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Biomedical subjects

T Schallert

Publications and source records attributed to T Schallert.

At least 73 records · Page 4Linked to original sources
PubMed1987

Ethanol and aging effects on movement initiation can be dissociated from general behavioral impairment using a high-speed lever-release task in rats.

An animal model of human reaction time was used to assess the effects of ethanol on reactive capacity (RC) as a function of age. Three doses of ethanol (0.5, 1.0 & 1.5 g/kg of 20% v/v, i.p.) were confirmed by gas chromatographic analysis of blood samples taken immediately following every behavioral test. Fisher 344 rats were trained to use their forepaws to hold down a lever until the onset of a buzzer and light that signalled impending foot shock, which occurred within 200-1000 msec of the stimulus. All rats were shaped to release the lever faster than 200 msec, which permitted them to avoid all shock under saline treatment. In the first experiment, only young adult rats (3-4 mos) were tested. Ethanol caused a dose-dependent impairment of RC. In a second experiment, rats aged 4, 12 and 24 mos were tested. As in previous work, RC was reduced by age. Ethanol caused a dose-dependent impairment of response speed (as indicated by the average of the fastest five RTs) that was exaggerated in the 24 mo-old rats. Ethanol also appeared to amplify the trial-by-trial variability in RC that was typical of the old rats under saline conditions. Nevertheless, if given enough time (1000 msec) most rats (except for a few in the oldest group) were able to avoid shock under ethanol as reliably as under saline conditions, even at the highest dose. Thus, ethanol specifically slowed reaction time while sparing memory and motivational and motor capacities required for success in this task. Both extensive practice and pre-test warm up sessions modified the effects of ethanol; however they did not do so differentially across ages.

Aging↗
PubMed1986

Recovery of function after brain damage: severe and chronic disruption by diazepam.

Following unilateral damage to the anterior-medial region of the neocortex (AMC) in rats a sensory asymmetry appeared, but recovered within a week. In a separate group of rats with AMC lesions daily 3-week exposure to diazepam (Valium, 5 mg/kg) beginning 12 h after surgery caused recovery to be delayed indefinitely. The efficiency and speed (as opposed to symmetry) of behavior was not impaired. More than 9 weeks after discontinuation of diazepam (12 weeks postsurgery), recovery was still not apparent. Postmortem analysis ruled out lesion size as a contributing factor. In a second experiment undrugged animals with AMC lesions were allowed to recover for at least 3 weeks before being exposed to diazepam. These animals showed only a transient (2-day) reinstatement of asymmetry despite continuous drug treatment. We conclude that important mechanisms serving recovery of function may be vulnerable during a short period soon after brain damage.

Animals↗
PubMed1985

Reactive capacity: a sensitive behavioral marker of movement initiation and nigrostriatal dopamine function.

Thirty-two Long Evans male rats with sham operations or unilateral 6-OHDA-induced damage to meso-telencephalic dopaminergic neurons were evaluated on a reactive capacity task that demanded high speed movement initiation. The task required lever manipulation to avoid signalled shock. The interval between the warning and the shock was incrementally reduced. A one-sleeved vest provided the opportunity to measure movement initiation of each limb independently. Extent of lesion was assessed by [3H]DA uptake, [3H]spiroperidol binding, or DA levels. Movement initiation latencies for each forelimb were found to be linearly related to interhemispheric striatal DA asymmetry induced by microinjections of 6-OHDA. Even those lesions resulting in small to moderate decreases in DA function, including deficits causing no chronic posture or sensory asymmetries, resulted in reactive capacity deficits and greatly slowed reaction time in the paw contralateral to the lesion. Following severe lesions, small yet substantial deficits were also seen in ipsilateral paw performance, which may be related to DA depletions found in the non-lesioned striatum. Thus, a reactive capacity task which requires the animal to react with maximal speed appears to be a potentially good index of nigrostriatal dopamine integrity even when the depletion is not severe.

Animals↗
PubMed1985

Neonatal hemidecortication and bilateral cutaneous stimulation in rats.

In humans, a dominant somatosensory consequence of extensive unilateral neocortex damage is "simultaneous extinction," which is an interhemispheric perceptual interaction that is operationally distinguishable from neglect. A tactile stimulus presented on the contralateral side of the body is detected when presented singly, but is completely masked during bilateral stimulation. Analogous tests designed to calibrate somatosensory asymmetries in rats were used to determine the long-term effects of hemidecortication sustained on postnatal Day 1. These data were compared with that observed in adult operated rats at a comparable postoperative period. In one respect the neonatal brain was more vulnerable than the adult brain. That is, unlike adult operated rats which were tested at 3 postoperative months, a sensory asymmetry appeared to be permanent in the neonatally operated rats, at least for the duration of testing (3-9 months). Further analysis suggested that in another way the neonates were more resistant to the effects of hemidecortication than were the adults. Neonatally operated rats appeared to be capable of processing input from both sides of the body simultaneously, even during markedly asymmetrical input. In other words, the early occurrence of brain damage may have spared them from a condition reminiscent of "simultaneous extinction." Finally, the adult operated and neonatally operated rats both displayed a subtle motor abnormality. Thus, depending on the test used, the neonatal operation yielded more severe, less severe, or comparable behavior deficits.

Animals↗
PubMed1984

Bilateral cutaneous stimulation of the somatosensory system in hemidecorticate rats.

An enduring somatosensory consequence of extensive neocortex injury in people is "simultaneous extinction," which is an interhemispheric perceptual interaction that is operationally distinguishable from neglect. A cutaneous stimulus presented on the contralateral side of the body is readily detected when presented singly but is actively masked during bilateral stimulation. In hemidecorticate rats, small adhesive stimuli were attached to the radial surface of each forelimb simultaneously, and the latencies to contact and to remove each stimulus were recorded. Neglect of the contralateral stimulus lasted 2-3 days. Thereafter the ipsilateral stimulus was removed first, followed immediately by the contralateral stimulus. This ipsilateral sensorimotor bias lasted several months. Further analysis with unremovable tactile stimuli provided evidence for true extinction. For a limited period (during the first 2 postoperative weeks), the contralateral stimulus did not appear to be detected in the presence of the ipsilateral stimulus. Rather than switching back and forth between the two stimuli, the animals ignored the stimulus on the contralateral limb and persisted in their attempts to remove the ipsilateral stimulus. A key feature of the "extinction" was its complete reversibility. Simply by adjusting the sensory fields occupied by the contralateral (C) and ipsilateral (I) stimuli (specifically, by increasing the C/I ratio), the sensorimotor bias was totally shifted to contralateral. During recovery, the size of the C/I ratio necessary to reverse sensorimotor asymmetry gradually decreased. Asymmetrical sensorimotor behavior and amphetamine-induced circling were examined in three additional groups of hemidecorticate rats, which were given their initial behavioral tests at 2, 12, or 52 postoperative weeks. This experiment confirmed the above findings and controlled for practice. Over the course of a year, apparently complete recovery occurred; however, there were residual effects. At each period, previously recovered symptoms were reinstated simply by turning on the room lights and opening the home cage slightly. These data underscore the importance of detailed behavioral analysis and the value of the rat as a model in studies of recovery of sensorimotor function.

Afferent Pathways↗
PubMed1983

Posture-independent sensorimotor analysis of inter-hemispheric receptor asymmetries in neostriatum.

Nigrostriatal dopaminergic neurons are thought to be critically important for somato-sensorimotor behavior. Following unilateral irreversible elimination of these neurons, an animal shows an ipsiversive postural bias and permanently fails to orient its head toward tactile stimuli placed on the contralateral side of the body. In response to apomorphine, a dopamine agonist, these rats display contraversive circling. This effect is thought to reflect denervation-induced proliferation of dopamine receptors in the ipsilateral striatum. We have developed a sensitive procedure that measures sensorimotor function independent of postural and circling biases. We record the latencies to remove small pieces of adhesive stimuli placed onto the snout or radial surface of the forelimbs. The stimuli are placed symmetrically and simultaneously, which is analogous to tactile-extinction procedures used clinically. In the first study we found that rats with unilateral 6-hydroxydopamine (6-OHDA)-induced lesions of the nigrostriatal pathway showed a contralateral sensorimotor bias in response to doses of apomorphine below those necessary to produce contraversive circling. In a second study, unilateral striatal microinjections of kainic acid (KA) were used to destroy the neurons on which the postsynaptic dopaminergic receptors of the nigrostriatal system are contained. Compared to 6-OHDA, KA produced unexpected results in standard orientation tests. None of the KA-treated rats showed contralateral neglect, and some even showed ipsilateral deficits. However, the standard orientation tests are confounded by postural asymmetries, which were irregular in the KA-treated group. Using again the posture-independent sensorimotor procedure, we found that all KA-treated rats, like the 6-OHDA-treated rats, uniformly displayed ipsilateral sensorimotor biases. Sensorimotor function relating to inter-striatal asymmetries may be more specifically assessed with the bilateral-adhesive tests.

Animals↗
PubMed1983

A behavior analysis of the offspring of "haloperidol-sensitive" and "haloperidol-resistant" gerbils.

The first generation (F1) offspring of haloperidol-sensitive (HS) and haloperidol-resistant (HR) gerbils were compared in a battery of motor ("catalepsy") tests, a novel cardboard-shredding (oro-facial stereotypy) test, and a holeboard (exploration) test. The F1 HS gerbils were more "cataleptic" than the F1 HR gerbils after haloperidol (1 and 3 mg/kg). The F1 HR gerbils showed more oro-facial stereotypy and more exploratory behavior than did F1 HS gerbils in undrugged tests. The F1 HS and F1 HR groups did not differ in "general activity" as measured by line crossings in an open field or by an electromagnetic monitor in the home cage. These results are preliminary behavioral evidence for a difference between HS and HR gerbils in dopaminergic or related functions.

Animals↗
PubMed1983

Sensorimotor impairment and recovery of function in brain-damaged rats: reappearance of symptoms during old age.

Following unilateral lesions in the posterior-lateral hypothalamic area, rats displayed impaired orienting behavior to tactile stimuli placed on the contralateral side of the body, whereas sham-operated animals showed no sensorimotor impairment. Recovery from this impairment occurred during the first postoperative month. As the animals became senescent, there was a reinstatement of contralateral sensorimotor impairment in the brain-damaged animals. Although preliminary, these data may have important implications for the study of aging-dependent neurological and psychiatric disorders.

Aging↗
PubMed1982

An assessment of the state hypothesis of animal "hypnosis' through an analysis of neocortical and hippocampal EEG in spontaneously immobile and hypnotized rabbits.

Hippocampal and neocortical EEG was studied in spontaneously immobile rabbits and in immobilized rabbits, "animal hypnosis.' Neocortical low voltage fast activity (LVFA) and hippocampal rhythmical slow activity (RSA) occurred spontaneously and were elicited by sensory stimulation, eserine and brain stimulation in normally immobile and hypnotized animals. Atropine sulfate blocked the LVFA and RSA that occurred during spontaneous immobility and hypnosis but not the LVFA and RSA that occurred during movement. RSA was also recorded from both CAI and dentate gyrus generators of the hippocampus during both types of immobility. The results show that hypnotized rabbits have the same type II (atropine-sensitive) EEG that is found in spontaneously immobile rabbits. The presence of type II EEG during hypnosis and its sustained sensitivity to stimulation is compatible with the view that the EEG activity is not uncoupled from its normal behavioral correlates. Perhaps normal EEG during animal hypnosis allows normal sensorimotor functions. This may permit the possibility of escape from predators at opportune moments once the immobility has served its defensive function.

Animals↗
PubMed1982

Adipsia produced by lateral hypothalamic lesions: facilitation of recovery by preoperative restriction of water intake.

Following lesions in the lateral hypothalamic area, animals failed to drink water for several postoperative days. This dysfunction was attenuated or prevented completely in rats that were subjected preoperatively to a restricted daily watering regimen. Postoperative drinking was vigorous and was not feeding associated. Reactivity to sensory stimuli was enhanced both pre- and postoperatively, particularly to stimuli associated with water. Larger lesions produced longer periods of adipsia which were resistant to the preoperative regimen. Restricted watering may exert its protective action by means of several central and peripheral mechanisms, but a behavioral/physiological conditioning hypothesis is emphasized.

Animals↗
PubMed1981

An analysis of feeding and sensorimotor abilities of rats after decortication.

Feeding and sensorimotor abilities of decorticate rats are described. Within 24 hr after surgery, the rats ate mash, unfamiliar foods, dry chow, and tap and sugar water from a spatula. They sampled nonnutritive substances but rejected noxious substances. Although initially anorectic, given mash, they arrested weight loss as early as 2 to 4 days. With training, they drank water from a spout by Day 10 and gained weight on dry food and water. Throughout survival they had difficulties with chewing food, lapping water, and trimming toenails. They showed sensorimotor neglect to objects touched to the body; they did not orient to the place in space where touched, they did not orient when touched on the head. There may be different types of orienting, one which is lost and one spared following decortication. When lifted from a surface, they showed limb and postural abnormalities; when dropped, righting responses were impaired. They showed stereotyped reflexive responses to surface and became trapped on platforms and in alleys. The range of abnormalities, from simple acts to more complex behaviors, considered within the context of feeding behavior in its broadest sense, shows the rats simplest environment. Furthermore, cortically controlled feeding seems partly independent from hypothalamically controlled feeding.

Animals↗
PubMed1981

Galloping induced by pontine tegmentum damage in rats: a form of "Parkinsonian festination" not blocked by haloperidol.

Localized lesions or local applications of gamma-aminobutyric acid (GABA) in the nucleus reticularis tegmenti pontis (NRTP) of rats cause rapidly accelerating forward locomotion. Such "festination" can coexist with blockade of the dopamine system. We suggest that (i) the akinesia produced by dopamine deficiency results at least in part from release of excessive inhibition of locomotion by a neural system whose final common inhibitory path includes the region of the NRTP and (ii) when it occurs in addition to nigrostriatal damage, destruction in the region of the NRTP might be the cause of a form of festination seen in some patients suffering from Parkinsonism.

Animals↗
PubMed1980

Morphine versus haloperidol catalepsy in the rat: a behavioral analysis of postural support mechanisms.

Our experiments demonstrate that morphine and haloperidol produce two distinct and contrasting behavioral states, which can be thought of as exaggerated, isolated, and simplified forms of organized adaptive behavioral states functioning as components of normal motivated behavior. Haloperidol catalepsy constitutes an organized state in which tonic reactions subserving the maintenance of stable static equilibrium prevail, at the expense of phasic locomotor reactions. In contrast, morphine produces an immobility state characterized by inhibition of the postural support subsystem, and compatible with or preparatory to locomotor rather than static postural reactions. haloperidol-treated rats (1, 2.5, 5, 10 mg/kg i.p.) display exaggeraged bracing reactions to passive displacement as well as to stimuli which do not actively challenge stable equilibrium. In contrast, rats treated with morphine sulfate (10, 20, 40, 80 mg/kg i.p.) show a dose-dependent suppression of bracing and an exaggerated tendency to run in response to stimuli which produce bracing in haloperidol-treated rats. Further evidence that haloperidol-treated rats are organized to stand still in stable equilibrium includes their typical posture during akinesia (i.e. broad-based support), bradykinesia, tonic grasping and enhanced postural components of contact- and air-righting. Under morphine, however, the postural support subsystem is dispensed with, as evidenced by the posture of akinesia (i.e. a frozen phase of the locomotor step cycle associated with loss of limb support), absence of tonic grasping, and nature of the deficits in contact- and air-righting. Furthermore, the opiate-induced immobility state is accompanied by an increased readiness to locomote. Morphine produces an alternation between two extreme behavioral states: complete immobility (inhibition of the postural support subsystem) versus locomotor paroxysms (varying degrees of 'explosive motor behavior'). We suggest that the postures or actions adopted by morphine-treated rats involve movement subsystems concerned with the adaptive behavioral state known as the 'immobility reflex' ('tonic immobility', 'animal hypnosis').

Animals↗