Orexin Neurons and the Fight or Flight Response

The “fight or flight” response is an involuntary chemical and physical reaction controlled by the autonomic nervous system. More specifically, the Hypothalamus has been proven to play a key role in the triggering of the response, but the exact “mechanisms” have been elusive (Tomoyukast, 2011). New research from the Kagoshima University in Japan has located the origins of the so called “defense response” and how,” the hypothalamus seems to act as a master switch for the fight or flight response” (Tomoyukast, 2011). The answer is orexin (hypocretin) neurons.

The orexin neuron or hypocretin neuron is also referred to as a hypothalamic neuro- peptide. These neurons are found in the dorsomedial hypothalamus, which has been known to be the area that controls the reward process, pain process, and regulates the autonomic response of the cardiovascular, respiratory, and nuroendocrine system (Natsuk, Akihiro, Kanako, Yo, & Kilduff, 2005). These Orexin neurons are however, found all throughout the cerebral cortex, brainstem, and other areas of the body. This has shown scientists that these neurons have widespread connections throughout specific parts of the body but most importantly the cardio-respiratory areas that are controlled by the fight or flight response (Tomoyukast, 2011). A study preformed on mice was devised to show the relationship to the fight or flight response and the orexin neurons. Mice were exposed to extreme cold to induce hyperthermia. The cold acts as a stressor which turns on the fight or flight response mechanisms. The orexin neurons then send signals to one another that in turn regulate the cardio vascular and reparatory stress responses, and at the same time also work to control body temperature to prepare the body for “fight or flight behavior” (Tomoyukast, 2011).

Orexin neurons are intricately connected within a very precise network of autonomic reflex pathways and conscious and unconscious receptors and regulators. These neurons connect the biological clock as well as the sleep/ wakefulness autonomic responses to the dorsal hypothalamus; which can then in turn send appropriate signals down the orexin neurons to trigger the fight of flight mechanisms (Natsuk, Akihiro, Kanako, Yo, & Kilduff, 2005). This network sends all the appropriate information simultaneously through the body by way of the orexin neurons. This seemingly instantaneous system is the mechanism in which the fight or flight response is accomplished. Orexin neurons are a very specific type of neuron with a very specific function; unfortunately the neurotransmitters used by these neurons are still unknown but some have been proposed such as; 5HT-1A and 5HT-3 (Tomoyukast, 2011). These two neurotransmitters are proposed to be used during the defense response within the cardiovascular reflex pathways (Natsuk, Akihiro, Kanako, Yo, & Kilduff, 2005).

From the dorsal hyper thalamus to the cerebral cortex and brainstem to the cardiovascular, respiratory, and endocrine systems (the list continues) one can find an orexin neuron. Without the specificity of this neuron the basic stress response of the fight of flight mechanism may not have been possible, and this would have had an unexplainable effect on a species survivability in the wild.

REFERENCES

--------------------------------------------------------------------------------------------------------

Tomoyukast, K. (2011). A key role of orexin (hypocretin) neurons in the fight-or-flight response. Physiology News Magazine, 1(83), Retrieved from http://www.physoc.org/uploadedfiles/documentlibrary/824.pdf

Natsuk, T., Akihiro, Y., Kanako, I., Yo, M., & Kilduff, T.S. (2005). Cholecystokinin activates orexin/hypocretin neurons through the cholecystokinin a receptor. The Journal of Neuroscience, 25(32), 7459-7469.