Global Cerebral Vasodilatation Elicited by Focal Electrical Stimulation within the Dorsal Medullary Reticular Formation in Anesthetized Rat

Abstract

Summary:We examined the effects of electrical stimu lation of a restricted area of the dorsal medullary reticular formation (DMRF) on regional cerebral blood flow (CBF) in anesthetized (by chloralose), paralyzed (by curare) rats. CBP was measured in tissue samples by the Kety prin ciple, with 14C-iodoantipyrine as indicator. Stimulation of DMRF elicited a widespread, significant increase in CBP in 12 of 13 areas. The increase in flow was greatest in cerebral cortex, up to 240% of control. However, it was also substantially increased in selected regions of telen cephalon, diencephalon, mesencephalon, and lower brainstem, but not cerebellum. In contrast, electricalIt has been believed for many years that the brainstem may control cerebral circulation. The ev idence has been derived largely from studies that have assessed the effects on cerebral blood flow (CBF) of locally altering neuronal activity by focal electrical stimulation (Reis, 1979). Such studies have demonstrated that modification of brainstem func tion may, in fact, alter CBF, thereby suggesting that the CNS can regulate its own circulation through intrinsic neuronal systems.These investigations, however, left two issues un resolved. First, since CBF was measured either across the entire brain (Langfitt and Kassell, 1968; Meyer et aI., 1969 Meyer et aI., , 1971Lang and Zimmer, 1974) or only qualitatively estimated from restricted brain regions, usually cerebral cortex (lngvar, 1958;Molnar and Szanto, 1964; Vern et aI., 1981; Reis et aI., 1982), they did not establish whether the evoked changes in flow were localized or global. Second, 270stimulation of the midline (interstitial nucleus of the me dial longitudinal fasciculus) I mm medial to the DMRF did not change CBF. The increase in CBP evoked by DMRF stimulation persisted after transection of the spinal cord at CI or cervical sympathetic trunk. We conclude that excitation of neurons originating in or passing through the DMRF can elicit a potent and virtually global increase of CBF. The effect appears to be mediated by intrinsic pathways of the central nervous system.

Stimulation of C1 Area Neurons Globally Increases Regional Cerebral Blood Flow but Not Metabolism

“…The increases in rCBF were, with the exception of the cerebellum, bilateral and symmetrical and included also seg ments of brain from cortex to brain stem. These increases in rCBF cannot be attributed to effects of stimulation on blood gases since these were com parable in control and experimental animals; nor can the changes be attributed to the controlled hem orrhage since (a) removal of similar amounts of blood does not affect resting rCBF (Iadecola et al, 1983) and (b) electrical stimulation of the parabra chial nucleus of the pons, which requires approxi mately the same amount of hemorrhage, decreases rCBF (Mraovitch et al, 1985); nor can the changes in rCBF be attributed to a nonspecific effect of elec trical stimulation, since stimulation with identical parameters in an adjacent brain stem site failed to alter rCBF.…”

Cerebrovascular Consequences of Obstructive Sleep Apnea

“…Other changes that potentially could affect CBF during an episode of OSA include vasoactive substances in blood or stimulation of vasoactive central neurons. 93,94 In addition, the sensory, sympathetic, or parasympathetic nervous system innervates cerebral arteries 95 and could influence CBF during an episode of OSA. In general, however, activation of the sympathetic nervous system has little effect on the cerebral circulation except during some pathological states.…”

Factors involved in the physiological regulation of the cerebral circulation

“…(After Nakai et al 1983) There are several provocative studies that suggest activation of other brain areas is able to affect CBF directly. Reis and colleagues Iadecola et al 1982Iadecola et al , 1983 have found that electrical activations of distinct intrinsic pathways in the brain have substantial effects on CBF. Activation of the dorsal medullary reticular formation results in widespread increases in CBF with accompanying increases in cerebral metabolism (Iadecola et al , 1983.…”

“…Reis and colleagues Iadecola et al 1982Iadecola et al , 1983 have found that electrical activations of distinct intrinsic pathways in the brain have substantial effects on CBF. Activation of the dorsal medullary reticular formation results in widespread increases in CBF with accompanying increases in cerebral metabolism (Iadecola et al , 1983. In contrast, activation of the fastigial nucleus also causes widespread increases in CBF, but is unaccompanied by increases in cerebral metabolism ( Fig.…”