Limb Flicking Research Articles

Behavioral and neurochemical effects of apomorphine in the cat

Administration of apomorphine (2–10 mg/kg i.p.) elicited a number of behaviors, such as limb flicking, abortive grooming, investigatory and hallucinatory-like responses, head and body shakes, and excessive grooming, which we have previously proposed as an animal model for studying the actions of LSD and related hallucinogens. Repeated administration of apomorphine resulted in a significant tolerance, which occurred within 2h of the initial injection, and completely dissipated within 24 h. A pronounced LSD-apomorphine cross tolerance was observed; however there was no significant apomorphine-LSD cross tolerance. Apomorphine-induced behavioral changes were blocked by prior treatment with haloperidol, but were unchanged by pretreatment with L-DOPA. Administration of L-DOPA, in combination with a peripheral decarboxylase inhibitor, did not elicit these characteristic behavioral changes. Increasing synaptic serotonin levels by monoamine oxidase inhibition, precursor administration, or reuptake blockade in general did not alter the behavioral response to apomorphine. Similarly, pretreatment with serotonin receptor blockers produced no large changes in apomorphine-induced behaviors. Prior serotonin depletion with chronic p-chlorophenylalanine administration, however, potentiated certain apomorphine-induced behaviors. Neurochemical studies revealed that apomorphine administration increased striatal dopamine, and decreased dopamine metabolites. Norepinephrine levels were generally decreased throughout the CNS by apomorphine treatment. Administration of apomorphine increased CNS serotonin and 5-hydroxyindoleactic acid levels, while tryptophan levels were unchanged. The biological bases of the limb flick model is discussed in the context of these pharmacological and neurochemical studies.

Behavioral effects of quipazine in the cat

Administration of quipazine to cats elicits a number of behaviors, such as limb flicking, abortive grooming, investigatory behavior and hallucinatory-like behavior, which we have previously proposed as an animal behavioral model for studying the actions of LSD and related hallucinogens. While recent studies have indicated that these model behaviors may not be totally specific for hallucinogenic drugs, the model can still be useful for studying drug action. Quipazine (0.5–5.0 mg/kg i.p.) produced significant increases in limb flicking, abortive grooming, investigatory behavior, hallucinatory-like behavior, grooming, head and body shakes, staring and yawning. These behavioral changes persisted for 1–6 h, depending on the dose of quipazine employed. Administration of quipazine (5.0 mg/kg per day) for 5 consecutive days produced no significant tolerance effect on any of these model behaviors. These quipazine induced behavioral changes were potentiated by pretreatment with apomorphine, and partially blocked by pretreatment with haloperidol. Quipazine-induced behavioral changes were potentiated by prior serotonin depletion with p-chlorophenylalanine, and completely blocked by pretreatment with a monoamine oxidase inhibitor or the serotonin precursor, L-5-hydroxytryptophan. These quipazine-induced behavioral changes were also blocked by pretreatment with the serotonin receptor blockers, cinnanserin, methysergide or cyproheptadine. The mechanism of action of quipazine, as well as the neuropharmacology of the limb flick model, is discussed in the context of these studies with serotonergic and dopaminergic drugs.

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

The centrally- and peripherally-acting muscarinic cholinergic agonist pilocarpine (PILO, 0.125–1.0 mg/kg, IP) elicited a significantly increased frequency of occurrence of limb flicking at 0.25–1.0 mg/kg, and significantly increased the frequency of occurence of other grooming behaviors, in 4–6 cats in the 90 min following its administration. These effects of PILO at 0.5 mg/kg were antagonized by the peripherally-acting antimuscarinic agent, N-methylscopolamine (MESCO, 0.5 mg/kg, IP), when MESCO was administered 15 min before PILO. The same MESCO pretreatment did not significantly antagonize the behaviors when they were elicited by LSD (0.01 mg/kg, IP) or lisuride (LIS, 0.05 mg/kg, IP). These results provide further evidence that a cat behavior model for LSD-like hallucinogens which employs limb flicking and similar grooming behaviors is not specific for hallucinogens; indicate that important “model behaviors” may be elicited by a peripheral mechanism; and show that a peripheral muscarinic cholinergic mechanism is not responsible for LSD- and LIS-elicited limb flicking. The results also suggest that the increased frequency of occurence of the model behaviors after PILO reflects their function as grooming behaviors, elicited by PILO's intense cholinergic effects, including salivation or sialorrhea and emesis.

Serotonergic and dopaminergic effects on 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 (0.25 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 of 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.

Dissociations between the effects of hallucinogenic drugs on behavior and raphe unit activity in freely moving cats

The hypothesis that the action of hallucinogenic drugs is mediated by a depression of the activity of brain serotonergic (raphe) neurons was testedby examining the behavioral effects of several hallucinogenic drugs while concurrently monitoring the activity of raphe neurons in freely moving cats. LSD produced a dose-dependent decrease in raphe unit activity and a dose-dependent increase in certain behaviors (e.g. limb flick and abortive groom), and the peak of the behavioral and unit changes were temporally correlated. However, there were three important dissociations between the behavioral and electrophysiological effects of LSD. Firstly, low doses of LSD produced only small decreases in raphe unit activity but significant behavioral changes. Secondly, the duration of LSD-induced behavioral changes significantly outlasted the depression of raphe unit activity. And thirdly, raphe neurons were at least as responsive to LSD during tolerance as they were in the nontolerant condition. Psilocin produced a dose-dependent decrease in raphe unit activity, while the behavioral changes were not dose-related. However, the peak behavioral changes corresponded to the maximal depression of raphe unit activity. The phenylethylamine hallucinogens. DOM and mescaline, both produced large behavioral changes but no overall effect on raphe neurons. Following administration of DOM or mescaline, some raphe units showed a significant increase, while some showed a significant decrease, othrs showed a significant increase, while some phenylethylamine hallucinogens may exert a depressant effect upon a subset of serotonin-containing neurons, and an amphetamine-like excitatory effect upon an other subset of these neurons. Consistent with previous studies, all hallucinogens produced a high concentration of slow waves in the cortical EEG. Following administration of LSD or psilocin, the appearance of slow waves in the EEG was often associated with a transitory decrease in unit activity, while this was not observed for the phenylethylamine hallucinogens. The present data, in conjunction with recent data from other laboratories, suggest that the serotonin hypothesis of hallucinogenic drug action should be re-evaluated.

Activity of a non-hallucinogenic ergoline derivative, lisuride, in an animal behavior model for hallucinogens.

The behavioral effects of IP administration of lisuride, a non-hallucinogenic iso-lysergic acid amide analog structurally related to d-lysergic acid diethylamide (LSD), were examined in 15 cats. Ten animals were given saline or 6.25, 12.5, 25, 50, or 100 micrograms/kg of lisuride and observed for 1 h by a rater blind to dose. There was a statistically significant effect of lisuride dose on the frequency of occurrence of the behaviors limb flicking, grooming, and abortive grooming. A time-course study with five cats at the most effective lisuride dose, 50 micrograms/kg, revealed that the frequencies of occurrence of these behaviors reached a maximum during the first 2 h post dose, and were comparable to frequencies after saline by 6 h post dose. An acute tolerance study with four cats scored for 90 min post dose revealed no significant tolerance to a 50 micrograms/kg lisuride test dose administered 6, 24, or 72 h after an initial 50 micrograms/kg dose. Acute cross tolerance studies with four cats scored for 90 min after an initial dose of 50 micrograms/kg of LSD or of lisuride, followed 24 h later by 50 micrograms/kg of lisuride or LSD, revealed no significant cross tolerance. The potency of lisuride relative to LSD was evaluated in six cats that were scored for 60 min following 25 and 50 micrograms/kg of LSD and of lisuride. On a molar basis, scores after lisuride were 51% and 67% those after LSD for limb flicking and grooming. These results indicate that lisuride, a non-hallucinogenic iso-lysergic acid derivative, is a false positive in the animal behavior model for hallucinogens.

On the specificity of a cat behavior model for the study of hallucinogens

LSD is the prototype for a cat behavior model for the study of hallucinogens. The model's specificity was tested with the nonhallucinogen methysergide, a d-lysergic acid amide derivative structurally similar to LSD. The frequencies of occurrence of the model behaviors limb flicking, grooming, and head plus body shaking show statistically significant dose dependency after i.p. methysergide (62.5–1000 μg/kg), and the maximum frequencies of the methysergide-elicited behaviors occur between 1–3 h post-dose. Methysergide produces statistically significant tolerance to limb flicking and grooming 24 h following an acute dose, and there is statistically significant methysergide-LSD and LSD-methysergide cross tolerance to limb flicking at 24 h. In addition, pretreatment with methysergide 15 min before LSD or lisuride antagonizes their elicitation of model behaviors. The dose-response, time course, and tolerance results with methysergide are analogous to those observed after LSD, showing that methysergide has all of the key properties of the model's prototype and, therefore, that the cat behavior model is not specific for hallucinogens.

Lack of specificity of an animal behavior model for hallucinogenic drug action

It has been proposed recently that the occurrence of drug-induced limb-flicking (LF) and abortive grooming (AG) in cats can serve as a viable animal behavior model for the actions of hallucinogens in humans. If this is the case, such behaviors should occur reliably following the administration of drugs that produce hallucinations in humans and should not occur after administration of other, non-hallucinogenic drugs—a hypothesis that was examined in the present experiment. The frequency of LF and AG were observed in 12 cats which were given a wide range of doses of the potent hallucinogen, d-LSD (0.01–0.16 mg/kg), as well as several other compounds. The results showed that three non-hallucinogenic agents which are related to LSD in various ways, the ergot derivative lisuride, the serotonin agonist, quipazine, and the dopamine agonist, apomorphine, significantly increased LF frequency. Lisuride and quipazine also caused AG. Cocaine did not elicit either behavior. Thus, it was concluded that the proposed model cannot be regarded as specific to hallucinogenic drugs. In addition, the frequency of these behaviors, as well as their reliability and robustness, were shown to be partly dependent on the environment in which observation occurs.

Following several days of continuous administration d-amphetamine acquires hallucinogenlike properties.

Rats injected with LSD or mescaline show the behavioral syndrome which has been previously reported following injections of hallucinogens in higher mammals: limb flicks and whole body shakes. Although these behaviors are not elicited by acute injections of amphetamine, they are present in rats which have been pretreated for 108 h with a slow-release amphetamine pellet, given a 12 h rest period, and then injected with d-amphetamine. Such pellet-pretreated animals also groom their body surface excessively. We propose that this novel syndrome which follows continuous amphetamine administration can serve as an animal model of the type of amphetamine psychosis that is produced by a similar drug regimen in humans.

Effects of 5-methoxy-N,N-dimethyltryptamine on behavior and raphe unit acitivity in freely moving cats

5-methoxy-N,N-dimethyltruptamine (5-MeODMT) produced a dose-dependent decrease in the discharge rate of serotonin-containing neurons in the dorsal raphe nucleus of freely moving cats. This ranged from a 15% decrease at 10μg/kg, i.m., to a virtual complete depression of activity at 250 μg/kg/ 5-MeODMT's effects of raphe units occurred with a very short latency (3–5 min) and its duration of acion was dose-dependent and limited to an hour or less. The degree of depression of raphe unit activity was directly related to the frequency of occurrence of a number of hallucinogen-specific cat behaviors such as limb flick and abortive groom. There was also a close temporal correlation between the depression of raphe unit activity and the occurrence of these behaviors. These data indicate that the effects of 5-MeODMT may be primarily dependent on its actions upon brain serotonin neurons.

Drugs that antagonize limb flick behavior induced by D-lysergic acid diethylamide (LSD) in cats.

In cats observed in their home cages limb flicks (LF) are a sensitive measure of the behavioral effects of LSD. LF induced by LSD (50 microgram/kg) were blocked by dextrorphan (0.6 mg/kg), dextromethorphan (0.6 mg/kg), and imipramine (5 mg/kg) at doses that did not produce ataxia or sleep. Levorphanol (0.6 mg/kg), a narcotic that is a congener of dextrorphan, did not block LF induced by LSD possibly because it produced an excitatory effect when given alone. Pentobarbital at low doses (2 and 4 mg/kg) increased the number of LF induced by LSD but at a high dose (8 mg/kg) decreased LF induced by LSD either by producing ataxia, so the cats tended to remain immobile, or by producing sleep. Chlorpromazine (CPZ) at three doses (2, 4, and 8 mg/kg) attenuated the effects of LSD on LF, but did not block LF as completely as the above three blocking drugs, and produced ataxia and sleep.

Serotonergic and dopaminergic involvement in the mechanism of action of R-(−)-2, 5-dimethoxy-4-bromoamphetamine (DOB) in cats

Intraperitoneally administered R-(−)- and S-(+)- enantiomers of 2,5-dimethoxy-4-bromoamphetamine were evaluated for their ability to induce head-body shake, limb flick and abortive grooming behaviors in cats. The R-(−)-enantiomer was consistently more effective than the S-(+)-isomer in all three behavioral measures. Dose-response relationships were evident for head-body shakes and limb flicks for both enantiomers, but reliable abortive grooming responses appeared only after the higher doses of R-(−)-DOB. Cinanserin and methysergide pretreatments effectively antagonized the induction of head-body shakes and limb flicks by 0.1 mg/kg R-(−)-DOB. In addition, haloperidol pretreatment significantly antagonized the appearance of these behaviors suggesting that dopaminergic as well as serotonergic stimulation is involved in the elicitation of these cat behaviors by R-(−)-DOB.

Behavioral effects of LSD in the cat: Proposal of an animal behavior model for studying the actions of hallucinogenic drugs

In the course of examining the complete dose-response relationship for the behavioral effects of LSD in the cat, we discovered that, in addition to large increases in investigatory and hallucinatory-like responses, two behaviors, not previously reported, are emitted with a high probability under LSD. Beginning from a baseline of essentially zero in saline-treated animals, limb flicks and abortive grooming increase in frequency in direct relation to the dose of LSD administered (2.5, 10, 25 and 50 μg/kg i.p.) and then decrease at higher doses (100 and 200 μg/kg). Limb flicks are a species-specific behavior seen in normal cats almost exclusively in response to the presence of a foreign substance, such as water, on the hindpaw or forepaw. In abortive grooming, the cat orients to the body surface as if to groom but does not emit the consummatory grooming response (bite, lick or scratch), or emits the response in midair. These behaviors can serve as an animal behavior model for the actions of LSD and related hallucinogens in humans. The specificity of these behavioral changes is indicated by the fact that they are never seen in response to other classes of psychoactive drugs such as d-amphetamine, atropine, caffeine and chlorpheniramine. They are, however, elicited by compounds such as psilocybin which are structurally and functionally related to LSD. The validity of the model is based on evidence indicating that it is: specific to hallucinogens, dose dependent, observed in a dose range effective in humans, parallels the major parameters of the actions of LSD in humans (see following paper), sensitive, robust, reliable, quantifiable and easy to score.

Usefulness of an animal behavioral model in studying the duration of action of LSD and the onset and duration of tolerance to LSD in the cat

LSD elicits a number of emergent behaviors in the cat, including limb flicking, abortive grooming, investigatory and hallucinatory-like behaviors, which we have proposed as an animal behavior model for studying the actions of LSD and related hallucinogens. These emergent behaviors were used in the present study to investigate the duration of action of LSD, as well as the onset and duration of tolerance. A dose of 10 μg/kg of LSD produced significant behavioral changes for up to 4 h, while a dose of 50 μg/kg produced changes lasting for at least 8 h. Tolerance to a test dose of 50 μg/kg of LSD is virtually complete one day after a single 50 μg/kg dose, and lasts for approximately 5 days. Tolerance to a test dose of 50 μg/kg of LSD one day after a single dose of 10 μg/kg is quite marked, and lasts for approximately 3 days. A significant tolerance to a test dose of 50 μg/kg of LSD occurs within 2 h after a single injection of 10 μg/kg. The limb flick was found to be the most sensitive index in all tests: it showed the longest time-course, as well as the most rapid and longest-lasting tolerance. These studies demonstrate that the LSD-induced behavioral syndrome in the cat parallels important parameters of the action of LSD in humans, and thus enhances the usefulness of the model.

An Animal Behavior Model for Studying the Actions of LSD and Related Hallucinogens

Cats injected with LSD (d-lysergic acid diethylamide) exhibit a group of behaviors that appear to be specific to hallucinogenic drugs. Two of these behaviors, limb flick and abortive grooming, have an extremely low frequency of occurrence in normal cats, but often dominate the behavior of LSD-treated cats. The frequency of occurrence of this group of behaviors is related to the dose of LSD. The behavioral changes are long-lasting following a single injection of LSD, and exhibit tolerance following the repeated administration of LSD. They are not elicited by a variety of control drugs, but are elicited by other indole nucleus hallucinogens. Because the behavioral effects are specific, reliable, easy to score, and quantifiable, they represent an animal model that can be used in studies of the effects of LSD and related hallucinogens.

LSD acts synergistically with serotonin depletion: Evidence from behavioral studies in cats

Administration of LSD (100 μg/kg, IP) or the serotonin depleting drug p-chlorophenylalanine (150 mg/kg/day for 5 days) both induce dramatic behavioral changes which include the common stereotyped responses of rapid flicking movements of the limbs and abortive attempts at grooming. The combined action of LSD and p-chlorophenylalanine results in a marked increase in the occurrence of these behaviors, suggesting that LSD acts synergistically with serotonin depletion. These data therefore support the hypothesis that the behavioral effects of LSD may be attributable to its well known electrophysiological effect of depressing the activity of serotonin containing neurons. In addition, limb flicking and abortive grooming may serve as a useful behavioral model for studying the actions of LSD, since these behaviors are quantifiable, easily scored, and occur with an extremely low frequency in normal cats.