Tulane, LSU team on stress-related shutdown
The team from Tulane and Louisiana State Universities, led by Shi Di, found that in both physiological and psychological stress situations, stress hormones act on the brain to stimulate the release of endogenous cannabinoids from neurons in the hypothalamus, which act as a local messenger within the hypothalamus to shut down the neuroendocrine stress response.
One explanation for this hormone feedback regulation of the stress response might be to prepare the brain to mount another response in case of the onset of another possible stressor. The endogenous cannabinoids may serve to link the stress response with other neuroendocrine functions controlled by the hypothalamus, such as feeding.
Di says that the "actions of the endocannabinoids on the synaptic circuits that control the activity of the hypothalamic neurons serve to rapidly inhibit hormone secretion from the pituitary gland, providing a rapid negative feedback mechanism for the regulation of neuroendocrine function during stress."
Japanese team finds inhibition of excitatory and inhibitory synaptic transmission
In an in vitro study, a multi-center Japanese team led by Atsushi Soya focused on the supraoptic nucleus (SON) where vasopressin and oxytocin are synthesized. They found that a synthesized cannbinoid (CP55,940) inhibited both excitatory and inhibitory synaptic transmission and that a balanced input can produce sustained changes in neuronal activity without damage to neuronal homeostasis.
"Our next step is to investigate cannabinoids' effects in various stress conditions," Soya said. "E ndocannabinoids may have possible involvement in stress-induced responses such as the changes of autonomic, endocrine and immune function."
Furthermore, Soya added, "cannabinoids are relevant to potential relief in such disease situations in the brain as multiple sclerosis and epilepsy, or feeding disorders. In these, their effects are similar to marijuana, except for the possible dangers of accidentally using the natural products at higher dosages."
Scottish team seeks social behavior answers
Nancy Sabatier of the University of Edinburgh, noted that "cannabis, or marijuana, is a drug that is widely abused because of the effects it can have on our mood and our social behavior. Cannabis works this way because it acts like substances that are produced inside our brains that are messengers between brain cells. Our work involves trying to understand what these substances, endocannabinoids, are for."
She said they are particularly interested in how endocannabinoids influence oxytocin cells in the brain, because because OT within the brain is involved in social behavior. "We have found that oxytocin cells produce endocannabinoids, and can release these to switch off other inputs to the oxytocin cells themselves. We are looking at what stimuli will cause oxytocin cells to release endocannabinoids to understand why this system might be important."
Sabatier noted that most related experiments are carried out in rats, "but we think that the basic ways in which these circuits work is very similar in all mammals. These brain circuits are very old in evolutionary terms, and they govern behaviors that are of fundamental importance to most species."