascular responses in conscious WAG/Rij rats with absence epilepsy. Intracerebroventricular administration of 0.3 and 0.5 nmol of bicuculline produces an increase in blood pressure and a slight bradycardia in non-epileptic Wistar rats. The blood pressure response to intracerebroventricular bicuculline is significantly potentiated in epileptic WAG/Rij rats. Bilateral lesions of the basolateral nucleus of the amygdala of WAG/Rij rats completely prevent the pressor response to 0.5 nmol of bicuculline, whereas unilateral lesion of the basolateral nucleus does not affect blood pressure changes in epileptic WAG/Rij rats. Additionally, the pressor effect of 0.5 nmol of bicuculline is not attenuated by bilateral electrolytic ablation of the central nucleus of the amygdala in WAG/Rij rats. Heart rate response to bicuculline is not significantly changed in the lesioned groups. These findings indicate (a) altered GABAergic function in blood pressure regulation; and (b) a critical role of the basolateral nucleus in GABA(A)-mediated blood pressure control in epileptic WAG/Rij rats.

EFFECTS OF GABA A RECEPTOR ANTAGONISM WITH BICUCULLINE ON SMOKE INHALATION IN SHEEP

S149 INTRODUCTION: Sensory nerves in the lower airways and lungs contain neuropeptides including substance P and neurokinin A, which released by a variety of irritant stimuli. This neuroinflammatory mechanism has been reported to contribute to the acute lung injury of smoke inhalation. [1] Sluka and colleagues have described a model of neuroinflammation in which a central neural reflex arc involving GABA A receptors and initiated by an injury in peripheral tissues produces antidromic impulses that feedback to sustain and amplify the initial injury by releasing neuropeptides from sensory nerves. [2] Intraspinal administration of the BABA A receptor antagonist, cicuculline reduced swelling and behavioral indicators of pain in an experimental model of peripheral inflammation. We examined the effect of bicuculline on the response to smoke inhalation in sheep. METHODS: Adult female sheep were prepared surgically for chronic study by placement of vascular catheters for hemodynamic monitoring and microsphere injection, placement of an inflatable cuff around the left pulmonary artery, and formation of a chronic lung lymph fistula. After 5 to 7 days for recovery from surgery the sheep were anesthetized with ketamine and a tracheostomy performed. Under deep halothane Anesthesia smoke inhalation injury was produced by insufflation of the lungs with cool smoke from burning cotton towels. Control animals received saline infusion while the treatment group received bicuculline 100 mg/24 hours beginning 30 minutes prior to smoke inhalation. These sheep received standard supportive treatment with mechanical ventilation and pulmonary toilet while data were collected. After 24 hours the animals were sacrificed and tissue samples obtained for analysis. RESULTS: Pulmonary gas exchange was impaired by smoke inhalation as indicated by decreases in the ration of PaO2 to FiO2 (P/F ratio). Sheep treated with bicuculline and high P/F ratios after 24 hours than the control animals (446 +/- 48 vs 309 +/- 47). Lymph flow increased in sheep with smoke insufflation. This was also reduced in sheep given bicuculline (13 +/- 4 ml/hr vs 29 +/- ml/hr at 24 hours). The wet to dry ration determined for a lung sample from a bicuculline animal was 2.36 compared to 3.5 in control animals. CONCLUSIONS: These data are consistent with central nervous system modulation of neuroinflammatory mechanisms during smoke inhalation injury in sheep.

Age-dependent local modulation of hippocampal-evoked responses to perforant path stimulation

Local modulation of hippocampal-evoked responses to perforant path stimulation was studied by leaking drugs from the recording pipette placed in the dentate gyrus of anesthetized young (3 months old), aging (17 months old) and old (28 months old) rats. In old rats, the excitatory postsynaptic potential (EPSP) slope was much reduced compared to young and aging rats. The population spike (PS) size was similar in all age groups. Bicuculline caused a marked increase in PS size relative to population EPSP, and reversed the response to the second pulse in a paired-pulse paradigm from inhibition to facilitation. The effect of bicuculline was only slightly reduced in old rats. The 5-HT1a agonist 8-OH-DPAT potentiated PSs in the dentate gyrus, while not affecting paired-pulse inhibition. The effect of 8-OH-DPAT was slightly reduced in old rats. Carbachol, a cholinergic agonist, reversed paired-pulse inhibition into facilitation in the young brain, but not in aging and old rats. These results demonstrate that age affects differentially the action of biogenic amines on hippocampal reactivity to afferent stimulation.

Bicuculline, AP-7 and behavioral activity in rats.

The effects of bicuculline (0.25 mg/kg i.p.) and AP-7 (5 nmols icv) on the processes of retrieval, consolidation of conditioned reflexes, object recognition and locomotor activity were tested in rats. Neither AP-7, nor bicuculline nor AP-7 with bicuculline changed locomotor and exploratory activity in the open field test. Co-administration of AP-7 with bicuculline however, facilitated retrieval of passive avoidance in rats, but was without effect on consolidation in this test. Also neither AP-7 nor bicuculline when were given alone had an effect on influenced consolidation. We found no differences in effects of either AP-7 or bicuculline on object recognition regardless whether administered alone or in combination.

Effect of bicuculline on thalamic activity: a direct blockade of IAHP in reticularis neurons.

The thalamic reticular nucleus (RTN) is the major source of inhibitory contacts in the thalamus and thus plays an important role in regulating the excitability of the thalamocortical network. Inhibition occurs through GABAergic synapses on relay cells as well as through GABAergic synapses between reticularis neurons themselves. Here we report that the role and mechanisms of this inhibition, which frequently have been studied using N-methyl derivatives of the gamma-aminobutyric acid-A (GABAA) receptor antagonist bicuculline, should be revisited. Using the whole cell patch-clamp technique in thalamic slices from young rats, we observed an enhancement by bicuculline methiodide, methobromide, and methochloride (collectively referred to as bicuculline-M; 5-60 microM) of the low-threshold calcium spike burst in RTN neurons that persisted in the presence of tetrodotoxin (1 microM) and was not reproduced in picrotoxin (100-300 microM). The effect did not involve activation of any GABA receptor subtype. Voltage-clamp recordings showed that bicuculline-M blocked the current underlying the low-threshold spike burst afterhyperpolarization (AHP), an effect that was mimicked by apamin (100 nM). Recordings from nucleated patches extracted from reticularis neurons demonstrated that this effect was not mediated by modulation of the release of an unidentified neurotransmitter but that bicuculline-M directly blocks small conductance (SK) channels. The AHP-blocking effect also was observed in other brain regions, demonstrating that although bicuculline-M is a potent GABAA receptor antagonist, it is of limited value in assessing GABAergic network interactions, which should be studied using picrotoxin or bicuculline-free base. However, bicuculline-M may provide a useful tool for developing nonpeptide antagonists of SK channels.

Tonic GABA A receptor-mediated neurotransmission in the dorsal vagal complex regulates intestinal motility in rats

Vagal motor outflow from the dorsal vagal complex is important in the regulation of intestinal motility. The aim of our study was to test the hypothesis that within the dorsal vagal complex, tonic GABA A-receptor mediated neurotransmission modulates intestinal motility. The GABA A receptor antagonist, bicuculline (methiodide), was microinjected into the dorsal vagal complex, and the effects on small intestinal and colonic motility were investigated. Rats were anesthetized and the mean arterial pressure and heart rate were monitored. Jejunal and colonic motility were measured manometrically, and motility indices were calculated manually. Bicuculline at concentrations of 0.25 or 0.5 mM in 30 nl was microinjected bilaterally into the dorsal vagal complex through stereotaxically placed micropipettes. The injection sites were confirmed histologically using the dye Alcian Blue. Bicuculline (0.5 mM) inhibited spontaneous jejunal motility by 76.3%, colonic motility by 51.7%, mean arterial pressure by 23.3% and heart rate by 27.6%. The lower concentration of bicuculline (0.25 mM) showed no inhibitory effects on intestinal motility but decreased mean arterial blood pressure by 24.1% and heart rate by 13.6%. Bilateral cervical vagotomy attenuated the bicuculline (0.5 mM)-induced inhibition of spontaneous jejunal motility, whereas the bicuculline effect on colonic motility was unaffected. The results of this study show that GABA A receptor-mediated neurotransmission in the dorsal vagal complex is involved in autonomic integration of motility of the small intestine and colon. Furthermore, our results indicate that the dorsal vagal complex regulation of jejunal motility involves vagal outflow, whereas vagal pathways do not participate in the bicuculline-induced inhibition of colonic motility.

Spinal effects of bicuculline: modulation of an allodynia-like state by an A1-receptor agonist, morphine, and an NMDA-receptor antagonist.

Single-unit recordings were made in the intact anesthetized rat of the responses of dorsal horn neurons to C-, Adelta-, and Abeta-fiber stimulation. The postdischarge and windup responses of the same cells along with responses to innocuous stimuli, prod and brush, also were measured. The effects of (-)-bicuculline-methobromide (0.5, 5, 50, and 250 microg) were observed on these neuronal responses. The C- and Adelta-fiber-evoked responses were facilitated significantly in a dose-dependent manner. The input was facilitated, but as the final overall response was not increased by the same factor, windup appeared to be reduced. However, postdischarge, resulting from the increase in the excitability produced by windup, tended to be facilitated. After doses of >/=5 microg bicuculline, stimulation at suprathreshold Abeta-fiber-evoked activity caused enhanced firing, mainly at later latencies corresponding to Adelta-fiber-evoked activity in normal animals. Few cells responded consistently to brush and so no significant change was observed. Responses evoked by innocuous pressure (prod) always were observed in cells that concurrently responded to electrical stimulation with a C-fiber response. This tactile response was facilitated significantly by bicuculline. The effects of N6-cyclopentyladenosine (N6-CPA), an adenosine A1-receptor agonist, was observed after pretreatment with 50 microg bicuculline, as were the effects of morphine and 7-chlorokynurenate (7-CK). N6-CPA inhibited prod, C- and Adelta-fiber-evoked responses as well as the initial and overall final response to the train of C-fiber strength stimuli. Inhibitions were reversed with 8(p-sulphophenyl) theophylline. Morphine, the mu-receptor agonist, also inhibited the postbicuculline responses to prod, C-, and Adelta-fiber responses and initial and final responses to a train of stimuli. Inhibitory effects of morphine were reversed partly by naloxone. 7-CK, an antagonist at the glycine site on the N-methyl-D-aspartate-receptor complex, inhibited the responses to C- and Adelta-fiber-evoked activity as well as prod. The postdischarges were inhibited by this drug. Again both the initial and overall responses of the cell were inhibited. To conclude, bicuculline caused an increase in the responses of deep dorsal horn cells to prod, Adelta-fiber-evoked activity, increased C-fiber input onto these cells along with the appearance of responses at latencies normally associated with Adelta fibers, but evoked by suprathreshold Abeta-fiber stimulation. These alterations may be responsible for some aspects of the clinical phenomenon of allodynia and hyperalgesia. These altered and enhanced responses were modulated by the three separate classes of drugs, the order of effectiveness being 7-CK, N6-CPA, and then morphine.