Stimulus-elicited investigation in apomorphine-treated gerbils

Effect of the dopamine receptor agonist apomorphine on sensory input

The study examines the hypothesis that changes in behavioural responsiveness induced by apomorphine reflect an effect of the drug on visual, tactile, vestibular, or proprioceptive sensory input. Rats were injected with apomorphine (1.25 mg/kg) and administered a neurological examination in which stimuli from the different sensory modalities were tested for their ability to elicit a limb placing response. Results indicate that these sensory stimuli were equally effective in eliciting reflex placing reactions in saline- and apomorphine-treated rats. Thus, contrary to the hypothesis, apomorphine does not appear to affect the reception of visual, tactile, vestibular, or proprioceptive sensory input. Tests of equilibration (righting) induced by static tilt revealed a fractionated response under apomorphine (0.6-5 mg/kg). Since the response to tilt probably involves striatal integration of vestibular and proprioceptive input, it is suggested that apomorphine disrupts sensory or sensorimotor integration.

Attention and habituation: separation of specific components in development

In four experiments using habituation procedures, it was shown that selective investigation of stimuli that are novel gradually developed between 13 and 28 days of age in gerbil pups. The youngest pups investigated the stimuli, but were highly variable in their responses to an object or to odors of conspecifics. Habituation could, but did not reliably, occur. By 21 days of age, investigation of a cup attenuated in a series of 5 one-minute trials and responses increased after the cup was moved to a new location. By 28 days of age, reliable habituation was shown 24 hours after a one-minute exposure to a cup. The data were used to infer how an immature process of selective attention may be responsible for variability in expression of habituation during development.

The gerbil: a unique model for research on aging

The Mongolian gerbil (Meriones unguicultatus) is suggested as a model for aging research because of its unique physiological attributes, ease of handling, and because of data previously collected. Factors that demonstrate the gerbils' suitability in fulfulling practical and scientific considerations important in determining a model for aging research are listed. Additionally, several unique physiological attributes of gerbils are described. Based on these attributes and on review of research in gerbils, it is suggested that gerbils can serve as animal models for behavioral and biological processes, and for normative and pathological aspects for aging.

Perseveration of attention to conspecific odors and novel objects in castrated gerbils

Castrated male and female gerbils were tested for odor preference and for attention to conspecific odors and a novel object. Castrated gerbils housed with sham-operates preferred home odors, discriminated between two groups of male gerbils by olfactory cues, and perseverated in attention to odors of male gerbils and to a novel object. Similar perseveration to male conspecific odors was shown in gerbils given injections of L-DOPA (30 mg/kg). Combined treatment (castration and L-DOPA) resulted in additive effects on perseveration. This research challenges two general hypotheses of gonadal hormone function. The first, that changes in odor preference after castration are due to a loss in testicular androgen, is insufficient, because (1) female as well as male gerbils showed similar perseveration to odors, (2) there was a significant correlation between LH and duration of investigation of male conspecific odors, and (3) L-DOPA, the dopamine precurser, also caused perseveration to conspecific odors. The second, that gonadal hormones are responsible for persistence of attention, cannot be broadly generalized, because castration with resultant elevation of LH and regression of ventral glands resulted in perseveration of attention in male and female gerbils.

Impairment of responses to novelty by apomorphine and its antagonism by neuroleptics in mice

The effects of several doses of apomorphine (AP: 0.062-8 mg/kg) on novelty preference (NP) in male Swiss mice were studied. AP induced a dose-dependent reduction of NP as well as of locomotor activity. The decrease in NP appeared to be related to the effect of the drug in reducing locomotion, and may be explained by a drug-induced increase in perseverance and stereotypy interfering with locomotion and NP by response incompatibility. These results contrast with those obtained with methamphetamine (MA) in a previous study (Misslin and Ropartz 1981) replicated here which also shows a reduction of NP. Furthermore, the neuroleptic thioridazine did not antagonize the effects of AP or MA on NP in mice, whereas the substituted benzamides tiapride and sulpiride did so. The substituted benzamides appear to act selectively on a restricted dopamine receptor population.

Differential effects of haloperidol and clozapine on attention

Haloperidol (0, 0.1, 0.3, or 1.0 mg/kg), the typical butyrophenone neuroleptic, decreased investigation of novel objects by gerbils following systemic injections. When given prior to apomorphine (1 or 3 mg/kg), haloperidol blocked apomorphine-induced disruption of selective attention in a dose-dependent manner. Thus, haloperidol acts like pimozide in this paradigm. In contrast, clozapine (0, 0.03, 0.1, 0.3, 1.0, or 3.0 mg/kg), the atypical dibenzodiazepine neuroleptic, increased frequency of investigation both soon after injection and 24h later, suggesting interference with maintenance of attention. When given with apomorphine (1.0 mg/kg), clozapine did not block apomorphine effects on selective attention. The results are related to differential effects of these neuroleptics on other behaviors and to their individual pharmacological profiles.

Multiple measures of hemispheric dysfunction in schizophrenia and depression

Electrodermal, electroencephalographic and perceptual measures of lateral hemispheric function were obtained from groups of chronic schizophrenics, depressives and normals on 2 occasions, separated by 4 weeks. The measures of hemispheric function were derived from previous research. About half of the schizophrenics were medicated on both occasions; the other schizophrenics underwent drug 'washout' before the first session. Results revealed that the measures of laterality were not strongly intercorrelated. In the perceptual task, the schizophrenics and normals displayed different laterality effects. Unlike the normals, the schizophrenics' left hemisphere function appeared to be inferior to the right hemisphere function in the perceptual task. The laterality effects of the depressives and normals differed on two electrodermal measures: skin conductance level and skin conductance response amplitude. The depressives' electrodermal activity from the right hand was diminished as compared with the left hand; the normals did not show this effect. Medication decreased electrodermal activity in the schizophrenics, but had no significant effect on laterality. These results suggest that the various measures of laterality used singly in previous research in psychopathology may not all assess the same phenomenon.

L-Dopa and piribedil alter different components of attentional behavior dependent on dose

L-Dopa (3, 10, 30, 100 mg/kg) given SC after carbidopa, and piribedil (10, 30, 100, 300 mg/kg) had biphasic effects on investigation of a novel cup. Gerbils given a low dose of L-Dopa (10 mg/kg) or piribedil (10 or 30 mg/kg) investigated the cup more than did vehicle-injected gerbils, whereas those gerbils given a high dose of L-Dopa (100 mg/kg) or piribedil (300 mg/kg) investigated it less. L-Dopa, but not piribedil, also had biphasic effects on investigation of conspecific odors. The increase in duration with no increase in frequency of investigation suggested an inability to shift attention normally. High-dose attenuation of investigation is considered nonspecific, as many other drugs have the same effect. Locomotor activity scores showed no concomitant increase following low doses, but only a dose-dependent decrease. In addition, L-Dopa (100 mg/kg), but not piribedil at any dose tested, prevented the normal decrement in response to the cup 24 h after injection. As a high response is normally only shown when the stimulus is novel, the data suggest that L-Dopa at the high dose, but not piribedil, interfered with selective attention. Thus, the different dopamine agonists affected different aspects of attention. The data are discussed in relation to neural effects of the drugs as reported in the literature.

Implications for multiple transmitter mediation of amphetamine-induced stereotypies

Gerbils were pretreated with the dopamine (DA) receptor blocker, pimozide, prior to stereotypy-inducing injections of d-amphetamine. Some of the stereotypies induced with amphetamine were blocked, but some were not, supporting the hypothesis that multiple neurotransmitters are involved in the mediation of amphetamine-induced stereotypy. In addition, when apomorphine hydrochloride was injected, different stereotypic motor behaviors were induced than were induced with amphetamine. The behavioral changes following amphetamine treatment could be classified into four groups: (1) those that are probably DA related, based on the fact that they were induced with either amphetamine or apomorphine, and amphetamine induction was blocked with pimozide; (2) those that are probably not DA related because they were not induced by apomorphine, and amphetamine induction was not blocked by pimozide; (3) those behaviors that may be incompatible with stereotypic behaviors, were reduced with either amphetamine or apomorphine, but were not maintained with pimozide; and (4) circling, which was induced with amphetamine, blocked with pimozide, but not induced with apomorphine.

Attention and habituation: catecholamine interactions and sex differences

Norepinephrine (NE)-dopamine (DA) interactions in mediation of long-term habituation were tested using the stimulus-elicited investigation paradigm. Systemic injections of clonidine hydrochloride (CLON), an alpha-adrenergic receptor agonist, given before apomorphine (APO) (1 mg/kg SC), a DA receptor agonist, prevented APO-induced disruption of the duration measure of habituation 25-hr later. A lower dose was effective in female gerbils than that required for male gerbils, suggesting that females are more sensitive to the effects of clonidine. In addition, apomorphine, with or without CLON (0.01 mg/kg), increased locomotor activity in male gerbils but reduced activity in female gerbils. The same dose of CLON that prevented APO-induced disruption of 24-hr habituation did not reverse APO-induced reduction of investigation of an object or an odor, or APO-induced changes in activity. Neither CLON nor desmethylimipramine, a blocker of NE reuptake, had any selective effects on investigation of novel stimuli or short-term habituation showing that relative NE-DA activity can be disrupted without interfering with the behavior, However, CLON interfered with the frequency measure of long-term habituation in male gerbils but not in female gerbils at any dose used (0.0100.3 mg/kg). THe data suggest important sex dependent NE-DA interactions in mediation of long-term habituation.