Descending brainstem mechanisms for the defense of homeostasis

The brainstem can powerfully alter the processing of pain information from the periphery.  Activation of neurons in the raphe magnus (RM) is capable of entirely suppressing withdrawal or other escape movements from painful stimuli, so that the animal acts as though the painful stimulus is not even there. The RM forms the backbone of the body’s endogenous analgesia system, a system that is invoked as being activated by horrific injuries such as those on the battlefield or at the site of a car accident.  Yet, current data clearly demonstrate that RM participates in processes beyond modifying pain.  Moreover, alterations in pain processing are invariably accompanied by additional physiological changes.  My laboratory is interested in understanding how pain modulation operates in a larger physiological context, in behaving animals under natural conditions. 

Our most recent work demonstrates a role for RM in defending critical behaviors from interruption, even from interruption by a painful stimulus.  RM appears to suppress unexpected, incoming sensory inputs, painful or not, while an animal is sleeping, voiding or feeding (eating or drinking).  Even casual observations reveal that cats and dogs are not responsive and do not startle while voiding.  Thus RM defends critical behaviors from interruption.  Because a big part of homeostasis is allowing an animal to perform survival behaviors unperturbed, RM’s function can be viewed as homeostatic in nature.  Certainly sleep is a needed process and sufficient sleep time is guarded just as sufficient blood oxygenation is.  Feeding is absolutely necessary as is emptying the bladder (to avoid bladder infections).  My laboratory aims to understand how RM brings about sensory, autonomic and motor adjustments needed to ensure homeostasis.