Endocannabinoid-mediated modulation of stress responses: physiological and pathophysiological significance.
- Department of Pharmacology and Therapeutics, NCBES Neuroscience Cluster and Centre for Pain Research, National University of Ireland, Galway, University Road, Galway, Ireland. [email protected]
The stress response is associated with a broad spectrum of physiological and behavioural effects including hypothalamo-pituitary-adrenal (HPA) axis activation, altered central nervous system activity, neuroimmune alterations, anxiety- and depressive-like behaviour and analgesia. While the acute stress response has essential survival value, chronic stress and dysfunction of the stress response can be maladaptive, contributing to the development and severity of psychiatric and pain disorders. The endogenous cannabinoid (endocannabinoid) system has emerged as an important lipid signalling system playing a key role in mediating and/or modulating behavioural, neurochemical, neuroendocrine, neuroimmune and molecular responses to stress. The weight of evidence, reviewed here, points largely to a system which serves to constrain HPA axis activity, facilitate adaptation or habituation of HPA axis and behavioural responses to stress, reduce anxiety- and depressive-like behaviour and mediate analgesic responses to unconditioned or conditioned stress. Possible involvement of the immune system and associated signalling molecules (e.g. cytokines) in endocannabinoid-mediated modulation of neuroendocrine and behavioural responses to stress is considered. The goal now should be to exploit our understanding of the role of the endocannabinoid system in fundamental stress physiology and pathophysiological processes to better understand and treat a range of stress-related disorders including anxiety, depression and pain.
Cannabinoids ameliorate impairments induced by chronic stress to synaptic plasticity and short-term memory.
- Department of Psychology, University of Haifa, Haifa, Israel.
Repeated stress is one of the environmental factors that precipitates and exacerbates mental illnesses like depression and anxiety as well as cognitive impairments. We have previously shown that cannabinoids can prevent the effects of acute stress on learning and memory. Here we aimed to find whether chronic cannabinoid treatment would alleviate the long-term effects of exposure to chronic restraint stress on memory and plasticity as well as on behavioral and neuroendocrine measures of anxiety and depression. Late adolescent rats were exposed to chronic restraint stress for 2 weeks followed each day by systemic treatment with vehicle or with the CB1/2 receptor agonist WIN55,212-2 (1.2 mg/kg). Thirty days after the last exposure to stress, rats demonstrated impaired long-term potentiation (LTP) in the ventral subiculum-nucleus accumbens (NAc) pathway, impaired performance in the prefrontal cortex (PFC)-dependent object-recognition task and the hippocampal-dependent spatial version of this task, increased anxiety levels, and significantly reduced expression of glucocorticoid receptors (GRs) in the amygdala, hippocampus, PFC, and NAc. Chronic WIN55,212-2 administration prevented the stress-induced impairment in LTP levels and in the spatial task, with no effect on stress-induced alterations in unconditioned anxiety levels or GR levels. The CB1 antagonist AM251 (0.3 mg/kg) prevented the ameliorating effects of WIN55,212-2 on LTP and short-term memory. Hence, the beneficial effects of WIN55,212-2 on memory and plasticity are mediated by CB1 receptors and are not mediated by alterations in GR levels in the brain areas tested. Our findings suggest that cannabinoid receptor activation could represent a novel approach to the treatment of cognitive deficits that accompany a variety of stress-related neuropsychiatric disorders.