The effect of peripheral noradrenaline depletion on responding on a schedule of differential reinforcement of low rates of response (DRL)

Behavioral analysis of motor and non-motor symptoms in rodent models of Parkinson's disease

Alongside the classical motor symptoms, non-motor symptoms are increasingly recognised to play a major role in the disability associated with Parkinson's disease in humans. Animal models based on experimental depletion of forebrain dopamine have traditionally focussed on the simple and easy to measure motor impairments, and they reproduce well the bradykinesia, rigidity and impairments in the initiation and sequencing of voluntary goal-directed movement. However, a more comprehensive analysis is now urgently required. In this chapter we summarise the predominant unilateral and bilateral dopamine lesion, toxin and genetic models of human parkinsonism, and review the consequences in more complex cognitive, motor learning and psychiatric ('behavioural') domains. Theoretical and experimental advances in our understanding of information processing and associative plasticity within the striatum are not only revolutionising our understanding of normal striatal function but also bear directly on our understanding of the processes that underlie non-motor as well as motor disability in human disease, including in Parkinson's disease.

Sympathoadrenal effects on extinction of rewarded running in the rat

Two groups of rats underwent adrenal demedullation or sham surgery before being trained to run in a straight runaway for food reward at a short intertrial interval (90 s). Half of each group of animals were then injected IP with the sympathetic neurotoxin, 6-hydroxydopamine HBr (6-OHDA; 30 mg/kg); the remainder received saline vehicle. After 3 more days of acquisition training, running was extinguished over 12 trials in all rats. Running times were similar in all groups at the start of extinction. In saline-injected animals, extinction proceeded more slowly in the demedullated than in the sham-operated group, but this effect was largely abolished by 6-OHDA. Consistent with previous results, there was evidence that 6-OHDA facilitated extinction, irrespective of adrenal demedullation, but this effect was most apparent in the time taken to emerge from the start-box. The rats were killed two days after the end of the experiment; cardiac noradrenaline levels were depleted by 83% of control values in 6-OHDA-treated animals. The results suggest that the adrenal medulla and sympathetic neurones have opposing and interacting effects on the response to nonreward.

Peripheral noradrenaline depletion does not impair extinction of food-rewarded running in the rat

To test whether the sympathetic nervous system influences the inhibition of non-rewarded running in the runway, we examined the effects of peripheral noradrenaline depletion, induced by 6-hydroxydopamine (6-OHDA HBr, 30 mg/kg, i.p.), on extinction of food-rewarded running in rats. This was done in two separate experiments. In the first, in which the inter-trial interval (ITI) was one day and rats were injected before acquisition, running times at the end of extinction did not differ. The 6-OHDA appeared to slow down running times at the end of acquisition and the start of extinction. In the second experiment (15 s ITI) therefore, rats were injected after stable running had been acquired; there was no effect on running in subsequent rewarded trials. In extinction, although the groups ran similarly at first, the 6-OHDA treated animals subsequently ran more slowly than the controls; that is they showed greater extinction. Taken together with other published evidence, the sympathetic nervous system does not appear to contribute to the extinction of continuously reinforced responses.

Central noradrenaline depletion during development and its effect on behaviour

Although early depletion of noradrenaline is known to affect the morphological development of various structures in the brain, it is not clear what implications this has for adult behaviour. In the present study, 6-hydroxydopamine (6OHDA) was injected into the lateral ventricles of 12 day old rats, permanently destroying most of the noradrenergic innervation of the spinal cord and of all the brain areas examined except for the pons/medulla, and reducing the dopamine content of the cerebral cortex considerably. The noradrenaline content of the heart, as well as general developmental parameters such as food intake and body weight, were unaffected. Despite the extensive noradrenaline depletion during development, these rats' spatial memory--as determined in a radial maze task--was no worse than that of controls. In a lever-pressing task the 6OHDA treated rats made no more errors than did controls, but performed more slowly. The results indicate that at least some aspects of learning, memory and sensory-motor ability can develop normally when the noradrenergic innervation of the brain is largely destroyed.