Research Summary

My laboratory examines the physiological context within which the medullary raphe influences multiple homeostatic functions including eating, micturition, sleep/wake, and thermoregulation.

Research Description

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.

Recent publications

Mason P, Physiological identification of pontomedullary serotonergic neurons in the rat. J Neurophysiol 77(1997):1087-1098.

Gao K, Chen DO, Genzen JR, and Mason P, Activation of serotonergic neurons in the raphe magnus is not necessary for morphine analgesia.  J Neurosci 18(1998):1860-1868. 

Leung CG and Mason P,  A physiological survey of medullary raphe and magnocellular reticular neurons in the anesthetized rat.  J Neurophysiol 80(1998):1630-1646.

Leung CG and Mason P,  Physiological properties of medullary raphe neurons during sleep and waking.  J Neurophysiol 81(1999):584-595.

Mason P, Contributions of the medullary raphe and ventromedial reticular region to pain modulation and other homeostatic functions.  Ann Rev Neurosci 25(2001):737-777. 

Brink TS and Mason P, Raphe magnus neurons respond to noxious colorectal stimulation.  J Neurophysiol 89(2003):2506-2515.

Foo H and Mason P, Discharge of raphe magnus on and off cells is predictive of the motor facilitation evoked by repeated laser stimulation.  J Neurosci 23(2003):1933-1940.

Baez MA, Brink TS and Mason P, Roles for pain modulatory cells during micturition and continence J Neurosci 25(2005):384-394. 

Mason P, Deconstructing endogenous pain modulation, J Neurophys 94(2005):1659-63. 

Foo H and Mason P, Sensory suppression during feeding. PNAS 102(2005):16865-16869.

Nason MW and Mason P, Medullary raphe neurons facilitate brown adipose tissue activation J Neurosci 26(2006):1190-8.

Brink TS, Hellman KM, Lambert, AM and Mason P, Raphe magnus neurons help protect reactions to visceral pain from interruption by cutaneous pain J Neurophysiol 96(2006):3423-32.

Recent reviews

Mason P, Contributions of the medullary raphe and ventromedial reticular region to pain modulation and other homeostatic functions. Ann Rev Neurosci 25(2001):737-777.

Mason P, Deconstructing endogenous pain modulation, J Neurophysiol 94(2005):1659-63.

Mason P, Ventromedial medulla: beyond pain modulation, J Comp Neurol 493(2005):2-8.

Mason P, Placing pain on the sensory map: classic papers by Ed Perl and colleagues, J Neurophysiol 97: 1871-1873, 2007. Click here for free access to this editorial.

top