Glucocorticoid hypersecretion following intracerebroventricular injection of ethylcholine mustard aziridinium ion in rats

Influences of cholinergic neurotoxin ethylcholine aziridinium ion on circadian rhythms in rats

To investigate whether damages of cholinergic neurons in the brain produce aging-like changes in circadian rhythms, we examined the influences of intracerebroventricular injection of cholinergic neurotoxin ethylcholine aziridinium ion (AF64A, 5 nmol/5 microl) on circadian rhythms in rats, by measuring locomotor activity and body temperature with the automatic behavioral measurement system combined with the telemetry. Daily rhythms in locomotor activity and body temperature were observed in AF64A-treated rats under a 12:12 h light:dark (LD) cycle, however, in AF64A-treated rats, the amplitude of activity and temperature rhythms was significantly decreased, the phase of the both rhythms was advanced and the amount of activity was decreased, compared with control rats. Locomotor activity and body temperature also showed a circadian rhythm in AF64A-treated rats under the constant dark condition with the period similar to that in the control rats. The present findings are in accordance with the observation in aged animals in which cholinergic hypofunction are often observed, suggesting that hypofunctions of the cholinergic systems in the brain might be involved in aging-like changes in the circadian rhythms.

Action of glucocorticoids on survival of nerve cells: promoting neurodegeneration or neuroprotection?

Extensive studies during the past decades provided compelling evidence that glucocorticoids (GCs) have the potential to affect the development, survival and death of neurones. These observations, however, reflect paradoxical features of GCs, as they may be critically involved in both neurodegenerative and neuroprotective processes. Hence, we first address different aspects of the complex role of GCs in neurodegeneration and neuroprotection, such as concentration dependent actions of GCs on neuronal viability, anatomical diversity of GC-mediated mechanisms in the brain and species and strain differences in GC-induced neurodegeneration. Second, the modulatory action of GCs during development and ageing of the central nervous system, as well as the contribution of altered GC balance to the pathogenesis of neurodegenerative disorders is considered. In addition, we survey recent data as to the possible mechanisms underlying the neurodegenerative and neuroprotective actions of GCs. As such, two major aspects will be discerned: (i) GC-dependent offensive events, such as GC-induced inhibition of glucose uptake, increased extracellular glutamate concentration and concomitant elevation of intracellular Ca(2+), decrease in GABAergic signalling and regulation of local GC concentrations by 11 beta-hydroxysteroid dehydrogenases; and (ii) GC-related cellular defence mechanisms, such as decrease in after-hyperpolarization, increased synthesis and release of neurotrophic factors and lipocortin-1, feedback regulation of Ca(2+) currents and induction of antioxidant enzymes. The particular relevance of these mechanisms to the neurodegenerative and neuroprotective effects of GCs in the brain is discussed.