The Neurochemically Diverse Intermedius Nucleus of the Medulla as a Source of Excitatory and Inhibitory Synaptic Input to the Nucleus

Sensory afferent signals from neck muscles have been postulated to influence central cardiorespiratory control as components of postural reflexes, but neuronal pathways for this action have not been identified. The intermedius nucleus of the medulla (InM) is a target of neck muscle spindle afferents and is ideally located to influence such reflexes but is poorly investigated. [This study carefully analyzed the InM in both mouse and rat] The intermedius nucleus of the medulla is neurochemically diverse, containing GABAergic [inhibitory] and glutamatergic [excitatory] neurons. [This study shows that] the InM contains neurochemically diverse neurons and sends both excitatory and inhibitory projections to the NTS. These data provide a novel pathway that may underlie possible reflex changes in autonomic variables after neck muscle spindle afferent activation. THESE AUTHORS ALSO NOTE: " Reflex changes in cardiorespiratory variables during body movements rely on interactions between the somatic and autonomic nervous systems. " " A prime example of such interaction is the somatosympathetic reflex, in which stimulation of thinly myelinated group III (A) and unmyelinated group IV (C-fiber) limb muscle afferent fibers can reflexly increase cardiorespiratory output. " " These reflexes are mediated via sensory afferent input to the spinal cord, which is then relayed to the nucleus tractus solitarius (NTS), a brainstem site for cardiorespiratory integration. " " Cardiorespiratory changes can also be evoked by stimulation of neck muscle afferents, proposed to contribute to alterations in cardiorespiratory outflow in preparation for a change in posture. "