Habituation of exploratory activity in rats: action of N6phenylisopropyladenosine, caffeine and their combination

Caffeine - treat or trigger? Disparate behavioral and long-term dopaminergic changes in control and schizophrenia-like Wisket rats

The influence of caffeine on behavioral functions in both healthy and schizophrenic subjects is controversial. Here we aimed to reveal the effects of repeated caffeine pre- and post-training treatments on motor and exploratory activities and cognitive functions in a reward-based test (Ambitus) along with a brain region-specific dopamine D₂ receptor profile in control and schizophrenia-like WISKET model rats. In the control animals, pre-treatment caused temporary enhancement in motor activity, while permanent improvement in learning function was detected in the WISKET animals. Post-treatment produced significant impairments in both groups. Caffeine caused short-lasting hyperactivity followed by a rebound in the inactive phase determined in undisturbed circumstance. Caffeine treatment substantially enhanced the dopamine D₂ receptor mediated G-protein activation in the prefrontal cortex and olfactory bulb of both groups, while it increased in the dorsal striatum and cerebral cortex only in the WISKET animals. Caffeine enhanced the maximal binding capacity in the hippocampus and cerebral cortex of WISKET animals, but it decreased in the prefrontal cortex of the control animals. Regarding the dopamine D₂ receptor mRNA expression, caffeine treatment caused significant enhancement in the prefrontal cortex of WISKET animals, while it increased the hippocampal dopamine D₂ receptor protein amount in both groups. This study highlights the disparate effects of caffeine pre- versus post-training treatments on behavioral parameters in both control and schizophrenia-like animals and the prolonged changes in the dopaminergic system. It is supposed that the delayed depressive effects of caffeine might be compensated by frequent coffee intake, as observed in schizophrenic patients.

Effects of acute caffeine on anxiety-related behavior in rats chronically exposed to the drug, with some evidence of possible withdrawal-reversal

For 20days male and female PVG/c hooded rats were provided with caffeinated (approximately 50mg/kg/day) or unadulterated drinking water, and then their anxiety-related behavior was observed in an open field and elevated plus maze. Their choices of a brightness change were also observed in a Y maze to assess any caffeine effects on spatial memory. 24h later, all rats were tested again following an intraperitoneal injection of 50mg/kg acute caffeine, or vehicle. Earlier chronic caffeine decreased ambulation, walking, rearing, center occupancy and increased immobility in the open field thereby suggesting increased anxiety. However, occupancy of the plus-maze open arms and the Y-maze novel arm were increased by caffeine for male rats, but decreased for females probably because of sex differences in control levels of the response rather than to drug effects on anxiety and memory respectively. Following caffeine withdrawal, acute caffeine had the opposite effect to chronic treatment namely, increased open-field ambulation, walking, center occupancy and decreased immobility and defecation for caffeine-naïve rats that were suggestive of decreased anxiety. Similar but more consistent effects (plus decreased emergence latencies from a darkened start box into the open field) also typified the caffeine-experienced rats which in this case may have been accentuated by caffeine withdrawal-reversal. There was no evidence of either chronic or acute caffeine affecting spatial memory measured in the Y maze. There were also examples of lower overall activity and higher anxiety in male rats, than in females, and some sex-dependent caffeine effects.

Purinergic signalling: from normal behaviour to pathological brain function

Purinergic neurotransmission, involving release of ATP as an efferent neurotransmitter was first proposed in 1972. Later, ATP was recognised as a cotransmitter in peripheral nerves and more recently as a cotransmitter with glutamate, noradrenaline, GABA, acetylcholine and dopamine in the CNS. Both ATP, together with some of its enzymatic breakdown products (ADP and adenosine) and uracil nucleotides are now recognised to act via P2X ion channels and P1 and P2Y G protein-coupled receptors, which are widely expressed in the brain. They mediate both fast signalling in neurotransmission and neuromodulation and long-term (trophic) signalling in cell proliferation, differentiation and death. Purinergic signalling is prominent in neurone-glial cell interactions. In this review we discuss first the evidence implicating purinergic signalling in normal behaviour, including learning and memory, sleep and arousal, locomotor activity and exploration, feeding behaviour and mood and motivation. Then we turn to the involvement of P1 and P2 receptors in pathological brain function; firstly in trauma, ischemia and stroke, then in neurodegenerative diseases, including Alzheimer's, Parkinson's and Huntington's, as well as multiple sclerosis and amyotrophic lateral sclerosis. Finally, the role of purinergic signalling in neuropsychiatric diseases (including schizophrenia), epilepsy, migraine, cognitive impairment and neuropathic pain will be considered.

The lesion of the rat substantia nigra pars compacta dopaminergic neurons as a model for Parkinson's disease memory disabilities

1. In this article we review the studies of memory disabilities in a rat model of Parkinson's disease (PD). 2. Intranigral administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to rats causes a partial lesion in the substantia nigra, compact part (SNc) and a specific loss of dopamine and its metabolites in the striatum of rats. 3. These animals present learning and memory deficits but no sensorimotor impairments, thus modeling the early phase of PD when cognitive impairments are observed but the motor symptoms of the disease are barely present. 4. The cognitive deficits observed in these animals affect memory tasks proposed to model habit learning (the cued version of the water maze task and the two-way active avoidance task) and working memory (a working memory version of the water maze), but spare long-term spatial memory (the spatial reference version of the Morris water maze). 5. The treatment of these animals with levodopa in a dose that restores the striatal level of dopamine does not reverse these memory impairments, probably because this treatment promotes a high level of dopamine in extrastriatal brain regions, such as the prefrontal cortex and the hippocampus. 6. On the other hand, the adenosine receptor antagonist, caffeine, partly reverse the memory impairment effect of SNc lesion in these rats. This effect may be due to caffeine action on nigrostriatal neurons, since it induces dopamine release and modulates the interaction between adenosine and dopamine receptor activity. 7. These results suggest that the MPTP SNc-lesioned rats are a good model to study memory disabilities related to PD and that caffeine and other selective A(2A) adenosine receptor antagonists are promising drugs to treat this symptoms in PD patients.

Caffeine reverses the memory disruption induced by intra-nigral MPTP-injection in rats

The present study was carried out to test the possible effects of caffeine in improving the memory deficits observed in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrindine (MPTP)-lesioned rats, an animal model of early stage Parkinson's disease. Caffeine at the doses of 0.1-0.3 mg/kg (intraperitoneal) reversed the impairing effect of the administration of MPTP (1 micromol/side) into the substantia nigra, compact part, of rats on the avoidance scores in the training and test sessions of a two-way active avoidance task. This effect was not due to a motor or sensory alteration because the caffeine-induced learning and memory improvement was independent of the locomotor stimulant effect of the drug and there were no differences in the reaction time of the animals to a footshock (unconditioned stimulus) or a sound cue (conditioned stimulus) after caffeine treatment. These results suggest that the reported dopamine/adenosine-receptor interaction can be used to restore defective learning and memory processes in Parkinson's disease and indicate that caffeine and other adenosine receptor antagonists are drugs with the potential for treatment of the cognitive disabilities of Parkinson's disease.

The effect of caffeine in animal models of learning and memory

In the present investigation we studied the effect of caffeine on memory task inhibitory avoidance and habituation to a new environment. Caffeine impaired retention scores in mice submitted to inhibitory avoidance and habituation when administered 30 min before training at the doses of 10-30 mg/kg. These effects cannot be explained by state-dependency since the administration of caffeine 30 min before the test session did not reverse the effect of pre-training caffeine administration, but can more probably be explained by an impairment in the acquisition or by interference with attentional processes. On the other hand, caffeine improved the inhibitory avoidance (but not habituation) retention scores when administered immediately after the training or 30 min before the test session at the doses of 1-30 mg/kg or 3-10 mg/kg, respectively. These results suggest that caffeine differentially affects the different stages of memory processing and that this effect depends on particularities of the memory task under study.