PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Picrotoxin”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed1977

The development of spontaneous motility in chick embryos interaction of picrotoxin and GABA.

The effect of the systemic administration of picrotoxin (1 mg/kg egg weight) and GABA (103 mg/kg e.w.) on the spontaneous motility of 11- to 21-day check embryos was studied intact eggs. Embryonal motility was recorded by the method of Kovach (1970). The activating effect of picrotoxin on 11- and 13-day embryos was unaffected by the administration of GABA. In 13- and 17-day-old embryos, GABA did not modify the paroxysmal effect of picrotoxin, but when the two substances were administered together, it prolonged the interparoxysmal intervals. The effect of GABA was most pronounced in 19- and 21-day-old embryos, in which it either stopped picrotoxin paroxysms from developing at all, or noticeably altered the length of the paroxysms, the amplitude of the movements and the length of the interparoxysmal intervals. The results show that the sensitivity of central apparatuses of embryonal spontaneous motility to GABA develops later than the early activatory effect of picrotoxin and are evidence of specific antagonism of these two neutrotropic substances.

Aminobutyrates↗
PubMed1977

Effect of elevated brain GABA concentrations on the actions of bicuculline and picrotoxin in mice.

gamma-Acetylenic GABA and gamma-vinyl GABA, two catalytic irreversible inhibitors of mammalian brain GABA transaminase that produce several-fold increases in brain GABA concentrations were tested for their effects on bicuculline and picrotoxin-induced seizures and mortality in mice. Neither inhibitor influenced the frequency of seizures or death produced by either bicuculline or picrotoxin. Both inhibitors, however, produced a dose-dependent prolongation of the time to onset of seizures and death induced by picrotoxin but by bicuculline. These results suggest differences in the antagonism by bicuculline and picrotoxin of GABA-mediated neural functions.

Aminobutyrates↗
PubMed1978

Development of spontaneous motility in chick embryos. The spinal and supraspinal component of strychnine and picrotoxin activation.

Activation of spontaneous motility produced by the systemic administration of strychnine (1 mg/kg egg weight) and picrotoxin (1 mg/kg egg weight) was studied in 13- and 17-day-old chick embryos. In both cases the effect was studied in normal embryos, in embryos decapitated 1, 24 and 48 hours previously and in embryos decapitated on the 2nd day of incubation at stage 11-13 according to Hamburger and Hamilton (1951). At 13 days, both substances had the same short-term activating effect on the controls and all the decapitated embryos. This result is evaluated as further evidence of non-participation of the supraspinal component in the spontaneous motility of chick embryos before the 15th day of incubation. In 17-day-old decapitated embryos, strychnine and picrotoxin activation of spontaneous motility was significantly smaller than in the controls. From a comparison of activation by strychnine and picrotoxin in normal and chronically decapitated embryos it was deduced that a spinal and a supraspinal component participated in their effect. The activating effect of strychnine and picrotoxin in 17-day-old embryos was found to be mediated largely by supraspinal factors.

Animals↗
PubMed1979

Picrotoxin- and bicuculline-sensitive inhibition of cardiac vagal reflexes.

Transmission in the cardiac vagal reflex pathway can be inhibited by stimulation of the hypothalamic defense region or somatic afferent nerves. A pharmacological analysis of inhibitory modulation of reflex vagal bradycardia was undertaken in the present study. Picrotoxin (0.5--1.5 mg/kg i.v.) or bicuculline (0.5--1.5 mg/kg i.v.) produced a dose-related blockade of inhibition of reflex vagal bradycardia elicited by stimulation of the lateral hypothalamus or branches of the brachial plexus in spinal (C1 or C8 transected) cats. In contrast, strychnine and pentylenetetrazol failed to change the heart rate responses produced by stimulation of the hypothalamus or brachial plexus afferents. Picrotoxin and bicuculline also blocked inhibition of reflex vagal bradycardia produced by stimulation of the inferior olive in decerebrate spinal cats. This observation supports the contention that these agents act in the brain stem to block inhibitory modulation of reflex vagal bradycardia. In addition, picrotoxin and bicuculline lowered basal heart rate in spinal cats but not in decerebrate spinal cats. This observation suggests that tonic suprabulbar inhibition of reflex vagal bradycardia also is sensitive to blockade by picrotoxin and bicuculline.

Afferent Pathways↗
PubMed1979

[Effect of strychnine and picrotoxin on the development of habituation in the visceral analyzer].

Effects of strychnine and picrotoxin on habituation of cortical potentials evoked by repeated stimulation of the splanchnic nerve were studied in anesthetized and immobilized cats. I. v. administration of strychnine (o.1 mg/kg) or picrotoxin (0.4 mg/kg) did not alter the decrement in evoked potentials. Larger doses of strychnine (0.3 or 0.6 mg/kg) and picrotoxin (0.8 or 2.0 mg/kg) did not block the habituation effects either. Picrotoxin applied to 2nd somatosensory area of the cortex effected amplitude of the negative component of the evoked potentials. Possible mechanisms of the habituation process are discussed.

Animals↗
PubMed1979

Modification of motor activity, passive avoidance conditioning and evoked potentials by microinjections of picrotoxin in both caudate nuclei in cats.

Inhibition of movements is the result of the caudate nucleus (CN) activity. This action seems to be necessary for passive avoidance conditioning (PAC). Much data indicates that GABA has inhibitory effects in the CN. The present report provides further evidence for GABA inhibition in th4 CN. In cats, the acquisition session of a PAC response was carried out following the bilateral administration of 6 microgram of picrotoxin or saline in the CN. Twenty four hours later (1st test session) the animals were placed in the security compartment and remained there during 600 sec. In the second test, the cats injected with picrotoxin crossed to the other compartment while the subjects injected with saline did not move. Another series of acute experiments were also carried out. Evoked potentials (EP) were recorded in the CN produced by nucleus centralis medialis electrical stimulation. After picrotoxin application the first and second peaks, which could represent EPSPs, incraeased while the third peak, which could represent IPSPs, decreased. In conclusion, it seems that GABAergic intracaudate transmission maintains a lower level of neuronal discharges and probably participates in the maintenance of a PAC but not in its acquisition.

Animals↗
PubMed1979

Effects of picrotoxin, naloxone, and vagotomy on chlordiazepoxide-induced respiratory depression.

Intravenous administration of chlordiazepoxide (CDP) caused respiratory depression in both rats and cats. The maximally tolerated dose of CDP was found to be 165 +/- 15 mg/kg, i.v., in rats. Pretreatment with picrotoxin (1.5 mg/kg) or naloxone (20 mg/kg, i.v.) significantly increased the maximally tolerated dose of CDP to 330 +/- 40 mg/kg, i.v., and 270 +/- 35 mg/kg, i.v., respectively. The protective effects of both naloxone and picrotoxin were absent in bilaterally vagotomized rats. Naloxone pretreatment (25 mg/kg, i.v.) was also found to block the respiratory depressant effects of CDP in anesthetized cats, but had no effect on the cardiovascular actions of CDP. It is possible that the respiratory effects of CDP are due to its actions on GABA receptors, and that peripheral GABA receptors may mediate the protective actions of picrotoxin and naloxone.

Animals↗
PubMed1976

Effect of antipsychotic drugs on the firing of dorsal raphe cells. II. Reversal by picrotoxin.

As reported in the preceding study, the ability of certain antipsychotic and adrenolytic agents to inhibit the spontaneous firing of serotonergic 5HT neurons in the dorsal raphe nucleus appeared to be related to adrenergic blocking efficacy. However, the interaction between adrenergic and serotonergic systems was apparently indirect. In this phase of the study we investigated the hypothesis that another transmitter system could mediate this interaction. We examined the effects of two inhibitory amino acid transmitters (GABA and glycine) for possible effects on dorsal raphe cell firing using single cell recording and microiontophoretic techniques. In addition, the ability of the GABA antagonist, picrotoxin and the glycine antagonist, strychnine to reverse the effects of the antipsychotic and alpha-blocking drugs on dorsal raphe firing was tested. Both GABA and glycine were found to inhibit raphe cell firing selectively, allowing for a possible neurotransmitter function for these amino acids within the dorsal raphe nucleus. However, picrotoxin but not strychnine was found to reverse the effects of the antipsychotic and alpha-blocking drugs on raphe firing. Based on these results, we propose that the adrenergic input may influence 5HT neurons indirectly via a GABAergic interneuron or interposed GABA neuron.

Animals↗
PubMed1976

Development of spontaneous motility in chick embryos. Normal development and the activating effect of strychnine and picrotoxin.

The longitudinal development of spontaneous motility in chick embryos was studied by Kovach's method (Kovach 1970) from the 10th day of incubation up to hatching, in completely intact eggs. From the 10th to 12th day of incubation, very low amplitude movements of a burst character predominated in spontaneous motility. From the 13th day, both low and high amplitude movements could be distinguished. From the 18th day, high amplitude movements alternating with intervals of motor inactivity preponderated. This discontinuous motility, which was most pronounced on the 20th day of incubation, changed to periodic strong hatching movements. Reduction of spontaneous motility after the 17th day of incubation was not confirmed. Strychnine already activated spontaneous motility in 11-day embryos, but typical convulsions did not appear until the 15th incubation day. With picrotoxin, motility was likewise stimulated in 11-day embryos and paroxysmal activation did not occur until the 15th incubation day. In older embryos, convulsions were gradually succeeded by a continuous increase in spontaneous motility. The effect of picrotoxin had a much longer latent period than the effect of strychnine.

Animals↗
PubMed1979

The effects of intranigral injections of picrotoxin and carbachol in cats with a lesioned nigrostriatal pathway.

Picrotoxin, carbachol and atropine were injected intranigrally through chronically implanted crannulae in cats. The drug-induced behavioural syndromes, mainly asymmetric behaviour, were analyzed. The changes in these syndromes after 6-hydroxydopamine (6-OHDA) lesion of the substantia nigra (SN) indicate that, in addition to the dopaminergic (DA), a non-catecholaminergic (non-CA) nigral output exists, both being responsible for asymmetric behaviour. It is further suggested that gamma-aminobutyric acid (GABA) receptors are present on both dopaminergic and non-CA nigral output neurons, while acetylcholine (ACh) receptors, responsible for asymmetric behaviour, are almost exclusively located on non-CA nigral output neurons.

Animals↗
PubMed1979

Turning behaviour induced by injection of muscimol or picrotoxin into the substantia nigra demonstrates dual GABA components.

Injection of the GABA agonist muscimol into rat caudal substantia nigra caused contralateral turning, whereas injection into the rostral substantia nigra caused ipsilateral turning. The GABA antagonist picrotoxin had the opposite effect. These findings support the hypothesis that GABA has dual actions in the substantia nigra. Ipsilateral turning induced by injection of muscimol into rostral nigra was abolished by haloperidol pretreatment, indicating the involvement of dopaminergic mechanisms. Haloperidol pre-treatment did not prevent turning induced by muscimol injected into the caudal nigra, supporting the existence of a non-dopaminergic nigral output system.

Animals↗
PubMed1979

Effects of picrotoxin and strychnine on fish retinal S-potentials: evidence for inhibitory control of depolarizing responses.

Simultaneous recording of the light evoked electrical signals from different classes of slow(S)-potential unit in the isolated fish retina established that picrotoxin, an antagonist of GABA, selectively suppresses the depolarizing component of C-type S-potentials. In contrast, equivalent concentrations of strychnine have no effect on S-potentials, but suppress a component of transient amacrine cell responses. On the basis of these and other experimental data [3,4] we propose a network diagram for the C-type S-potential units in the cyprinid fish retina. This network includes a GABA-ergic feed-back loop and is essentially similar to that proposed by Fuortes and Simon [5].

Animals↗
PubMed1979

The effect of strychnine, bicuculline, and picrotoxin on X and Y cells in the cat retina.

The effect of intravenous strychnine and the GABA antagonists picrotoxin and bicuculline upon the discharge pattern of center-surround-organized cat retinal ganglion cells of X and Y type were studied. Stimuli (mostly scotopic, and some photopic) were selected such that responses from both on and off-center cells were either due to the center, due to the surround, or clearly mixed. Pre-drug control responses were obtained, and their behavior following administration of the antagonists was observed for periods up to several hours. X-cell responses were affected in a consistent manner by strychnine while being unaffected by GABA antagonists. All observed changes following strychnine were consistent with a shift in center-surround balance of X cells in favor of the center. For Y-cell responses to flashing annuli following strychnine, there was either no shift or a relatively small shift in center-surround balance. Compared to X-cell responses to flashing lights, those of Y cells were very little affected by strychnine and in most cases were unaffected. It thus appears that glycine plays a similar role in receptive field organization of X cells as does GABA in Y cells (Kirby and Enroth-Cugell, 1976. J. Gen. Physiol. 68:465-484).

Action Potentials↗
PubMed1978

Comparative effects of centrophenoxine on the picrotoxin convulsive-seizure threshold in non-irradiated and irradiated mice.

A comparative study is made of the effect of centrophenoxine (CP) on the picrotoxin convulsive-seizure threshold (PCST) in non-irradiated and irradiated 3 and 7 days previously male mice. It is found that the CP appliked intracerebroventricularly in doses of 200 and 400 micrograms/mouse (weight 18-22 g), increases PCST. In non-irradiated mice the PCST-increasing effect of CP occurs rapidly (5 min) and it is brief (it can be observed until the 15th min). When the irradiation is performed three days previously, the PCST-increasing effect of CP is prolonged (it is observed until the 6th hour after its application). When the irradiation is performed seven days previously the characteristic features of the PCST-increasing effect of CP are similar to those in the early stage (3 days), the only difference being that the duration of the effect is prolonged to 120 min. Generally, these specificities of the CP effect are valid for all three phases of the convulsive seizure (general excitation, clonic convulsive seizure and tonic convulsive seizure.

Animals↗
PubMed1979

Facilitation of bicuculline- and picrotoxin-induced seizures by sodium valproate in rats.

Paralysed rats anaesthetized with urethane or halothane were injected with bicuculline or picrotoxin at doses which induced seizure activity in the EEG. Sodium valproate (50--1200 mg/kg) or saline was injected i.p. and its effect on the amplitude and duration of the seizures was measured. The seizures induced by either convulsant were increased significantly by doses of valproate greater than or equal to 200 mg/kg. The sites of action of the drugs in the brain, and the possible transmitter mechanisms involved, are discussed.

Animals↗
PubMed1977

[Behavior modifications induced by unilateral administration of picrotoxin into rat substantia nigra].

Intranigral injection of picrotoxin in Rats induced contralateral rotation and stereotyped behaviour. These responses were significantly altered following neuroleptic treatment (haloperiod, pimozide) or ipsilateral striatal electrolytic destruction. The present results provide behavioural evidence for gamma-aminobutyric acid-mediated inhibition of the dopaminergic nigrostriatal pathway.

Animals↗
PubMed1979

Hypersynchronisation and sedation produced by GABA-transaminase inhibitors and picrotoxin: does GABA participate in sleep control?

Systemic administration of GABA-transaminase inhibitors, gamma-acetylenic GABA (100 mg/kg) or gamma-vanylic GABA (1200 mg/kg) produces behavioral picture of somnolence accompanied by EEG hypersynchronisation reminiscent of electrographic signs of petit mal epilepsy. Similarly, systemic administration of GABA antagonist, Picrotoxin (3--4 mg/kg) produces a short lasting period of sedation preceding the development of myoclonic jerks which is also accompanied by Wave-spike discharges. The role of GABA in sleep control is discussed. Although the area is not ready for firm conclusions, the results suggest that hyperactivity of GABA-ergic system as well as its hypoactivity could mediate pathological somnolence associated with different forms of epilepsy.

4-Aminobutyrate Transaminase↗