Accession Number:



Bioreactivity: Studies on a Simple Brain Stem Reflex in Behaving Animals

Descriptive Note:

Annual rept. 1 Jun 1987-31 May 1988

Corporate Author:


Personal Author(s):

Report Date:


Pagination or Media Count:



A major problem in attempting to understand complex physiological processes, such as brain neuromodulation, or complex behavioral processes, such as arousal, is finding a simple system that will permit such analyses. The brain stem masseteric jaw closure reflex in cats is such a system. It is simple, containing only one synapse in brain, and receives dense inputs from two neurochemical systems important in neuromodulation and arousal. Initial pharmacologic studies showed that locally applied norepinephrine facilitated the reflex response. More importantly, physiologic conditions, known to activate the brain norepinephrine system, also facilitated the response. This latter finding was shown to be causal, rather than correlative, by a study which found that the facilitation could be blocked by prior destruction of the norepinephrine input specifically to the reflex circuitry. These data represent the first definitive example of an activational effect in an intact and behaving organism being attributable to a particular central neurotransmitter acting at a specific brain site. The masseteric reflex, is not simply a randomly chosen piece of behavior. Jaw closing or clenching is a well known response to stress and a component of the anxiety syndrome. Experimental evidence from studies in humans directly demonstrates that the masseteric reflex response is augmented by fear or anxiety. Thus, the masseteric reflex represents a simple behavior having direct relevance to bioreactivity.

Subject Categories:

  • Psychology
  • Biochemistry
  • Anatomy and Physiology

Distribution Statement: