Effect of Sympathetic Nervous System on Cerebral Blood Flow in the Newborn Piglet

Abstract

The role of the sympathetic nervous system on cerebral blood flow (CBF) autoregulation was evaluated in newborn piglets. Six animals were studied after ablation of the right superior sympathetic ganglion and compared to 6 control animals. Mean arterial blood pressure (MABP) was decreased by successive blood withdrawal and CBF was measured by radioactive microspheres. In denervated animals, MABP and CBF correlated positively according to a parabolic curve showing an absence of autoregulation when MABP is above 50 mm Hg (y = 0.079x² –– 5.9x + 154, p < 0.01). In control animals, CBF remains stable throughout the experiment (y = 0.28x + 5). These data suggest a shift to the left of the upper limit of the autoregulation range in denervated animals and consequently a poor adaptation to increased MABP.

Cerebral Autoregulation Is Minimally Influenced by the Superior Cervical Ganglion in Two- Week-Old Lambs, and Absent in Preterm Lambs Immediately Following Delivery

“…Our finding that removal of the SCG resulted in a more pressure-passive increase in ipsilateral CBF during hypertension indicates that the SCG does contribute to autoregulation of flow during brief hypertensive episodes. This result is consistent with previous studies in newborn piglets [8] and adult cats [9], monkeys [7], and baboons [42], in which unilateral removal of the SCG resulted in impaired autoregulation. The loss of autoregulation is especially evident under conditions of hypertension in these animal models [9], [42].…”

“…Studies to determine whether these nerves facilitate autoregulation have yielded conflicting results. Removal of the SCG increases baseline CBF in newborn piglets [8] and increases CBF in adult primates, dogs, and cats during acute hypertension [7], [9]. In addition, electrical stimulation of the SCG reduces CBF and pial arteriolar diameter in a number of animal species [9]–[17].…”

Fetal Cerebrovascular Maturation: Effects of Hypoxia

“…In support of this view, decreases in cerebral perfusion of the neonatal brain increase interstitial concentrations of adenosine 151,152 , as well as prostanoids 153,154 , opioids 155 , and other vasodilator molecules. To an extent limited by the functional maturation of the perivascular innervation, sympathetic adrenergic mechanisms also can contribute to cerebral autoregulation, and extend the upper limit in neonates 156,157 , as in adults 158 . Given that cerebral autoregulation depends on mechanisms that are not fully mature in fetal and neonatal cerebral arteries, such as the extent of contractile differentiation of cerebrovascular smooth muscle and the functional efficiency of the perivascular innervation, it follows that neonatal cerebral autoregulation is somewhat fragile and highly vulnerable to many insults 159 including acidosis 160 , sustained or severe hypoxia 161 , asphyxia 162 , cerebral ischemia 153 , and intracranial hemorrhage 163 .…”

Intracranial dynamics in pre-term infants and neonates: implications for physiotherapists

“…The sympathetic nervous system (SNS) is not fully developed in the preterm infant (Rogers et aI1980), thus the SNS cannot control increases in blood pressure and the force of any such increase is likely to be transmitted straight to the vascular bed. It appears, however (Monin et al 1990), that in full term infants, the SNS is closely involved in autoregulation of CBF flow. The parasympathetic nervous system is less mature than the SNS, especially in pre-term infants, so alterations in blood pressure below the autoregulatory limits (ie a decreasein blood pressure) may result in -ischaemia.…”