Sympathetic nervous control of the cerebral circulation in sleep
Cerebral vessels are extensively innervated by sympathetic nerves arising from superior cervical ganglia, and these nerves might play a protective role during the large arterial pressure surges of active sleep (AS). We studied lambs (n = 10) undergoing spontaneous sleep–wake cycles before and after bilateral removal of the superior cervical ganglia (SCGx, n = 5) or sham ganglionectomy (n = 5). Lambs were instrumented to record cerebral blood flow (CBF, flow probe on the superior sagittal sinus), carotid arterial pressure (Pca), intra-cranial pressure (Pic), cerebral perfusion pressure (Pcp = Pca−Pic) and cerebral vascular resistance (CVR). Prior to SCGx, CBF (mL min−1) was significantly higher in AS than in Quiet Sleep (QS) and Quiet Wakefulness (QW) (17 ± 2, 13 ± 3, and 14 ± 3 respectively, mean ± SD, P < 0.05). Following SCGx, baseline CBF increased by 34, 31, and 29% respectively (P < 0.05). CVR also decreased in all states by ∼25% (P < 0.05). During phasic AS, surges of Pca were associated with transient increases in Pcp, Pic and CBF. Following SCGx, peak CBF and Pic during surges became higher and more prolonged (P < 0.05). Our study is the first to reveal that tonic sympathetic nerve activity (SNA) constricts the cerebral circulation and restrains baseline CBF in sleep. SNA is further incremented during arterial pressure surges of AS, limiting rises in CBF and Pic, possibly by opposing vascular distension as well as by constricting resistance vessels. Thus, SNA may protect cerebral microvessels from excessive distension during AS, when large arterial blood pressure surges are common.
Document Type: Research Article
Affiliations: 1: Pole Genie Biomedical Perinatalite-Enfance, Universite de Picardie Jules Verne, ETPAPC (EA 2088), Faculte de Medecine, 3 rue des Louvels, Amiens Cedex, France 2: Ritchie Centre for Baby Health Research, Monash Institute of Medical Research, Monash University, Clayton, Victoria, Australia 3: Dipartimento di Fisiologia Umana e Generale, Universita Degli Studi di Bologna, Piazza di Porta S. Donato, Bologna, Italy
Publication date: September 1, 2005