Hyperactivity following posterior cortical injury is lateralized, sensitive to lesion size and independent of the nigrostriatal dopamine system

Unilateral hemispherectomy at adulthood asymmetrically affects motor performance of male Swiss mice

Evidence exists indicating that cerebral lateralization is a fundamental feature of all vertebrates. In humans, a series of studies demonstrated that the left hemisphere plays a major role in controlling movement. No such asymmetries have been identified in rodents, in spite of the fact that these animals have been frequently used in studies assessing motor behavior. In this regard, here, we used unilateral hemispherectomy to study the relative importance of each hemisphere in controlling movement. Adult Swiss mice were submitted to right unilateral hemispherectomy (RH), left unilateral hemispherectomy (LH) or sham surgery. Fifteen days after surgery, motor performance was assessed in the accelerating rotarod test and in the foot-fault test (in which performance depends on skilled limb use) and in the elevated body swing test (in which performance depends on trunk movements). The surgical removal of the right hemisphere caused a more pronounced impairment in performance than the removal of the left hemisphere both in the rotarod and in the foot-fault tests. In the rotarod, the RH group presented smaller latencies to fall than both LH and sham groups. In the foot-fault test, while both the sham and the LH groups showed no differences between left and right hind limbs, the RH group showed significantly worse performance with the left hind limb than with the right one. The elevated body swing test revealed a similar impairment in the two hemispherectomized groups. Our data suggest a major role of the right hemisphere in controlling skilled limb movements in mice.

Evolution of hemispheric specialisation of antagonistic systems of management of the body's energy resources

Excellent and rich reviews of lateralised behaviour in animals have recently been published indexing renewed interest in biological theorising about hemispheric specialisation and yielding rich theory. The present review proposes a new account of the evolution of hemispheric specialisation, a primitive system of "management of the body's energy resources". This model is distinct from traditionally evoked cognitive science categories such as verbal/spatial, analytic/holistic, etc., or the current dominant neuroethological model proposing that the key is approach/avoidance behaviour. Specifically, I show that autonomic, immune, psychomotor, motivational, perceptual, and memory systems are similarly and coherently specialised in the brain hemispheres in rodents and man. This energy resource management model, extended to human neuropsychology, is termed here the "psychic tonus" model of hemispheric specialisation.

Neonatal exposure to a type-I pyrethroid (bioallethrin) induces dose-response changes in brain muscarinic receptors and behaviour in neonatal and adult mice

This study shows that neonatal exposure to the insecticide bioallethrin has a dose-dependent effect on muscarinic cholinergic receptors (MAChR) in the neonatal mouse, leading to permanent changes in MAChR and in spontaneous behaviour in adult mice. Neonatal NMRI mice, given oral doses of either bioallethrin or the vehicle, once daily between the 10th and 16th postnatal day, were killed at the age of 17 days or 1 week after the spontaneous motor behaviour tests at 4 months. The MAChR were assayed in the cerebral cortex by using the antagonist quinuclidinyl benzilate ([3H]QNB) and the agonist carbachol. In the 17-day-old mice bioallethrin exposure elicited a significant dose-dependent increase in the specific [3H]QNB binding. The competition study showed that the proportion of low-affinity binding was significantly increased in the 17-day-old mice compared with controls. In the adult mouse there was a significant dose-dependent decrease in specific [3H]QNB binding. In these adult mice the behavioural variables 'locomotion' and 'total activity' showed significant (P < or = 0.01) dose-dependent increases at all doses up to and including 0.70 mg/kg b.wt.

The effect of cortical lesion on systemic penicillin epilepsy in rats

There is a certain recovery of function following brain damage, due to neuronal plasticity. The experiments were performed in order to investigate the effects of cortical lesion on seizural activity in rats induced by systemic application of penicillin. The sensorimotor cortex was unilaterally removed in the lesioned animals, while the control animals were only sham operated or non-operated (before implantation of the electrodes). Seizural activity was recorded by means of electroencephalograms before and after penicillin treatment (1,000,000 I.U./kg, i.p). Testing of penicillin started at least 30 days after cortical lesion. Seizural activity was characterized by spike and wave complexes accompanied by vigilance reduction and sometimes by mild myoclonic jerks in both control and lesioned animals. The early period (about 2 h after penicillin administration) with appearance of the spike-wave discharges with relative increase of the mean total electroencephalogram powers as well as the succeeding period 2.5-5.5 h after penicillin administration) with maximum number of spike-wave discharges did not differ in the electroencephalogram of the control and lesioned animals. The late period of penicillin effect (from 6-11 h after penicillin administration) with frequent spike-wave discharges and still large mean total electroencephalogram powers was observed only in lesioned animals. It is concluded that a cortical lesion destabilizes the brain function in the rat model of epilepsy induced by parenteral administration of penicillin.

Exposure to DDT during a defined period in neonatal life induces permanent changes in brain muscarinic receptors and behaviour in adult mice

DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane] is a potent neurotoxicant in both vertebrate and invertebrate species. We have previously reported that neonatal exposure to DDT affects the muscarinic cholinergic receptors (MAChR) in the cerebral cortex in the neonatal mouse, leading to permanent disturbances in the cholinergic system and behaviour of the animals as adults. In order to determine if there is a critical period for these effects, mice at the ages of 3-days, 10-days and 19-days were given a single low oral dose of DDT (0.5 mg/kg b.wt.). At adult age (4 months) the mice were tested for spontaneous behaviour: 'locomotion', 'rearing' and 'total activity', and were subsequently sacrificed for measurement of the density of MAChR and subpopulations of MAChR in the cerebral cortex by using the muscarinic antagonist quinuclidinyl benzilate, [3H]QNB, and agonist carbachol, respectively. A significant increase in spontaneous motor behaviour and a significant decrease in MAChR density in the cerebral cortex was only observed in adult mice receiving DDT at the age of 10 days. The induction of these disturbances is limited to peaks in the development of spontaneous behavioural activity and MAChR in the neonatal rodent.

Innate versus learned factors determining limb preference in the rat

The basic factors determining forelimb preference in the performance of different skilled movements were studied in white rats. To analyse whether limb preference actually reflects an initial individual motor asymmetry or is a result of instrumental learning (the first successful movement becoming fixed), the method of retrograde amnesia from electroconvulsive shock was used. It was shown that limb preference is initial and not a results of learning and, evidently, is due to intrinsic factors. The preferred limb can be identified in as few as 3 successful movements. There is a gradation among animals according to the degree of initial limb preference and its resistance to rearrangement of the motor task. The differences of limb preference in different movements were also analysed. Dependence of the preference on the character of the required movement was shown. Four basic types of movement were revealed by factor analysis. As different muscular groups (distal and proximal), controlled by different descending motor systems can be involved in the performance of different movements, it is assumed that the initial motor asymmetry in each movement is a result of asymmetry of central motor structures involved in the realization of the movement. In the same animal asymmetry of different motor structures might be different. This could explain different limb preference in different movements.