Some biochemical correlates of inherited behavourial differences

Dopamine characteristics in rat genotypes with distinct susceptibility to epileptic activity: apomorphine-induced stereotyped gnawing and novelty/amphetamine-induced locomotor stimulation

Rat genotypes differ in their susceptibility to spontaneously occurring spike-wave discharges and in their dopaminergic properties. In a previous study, it was found that spike-wave discharge incidence decreased in the following order in four rat genotypes during baseline and following injection with the dopamine antagonist haloperidol: apomorphine-susceptible (APO-SUS) > WAG/Rij > apomorphine-unsusceptible (APO-UNSUS) and ACI rats. The question in the present study was to what extent certain dopaminergic properties are pathognomonic for epileptic rats. Therefore, behavioral responses were assessed in order to investigate the dopaminergic properties in the four rat genotypes. Apomorphine-induced gnawing data imply that the dopamine activity of the nigrostriatal system in the WAG/Rij rats is higher than in APO-SUS but lower than in the ACI and APO-UNSUS rats. Furthermore, in previous studies APO-SUS have been shown to have a higher novelty/amphetamine-induced locomotion, indicative of a higher dopamine reactivity of the mesolimbic system as compared to APO-UNSUS rats. Results from the present study showed that WAG/Rij rats have a higher locomotor responsiveness to novelty/amphetamine, indicating a higher dopamine reactivity of the mesolimbic system in comparison to the ACI rats. It is suggested that the functional dopaminergic mesolimbic dominance is an important factor in the susceptibility to show spontaneously occurring spike-wave discharges.

The Maudsley reactive and nonreactive strains: a North American perspective

The Maudsley experiment involving bidirectional selection for differences in open-field defecation (OFD) is briefly reviewed. Attention is focused on the North American stocks of these strains since problems have been encountered with regard to the open-field behavior and continued viability of the British stocks. The open-field behavior of the colonies of the Maudsley strains at the National Institutes of Health and at the University of Northern Iowa closely resembles that originally exhibited by the British strains, provided they are compared under standard conditions. On more complex behaviors, such as escape-avoidance conditioning, serious discrepancies have emerged between the British and North American findings. These may be resolved when attempts are made to replicate more closely the procedures used in the British studies. Particular emphasis has been placed on the potential of a second nonreactive strain, the MNRA/HAR strain, to serve as a replicate of selection for decreased emotionality. The value of the RXNRA group of recombinant-inbred strains, developed and maintained by the author, for examining the reliability of associations between traits is also stressed. A correlation between OFD and biochemical aspects of sympathetic function has been found in the Maudsley strains. This finding lends credibility to Hall's claim that the expression of emotionality is linked to autonomic arousal.

Analysis of two-way escape-avoidance conditioning measures from a diallel cross of eight strains of rats

In a study designed to investigate genotype-environment interaction, eight strains of laboratory rats were crossbred in a replicated diallel cross employing infantile stimulation and its absence as environmental treatments. This paper reports on measures of the acquisition of two-way escape-avoidance conditioning, comprising number of avoidances, avoidance and escape latencies, and intertrial and presessional crossings, which were subjected to biometrical genetical analysis, all but the last successfully. Additive variation was prominent throughout and some measures showed directional dominance. Effects of stimulation were seen in avoidance number and crossings. The analysis of avoidances by successive blocks of trials using covariance:variance graphs revealed differences in the way the strains varied with respect to the changing relationships of proportions of dominant and recessive alleles governing this behavior. The results are discussed in the light of previous data and of their evolutionary implications.

The effect of increased brain GABA produced by amino-oxyacetic acid on arousal in rats

Previous work has reported behavioral arousal in the rat to be inversely related to cortical GABA production. Therefore the effects of an increase in brain GABA levels, induced by amino-oxyacetic acid, on measures of behavioural arousal such as rearing and ambulation were examined. The increase in GABA was immediately associated with decreased rearing, however the behaviour was later indistinguishable from control values while the levels of brain GABA remained raised. It was suggested that the return to normal behaviour that occurred while brain GABA levels were increased, reflected an interaction between excitatory and inhibitory systems, and that a compensation had occurred to return the balance to normal. The pre-treatment with alpha-methyl-p-tyrosine, known to deplete brain noradrenaline and dopamine, prevented the characteristic return of normal behaviour that followed the injection of amino-oxyacetic acid. This data is consistent with GABA and noradrenaline or dopamine-mediated systems interacting in the control of behavioural arousal. The depletion of serotonin with p-chloro-phenylalanine did not prevent the characteristic recovery of behaviour that followed the injection of amino-oxyacetic acid.

The Maudsley reactive and nonreactive strains of rats: a survey

Experiments with two strains of rats, the Maudsley Reactive and Nonreactive, developed in London, England, and which were performed during 1964--1974 by a variety of investigators are summarized in a table. It is concluded that the results support the strains' standing as exemplars of differences in emotional reactivity.