Action-inhibition hierarchies: Using a simple gastropod model to investigate serotonergic and dopaminergic control of action selection and reinforcement learning

IntroductionBasal ganglia (BG) activity plays an important role in action selection and reinforcement learning. Inputs from and to other areas of the brain are modulated by a number of neurotransmitter pathways in the BG. Disturbances in the normal function of the BG may play a role in the aetiology of psychiatric disorders such as schizophrenia and bipolar disorder.AimsDevelop a simple animal model to evaluate interactions between glutamatergic, dopaminergic, serotonergic and GABAergic neurones in the modulation of action selection and reinforcement learning.ObjectivesTo characterise the effects of changing dopaminergic and serotonergic activity on action selection and reinforcement learning in an animal model.MethodsThe food seeking / consummation (FSC) activity of the gastropod Planorbis corneus was suppressed by operant conditioning using a repeated unconditioned stimulus-punishment regime. The effects of elevated serotonin or dopamine levels (administration into cerebral, pedal and buccal ganglia), on operantly-conditioned FSC activity was assessed.ResultsOperantly-conditioned behaviour was reversed by elevated ganglia serotonin levels but snails showed no food consummation motor activity in the absence of food. In contrast, elevated ganglia dopamine levels in conditioned snails elicited food consummation motor movements in the absence of food but not orientation towards a food source.ConclusionsThe modulation of FSC activity elicited by reinforcement learning is subject to hierarchical control in gastropods. Serotoninergic activity is responsible establishing the general activity level whilst dopaminergic activity appears to play a more localised and subordinate ‘command’ role.

Passing as an Indicator of Social Dominance Among Female Wild and Domestic Norway Rats

The most frequent form of social interaction between pairs of wild or domestic rats (Rattus norvegicus) was passing behaviour in the narrow burrows and open field of seminatural environments. This behaviour occurs when a moving rat approaches another, either head-to-head or head-to-tail; the passed animal freezes while the passing rat continues, side touching side. The social dominance manifest by this behaviour correlated significantly with fighting dominance, particularly among female wild and domestic rats. In addition, dominance during displacements for access to food and water correlated with the dominance relationship in passing within pairs of domestic female rats. Although both passing and general activity had the same crepuscular daily rhythm, passing dominance did not correlate with individual differences in general activity level. Thus passing indicates social order and is not simply a by-product of general activity. Because passing occurs ten times more frequently than fights, in future studies it may be a more powerful indicator of female dominance and social order.

Temperament, Communicative Competence and the Psychological Adjustment of Kindergarten Children

This study examined different aspects of children's psychological adjustment within 8 traditional kindergarten classrooms in relation to both characteristics of temperament and communicative abilities. The sample consisted of 122 boys and 95 girls ( N = 217, M age = 70 mo.) from middle-class Caucasian families residing in the Upper Midwest. Communicative competence and the temperament dimensions of approach/withdrawal, mood and general activity level were significantly predictive of various manifestations of adjustment/maladjustment during the early phases of kindergarten, including peer relations, dependency, hostility, and productivity. In addition, the sex and age of the children were predictive of their dependency, productivity, and withdrawal as evaluated by teachers within the school environment.

Factors Affecting Perceptual Functioning and Activity in Albino Rats

The effects of crowding and estrus cycling upon visual observing behavior and general activity level in the albino rat were investigated. Experimental groups were composed of non-estrus or estrus females and were subjected to one of three different crowding conditions. Measures of the frequency and duration of observing of photographic slides were taken as well as a measure of general activity. Slides were composed of either geometric patterns or color photographs depicting rats in various social postures. Contrary to previous reports, observing measures did not vary with levels of crowding or stage of estrus. There were, however, differences among the various crowded conditions on a measure of general activity. Relatively short-term crowding was shown to affect estrus based cyclical variation in activity and observing.

Effects of Amobarbital Sodium and Meprobamate on Acquisition of Conditioned Avoidance

The purpose of these experiments was to study the effects of two “fear-reducing” drugs, amobarbital sodium and meprobamate, on the acquisition of a conditioned avoidance response in albino rats, and how this response is related to general activity level and freezing behavior. Both drugs facilitated acquisition of the avoidance response and increased activity level as measured by the number of spontaneous inter-trial hurdle crossings. Thus, these results seemed at variance with Mowrer's theory regarding the relationship of fear to the avoidance response. However, the results were compatible with the theory that the relationship of performance to motivation is an inverted U-shaped function, which suggests that amobarbital and meprobamate exerted their facilitating effects on avoidance performance by obtunding the strong fear-freezing response which is known to be incompatible with the emission of the avoidance response.

Effect of Morphine Sulfate on Spontaneous Activity Level of the Albino Rat

In two experiments involving 40 albino rats and two dosage levels of morphine sulfate it was found that relatively high analgesic dosages of morphine significantly depressed general activity level in the revolving drum. Also, there was a significant interaction between drug effect and hunger drive. In the case of moderate analgesic doses (7 mg/kg) no systematic effect of morphine on activity-wheel performance was noted.