Pilocarpine, a non-hallucinogenic cholinergic agonist, elicits limb flicking in cats

Metabolite involvement in the behavioral effects of bromocriptine in cats

There is a lag phase of 30-60 min before the onset of bromocriptine (BC) action. This delay may be necessary for the formation of active metabolites. The objective was to determine whether the abnormal behavioral effects induced by BC involve active hepatic metabolites. Thus, we studied the effect of an inhibitor of hepatic hydroxylation metabolism (SKF 525A) on the behavior of BC-treated cats. Experiments began after six weeks of habituation and involved i.p. injections of: (1) propylene glycol (drug vehicle); (2) SKF 525A (70 mg/kg); (3) BC (10 mg/kg); and (4) SKF 525A followed 30 min later by BC. Each cat received the four treatments with two weeks elapsing between consecutive experiments. The frequency of 12 behaviors was scored for 60 min after 1 h posttreatment. BC alone induced emergent behavioral changes (hallucinatory-like, limb flicks, abortive grooms) that were not observed following control injections (vehicle and SKF 525A). There was a complete elimination of BC-induced hallucinatory-like behavior/escape by SKF 525A pretreatment. Other emergent behaviors were similarly reduced but persisted in all cats. The large frequency of grooming induced by BC was significantly reduced. SKF 525A pretreatment was correlated with a significant increase in staring and quiet sitting and a failure of BC to increase activities such as rubbing, treading and kneading. But many other BC-induced behaviors showed no changes. The data demonstrated that particular BC-induced changes in cats are antagonized by SKF 525A. The behavioral suppression caused by SKF 525A is compatible with the involvement of active hepatic metabolites from BC.(ABSTRACT TRUNCATED AT 250 WORDS)

Pilocarpine-induced reciprocal hindlimb scratching in mice

Intrathecal (IT) administration of pilocarpine (0.25-2.0 micrograms) to mice produced a vigorous and dose-related reciprocal hindlimb scratching response that lasted for 10-15 minutes. Neither the intracerebroventricular administration of pilocarpine at up to 10 times the intrathecal ED90 dose nor the subcutaneous administration of 10 mg/kg pilocarpine caused as robust an effect as IT administration. The reciprocal hindlimb scratching produced by the ED90 dose of pilocarpine (2 micrograms, IT) was antagonized in a dose-related manner by simultaneous IT administration of atropine (ID50 = 0.002 micrograms), methysergide (ID50 = 1.89 micrograms), the substance P antagonist [D-Pro2,D-Trp7,9]-SP (ID50 = 4.94 micrograms), and the putative neurokinin B antagonist [D-Pro2,D-Trp6,8,Nle10]-NK (ID50 = 3.33 micrograms), but not by yohimbine (5 micrograms), phentolamine (2 micrograms), or naloxone (2.5 micrograms). These results suggest that pilocarpine-induced reciprocal hindlimb scratching is mediated spinally, that the effect is produced by an action of pilocarpine on muscarinic receptors in the spinal cord, and that neurokinin, and perhaps 5-HT, mechanisms might also be involved.

Long-lasting behavioral effects of bromocriptine in cats

The objective was to determine the behavioral effects and duration of action of bromocriptine (BC) doses from 6 to 60 mg/kg i.p. Cats were housed in large outdoors cages designed for prolonged observation using an ethological approach. Baseline behavior was measured after a 3 month period of habituation. The frequency of 12 behaviors was then scored continuously over 12 h following BC administration. Cats were also observed for one h at 24, 30, 36 and 48 h post-drug. The behavioral effects of BC were remarkably similar to those of LSD and psilocybin but lasted much longer. Treated cats showed hallucinatory-like and escape behavior. Abnormal involuntary movements such as limb flicks, abortive grooming, and head and body shakes were also evoked with a dose-dependent frequency. Lower doses (6-20) produced generalized arousal, but larger doses (30-60) resulted in a decrease in arousal. After 30 mg/kg, hallucinatory-like behavior and general activity (rubbing, treading, kneading) were high at 48 h post-drug, but there were no longer abnormal movements. Behavioral suppression followed the 60 mg/kg dose and peak effects were at 96 h post-injection. This model may prove useful to further study the neural basis of the psychoactive effects of BC.

Some behavioral effects of hallucinogens are mediated by a postsynaptic serotonergic action: evidence from single unit studies in freely moving cats

Although central serotonergic systems appear to be linked importantly to the mechanism of action of a variety of hallucinogenic drugs, the nature of this interaction has remained unclear. In the present study, the question of whether the critical link is presynaptic or postsynaptic was examined in cats. Behaviorally inactive doses (1.0 mg/kg) of the serotonin receptor antagonists mianserin, ketanserin or metergoline effectively blocked behavior, as measured by the cat limb flick response, elicited by either LSD (50 micrograms/kg) or DOM (250 micrograms/kg) but not that resulting either from lisuride (50 micrograms/kg) or a high dose of apomorphine (4 mg/kg). Pretreatment with 1.0 mg/kg of mianserin, which completely attenuated LSD's behavioral effect, failed to alter LSD-induced depression of mesencephalic serotonergic neuron discharge. These results demonstrate that at least some of the behavioral effects of LSD can be blocked by pharmacological antagonism of postsynaptic serotonin receptors which leaves LSD's presynaptic effect unaffected. Thus, the behavioral, and possibly psychoactive, effects of hallucinogens appear to be attributable to an action at 5HT2 receptors, presumably located postsynaptically.

Antagonism of a behavioral effect of LSD and lisuride in the cat

These experiments investigated the role of serotonin 5-HT) and dopamine (DA) receptors in the limb-flick (LF) response elicited by the hallucinogenic ergot LSD and its nonhallucinogenic structural congener lisuride. Pretreatment with either the 5-HT antagonist pizotifen (BC-105) or the DA antagonist haloperidol significantly attenuated LF elicited by either LSD or lisuride. Thus, the LF model failed to differentiate the neuropharmacological actions of LSD and lisuride. Cocaine also prevented LSD- and lisuride-elicited LF simply by reducing the activity of cats (response competition) suggesting the need for caution in interpreting 'antagonism' of the LF response.

Serotonergic and dopaminergic effects of yawning in the cat

The serotonergic agents LSD (0.01-0.05 mg/kg) and lisuride (0.025 and 0.05 mg/kg) elicited a high frequency of limb flicking in the cat after IP doses; LSD, but not lisuride, elicited a significantly increased frequency of yawning as well. In combination, LSD plus lisuride (0.025 mg/kg each) gave additive frequencies of limb flicking, but the frequency of yawning was half that after LSD alone. The dopamine agonist apomorphine had no significant effect on either yawning or limb flicking over the dose range 0.006 to 3.2 mg/kg. Pretreatment of cats with 1.0 mg/kg of apomorphine (but not with 0.05 mg/kg) significantly reduced the frequency of yawning elicited by 0.01 or 0.025 mg/kg of LSD, but had no effect on limb flicking. The dopamine antagonist haloperidol had no effect on limb flicking at doses from 0.008 to 0.512 mg/kg, but produced a significantly increased frequency of yawning at 0.256 mg/kg, an effect antagonized by lisuride administration. Given that lisuride has more potent dopamine agonist properties than LSD, these results are consistent with serotonergic elicitation of yawning, dopaminergic inhibition of yawning, and with their concomitant interaction in the expression of drug-induced yawning in the cat. The behavioral pharmacologies of limb flicking and yawning are different in this species.