The hindlimb extension reflex is not a reliable marker of post-decapitation convulsions or spinal noradrenaline depletion in rats

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.

Effects of alpha-adrenoceptor agonists in chronic morphine administered DSP4-treated rats: evidence for functional cross-sensitization

Five experiments were performed to study the effects of the Alpha-adrenoceptor agonists, clonidine and guanfacine, upon spontaneous motor activity in chronically morphine administered DSP4-treated and control rats. DSP4 (2 x 50 mg/kg, with a 10-day interval between injections) and vehicle (distilled water) were injected i.p., on each occasion 30 min after zimeldine (20 mg/kg). Morphine dosages were raised incrementally from 5 mg/kg (Days 1-3), through 10 mg/kg (Days 4-7) and 20 mg/kg (Days 8-14), to 30 mg/kg (Days 15-20). Motor activity testing occurred on Day 21, Day 22 as well as in Experiments II-V, (from 1st morphine injection). DSP4 pretreatment and chronic morphine injections each reduced motor activity during the first 30 min of testing; combined DSP4 and morphine treatment potentiated the hypoactivity. Habituation quotients indicated deficits in habituation to the novel test environment by the Vehicle-morphine (Quoteint2 only) and DSP4-morphine groups. Acute clonidine treatment (0.04 mg/kg s.c.) reduced motor activity during the first 30 min of testing but attenuated or blocked the morphine-induced hypoactivity in DSP4-treated and control rats. During the 60-90 min test period, clonidine, but not guanfacine (0.08 mg/kg), potentiated morphine-induced hyperactivity in control rats; acute clonidine enhanced this effect, whereas acute guanfacine reduced it, in the DSP4-treated rats. The enhanced hyperactivity of morphine-clonidine suggest a cross-sensitivity effect. Naloxone (0.1 mg/kg s.c.), injected after the 1st 30-min of testing, potentiated markely the clonidine-induced elevations of motor activity in morphine-administered control rats; in the DSP4-treated rats, these effects were dramatically potentiated, underlining the cross-sensitivity effect. Acute guanfacine treatment reduced motor activity during the first 30 min of testing but did not attenuate reliably morphine-induced hypoactivity in control or DSP4 rats. Naloxone did not potentiate the guanfacine-induced hyperactivity of morphine-administered control rats but induced a marked enhancement in the DSP4-treated rats, a specific case of cross-reactivity. The major findings pertain to a cross-sensitization effect of morphine upon clonidine-induced motor activity in both DSP4-treated and control rats, and to a lesser extent between morphine and guanfacine in NA-denervated rats only. The results may offer interactive implications for noradrenergic-opiate system functioning that may be of influence under neuropathological conditions.

Effects of clonidine and alpha-adrenoceptor antagonists on motor activity in DSP4-treated mice I: dose-, time- and parameter-dependency

In three experiments the acute effects of clonidine administration upon locomotor and rearing behaviour of mice pretreated with the selective noradrenaline (NA) neurotoxin, DSP4 (1 x 75 mg/kg, i.p.) 10-12 days previously, were studied. Clonidine (0.01, 0.05, 0.25, 1.25 and 3.0 mg/kg, i.p.) induced a dose-dependent reduction of motor activity during the initial 30 min of testing in both DSP4-treated and control mice; this effect was attenuated by DSP4 treatment in the 0.01, 0.05, 0.25 and 3.0 mg/kg dose groups. By the third 30-min period of testing (60-90 min), each clonidine dose group, except the highest (3.0 mg/kg) dose for locomotion and the two highest (1.25 and 3.0 mg/kg) doses for rearing, induced increases in motor activity in the control mice. In DSP4-treated mice, a large increase in locomotor counts was produced by the 0.05 mg/kg dose of clonidine with lesser increases induced by the 0.01 mg/kg dose group, whereas a lesser effect of the 0.05 mg/kg group (30-60 min) was obtained for rearing but a larger effect of the 0.25 mg/kg group (60-90 min). Yohimbine (0.5 mg/kg, i.p., 15 min before clonidine) attenuated the suppressive effects of clonidine (0.01 and 0.05 mg/kg) during the initial 30 min of testing and markedly increased locomotor and rearing counts, both by itself and in combination with each dose of clonidine, in both DSP4-treated and control mice over the following 90 min of testing. Yohimbine treatment attenuated the large increase in locomotor counts induced by the 0.05 mg/kg dose of clonidine in the NA-denervated mice. Dihydroergotamine (0.5 mg/kg, i.p., 15 min before clonidine) did not antagonise either the initial suppressive effect or the later supersensitivity effect of the 0.05 mg/kg dose of clonidine. DSP4 treatment by itself reduced motor activity. The effects of clonidine, dose- and time-dependently, by itself or in co-administration with alpha-adrenoceptor antagonists, in DSP4-treated or control mice displayed denervation-induced supersensitivity that appear to reflect mainly postsynaptic alpha2-adrenoceptor mediation.