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

Intoxication of dogs and cats with common stimulating, hallucinogenic and dissociative recreational drugs

Pets can have accidental, intentional, or malicious exposure to illicit drugs. It is a growing concern over the last decade because there is an increase in usage of illicit drugs in humans and diagnosis is difficult. Owners are often not aware of exposure, or they are reluctant to admit possession of recreational drugs in the household due to potential legal consequences. In addition, illicit drugs sold on the black market are often adulterated with other substances resulting in non-specific clinical presentation and aggravation of symptoms. There are affordable onsite diagnostic tests on the market which could facilitate diagnosis of intoxication with illicit drugs, but they give a lot of false positive results due to low specificity of the tests. In this paper we gathered information about the most common recreational drugs such as amphetamines, methamphetamine, 3,4-methylenedioxy-methamphetamine (MDMA), phencyclidine (PCP), lysergic acid diethylamide (LSD), psilocybin mushrooms and cocaine in terms of toxicokinetic properties, mechanism of toxic action, clinical presentation and treatment in dogs and cats.

Effect of Hallucinogens on Unconditioned Behavior

Because of the ethical and regulatory hurdles associated with human studies, much of what is known about the psychopharmacology of hallucinogens has been derived from animal models. However, developing reliable animal models has proven to be a challenging task due to the complexity and variability of hallucinogen effects in humans. This chapter focuses on three animal models that are frequently used to test the effects of hallucinogens on unconditioned behavior: head twitch response (HTR), prepulse inhibition of startle (PPI), and exploratory behavior. The HTR has demonstrated considerable utility in the neurochemical actions of hallucinogens. However, the latter two models have clearer conceptual bridges to human phenomenology. Consistent with the known mechanism of action of hallucinogens in humans, the behavioral effects of hallucinogens in rodents are mediated primarily by activation of 5-HT2A receptors. There is evidence, however, that other receptors may play secondary roles. The structure-activity relationships (SAR) of hallucinogens are reviewed in relation to each model, with a focus on the HTR in rats and mice.

Dopamine, schizophrenia, mania, and depression: Toward a unified hypothesis of cortico-striatopallido-thalamic function

Considerable evidence from preclinical and clinical investigations implicates disturbances of brain dopamine (DA) function in the pathophysiology of several psychiatric and neurologic disorders. We describe a neural model that may help organize theseindependent experimental observations. Cortical regions classically associated with the limbic system interact with infracortical structures, including the nucleus accumbens, ventral pallidum, and dorsomedial nucleus of the thalamus. In our model, overactivity in forebrain DA systems results in the loss of lateral inhibitory interactions in the nucleus accumbens, causing disinhibition of pallidothalamic efferents; this in turn causes rapid changes and a loss of focused corticothalamic activity in cortical regions controlling cognitive and emotional processes. These effects might be manifested clinically by some symptoms of psychoses. Underactivity of forebrain DA results in excess lateral inhibition in the nucleus accumbens, causing tonic inhibition of pallidothalamic efferents; this perpetuates tonic corticothalamic activity and prevents the initiation of new activity in other critical cortical regions. These effects might be manifested clinically by some symptoms of depression. This model parallels existing explanations for the etiology of several movement disorders, and may lead to testable inferences regarding the neural substrates of specific psychopathologies.

LSD but not lisuride disrupts prepulse inhibition in rats by activating the 5-HT(2A) receptor

RATIONALE

Compounds that activate the 5-HT(2A) receptor, such as lysergic acid diethylamide (LSD), act as hallucinogens in humans. One notable exception is the LSD congener lisuride, which does not have hallucinogenic effects in humans even though it is a potent 5-HT(2A) agonist. LSD and other hallucinogens have been shown to disrupt prepulse inhibition (PPI), an operational measure of sensorimotor gating, by activating 5-HT(2A) receptors in rats.

OBJECTIVE

We tested whether lisuride disrupts PPI in male Sprague-Dawley rats. Experiments were also conducted to identify the mechanism(s) responsible for the effect of lisuride on PPI and to compare the effects of lisuride to those of LSD.

RESULTS

Confirming a previous report, LSD (0.05, 0.1, and 0.2 mg/kg, s.c.) reduced PPI, and the effect of LSD was blocked by pretreatment with the selective 5-HT(2A) antagonist MDL 11,939. Administration of lisuride (0.0375, 0.075, and 0.15 mg/kg, s.c.) also reduced PPI. However, the PPI disruption induced by lisuride (0.075 mg/kg) was not blocked by pretreatment with MDL 11,939 or the selective 5-HT(1A) antagonist WAY-100635 but was prevented by pretreatment with the selective dopamine D(2)/D(3) receptor antagonist raclopride (0.1 mg/kg, s.c).

CONCLUSIONS

The effect of LSD on PPI is mediated by the 5-HT(2A) receptor, whereas activation of the 5-HT(2A) receptor does not appear to contribute to the effect of lisuride on PPI. These findings demonstrate that lisuride and LSD disrupt PPI via distinct receptor mechanisms and provide additional support for the classification of lisuride as a non-hallucinogenic 5-HT(2A) agonist.

Acute effects of LSD on rhesus monkey operant test battery performance

The acute effects of LSD were assessed in rhesus macaques using behavior in several complex tasks designed to model aspects of time estimation, short-term memory and attention, motivation, learning, and color and position discrimination. The end points monitored included percent task completed, response rate, and accuracy. LSD (0.0003-0.03 mg/kg intravenously) significantly decreased percent task completed and accuracy in the time estimation task at doses < or = 0.003 mg/kg, but did not significantly affect response rate in this task at any dose tested. Accuracy in the short-term memory task was significantly decreased at the highest dose tested (0.03 mg/kg), but no other end points were affected in this task. Response rate was decreased in both the motivation and learning tasks at doses (0.01 and 0.003 mg/kg, respectively) lower than those affecting other end points. In the color and position discrimination task, only response rate was affected (0.01 and 0.03 mg/kg). These data demonstrate that in rhesus monkeys, performance of tasks believed to depend on aspects of time estimation and motivation are more sensitive to the acute disruptive effects of LSD than are tasks thought to model learning, short-term memory, and color and position discrimination.

The head-twitch response in the least shrew (Cryptotis parva) is a 5-HT2- and not a 5-HT1C-mediated phenomenon

Our initial studies suggested that the 5-HT2/1C agonist (+/-)-1-(2,5-dimethoxy-4-iodophenyl-2-aminopropane [(+/-)-DOI] produces both the head-twitch response (HTR) and the ear-scratch response (ESR) in mice via stimulation of 5-HT2 receptors. However, challenge studies revealed that these behaviors are produced via two different receptors (possibly 5-HT2 and 5-HT1C). Due to a lack of selective agents one cannot designate a particular response for the activation of a specific receptor. The purpose of the present study was to investigate such behaviors in the least shrew, which is more sensitive to (+/-)-DOI than rodents. IP injection of (+/-)-DOI in shrews produced a dose-dependent (bell-shaped) and time-dependent increase in the HTR frequency. The (+/-)-DOI-induced HTR was equipotently and completely attenuated by the 5-HT2/1C antagonists ketanserin and spiperone. The 5-HT1C antagonist with 5-HT2 agonist action, lisuride, also produced the HTR in a bell-shaped dose- and time-dependent fashion. Central injections of both (+/-)-DOI (0.2 microgram) and lisuride (0.5 microgram) also induced the behavior. Both peripheral and central administration of lisuride failed to produce the ESR. (+/-)-DOI significantly induced the ESR only at the highest dose tested (2.5 mg/kg, IP). Centrally administered (+/-)-DOI (0.2 microgram) produced more ESRs relative to vehicle controls; however, the difference did not attain significance. At low doses (0.31 and 0.63 mg/kg), (+/-)-DOI had no effect on locomotor activity, but it significantly attenuated the behavior at larger doses. Both low and high doses of lisuride increased the motor activity. Spiperone dose-dependently suppressed locomotion, whereas ketanserin had no effect. The present results suggest that the HTR is a 5-HT2 receptor-mediated event and changes in locomotor activity do not affect the induced HTR.

Central effect of yohimbine on sexual behavior in the rat

A large range of doses of yohimbine (Y) was administered intracerebroventricularly (ICV) (5-100 micrograms/rat) or intraperitoneally (IP) (0.35-10 mg/kg) to male rats and the effects on sexual, locomotor and general behavior were evaluated. For both routes there was a clear-cut inverted-U effect (stimulating/depressing), calculable as parabolic regressions on the log of administered doses. The maximal stimulating doses (15 micrograms/rat ICV and 1 mg/kg IP) significantly shortened mount, intromission and ejaculation latencies and the mean interintromission interval. These data indicate the importance of CNS mechanisms in the sexual effect of Y.

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.

Pizotifen (BC-105) attenuates orienting and Pavlovian heart rate conditioning in rabbits

The cardiac component of the orienting reflex (OR) was elicited in rabbits by 75 dB, 4-sec duration tones of either 304 or 1216 Hz. The conditioned cardiac response was also studied using the same tones and paraorbital electric shock as conditioned and unconditioned stimuli, respectively, using a differential Pavlovian conditioning paradigm. Subcutaneous injections of the central 5-HT antagonist pizotifen (BC-105), the peripheral 5-HT antagonist xylamidine, the central 5-HT agonist d-lysergic acid diethylamide (LSD), and LSD in conjunction with BC-105 were administered 15 min prior to behavioral assessment. Both the heart rate (HR) conditioned response (CR) and the OR consisted of bradycardia. BC-105 attenuated, but xylamidine had no effect on, OR habituation. LSD reduced the magnitude of the OR, an effect which was blocked by BC-105. BC-105 also produced a dose-related attenuation of the bradycardiac HR CR; however, xylamidine had no effect on HR conditioning, suggesting that the attenuation of the HR CR by BC-105 was central rather than peripheral in origin. LSD potentiated the bradycardiac HR CR, but BC-105 in conjunction with LSD attenuated this response. These results suggest that central 5-HT neurons may modulate the magnitude of bradycardiac responses during orienting and aversive Pavlovian conditioning.

Dissociations between the effects of hallucinogens on behavior and raphe unit activity in behaving cats

The hypothesis that hallucinogenic drugs exert their behavioral effects by an action at pre- or postsynaptic serotonin receptors was evaluated by co-administering various drugs that possess either serotonin agonist or antagonist properties, while concurrently monitoring behavior and the electrophysiological activity of serotonin-containing dorsal and median raphe neurons in freely moving cats. Co-administration of the serotonin receptor blockers, metergoline or mianserin, with lysergic acid diethylamide (LSD) produced no change in the inhibitory effects of LSD on raphe neurons, but produced a dose-dependent blockade of the behavioral effects of LSD in the cat. The latter data suggest that perhaps LSD exerts its behavioral effects by an action at postsynaptic serotonin receptors. Co-administration of drugs that increase synaptic serotonin, L-5-hydroxytryptophan, tranylcypromine, fluoxetine or p-chloramphetamine with LSD greatly potentiated the inhibitory effect of LSD on raphe unit activity, but also produced dose-dependent decreases in these behavioral effects of LSD in the cat. Thus, both enhancing the activity at postsynaptic serotonin receptors and receptor antagonism blocked the behavioral effects of LSD. Co-administration of dopamine receptor blockers, haloperidol or chlorpromazine, produced no significant change in the response of raphe neurons to LSD, but these drugs also produced a dose-dependent blockade of the behavioral effects of LSD in the cat. Co-administration of the dopamine agonists, apomorphine or d-amphetamine, however, potentiated the behavioral effects of LSD, while producing a partial reversal of the inhibitory effects of LSD on raphe unit activity. The results are discussed in the context of using animal models to study the possible actions of hallucinogens in humans.

Action of a chronic administration of mescaline in dynamic behavioural situations

The modifications of the rat behaviour caused by a chronic administration of mescaline were studied in two schedules of operant conditioning. In the "periodic conditioning" test, the schedule of reinforcement was changed from a fixed ratio to a fixed interval schedule. Mescaline (4 mg/kg/day and 10 mg/kg/day) caused no modification of the ability of the rat to adapt its behaviour to the new experimental situation. In the "reversal test" the contingency for food delivery was switched from one lever, where responses were previously reinforced to the other lever where responses had no programmed consequences. A chronic administration of mescaline (4 mg/kg/day) caused a total incapacity of the rat to switch to the lever which became reinforced in the reversal trial. A chronic administration of 9 mg/kg/day of mescaline had an excitatory effect and the number of reinforced responses in the II and III reversals exceeded the unreinforced responses in a measure greater than in the controls.

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.

Ontogeny of the behavioral effects of lysergic acid diethylamide in cats

The ontogeny of the behavioral effects of lysergic acid diethylamide (LSD) was examined in cats between the ages of 4 and 112 days postpartum. The kittens showed little LSD-induced behavioral change prior to 14 days of age. By the age of 21 days, however, the kittens exhibited many of the behavioral signs characteristic of LSD-induced behaviors in adult cats. These behaviors include limb-flicking, abortive grooming, head-shakes, grooming, and investigatory responses. In general, these behaviors began at a low frequency of occurrence, then increased rapidly with advancing age, reaching adult values by approximately 35-40 days of age, and remained relatively constant through 112 days postpartum. The time course for the behavioral effects following an acute injection of LSD showed the adult pattern, i.e., persisting for approximately 8 hr post-injection, from their earliest appearance during ontogeny. Young kittens (21-42 days of age) were resistant to the development of tolerance following repeated administration of the drug. LSD was capable of eliciting certain behaviors, such as head-shakes and grooming, well in advance of the age at which they normally appear spontaneously. This indicates that the neuronal and musculature substrata are developed for the performance of these behaviors long before the kitten naturally employs them.

Tolerance to the behavioral effects of bromocriptine in cats

Repeated daily administration of LSD and related hallucinogens produces tolerance to their behavioral effects. The objective was to test whether repeated administration of bromocriptine (BC) produced behavioral tolerance. Experiments began after 4 weeks of habituation and baseline measurements. Cats were then injected daily with BC (10 mg/kg i.p.) for 7 days. The frequency of 40 different behaviors and neurological signs were scored for 60 min after one h post-injection. There was a rapid tolerance to the 'emergent' behavior induced by BC. In the case of hallucinatory-like behavior/escape, tolerance to a second dose of BC one day after a first dose was virtually complete. A substantial tolerance to BC effects such as abortive grooming, increased investigatory-play behavior and grooming occurred within one day. The decrease in sleep produced by BC was absent at the fourth day. Limb flicks and body shakes decreased but persisted until the seventh day. There was also tolerance to emotional behavior (irritability, rage, threat, flight) but motor effects (circling, ataxia, hypokinesia) remained throughout the week. Autonomic reactions were unaffected by BC. The results indicated that the psychotomimetic effects (but not the motor or autonomic) of BC showed rapid and long-lasting tolerance. These studies suggest that BC-induced alterations in cats parallel parameters of action of hallucinogens in humans.

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.

Behavioral effects of serotonergic and dopaminergic drugs in cats following chronic amphetamine administration

Chronic administration of amphetamine to cats (twice daily, in doses increasing from 5 to 15 mg/kg over a 10-day period) elicited a number of behaviors e.g., limb flicking, abortive grooming, and excessive head shaking, which were originally proposed as an animal behavioral model for studying the actions of hallucinogens that depress central serotonergic neurotransmission. This drug treatment produced large decreases (approximately 50%) in central nervous system serotonin (5HT) and its major metabolite, 5-hydroxyindoleacetic acid, and even larger decreases (approximately 90%) in the levels of dopamine (DA) and norepinephrine. Administration of the 5HT precursors L-tryptophan (25 mg/kg i.p.) or L-5-hydroxytryptophan (12.5 mg/kg i.p.), a direct-acting 5HT agonist (quipazine, 1 mg/kg i.p.) or a monoamine oxidase inhibitor (tranylcypromine, 4 mg/kg i.p.) produced no significant changes in these behaviors in cats treated chronically with amphetamine. Administration of a 5HT reuptake blocker (fluoxetine, 5 mg/kg i.p.) produced a small, but significant, decrease in the frequency of occurrence of these behaviors in amphetamine-treated cats. L-Dihydroxyphenylalanine (L-DOPA, 20 mg/kg i.p.) greatly potentiated these behaviors in cats chronically treated with amphetamine, but L-DOPA was totally ineffective in eliciting these behaviors in naive animals. The behavioral effects of apomorphine (2 mg/kg i.p.) were also significantly potentiated by chronic amphetamine pretreatment. The amino acid precursor of DA, L-tyrosine (25 mg/kg i.p.), and a DA reuptake blocker, bupropion (5 mg/kg i.p.) were without significant effect on these behaviors in amphetamine-treated cats. The data suggest that these cat behaviors are elicited by an action at central DA receptors and that these receptors become supersensitive following chronic amphetamine administration. Furthermore, there may be a qualitative change in DA receptors, since L-DOPA is very effective in potentiating these behaviors in cats treated chronically with amphetamine, but is totally ineffective in naive cats.

Acute and chronic effects of LSD and 5-MeODMT on raphe-evoked dorsal root potentials in the cat

Both acute and chronic effects of lysergic acid diethylamide (LSD) and 5-methoxy-N,N-dimethyltryptamine (5-MeODMT) on the dorsal root potential (DRP), evoked by stimulation of the nucleus raphe magnus of the cat, were examined. Single injections of LSD potentiated while those of 5-MeODMT inhibited the raphe-evoked DRP. The electrophysiologic response produced by each drug correlates well in dosage and time-course with their reported behavioral effects. Following four consecutive daily injections of LSD, complete tolerance developed to the potentiating effect of LSD on this potential. A similar pretreatment schedule with 5-MeODMT failed to alter its acute inhibitory effect on the DRP. These results correlate well with the development of tolerance to the behavioral effects of LSD and 5-MeODMT. This system may thus provide a unique electrophysiological model to examine the effects of these drugs.

Mescaline elicits behavioral effects in cats by an action at both serotonin and dopamine receptors

The characteristic behavioral effects of mescaline in cats were nearly completely blocked by pretreatment with low doses of either a specific serotonin antagonist (methysergide) or a dopamine specific antagonist (haloperidol). These blocking effects were not due to non-specific actions, since methysergide did not block the behavioral effects of apomorphine, and haloperidol did not block the behavioral effects of 5-methoxy-N,N-dimethyltryptamine. Thus, it appears that the behavioral effects of mescaline are dependent upon the simultaneous action of the drug at both serotonin and dopamine receptors.

Differential effects of lysergic acid diethylamide, methysergide, and cyproheptadine on modality-specific and nonspecific sensory evoked potentials

The effects of lysergic acid diethylamide (LSD), methysergide, and cyproheptadine on activity in classical primary pathways of the visual and somatosensory systems were compared with their effects on activity in sensory convergent (association) regions in alpha-chloralose-anesthetized cats. Those effects were blocked by cyproheptadine whereas methysergide potentiated the actions of LSD on visual primary activity. In contrast, LSD depressed the primary somatic pathway, at small doses (25 to 50 micrograms/kg) and facilitated the response at larger doses (200 micrograms/kg). Cyproheptadine and methysergide did not agonize these actions of LSD. The anterior marginal cortex, nucleus central median-parafascicularis, nucleus lateral posterior, and the superior colliculus, all sites of heterosensory convergence, were depressed by LSD. The depression of responses at heterosensory sites by LSD was blocked by cyproheptadine. Methysergide potentiated the LSD-induced depression of visual-evoked activity but not somatosensory activity. These results suggest that LSD depresses sensory activity in regions which integrate multiple sensory modalities independently of actions on sensory-specific pathways. These effects appear to involve a cyproheptadine-sensitive system.

Harmaline effects on the sensory-motor reactivity: modifications of the acoustic startle pattern

The effects of harmaline, an indoleamine and a MAOI, were tested on the acoustic startle pattern. EMG measures of the startle reflex, the pinna reflex as well as the characters of the vertex evoked responses to brief intense tone bursts (60 msec, 110 dB, 8000 Hz) were simultaneously studied in 4 alert guinea-pigs. The basic experimental design was a 4 by 4 latin square, with the treatments being given at 2 day intervals. The four harmaline-HCl treatments were isotonic saline, 0.25, 5.0, and 10.0 mg/kg. Compared with saline baselines, all the doses resulted, throughout the 60 min session, in overall high significant depressions of the startle reflex, the pinna reflex and the initial wave of the acoustic evoked potential at the vertex. In contrast, harmaline had little or no influence on amplitude and latency of the late wave of the vertex response. The effects of harmaline on the general behavior of the guinea-pig are also reported. These results may support an involvement of serotonergic systems in the modulation of the sensory-motor reactivity at the brainstem level. Nevertheless, the probably more complex cortical processes involved in startle responsiveness do not appear univocally affected by the indoleamine drugs such as harmaline.

Chloral hydrate anesthesia alters the responsiveness of dorsal raphe neurons to psychoactive drugs

The effects of several psychoactive drugs on raphe unit activity in freely moving cats was compared with drug-induced effects in chloral hydrate anesthetized cats. The anesthesia greatly potentiated the depressant effects of LSD, phenoxybenzamine, clonidine, methiothepin, clozapine, and chlorimipramine on raphe units, but partially antagonized the depressant effects of diazepam. These results demonstrate that apparently discrepant reports of the affects of these drugs on raphe neurons in anesthetized rats versus freely moving cats are attributable to the use of anesthesia in rat studies. These data underscore the importance of conducting such drug studies in awake, freely moving animals, for which the results would be far more relevant to the issue of human drug use.

Dissociations between the behavioral effects of LSD and tolerance development during ontogeny in cats: a novel approach to the study of tolerance mechanisms

The characteristic behavioral effects of d-lysergic acid diethylamide (LSD) in cats first appeared at approximately 25 days of age and increased rapidly in magnitude over the next 10 days. However, 25 day old kittens showed no tolerance to the repeated administration of the drug. While the behavioral response to the initial dose of LSD remained relatively constant between 35 and 112 days of age, the tolerance gradually became more pronounced throughout this time period, reaching an adult level of virtually complete tolerance at 112 days. These findings provide new insight into the nature of the relationship between the primary drug action and the development of tolerance, and suggest a new strategy for investigating the neural bases of tolerance, i.e., examining the neurochemical effects of repeated LSD administration in kittens during various stages of tolerance development.

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.

Chronic intraventricular administration of lysergic acid diethylamide (LSD) affects the sensitivity of cortical cells to monocular deprivation

In kittens, but not in adult cats, depriving one eye of pattern vision by suturing the lids shut (monocular deprivation or MD) for one week reduces the proportion of binocular units in the visual cortex. A sensitivity of cortical units in adult cats to MD can be produced by infusing exogenous monoamines into the visual cortex. Since LSD interacts with monoamines, we have examined the effects of chronic administration of LSD on the sensitivity to MD for cortical cells in adult cats. Cats were assigned randomly to one of four conditions: MD/LSD, MD/No-LSD, No-MD/LSD, No-MD/No-LSD. An osmotic minipump delivered either LSD or the vehicle solution alone during a one-week period of MD. The animals showed no obvious anomalies during the administration of the drug. After one week the response properties of single units in area 17 of the visual cortex were studied without knowledge of the contents of the individual minipumps. With the exception of ocular dominance, the response properties of units recorded in all animals did not differ from normal. In the control animals (MD/No-LSD, No-MD/LSD, No-MD/No-LSD) the average proportion of binocular cells was 78%; similar to that observed for normal adult cats. However, in the experimental animals, which received LSD during the period of MD, only 52% of the cells were binocular. Our results suggest that chronic intraventricular administration of LSD affects either directly or indirectly the sensitivity of cortical neurons to MD.

Lack of synergism and cross tolerance between tactile stimulus- and LSD-induced limb flicking in the cat

The hypotheses that LSD-induced limb flicking, as well as tolerance to this behavioral effect following repeated drug administration, are due to alterations in somatosensory thresholds were tested by examining the rate of limb flicking to LSD alone, saline plus water on the limbs, or LSD plus water on the limbs, and by comparing the limb flick rate with water on the limbs in drug tolerant versus non-tolerant conditions. Cats exhibited the same rate of limb flicking in response to water on the limbs regardless of whether they were pretreated with saline of LSD. Furthermore, there was no significant difference in the tactile stimulus-induced rate of limb flicking in the tolerant versus non-tolerant states. These data suggest that LSD-induced limb flicking is not simply a function of drug-induced altered somatosensory thresholds, but is apparently reflective of more complex neural processes.

Raphe unit activity in freely moving cats: effects of quipazine

Quipazine 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 10% decrease at 0.5 mg/kg, (i.p.), to a virtually complete depression of activity at 5.0 mg/kg. The effects of quipazine on raphe units occurred with a short latency (5--10 min) and its duration of action was dose-dependent and lasted from 1 to 6 hr. The degree of depression of raphe unit activity was directly related to the frequency of occurrence of a number of behaviors such as limb flicking and abortive grooming. There was a close temporal correlation between the depression of raphe unit activity and the occurrence of these behaviors. These data reveal that quipazine produces behavioral and raphe unit changes similar to those observed after administration of hallucinogens with an indole nucleus.

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 2 h 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 tolerance. Apomorphine-induced behavioral changes were blocked by prior treatment with haloperidol, but were unchanged by pretreatment with L-DOP[A. 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-hydroxyindoleacetic 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 content of these studies with serotonergic and dopaminergic drugs.