Quantitative multiregional blood flow measurements during cervical sympathetic stimulation

Effects of Cryotherapy after Contusion Using Real-Time Intravital Microscopy

PURPOSE

To examine effects of local tissue cooling on contusion-induced microvascular hemodynamics and leukocytes behavior using real-time intravital microscopy.

METHODS

Male Wistar rats (N = 21, 130-150 g) were randomly assigned to intensive cooling group (3 degrees C, N = 7), a moderate cooling group (27 degrees C, N = 7), or control group (37 degrees C, N = 7). Contusion was induced by dropping a plastic ball on exposed cremaster muscle. After 5 min, the cremaster muscle was superfused with a saline solution for 10 min at controlled temperature of either 3 degrees C (cooling), 27 degrees C (moderate cooling), or 37 degrees C (control). Microvascular hemodynamics (vessel internal diameter, blood flow rate and erythrocyte velocity) and leukocyte behavior (rolling and adhesion) were measured from recorded videotapes in the same venules before and after contusion, and after cooling.

RESULTS

Cooling-induced vasoconstriction was marked at 3 degrees C and moderate at 27 degrees C compared with that at 37 degrees C. Blood flow rate and erythrocyte velocity were markedly lower at 3 degrees C compared to 37 degrees C. At 27 degrees C, erythrocyte velocity was higher than that at 37 degrees C, but blood flow rate was maintained at a level similar to that at 37 degrees C. The number of rolling and adhering leukocytes at 3 degrees C and 27 degrees C were significantly less than at 37 degrees C.

CONCLUSION

Our results suggest that local tissue cooling, similar to cryotherapy, improves edema and inflammatory reaction, and may be useful for reducing inflammatory response without inhibiting blood flow after contusion.

Evidence for a central pathway in the cerebrovascular effects of spinal cord stimulation

OBJECTIVE

Cervical spinal cord stimulation (SCS) augments cerebral blood flow (CBF) in a number of animal models. The mechanisms underlying the cerebrovascular effects of SCS are not yet well delineated. In this study, we analyzed two alternative pathways in CBF alterations induced by SCS in rats, one involving direct modulation of sympathetic outflow and the other through central vasomotor influence.

METHODS

Resection of the superior cervical ganglion (SCG), SCS alone, or SCS after SCG removal was performed in adult male Sprague-Dawley rats. CBF was measured with (14)C-inosine monophosphate radiotracer studies. In another set of experiments, SCS was performed after spinalization at the cervicomedullary junction or after laminectomy alone.

RESULTS

Baseline CBF in the SCG removal group was 71 +/- 8 ml/100 g/min, similar to controls. SCS alone significantly increased blood flow to 100 +/- 10 ml/100 g/min (P < 0.05). Animals that underwent SCS after SCG removal demonstrated a similar robust augmentation in CBF. SCS-induced changes in CBF were completely attenuated by spinalization.

CONCLUSION

The profound effects of spinal cord transection on SCS-induced CBF augmentation, together with the lack of effect of surgical sympathectomy, suggest that the mechanisms underlying the effects of SCS involve central influences rather than cervical sympathetic outflow. These findings suggest a possible role for brainstem vasomotor centers in the cerebrovascular effects of SCS.

Noradrenergic constriction of cerebral arteries as detected by transcranial Doppler (TCD) in the rabbit

Interpretation of transcranial Doppler (TCD) recordings requires assumptions about flow or diameter of the insonated vessel. This study aimed at assessing if activation of the sympathetic system could affect blood velocity (bv) in basal cerebral arteries. In anaesthetized rabbits, stimulation of cervical sympathetic nerve (cervSN) was used selectively to activate the sympathetic pathway to the head while monitoring bv in all major cerebral arteries. cervSN stimulation at 10 Hz produced: 1. in internal carotid artery (ICA) and ICA-supplied arteries (ICA-s), a consistent bv increase ranging between 20 and 70%, 2. in the basilar artery, a transient decrease by 15-30%. These effects were mimicked, in both territories, by injection of phenylephrine into the ICA. Because cerebral blood flow is known to be reduced by cervSN stimulation, the increase in bv in ICA and ICA-s must be ascribed to constriction of the insonated vessels. These effects should be considered when monitoring bv during sympathetic activation tests or exercise.

Sympathetically-induced changes in microvascular cerebral blood flow and in the morphology of its low-frequency waves

The effect of bilateral cervical sympathetic nerve stimulation on microvascular cerebral blood flow, recorded at various depths in the parietal lobe and in ponto-mesencephalic areas, was investigated by laser-Doppler flowmetry in normotensive rabbits. These areas were chosen as representative of the vascular beds supplied by the carotid and vertebro-basilar systems, which exhibit different degrees of sympathetic innervation, the former being richer than the latter. Sympathetic stimulation at 30 imp/s affects cerebral blood flow in 77% of the parietal lobe and in 43% of the ponto-mesencephalic tested areas. In both cases the predominant effect was a reduction in blood flow (14.7 +/- 5.1% and 4.1 +/- 2.4%, respectively). The extent of the reduction in both areas was less if the stimulation frequency was decreased. Sometimes mean cerebral blood flow showed a small and transient increase, mainly in response to low-frequency stimulation. The morphology was analysed of low-frequency spontaneous oscillations in cerebral blood flow, attributed to vasomotion. Present in 41% of the tested areas (frequency 4-12 cycles/min, peak-to-peak amplitude 10-40% of mean value), these waves decreased in amplitude and increased in frequency during sympathetic stimulation, irrespective of changes in mean flow. The possibility has been proposed that the sympathetic action on low-frequency spontaneous oscillations may contribute to the protective influence that this system is known to exert on the blood-brain barrier in hypertension.

Effect of cervical sympathectomy and hypoxia on the heterogeneity of O2 saturation of small cerebrocortical veins

This study evaluated the hypothesis that the sympathetic nervous system was one of the factors increasing the heterogeneity of cerebrocortical venous O2 saturation and this heterogeneity would be greater during hypoxia when cervical sympathetic activity was elevated. Thirty-two male Long-Evans rats were either sham operated (n = 16) or received bilateral cervical sympathectomy (n = 16). One-half of the animals (n = 8) in each treatment were challenged by hypoxia (8% O2 in N2). Cerebral blood flow was determined in five brain regions with [14C]iodoantipyrine. Oxygen saturation was measured microspectrophotometrically in small cerebrocortical arteries and veins. The degree of hypoxic hyperemia was not significantly different between sham-operated and sympathectomized rats. Cortical venous O2 saturations, indicating the balance between O2 supply and consumption, were significantly more heterogeneous in the sham-operated group under both normoxic and hypoxic conditions. The coefficient of variation (CV = 100 x SD/mean) for the normoxic sham-operated animals was 24.9% and the average venous O2 saturation was 53.8%. During hypoxia, venous O2 saturation was significantly decreased to 43.1% without a change in CV (24.5%). Sympathectomy significantly reduced this heterogeneity through a reduction in the number of low O2 saturation veins (CV = 13.2%) under normoxic conditions and the effect was similar under hypoxic conditions (CV = 15.3%). In both sham-operated and sympathectomized groups, hypoxia elicited a significantly higher cerebrocortical O2 consumption. Thus, bilateral cervical sympathectomy improved the O2 supply in selective cerebrocortical regions with high O2 extraction. However, the effect of sympathetic innervation on the heterogeneity of cerebrocortical venous O2 saturation was not potentiated by hypoxia.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of regional cerebral blood flow by cholinergic fibers originating in the basal forebrain

We review mainly recent studies on vasodilative regulation of cortex and hippocampus by central cholinergic nerves originating in the basal forebrain. We also briefly review the influence of other central noradrenergic fibers originating in the locus ceruleus, serotonergic fibers originating in the dorsal raphe nucleus, dopaminergic fibers originating in the substantia nigra, and peripheral sympathetic and parasympathetic nerve fibers upon regulation of regional cerebral blood flow. Local metabolites have long been considered to play an important physiological role in regulating regional cerebral blood flow. However, the evidence reviewed here emphasizes that the regulation of regional cerebral blood flow by these central cholinergic nerves is independent of regional metabolism. We propose through this review that although studies investigating neural regulation of cortical and hippocampal blood flow by cholinergic fibers originating in the basal forebrain have added much to the understanding of regulation of regional cerebral blood flow further studies are needed to determine the physiological relevance of regional cerebral blood flow in relation to higher nervous functions such as memory, learning, and personality, and changes in these cognitive functions with aging and pathology such as Alzheimer's disease.

Effect of chronic cervical sympathectomy on local cerebral blood flow during limbic seizures in rat

The vascular changes in the hippocampus and neocortex during kainic acid-induced seizures were investigated in control rats and in rats with chronic, bilateral, cervical sympathectomy. Seizures were induced in unanesthetized, spontaneously breathing rats. The increase in blood flow in the hippocampus of the sympathectomized rats was significantly reduced during the motor seizures, while the reduction in the neocortex was only significant when the increased blood flow was maximal.

Amine-induced responses of pial and penetrating cerebral arteries: evidence for heterogeneous responses

Middle cerebral arteries (MCAs) of rabbits were compared with two types of small branches (less than 100-microns outer diameter), penetrating arteries (PAs) and surface arteries (SAs), by determining their mechanical reactivity to several amines and standard contractile agents. Two techniques were employed: (a) measurement of isometric tension of 1-mm rings (MCA, PA, or SA); (b) measurement of perfusion pressure of segments consisting of essentially MCA or essentially PA. Both techniques revealed similar reactivity of the different types of vessel to acetylcholine, i.e., relaxations to a maximum of 52-78%, and similar strong contractile responses to histamine, although the MCA was more sensitive. Under H1 blockade, histamine dilated the PA (both techniques) and the MCA (perfusion technique), but not the SA. Relatively weak contractile responses to serotonin were observed in the MCA (both techniques) and the PA (perfusion technique), but not the SA (isometric tension only); no dilative responses could be elicited. Responses to noradrenaline varied with the vessel considered: The MCA contracted only, whereas the PA weakly contracted or relaxed at basal tone, and many preparations relaxed after precontraction with uridine triphosphate; the SA did not react. Relaxation of precontracted PA by noradrenaline occurred at relatively low concentrations and was antagonized by propranolol at 3 x 10(-7) or 3 x 10(-6) M. These results reveal very significant differences in the segmental reactivity to amines and suggest that noradrenaline released from sympathetic fibers might have opposing actions in the major pial arteries and the smaller penetrating branches.

Local distribution of the effects of sympathetic stimulation on cerebral blood flow in the rat

Although the density of sympathetic fibres on the cerebral vessels varies regionally, the cerebral circulatory effects of electrical stimulation of these fibres on the cerebral circulation have not been mapped in detail. In the present study the effects of sympathetic stimulation on local cerebral blood flow were examined in urethane anaesthetized rats using autoradiographic techniques. Initial experiments determined that unilateral stimulation of the superior cervical ganglion altered cerebral circulatory dynamics to an extent sufficient to reduce cerebral venous pressure by 1.1 +/- 0.2 mm Hg. Local cerebral blood flow was measured with iodo[14C]antipyrine autoradiography in 4 groups: (1) sham; (2) sham + unilateral sympathetic nerve section; (3) unilateral stimulation of the superior cervical ganglion; and (4) unilateral sympathetic stimulation + contralateral sympathetic nerve section. In the sham animals, local cerebral blood flow was equivalent in the innervated and denervated hemispheres. During stimulation plus contralateral nerve section, a regionally heterogeneous response to sympathetic stimulation was observed. Local cerebral blood flow was reduced 11-19% on the stimulated side in over one half (15/28) of the regions examined (e.g. thalamic nuclei and caudate nucleus). In general, ipsilateral reductions in flow occurred in the territory supplied by the middle cerebral, posterior cerebral and posterior communicating arteries and their branches. Cerebral blood flow was symmetrical in regions supplied by the basilar and anterior cerebral arteries and in some midline structures.

Effects of electrical stimulation of the dorsal raphe nucleus on local cerebral blood flow in the rat

We have studied the effects of electrical stimulation of the dorsal raphe nucleus on local cerebral blood flow (LCBF), as assessed by the quantitative [14C]-iodoantipyrine autoradiographic technique. Stimulation of the dorsal raphe nucleus in the alpha-chloralose anesthetized rat caused a significant decrease in LCBF, ranging from -13 to -26% in 24 brain structures out of 33 investigated. The most pronounced decreases (-23 to -26%) were observed in the accumbens, amygdaloid, interpeduncular nuclei and in the median raphe nucleus, limbic system relays. The decreases also concerned cortical regions and the extrapyramidal system. These results indicate that activation of ascending serotonergic system produces a vasoconstriction and that the dorsal raphe nucleus has a widespread modulatory influence on the cerebral circulation.

Subtypes of adrenergic and dopaminergic receptors in bovine cerebral blood vessels

Binding of the radiolabelled antagonists [3H]rauwolscine, [3H]SCH 23390 and (-)-[3H]dihydroalprenolol revealed the presence of alpha 2-adrenergic greater than DA1 dopaminergic greater than beta-adrenergic receptors in membrane preparations of calf basal cerebral arteries (basilar artery and circle of Willis) and pial vessels of the cerebral convexity. Computer-assisted analysis of ICI 118 551/(-)-[3H]dihydroalprenolol competition binding curves indicated the existence of beta 1- and beta 2-adrenergic receptor subtypes (beta 2/beta 1 ratio 7:3). No specific binding of [3H]prazosin (to alpha 1-adrenergic receptors) and [3H]spiroperidol (to DA2 dopaminergic receptors) was detected. Whereas DA1, beta 1- and beta 2-receptor densities were very similar in both blood vessel types, the alpha 2-receptor density was 3-fold higher in the pial vessels of the convexity. This suggests a functionally more important vasoconstrictor adrenergic control of the cerebral circulation in pial vessels of the convexity than in the arteries at the base of the brain.

Local glucose utilization of the brain and pineal gland during stimulation of the cervical sympathetic trunk

The quantitative autoradiographic 2-[14C]deoxyglucose method was employed to map the metabolic activity of the superior cervical ganglion and the entire brain during unilateral electrical stimulation of the cervical sympathetic trunk in the urethane-anesthetized rat. Stimulation of the cervical sympathetic trunk increased glucose utilization in the ipsilateral superior cervical ganglion (+95%) but did not produce side-to-side differences in glucose utilization in any of the brain structures examined in this study. Compared to the control nonstimulated animals, the rate of glucose metabolism in the pineal gland was increased 71% following stimulation of the cervical sympathetic trunk. The pineal gland was the only brain region out of 87 structures examined in which glucose utilization was increased by electrical stimulation of its sympathetic innervation.

Exogenous norepinephrine constricts cerebral arterioles via alpha 2-adrenoceptors in newborn pigs

The purpose of this study was to determine whether exogenous norepinephrine mediates cerebrovascular constriction via alpha 1- or alpha 2-adrenoceptors in anesthetized neonatal pigs. Diameters of pial arterioles in anesthetized piglets, 1--6 days old, were investigated using a "closed" cranial window. We examined constrictor effects of norepinephrine on pial arterioles in the absence and presence of relatively selective alpha 1-(prazosin) and alpha 2-(yohimbine) adrenoceptor antagonists (1 mg/kg i.v.). Yohimbine and prazosin inhibited pial arteriolar constriction induced by topical application of clonidine and phenylephrine (10(-6) and 10(-4) M, respectively), and yohimbine did not affect the response to topical phenylephrine. In one group diameter was 188 +/- 13 (mean +/- SEM) micron during control and 146 +/- 12 micron during 10(-5) M norepinephrine (22 +/- 5% constriction). Following yohimbine the same vessels did not constrict significantly. In another group 10(-5) M norepinephrine constricted arterioles by 22 +/- 5%, and this response was unaffected by prazosin (24 +/- 5% constriction). We conclude that pial arterioles are responsive to both alpha 1- and alpha 2-adrenoceptor agonists, that intravenous administration of prazosin and yohimbine results in these drugs crossing the blood-brain barrier and inhibiting constrictor effects of agonists, and that norepinephrine constricts pial arterioles predominantly via alpha 2-adrenoceptors.

Immediate vs. long-term desmethylimipramine or chlorimipramine: effects on regional cerebral blood flow

The immediate vs. long-term effects of desmethylimipramine (DMI) or chlorimipramine (CMI) on cerebral blood flow (CBF) were determined in 17 rabbit brain regions using radioactively tagged microspheres (15 +/- 3 micron in diameter). A single administration of either drug did not alter average CBF or its regional distribution 1 h later. Desmethylimipramine, an agent which primarily blocks re-uptake in presynaptic noradrenergic neurons, significantly increased CBF when administered daily for 21 consecutive days. The regional effects of DMI were not restricted to those areas dense in noradrenergic receptors. Flow was significantly increased in the hypothalamus, olfactory cortex, globus pallidus-putamen and midbrain. These flow increases probably reflect integrated cerebral metabolic, synthetic and/or functional activity which were associated with altered receptor sensitivity and/or number, rather than a direct cerebral vasodilatory effect. In contrast, CMI, a tricyclic antidepressant which primarily blocks presynaptic re-uptake in serotonergic neurons, and produced sedation, had little effect on CBF when administered daily for 21 consecutive days. The immediate effects of these agents on presynaptic re-uptake was not associated with altered CBF. The long-term antidepressant activity of these two agents on receptor sensitivity was probably not correlated with CBF, as evidenced by the lack of effect which CMI had on this parameter. Rather, CBF response appears to be correlated with the therapeutic spectrum of DMI which increases psychomotor activity in retarded depression.

Cerebral circulation in acute arterial hypertension--protective effects of sympathetic nervous activity

The cervical sympathetic chain was stimulated electrically at 6 or 3 Hz on one side in anesthetized cats. Acute arterial hypertension was induced by ligation of the aorta. Evans blue was given as tracer for protein leakage. The regional blood flow in the brain was determined by using labelled microspheres. At high blood pressures there was a multifocal breakdown of the blood-brain barrier. The regions with breakdown had 10-20 times the normal flow rates. With a maintained hypertension regions which were overperfused at 5 min were still overperfused at 10 min, but there was little addition of new overperfused areas. Normalization of the pressure resulted in almost twice the normal flow rates in previously overperfused regions. The breakdown of the blood-brain barrier was restricted to the non-stimulated side, or more marked on that side. The protective effect of the sympathetic stimulation lasted more than 10 min. The results indicate that acute arterial hypertension tends to cause forced and long-lasting vasodilation in some areas in the brain but regions which are resistant to the acute rise have an increase in the vascular tone. Sympathetic activity helps in developing this tone. Normalization of the blood pressure results in partial recovery of the vascular tone in previously overperfused regions and normalization in other areas.

Validity of cerebral blood flow measurements obtained with quantitative tracer techniques

A great number of results for the cerebral blood flow obtained in the animal with quantitative tracer techniques have been collected from the literature. They are exposed in order to compare both normal flow values in different laboratory species, and the characteristics, accuracy and sensitivity of each technique. A dramatic overall dispersion of flow values is observed, allowing neither the flow level particular to each species to be estimated, nor the average value provided by a given technique to be found. The physiological and technological causes of such a dispersion are discussed. Several techniques seem to have limitations which even alter the interpretation of their results, and especially the origin of the local or regional blood flow results. Other techniques may be criticized from the quantitative standpoint, but give more reliable results.

Early effects of cervical sympathetic stimulation on cerebral, ocular and cochlear blood flow

Autoregulatory mechanisms may be expected to modify effects of vasomotor nerve stimulation in many tissues. Attempts were made to reveal a distinct early, but transient effect of cervical sympathetic stimulation on cerebral, retinal and cochlear blood flow. The labelled microsphere method was used to determine regional blood flow during electrical stimulation of the cervical sympathetic chain for 15-25 s and 5 min. At a frequency of 6 Hz there was 5% reduction in cerebral flow at 15-25 s and 7% at 5 min. In the choroid plexus the mean reduction was 22% at 15-25 s but decreased 10% after 5 min. In the cerebellum, optic nerve and retina, sympathetic stimulation had no appreciable effect on the blood flow. In the cochlea and iris, the blood flow reductions were 25 and 32%, respectively, on both occasions. In the choroid, vasoconstriction increased with time, whereas in the masseter muscle there was a decrease. Thus in the present experiments no indication was found of an autoregulatory escape phenomenon in the brain, the eye or the cochlea. Some escape was noted in the masseter muscle.

Parasympathomimetic influence of carbachol on local cerebral blood flow in the rabbit by a direct vasodilator action and an inhibition of the sympathetic-mediated vasoconstriction

1 Two sorts of effect of carbachol on local cerebral blood flow (caudate nucleus) have been studied: (a) a direct action on the arterial smooth muscle; (b) an interaction with the adrenergic (sympathetic) constrictor system which innervates the vascular system of this nucleus. 2 Continuous measurements of the following variables were performed in lightly anaesthetized rabbits: local blood flow (caudate nucleus), arterial blood pressure, PaO2, PaCO2. 3 After blockade of the nicotinic synapses in the superior cervical sympathetic ganglion by local hexamethonium injection, carbachol was infused into the common carotid artery, thus minimizing systemic effects of this drug. Infusions of 0.6, 1.3 and 2.5 micrograms kg-1 min-1 induced mean increases in caudate blood flow of about 8, 17 and 37% respectively, without notable modifications of other variables measured. 4 The dilator effect of 2.5 micrograms kg-1 min-1 carbachol was reduced to a mean of 12% after intravenous injection of 0.5 mg/kg atropine, and could be totally abolished by higher doses (1 to 1.5 mg/kg). 5 Administration of 2.5 micrograms kg-1 min-1 of carbachol diminished by more than 50% the reduction in caudate blood flow induced by postganglionic stimulation of the cervical sympathetic chain, but did not affect the reduction of flow obtained by intravenous infusion of noradrenaline (2.5 to 5.0 micrograms kg-1 min-1). This inhibition of the adrenergic (sympathetic) system by carbachol was not modified by high doses of atropine (1 mg/kg i.v.). 6 We conclude that: (a) the local cerebral blood flow of a deep structure can be significantly modified by activation of vascular muscarinic receptors; (b) activation of non-muscarinic prejunctional cholinoceptors can cause inhibition of the sympathetic fibres innervating the vascular bed of the same structure.

Multiregional cerebral blood flow changes induced by a cholinomimetic drug

The effect of parasympathomimetic drug, carbachol, on regional cerebral blood flow was tested in the rabbit with the 14C-ethanol tissue sampling technique. Intracarotid injection of carbachol significantly increased flow with respect to untreated control animals in 6 out of 10 structures sampled. However, compared with animals to which atropine was also administered, the flow increases were greater with carbachol alone. These effects are discussed in terms of muscarinic and nicotinic activation.

Quantitative changes in regional cerebral blood flow of rats induced by alpha- and beta-adrenergic stimulants

Cerebral blood flow was measured with the 14C-ethanol technique in 8 regions (frontal, parieto-temporal and occipital cortex, caudate nucleus, thalamus, cerebellum, mesencephalon, and pons) of rats. The highest flow values (83-89.5 ml/100 g/min) were found in cortical areas, whereas pons had the lowest flow (48 ml/100 g/min). Intravenous infusion of noradrenaline or adrenaline markedly reduced rCBF (by 22-48% of control levels) in all regions except thalamus, mesencephalon, and pons. The noradrenaline-induced reduction was blocked, and the effect of adrenaline reversed, after pretreatment with the alpha-receptor antagonist, phentolamine. Isoprenaline infusion markedly augmented rCBF in thalamus, mesencephalon, pons, and also in the caudate nucleus. The response was reduced by the beta-receptor antagonist, propranolol. The experiments show the presence and heterogenous distribution in the cerebrovascular bed of slpha- and beta-adrenoceptors that can be activated by sympathomimetics given systematically. If noradrenaline was allowed to pass the blood-brain barrier after osmotic opening with urea, an increased regional flow was obtained, probably due to a mechanism where the vasodilator effect secondary to activation of cerebral metabolism predominated over the direct vasoconstrictor effect of the amine.