The masseteric jaw closure reflex was utilized as a model system with which to gauge the functional activity of central noradrenergic neurons. This system was chosen because it is a simple monosynaptic reflex the neuronal substrate of which receives a dense noradrenergic input. The modulatory effects of @entity1063 (NE) on this response in the intact, chloral @entity19695 -anesthetized @entity35 were studied with a variety of pharmacological strategies. Initially, a reflex facilitation was obtained with the @entity2922 precursor @entity3034 . Manipulations with greater specificity of action on the noradrenergic system were then employed. First, we used the presynaptic alpha-2 noradrenergic agonist @entity1338 , which acts to decrease noradrenergic transmission. @entity1338 attenuated the amplitude of the reflex, and this suppression was blocked by pretreatment with the alpha-2 antagonist @entity3160 . The effects of @entity3160 itself were then examined, and a biphasic effect was obtained. At low doses, at which it preferentially acts as an antagonist at presynaptic alpha-2 receptors and increases noradrenergic transmission, @entity3160 enhanced the reflex. At higher doses, at which it also displays postsynaptic alpha-1 antagonist activity, @entity3160 depressed the reflex. This reflex modulation by @entity3160 was blocked by pretreatment with the alpha-1 antagonist @entity3159 . The anatomical site of the observed effect was then localized to the direct noradrenergic innervation of the reflex circuitry by locally destroying, with @entity2955 , the noradrenergic terminals in the trigeminal motor nucleus mediating the response. This significantly attenuated the reflex modulation by @entity3160 , without affecting elicitation of the reflex itself.(ABSTRACT TRUNCATED AT 250 WORDS)

Noradrenergic modulation of sensorimotor processes in intact XXXX : the masseteric reflex as a model system.

@entity3160 :: ('MESH:D015016', 'Chemical') :: ['yohimbine'] @entity3034 :: ('MESH:D007980', 'Chemical') :: ['L-DOPA'] @entity1338 :: ('MESH:D003000', 'Chemical') :: ['Clonidine', 'clonidine'] @entity3159 :: ('MESH:D011224', 'Chemical') :: ['prazosin'] @entity2955 :: ('MESH:D016627', 'Chemical') :: ['6-hydroxydopamine'] @entity19695 :: ('CHEBI:35505', 'Chemical') :: ['hydrate'] @entity2922 :: ('CHEBI:33567', 'Chemical') :: ['catecholamine'] @entity35 :: ('10116', 'Species') :: ['rat'] @entity1063 :: ('MESH:D009638', 'Chemical') :: ['norepinephrine']
@entity35 :: (10116,Species) :: ['rats']
