The effect of 5,6-dihydroxytryptamine on post-decapitation convulsions

Mechanism of Delayed Convulsion in Fish: The Actions of Norepinephrine in Spinal Cord

Cranial spiking (CS) is among the most popular slaughtering methods for delaying the rigor mortis progress of fish muscles. However, it may cause a convulsion (subsequently referred to as delayed convulsion), which undermines the meat quality and taste. This study aimed to elucidate the mechanism underlying the delayed convulsion and examine its influence on ATP consumption. Ten carps, nine tilapias, ten rainbow trouts, two ayus, three greenling, thirty-five red seabreams, two striped jack and two stone flounders underwent CS around the medulla oblongata area, which induced different delayed convulsion profiles specific to each species. To investigate the norepinephrine (NE) actions related to delayed convulsion, 27 red seabreams, a representative fish species that exhibits delayed convulsion, were treated with a monoamine-depleting agent, reserpine, or with a monoamine oxidase inhibitor, pargyline, two hours before CS. Spinal cord destruction (SCD) was employed to completely prevent spinal cord functions of the fish in another group. Compared with the control group (CS only), the reserpine, pargyline, and SCD groups showed significantly inhibited delayed convulsion and ATP consumption. This suggests that delayed convulsion is the main ATP-consuming response. Our findings suggest that delayed clonic convulsion in red seabreams is associated with the rapid decrease in spinal cord NE levels, which triggered the rebound motor neuron hyperactivity.

Benzodiazepines increase tonic component of postdecapitation convulsions in mice

The effects of benzodiazepines (BDZs) and GABA system on tonic and clonic component of postdecapitation convulsion (PDC) were studied in mice. Mice decapitated at the occipito-cervical junction, exerted biphasic convulsions, i.e., initially tonic and subsequently clonic convulsions. BDZs such as diazepam or clonazepam increased tonic and clonic components of PDC. These effects were not antagonized by Ro 15-1788, a benzodiazepine receptor antagonist. The increased tonic component was antagonized by the GABA receptor antagonists, bicuculline and picrotoxin, whereas the clonic component was augmented by them. Aminooxyacetic acid, which increases the endogenous GABA content by inhibiting the GABA-transaminase, increased the tonic component significantly; this increase was antagonized by both bicuculline and picrotoxin. Muscimol, a GABA agonist, however did not affect the tonic components but rather augmented the clonic component. Bicuculline and picrotoxin did not antagonize this effect of muscimol. These results indicate that endogenous GABA may play a crucial role in mediating the tonic component of PDC and the facilitation of this component by BDZs may also be due to the activation of GABA in the spinal cord. Furthermore, the mechanisms of the tonic component may be different from that of the clonic component.

Modulation of postdecapitation convulsions in rats by alpha-adrenergic and 5-hydroxytryptamine1A agents

Postdecapitation convulsions were analyzed in rats after the administration of a variety of adrenergic and serotonergic agents. Drugs were selected on the basis of their relative affinities for 5-hydroxytryptamine1A, alpha 2-adrenergic and/or alpha 1-adrenergic receptors. The 5-hydroxytryptamine1A-selective agonists, 8-hydroxy-N,N-dipropyl-2-aminotetralin and buspirone, significantly increased the duration of the convulsions. The alpha 2-adrenergic antagonists, yohimbine and corynanthine, had no affect on either the latency or duration of the convulsions. By contrast, each of the three alpha 1-adrenergic agents increased the latency and decreased their duration. However, the order of potency was WB 4101 greater than ipsapirone greater than prazosin and this rank order did not correlate with drug potencies for the alpha 1-adrenergic receptor as determined by radioligand binding studies. The high potency of both ipsapirone and WB 4101 in inhibiting the postdecapitation convulsions may relate to the combined effects of the drugs at both alpha 1-adrenergic and 5-hydroxytryptamine1A receptors.

5-Hydroxytryptamine antagonists and the 5-methoxy-N,N-dimethyltryptamine-induced changes of postdecapitation convulsions

The ability of various compounds to antagonise the 5-MeODMT induced prolongations of latency and duration of postdecapitation convulsions (PDCs) were compared. The 5-hydroxytryptamine (5-HT) receptor antagonists, mianserin, methergoline, cinanserin and methysergide antagonised the 5-MeODMT (0.5 to 4.0 mg/kg) induced prolongations of latency to onset of convulsions substantially and to a lesser extent the prolongation of duration. The efficacy of the 5-HT antagonists for blocking 5-MeODMT changes of PDCs was roughly of the order mianserin greater than cinanserin greater than methysergide greater than methergoline. Pirenperone, the 5-HT2 antagonist, and pimozide, the dopamine receptor antagonist did not antagonise the 5-MeODMT induced changes. Mianserin, methergoline, cinanserin and methysergide, by themselves, prolonged the duration of PDCs but did not affect latency. Pirenperone (0.25 mg/kg) prolonged both the latency and duration of the PDCs while pimozide (0.5-2.0 mg/kg) had no effect upon PDCs. This evidence suggests that 5-MeODMT induced changes of PDCs are mediated via 5-HT1 receptors and thus a reliable model to combine with other measures of spinal function is suggested.

Antagonism of 5-methoxy-N,N-dimethyltryptamine-induced changes in postdecapitation convulsions in rats by repeated treatment with drugs enhancing 5-hydroxytryptamine neurotransmission

Repeated administration of drugs that increase tryptaminergic neurotransmission antagonized the increase in latency to onset and the duration of postdecapitation convulsions (PDCs) induced by an acute 5-methoxy-N,N-dimethyltryptamine (5-MeODMT) injection; Zimelidine (2 X 5 mg kg-1), fluoxetine (2 X 5 mg kg-1), amiflamine (2 X 2.5 mg kg-1) and alpha-ethyltryptamine (2 X 2.5 mg kg-1) administered orally over 10 days caused a substantial blockade of the increase in latency to onset and duration of PDCs following 5-MeODMT, whereas alaproclate (2 X 5 mg kg-1), clorgyline (1 X 1 mg kg-1) and pargyline (2 X 2.5 mg kg-1) caused a lesser blockade. Repeated 5-MeODMT (3 X 2 mg kg-1) administration blocked the acute effects of 5-MeODMT (2 and 4 mg kg-1) upon PDCs completely. These findings indicate down-regulation of the 5-hydroxytryptamine receptors which mediate the action of 5-MeODMT on the PDCs and offer a simple model system for studying 5-HT receptor sensitivity changes at the spinal level.

Effects of acute administration of 5-methoxy-N,N-dimethyltryptamine upon the latency and duration of post-decapitation convulsions

The effect of acute administration of rats with the 5-hydroxytryptamine (5-HT) agonist drug 5-methoxy-N,N-dimethyltryptamine on the convulsions released by decapitation was examined. The postsynaptic agonist, 5-methoxy-N,N-dimethyltryptamine, prolonged the latency and duration from the 0.5 mg/kg dose upwards. Methergoline, 2.0 mg/kg intraperitoneally injected immediately prior to 5-methoxy-N,N-dimethyltryptamine, caused some considerable blockade of the effects of the 5-HT agonist on post-decapitation convulsions (PDG's). Long-term p-chloroamphetamine (2x10 mg/kg) and p-chlorophenylalanine (1 x 300 mg/kg) did not antagonise the 5-methoxy-N-N-dimethyltryptamine induced changes of PDC's but, by themselves, prolonged PDC duration. The utility of the 5-methoxy-N,N-dimethyltryptamine-PDC method for studying 5-HT receptor mechanisms may be worth considering.

The effect of opiate treatment on the postdecapitation reflex and monoamine metabolism in the rat spinal cord

Post-decapitation seizures (PDR) are a spinal reflex which seems regulated by some monoaminergic neurons present in the spinal cord (S.C.). In order to better characterize the role of dopaminergic neurons in PDR, we studied the effect of treatment with opiates, which are known to increase dopamine (DA) and serotonin (5HT) metabolism in the brain, on the duration of PDR and on the metabolism of DA and 5HT in S.C. Morphine, given either IP or ICV, reduced the duration of PDR and increased DA metabolism. Both effects were more evident after systemic administration. [D-Ala2]Met5 enkephalin amide acted similarly to ICV administered morphine. Biochemical and behavioral effects were significantly correlated.

Studies on the role of serotonin in different regions of the rat central nervous system on pentylenetetrazol-induced seizures and the effect of di-n-propylacetate

5,7-Dihydroxytryptamine (5,7-DHT) injections which caused selective depletion of serotonin in the forebrain enhanced the seizures caused by pentylenetetrazol (PTZ 90 mg/kg s.c.) in rats. No effect was observed in rats with 5,7-DHT-induced depletion of spinal serotonin or treated with metergoline (1 mg/kg i.p.) or methysergide (10 mg/kg i.p.). The various procedures aimed at decreasing serotonin transmission did not significantly modify the effect of di-n-propylacetate (DPA) on tonic seizures and mortality caused by PTZ but significantly reduced the DPA-induced increase in the latency to the first convulsion. More animals with clonic seizures were seen in the DPA-treated group which had been subjected to selective depletion of spinal serotonin or treated with methysergide than in DPA-treated controls. Combined treatment with d-fenfluramine (1.25 mg/kg i.p.) and DPA (75 mg/kg i.p.), doses which by themselves had no significant effect, reduced tonic seizures and mortality caused by PTZ. The results show that a diffuse deficit in forebrain serotonin enhances PTZ-induced seizures. Serotonin does not play an important role in the effect of DPA against PTZ-DPA on clonic convulsions. Agents increasing serotonin transmission may enhance the anticonvulsant activity of DPA.

The ontogeny of spinal cord monoamines and the post-decapitation reflex

The ontogeny of the post-decapitation reflex (PDR) was examined in neonatal systemic 6-hydroxydopamine (6-OHDA) treated rats. The PDR was absent in the youngest (5 day) and oldest (60 day) 6-OHDA treated rats but present with attenuated characteristics at around 15 and 20 days. The reappearance of the PDR in these rats closely paralleled age-related fluctuations in spinal cord noradrenaline (NE) which increased until 15 days, then precipitously declined, but did not correlate with spinal dopamine (DA) or serotonin (5-HT). The failure of the alpha noradrenergic blocking agents chlorpromazine, phenoxybenzamine, prazosin, or yohimbine to eliminate the vestigial PDR in the 15-20-day-old, 6-OHDA-treated rats indicates that this is probably not mediated by remaining, undamaged spinal NE neurons at this age. Neither is it likely to be mediated by spinal 5-HT neurons since inhibition of 5-HT synthesis had no effect upon the PDR latency in normal or neonatal 6-OHDA-treated, 17-day-old rats. In contrast to NE levels which increased with age in normal rats, spinal cord 5-HT and DA levels at least as high at 5 days of age as at adulthood.

Selective depletion of spinal noradrenaline inhibits post-decapitation convulsions in rats

Local administration of 6-hydroxydopamine in the subarachnoidal space of the spinal cord in rats resulted in a selective long-lasting depletion of spinal noradrenaline, but not of dopamine, and prevented the occurrence of post-decapitation convulsions.

Importance of the Locus coeruleus and involvement of alpha-adrenergic receptors in the post-decapitation reflex in the rat

The latency, duration, hindlimb kick frequency, and total activity components of the post-decapitation reflex (PDR) were measured in the rat using a movement-sensitive transducer. Reduction of brain and spinal cord norepinephrine (NE) caused by neonatal administration of 6-hydroxydopamine (6-OHDA) or 5,7-dihydroxytryptamine, which also reduced brain serotonin, decreased all components of the PDR. Depletion of serotonin or dopamine alone reduced the vigor of the reflex, suggesting that these pathways can influence the PDR but are not essential for the response. Lesions of neurons in the Locus coeruleus, made electrolytically or with 6-OHDA, decreased the intensity of the PDR, with the 6-OHDA-induced lesion being more effective. Depletion of forebrain NE terminals with 6-OHDA did not alter the PDR, consistent with a critical involvement of spinal noradrenergic fibers. The PDR was also decreased by phentolamine and prazosin, but not by propanolol, suggesting an involvement of alpha-adrenergic receptors in the response. This hypothesis was further supported by the finding that the efficacy of a variety of drugs (such as tricyclic antidepressants, phenothiazines, and anti-hypertensive compounds) for blocking the reflex was apparently related to their affinity for alpha-adrenergic receptors. Thus, the PDR is dependent on noradrenergic fibers in the spinal cord and may provide a simple screen for drugs with suspected alpha-adrenergic blocking properties or for agents that disrupt the function of central noradrenergic fibers.

The role of locus coeruleus in decapitation convulsions of rats

The role of the central norepinephrine (NE) system, especially the locus coeruleus (LC), in the occurrence of decapitation convulsions was investigated in rats. Intraspinal injection of 6-hydroxydopamine (6-OHDA) caused a significant inhibition of decapitation convulsions as shown by prolongation of the latency and shortening of the convulsion's duration, as well as decreasing the NE content of the spinal cord to 35% of the control value without affecting the NE content of the various regions in the brain. Chemical lesion of the descending bundle from the LC by treatment with 6-OHDA significantly inhibited decapitation convulsions in a similar manner. Moreover, there was a decrease in the NE content of the spinal cord and hypothalamus to 24% and 47% of the control value, respectively. Bilateral electrolytic lesion of the LC also significantly inhibited decapitation convulsions and decreased the NE content of the cortex and spinal cord to 15% and 74% of the control value, respectively. However, lesions of the dorsal and ventral NE bundle by treatment with 6-OHDA, which caused a marked decrease in the NE content of the cortex and hypothalamus, respectively, did not affect the decapitation convulsion. Intraspinal injection of 5,6-dihydroxytryptamine resulted in a decrease in the 5-hydroxytryptamine content of the spinal cord only; moreover, it did not change the decapitation convulsion. These results suggest that coeruleospinal NE neurons play an important role in the occurrence of decapitation convulsions.

Physiological function of descending noradrenaline projections to the spinal cord: role in post-decapitation convulsions

Destruction of the descending noradrenergic innervation to the spinal cord, but not that to the cerebellum or the forebrain, by the use of intracerebral injection of 6-hydroxydopamine completely prevented the occurrence of the usual itation convulsion. Depletion of brain noradrenaline by synthesis inhibition with DDC, FLA 57 or FLA 63 g reduced the duration of the post-decapitation convulsion. Blockade of alpha-noradrenergic receptors by phentolamine or phenoxybenzamine, but not of beta-receptors by propranolol, also reduced the duration of the convulsion. The presynaptic alpha-agonist, clonidine, at either 1 mg/kg or 0.05 mg/kg also reduced the magnitude of the convulsion but either blockade of dopamine receptors with pimozide or destruction of the ascending dopamine systems by 6-hydroxydopamine was without effect. It is concluded that dopamine systems are not involved in post-decapitation convulsions and that the noradrenergic involvement is by the descending spinal projections acting on a post-synaptic alpha-receptor in the spinal cord, but also modulated by presynaptic alpha-receptors possibly on the locus coeruleus perikarya.