Inhibition of post-decapitation convulsions in the rat by dibenzothiepin neuroleptics via alpha 1-adrenoceptor blockade

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.

Hyperthermia induced by the dopamine D1 receptor agonist SK&F38393 in combination with the dopamine D2 receptor agonist talipexole in the rat

The present experiments were performed to investigate the effects of dopamine D1 receptor agonists given alone or in combination with dopamine D2 receptor agonists on body temperature in rats. The selective dopamine D1 receptor agonist, 1-phenyl-2,3,4,5-tetrahydro-(1H)-3-benzazepine-7,8-diol (SK&F38393), produced hyperthermia. However, the dopamine D2 receptor agonist, B-HT 920 (talipexole), and the newly synthesized dopamine D2 receptor agonist, (S)-2-amino-4,5,6,7-tetrahydro-6-propylamino-benzothiazole (SND 919), did not change the temperature. Interestingly, the SK&F38393-induced hyperthermia was enhanced by talipexole and SND 919. The drastic hyperthermia induced by combined administration of dopamine D1 and D2 receptor agonists was blocked by either the dopamine D1 receptor antagonist, SCH23390, or the dopamine D2 receptor antagonist, spiperone. On the other hand, treatment with prazosin, yohimbine, propranolol, scopolamine, or methysergide failed to affect the marked hyperthermia. The present results suggest that a functional link between dopamine D1 and D2 receptors may be synergistic in the regulation of body temperature and that concurrent stimulation of both dopamine D1 and D2 receptors thereby produces marked hyperthermia in the rat.

Dopamine receptor blocking action of a dibenzothiepin derivative isofloxythepin in rats

1. Subcutaneous injection of isofloxythepin or haloperidol inhibited exploratory behaviour, methamphetamine (3 mg/kg)-induced hyperactivity and bromocriptine (15 mg/kg)-induced yawning, and also elicited catalepsy. 2. Isofloxythepin and haloperidol increased concentrations of dihydroxyphenylacetic acid in the striatum and elevated serum prolactin levels. 3. The results suggest that isofloxythepin, as well as haloperidol, blocks the action of the dopamine D2-receptors in the striatum, nucleus accumbens and pituitary.

Effects of isofloxythepin enantiomers on prolactin secretion and postdecapitation convulsions in rats

Racemic isofloxythepin and its enantiomers (0.05-1.0 mg/kg) administered subcutaneously increased serum prolactin levels in a dose-dependent manner in rats. The potencies of the drugs were equal for this variable. They (0.05-1.0 mg/kg, SC) also decreased dose-dependently the incidence and duration of postdecapitation convulsions, the convulsions being abolished at 1.0 mg/kg in all groups. Although (-)-enantiomer had slightly stronger effects than those of raceme and (+)-enantiomer, there were no great differences in their inhibitory effects on postdecapitation convulsions. The results indicate that isofloxythepin enantiomers in addition to raceme increase serum prolactin levels and inhibit postdecapitation convulsions and that they seem to have similar potency in blocking of dopamine receptors and alpha 1-adrenoceptors.