title: Locus coeruleus modulates thalamic nociceptive responses via adrenoceptors.
abstract: This study investigated the parafascicular (PF) neuronal nociceptive responses and their modulation following electrical stimulation of the locus coeruleus (LC) and intrathecal (i.t.) or intracerebroventricular (i.c.v.) administration of two alpha-adrenoceptor antagonists, the alpha2-antagonist, yohimbine, and the alpha1-antagonist, prazosin. The main results were as follows: (1) the nociceptive evoked discharges in PF neurons were suppressed by preceding stimulation of LC; (2) the suppressive effect of LC stimulation on PF neurons was replaced by a facilitatory effect following pretreatment of i.t. yohimbine in 14 units tested, while i.t. prazosin failed to alter the LC-induced suppression, even when the prazosin dose was doubled; (3) i.c.v. pretreatment with prazosin strengthened the suppressive effect of LC stimulation on PF neurons; (4) i.c.v. norepinephrine (NE) administration induced, in PF neurons, a biphasic response to noxious stimulation; an early, brief (about 10 min) inhibitory effect followed by a late, long-lasting facilitatory effect; and (5) i.c.v. pretreatment of yohimbine or prazosin prevented the inhibitory or facilitatory responses released by NE, respectively. These results provide evidence that: (1) the LC-descending projections exhibit a suppressive effect on nociceptive transmission at the spinal level through alpha2-receptors; and (2) the LC-ascending projections exhibit dual effects, facilitatory and inhibitory, at the medial thalamus (PF) level through alpha1- and alpha2-receptors, respectively.
authors.affiliation: Department of Neurobiology, Shanxi Medical College, Taiyuan, Shanxi 030001, China.
authors.forename: C
authors.initials: C
authors.lastname: Zhang
authors.forename: Y Q
authors.initials: YQ
authors.lastname: Guo
authors.forename: J T
authors.initials: JT
authors.lastname: Qiao
authors.forename: N
authors.initials: N
authors.lastname: Dafny
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000008:administration & dosage / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D005260:Female; D007276:Injections, Intraventricular; D007278:Injections, Spinal; D008125:Locus Coeruleus / Q000502:physiology*; D008297:Male; D009619:Nociceptors / Q000502:physiology*; D009638:Norepinephrine / Q000008:administration & dosage / Q000494:pharmacology; D011224:Prazosin / Q000008:administration & dosage / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D011941:Receptors, Adrenergic / Q000008:administration & dosage / Q000502:physiology*; D013238:Stereotaxic Techniques; D013788:Thalamus / Q000502:physiology*; D015016:Yohimbine / Q000008:administration & dosage / Q000494:pharmacology
chemical_list: D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D011941:Receptors, Adrenergic; D015016:Yohimbine; D009638:Norepinephrine; D011224:Prazosin