Disruption of selective attention by apomorphine, but not amphetamine, in the Mongolian gerbil

Influence of short-term hypoxic exposure on spatial learning and memory function and brain-derived neurotrophic factor in rats-A practical implication to human's lost way

The present study aimed to investigate the effects of a short period of normobaric hypoxic exposure on spatial learning and memory, and brain-derived neurotrophic factor (BDNF) levels in the rat hippocampus. Hypoxic conditions were set at 12.5% O2. We compared all variables between normoxic trials (Norm), after 24 h (Hypo-24 h), and after 72 h of hypoxic exposure (Hypo-72 h). Spatial learning and memory were evaluated by using a water-finding task in an open field. Time to find water drinking fountains was significantly extended in Hypo 24 h (36.2 ± 21.9 s) compared to those in Norm (17.9 ± 12.8 s; P < 0.05), whereas no statistical differences between Norm and Hypo-72 h (22.7 ± 12.3 s). Moreover, hippocampal BDNF level in Hypo-24 h was significantly lower compared to Norm (189.4 ± 28.4 vs. 224.9 ± 47.7 ng/g wet tissue, P < 0.05), whereas no statistically differences in those between Norm and Hypo-72 h (228.1 ± 39.8 ng/g wet tissue). No significant differences in the changes in corticosterone and adrenocorticotropic hormone levels were observed across the three conditions. When data from Hypo-24 h and Hypo-72 h of hypoxia were pooled, there was a marginal negative relationship between the time to find drinking fountains and BDNF (P < 0.1), and was a significant negative relationship between the locomotor activities and BDNF (P < 0.05). These results suggest that acute hypoxic exposure (24 h) may impair spatial learning and memory; however, it recovered after 72 h of hypoxic exposure. These changes in spatial learning and memory may be associated with changes in the hippocampal BDNF levels in rats.

[Learning/memory and drug dependence]

We investigated the possible mechanisms of development of latent learning and morphine dependence by the methods of behavioral pharmacology and confirmed them by using mutant mice. The heterozygous mice for the tyrosine hydroxylase (TH) gene and for the cyclic AMP (cAMP) response element binding protein (CREB) binding protein (CBP) gene showed the impairment of latent learning in the water finding task, and these mice did not develop morphine dependence. The spatial learning and hippocampal long-term potentiation (LTP) were normal in the both mutants. TH heterozygous mice showed a reduction of high K(+)-evoked noradrenaline release in the frontal cortex measured by the microdialysis technique and of cAMP content in the brain. In conclusion, the results of mutant mice suggest that the alternation of catecholamine biosynthesis and cAMP signal pathways may play a key role in development of latent learning and morphine dependence, and they furthermore show that the expression of genes mediated by phosphorylated CREB may be involved in the development of latent learning and morphine dependence.

Hyperfunction of dopaminergic and serotonergic neuronal systems in mice lacking the NMDA receptor epsilon1 subunit

NMDA receptors, an ionotropic subtype of glutamate receptors (GluRs) forming high Ca(2+)-permeable cation channels, are composed by assembly of the GluRzeta subunit (NR1) with any one of four GluRepsilon subunits (GluRepsilon1-4; NR2A-D). In the present study, we investigated neuronal functions in mice lacking the GluRepsilon1 subunit. GluRepsilon1 mutant mice exhibited a malfunction of NMDA receptors, as evidenced by alterations of [(3)H]MK-801 binding as well as (45)Ca(2+) uptake through the NMDA receptors. A postmortem brain analysis revealed that both dopamine and serotonin metabolism were increased in the frontal cortex and striatum of GluRepsilon1 mutant mice. The NMDA-stimulated [(3)H]dopamine release from the striatum was increased, whereas [(3)H]GABA release was markedly diminished in GluRepsilon1 mutant mice. When (+)bicuculline, a GABA(A) receptor antagonist, was added to the superfusion buffer, NMDA-stimulated [(3)H]dopamine release was significantly increased in wild-type, but not in the mutant mice. GluRepsilon1 mutant mice exhibited an increased spontaneous locomotor activity in a novel environment and an impairment of latent learning in a water-finding task. Hyperlocomotion in GluRepsilon1 mutant mice was attenuated by treatment with haloperidol and risperidone, both of which are clinically used antipsychotic drugs, at doses that had no effect in wild-type mice. These findings provide evidence that NMDA receptors are involved in the regulation of behavior through the modulation of dopaminergic and serotonergic neuronal systems. In addition, our findings suggest that GluRepsilon1 mutant mice are useful as an animal model of psychosis that is associated with NMDA receptor malfunction and hyperfunction of dopaminergic and serotonergic neuronal systems.

[Possible mechanisms in latent learning formation investigated by using mutant mice]

We examined possible mechanisms in the development of latent learning by methods of behavioral pharmacology and confirmed them by using mutant mice. Mice that received dopamine agonists, a noradrenergic neurotoxin or a traumatic brain injury showed impairment of latent learning. This impairment was suggested to be mediated by imbalance of dopaminergic and noradrenergic systems since the impairment was attenuated by a noradrenaline uptake inhibitor or a dopamine-D2 antagonist. The heterozygous mice for the tyrosine hydroxylase (TH) gene and for the cyclic AMP (cAMP) response element binding protein (CREB) binding protein (CBP) gene showed impairment of latent learning in the water finding task. The spatial learning and hippocampal long-term potentiation (LTP) were normal in both the mutants. TH heterozygous mice showed a reduction of high K(+)-evoked noradrenaline release in the frontal cortex by the microdialysis technique and a reduction of cAMP of the brain cAMP content. The central noradrenergic systems and/or cAMP signal pathways play an important role in latent learning, but not spatial memory. In contrast with TH and CBP mutant mice, nociceptin-knockout mice showed an enhanced retention of latent learning in the water finding task, greater learning ability in the water maze task and larger LTP than wild-type mice. Such mice showed hyperfunction of dopaminergic systems in the cortex. Nociceptin itself induced latent learning impairment in wild-type mice. These results suggest that the nociceptin system seems to play negative roles in learning and memory. In conclusion, the results of mutant mice further supported our previous results of behavioral pharmacology and suggest that the alternation of catecholamine biosynthesis and cAMP signal pathways may play a key role in development of latent learning. They further suggest that the expression of genes mediated by phosphorylated CREB may be involved in the development of latent learning.

Neurobehavioral alterations in mice with a targeted deletion of the tumor necrosis factor-alpha gene: implications for emotional behavior

Tumor necrosis factor-alpha (TNF-alpha) is emerging as an important modulator of the function of the central nervous system. In the present study, we investigated a role of endogenous TNF-alpha in cognitive and emotional function using mice with targeted deletions of the TNF-alpha gene. TNF-alpha-(-/-) mice showed normal diurnal rhythms of spontaneous locomotor activity and cognitive functions. Emotional behavior in the mutant mice, however, was significantly altered, which manifested in the performance in the open-field, elevated plus maze, and forced swimming tests. The altered performance in the elevated plus maze test was significantly alleviated by treatment with diazepam. Postmortem brain analysis of TNF-alpha-(-/-) mice revealed a significant increase in serotonin metabolism in the brain. These findings suggest a role for endogenous TNF-alpha in emotional behavior, which may possibly be related to alterations of serotonine metabolism.

Attention effects of abrupt-onset precues with central, single-element, and multiple-element precues

Endogenous and exogenous processes of attention have been inferred with different types of precues used in allocation of attention to a target location. In the present research, a comparison was made between the typical peripheral single-element precue (SEP), a central precue, and a multiple-element precue (MEP) in order to further understanding of the processes involved in allocation of attention. Two precues were used on each trial in these experiments. An abrupt-onset precue appeared with an SEP, an MEP, or a central precue and was followed 50 or 300 ms later by a screen containing a target and two distractor characters. The abrupt-onset precue and the other precue each could be valid or invalid in indicating the location of the target, as in the study by Juola, Koshino, and Warner (1995). Response times to the targets showed that validity effects of the abrupt-onset precue and the MEP or central precue were additive, whereas those of the abrupt-onset precue and the SEP were interactive. These data suggest that, like a central precue, an MEP is an endogenous precue that guides conscious control of attention and has its attentional effects at a different processing level from an SEP, which is an exogenous precue and may compete for attentional resources with an abrupt-onset precue.

Characterization of learning and memory deficits in C57BL/6 mice infected with LP-BM5, a murine model of AIDS

Mice infected with an immunosuppressive murine leukemia virus mixture, LP-BM5 show a profound immunosuppression described as murine acquired immune deficiency syndrome (AIDS). In the present study, we characterized learning and memory deficits in C57BL/6 mice infected with LP-BM5. Spontaneous alternation behavior in a Y-maze and latent learning (spatial attention) in a water-finding test, as well as spatial reference and reversal learning in a water maze test, were significantly impaired in the mice infected with LP-BM5. These deficits appeared in the absence of any motoric and visual impairment as assessed by open-field, rotarod and visual water maze tests. These results suggest that cognitive functions are impaired in the mice infected with LP-BM5. Furthermore, LP-BM5-infected mice may be useful as a model for the AIDS dementia complex.

A new method to quantify behavioral attention to a stimulus object in a modified open-field

A new method was developed to measure locomotion and attention to a stimulus object in a typical open-field environment using a video image-analyzer system. A computer-generated central zone (CZ) composing 1/9 of the open-field floor area was monitored independently from the rest of the area. Intermittently, a 4 x 4 x 2 cm object was placed in the CZ. In 10 min test sessions, the presence of the object repeatedly and consistently increased the animal's time spent in the CZ as compared with tests when the object was absent. The presence of the object, however, did not increase either the number of entries to the CZ or overall locomotor activity. The object reliably elicited an investigatory response when the animal enter the CZ but otherwise was behaviorally neutral. Thus, by incorporating a stimulus object in a conventional open-field test environment, the present methodology extends the open-field test beyond the measurement of overall spontaneous activity to include an assessment of behavioral processes linked to attention mechanisms.

Effects of dopamine receptor agonists on passive avoidance learning in mice: interaction of dopamine D1 and D2 receptors

The present study examined the effects of dopamine D1 and D2 receptor agonists on the acquisition stage of passive avoidance learning and on locomotor activity in mice. The D2 agonist, RU 24213 (1-10 mg/kg s.c.), and the non-selective agonist, apomorphine (0.3-3 mg/kg s.c.), but not the D1 agonist, SKF 38393 (1-10 mg/kg s.c.), impaired learning and activated locomotion. RU 24213 (1 mg/kg s.c.) was more effective in impairing learning than in activating locomotion. The concurrent administration of SKF 38393 (10 mg/kg i.p.) and RU 24213 (1 and 3 mg/kg s.c.) produced a synergistic effect in both behavioral situations. The D1 antagonist, SCH 23390 (0.025 mg/kg i.p.), slightly inhibited the effects of apomorphine and of the combination of SKF 38393 and RU 24213 on learning but not on locomotion. The D2 antagonist, (-)-sulpiride (40 mg/kg i.p.), completely blocked these effects in both situations. These results suggest that dopamine receptor agonists impair passive avoidance learning through the D2 receptor, and that D1 and D2 receptors act synergistically in this impairment, as they do in their effects on locomotion. The involvement of D1 and D2 receptors is qualitatively similar in each of these behaviors, although some small differences may exist.

Motor, but not sensory, cortical potentials are amplified by high-protein diet

Animals fed a high-protein diet (50% casein) are hyperactive and more responsive to nociceptive stimuli than those fed either a normal- or low-protein diet. The mechanisms mediating dietary protein-induced behavior are unknown and may include both central and peripheral neural effects. Adult, Sprague-Dawley rats were fed 50% casein (treatment group) and 24% casein (control group) ad lib for 36-40 weeks. The animals were anesthetized with alpha-chloralose and urethane (50 mg/kg and 1.5 mg/kg, IP). EEG recordings were averaged while the anesthetized animal was conditioned using an alerting stimulus-imperative stimulus (AS-IS) paradigm. AS consisted of a 1.5 kHz, 90 dB tone cue. This was followed 2 seconds later by IS, an electrical tail stimulation (11 V, 1.4 s duration). Two negative deflections (N1 and N2) were generated by the frontal cortex during the AS-IS interstimulus interval. N1, an alerting response, was not different between the two groups. N2 amplitude and peak latency were significantly increased in the high-protein group (205% and 117% of control, respectively; p less than 0.05). N2 represents the activation of cells in the motor cortex. Brainstem auditory-evoked responses and somatosensory-evoked potentials also were recorded, but no differences were observed between the two diet groups. These data suggest that consumption of a high-protein diet results in an increase in central arousal mechanisms (measured by cortical negativity response), specifically involving increased excitability of the motor cortex, that is not associated with a disorder of information processing in the cerebral cortex (measured by brainstem auditory-evoked responses and somatosensory-evoked potentials).

Differential effects of pimozide and SCH 23390 on acquisition of learning in mice

Our main purpose was to clarify the differences between the effects of dopamine D-1 (SCH 23390) and D-2 (pimozide) antagonists on memory acquisition in a water-finding and a one-trial passive avoidance task with ddY mice. In the water-finding task, pimozide (0.1 and 0.2 mg/kg i.p.) enhanced the acquisition of latent learning of mice although it suppressed exploratory behavior. In contrast, SCH 23390 (0.1 mg/kg i.p.) attenuated the acquisition of latent learning and suppressed exploratory behavior. In the passive avoidance task, pimozide (0.1 and 0.2 mg/kg i.p.) enhanced the acquisition of the passive avoidance response of mice. SCH 23390 (0.05 and 0.1 mg/kg i.p.) failed to enhance the acquisition of the passive avoidance response. These results could suggest that a moderate block of D-2 receptors enhances memory acquisition but blocking D-1 receptors affects it in an opposite way.

Comparative study of the behavioral changes evoked by d-amphetamine and apomorphine in adult cats. Dose-response relationship

The behavioral effects of d-amphetamine and apomorphine administration were studied in 17 adult cats. The doses of amphetamine administered were 0.1, 0.5, 1.0 and 5.0 mg/kg; those of apomorphine, 0.1, 0.5, 1.0 and 2.0 mg/kg. These two drugs evoked in the same animal marked differences in behavioral responses. Amphetamine induced a dose-dependent hypomotility, which was marked with the higher doses. In addition, rhythmic, bilateral slow movements of the head as a mode of stereotypy, indifference to the environment and dose-dependent increase in respiratory rate. Apomorphine elicited limb flicking, dose-dependent hypermotility and increase in olfactory behavior, the last two reactions with stereotypy characteristics. The animals appeared as if being scared, hyperreacting to sudden stimuli and showing total indifference to the surrounding environment. There were marked differences in behavioral responses evoked by these two agonists of the catecholaminergic system. These data do not conform with the behavioral reactions reported in the rat by other investigators. The disagreement with other communications is probably due to differences in reactivity of the species employed. The processes involved in the diversity of the behavioral responses of the cat to the administration of amphetamine and apomorphine have not been delucidated.

Facilitatory effect of ventral tegmental area A10 region on the attack behaviour in the cat: possible dopaminergic role in selective attention

Lateral hypothalamus (LH) stimulation in cats which do not spontaneously attack rats, produces an attack pattern which may be divided into 3 main stages: the first, defined as exploratory time (ET), begins with an environmental search and culminates in orienting towards the prey; in the second, defined as attack time (AT), the cat stalks the rat; the last is the biting stage in which the cat seizes and kills the prey by biting its head and neck. The effects of ventral tegmental area (VTA) stimulation on the latency of the whole sequence and on the different stages of the attack pattern were studied. VTA activation resulted in a significant decrease of biting latency, due to the reduction of exploratory time. Moreover, a significant period of prey fixation, seldom present during LH stimulation alone, was observed after VTA-LH co-stimulation. Sulpiride injection caused the disappearance of VTA effects on the predatory pattern. The results indicate that VTA activation induces a decrease in behaviour related to exploration of the environment, and an increase in the focusing of attention on the prey, which seems an important component in the regulation of the predatory pattern. Pharmacological evidence indicates that the VTA effect is mediated by the mesolimbic-mesocortical dopaminergic (DA) system.

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.

Initial environment influences amphetamine-induced stereotypy: subsequently environment change has little effect

Saline-treated and amphetamine-treated (7 mg/kg, ip, immediate) male rats from a Sprague-Dawley substrain were observed in two test environments designed to elicit different investigative responses in normal rats. Snout contact with the substrate was generated by placing the rat in a small enclosed cage. Absence of snout contact was induced by placement of the rat on a square elevated platform. Detailed ethological records were kept of locomotion, rearing, sitting, grooming, gnawing, and sleeping throughout the 90-min session. Amphetamine-treated rats incorporated environmentally contingent bodily postures into their forms of stereotyped behavior. The postures were characteristic of those evinced initially by the saline-treated rats in the same test environment. The control rats showed appropriate changes in their investigative behavior when the apparatus was changed at 10 and at 30 min postinjection. The amphetamine-treated rats, however, were completely unresponsive to such changes at 30 min and only partially so at 10 min postinjection. It was concluded that there is a temporal gradient of decreasing readiness to modify repetitive behavior after a single, large dose of amphetamine.

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.

Amphetamine, apomorphine and investigatory behavior in the rat: analysis of the structure and pattern of responses

In the present experiments, the effects of a wide range of doses of d-amphetamine and apomorphine were studied on investigatory behavior in an automated eight-hole box. Amphetamine (0.125, 0.25, 0.5, 1.0, 3.0, 5.0 mg/kg) increased frequency and total duration of responses, and decreased mean duration in a dose-dependent manner. The strategy and organization of responses, as measured by the order of hole-visits and hole-switching, were unchanged at lower doses of amphetamine but were altered at higher doses. Perseverative hole-poking was observed at the highest dose (5.0) as indicated by increased number of hole-pokes per hole-visit. Apomorphine (0.05, 0.1, 0.2, 0.4, 0.8, 1.6, 3.2 mg/kg) decreased mean duration of responses, but in contrast to amphetamine markedly diminished frequency. Locomotor activity was also measured at all doses of both drugs. Our observations indicate that these two stimulant drugs both of which increase motor activity, have markedly different effects on investigatory responses. It is likely that amphetamine increases prepotent response tendencies (i.e., hole-poking), although this does not necessarily reflect enhanced exploration. Further, the results obtained with amphetamine support predictions made by the Lyon-Robbins behavioral theory of amphetamine effects.

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.

Behavioral effects of d-amphetamine and apomorphine in the hamster

The effects of d-amphetamine sulfate (0-50 mg/kg) and apomorphine HCl (0-12 mg/kg) on several hamster behaviors were studied. Gnawing, grooming, sniffing, locomoting, circling, rearing, and back arching were measured by direct observation during the period 25-44 min after drug injection. Large doses of d-amphetamine produced significant decreases in grooming and rearing, but significantly increased circling; back arching, sniffing, or gnawing were not affected. Large doses of apomorphine produced significant increases in gnawing and decreases in sniffing, but did not affect grooming, rearing, circling, or back arching. In general, response to either drug was highly variable. The results are discussed in comparison with published data from rats.

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.

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.

Haloperidol and clonidine increase, and apomorphine decreases ultrasonic vocalizations by gerbils

Ten psychotropic drugs that have putative effects on central brain neurotransmitters were assessed for influences on ultrasonic signaling relative to general activity in male Mongolian gerbils. Haloperidol (1 mg/kg IP), a dopamine antagonist, and clonidine (0.1 mg/kg IP), a norepinephrine agonist, increased ultrasonic signaling, and apomorphine (5 mg/kg IP), a dopamine agonist, decreased ultrasonic signaling. Catecholamines may modulate ultrasonic signaling in the gerbil. Body temperature changes were positively with ultrasonic emission in tests after saline, haloperidol, apomorphine, and 5-hydroxytryptophan (30 mg/kg IP).