T. Delgado

Brain Stem Terminations of the Trigeminal and Upper Spinal Ganglia Innervation of the Cerebrovascular System: WGA-HRP Transganglionic Study

The central projections of the nerve fibers innervating the middle cerebral and basilar arteries were investigated by transganglionic tracing of wheat germ agglutinin conjugated with horseradish peroxidase (WGA-HRP) in the rat. WGA-HRP was applied to the exposed basilar and/or middle cerebral arteries. Sections of the brain, trigeminal and upper spinal ganglia were reacted with tetramethylbenzidine for detection of the tracer. The results demonstrate that trigeminal neurons that innervate the middle cerebral artery project to the trigeminal main sensory nucleus, pars oralis, and the dorsocaudal two-fifths of pars interpolaris of the trigeminal brain stem nuclear complex. Terminals were also visible in the ipsilateral nucleus motorius dorsalis nervi vagi (dmnX) and in the lateral nucleus tractus solitarius (nTs) bilaterally at the level of the obex. The ventral periaqueductal gray, including the dorsal raphe and C2 dorsal horn, were also innervated by nerve fibers from the middle cerebral artery. Ipsilateral trigeminal rhizotomy prior to WGA-HRP application over the middle cerebral artery impeded the visualization of nerve terminations throughout the brain stem. Pretreatment with capsaicin reduced the density of labeled neurons and terminals within the trigeminal ganglion and the brain stem, respectively, following WGA-HRP application over the middle cerebral artery. Basilar artery fibers terminate in the C2 dorsal horn, the cuneate nuclei, dmnX, and nTs bilaterally. A few projections were also labeled in the ventral periaqueductal gray. Unilateral upper two spinal dorsal rhizotomy prior to WGA-HRP application over the exposed basilar artery resulted in terminal labeling within the C2 dorsal horn, the cuneate nucleus, dmnX, and nTs contralateral to the rhizotomy, whereas the ipsilateral side was devoid of any labeling. Bilateral superior cervical ganglionectomy prior to WGA-HRP administration to the middle cerebral and basilar arteries did not alter the visualization of nerve terminations throughout the brain stem.

Subarachnoid hemorrhage in the rat: cerebral blood flow and glucose metabolism during the late phase of cerebral vasospasm

A double-isotope technique for the simultaneous measurement of CBF and CMRglu was applied to a subarachnoid hemorrhage (SAH) model in the rat. Cisternal injection of 0.07 ml blood caused a rather uniform 20% reduction in CBF together with an increase in glucose utilization of 30% during the late phase of vasospasm. In one-third of the SAH animals, there were focal areas where the flow was lowered to 30% of the control values and the glucose uptake increased to ∼250% of control. We suggest that blood in the subarachnoid space via a neural mechanism induces the global flow and metabolic changes, and that the foci are caused by vasospasm superimposed on the global flow and metabolic changes. In the double-isotope autoradiographic technique, [14C]iodoantipyrine and [3H]deoxyglucose were used for CBF and CMRglu measurements, respectively, in the same animal. In half of the sections, the [l4C]iodoantipyrine was extracted using 2,2-dimethoxypropane before the section was placed on a 3H- and 14C-sensitive film. The other sections were placed on x-ray film with an emulsion insensitive to 3H. The validity of the double-isotope method was tested by comparing the data with those obtained in animals receiving a single isotope. The CBF and metabolic values obtained in the two groups were similar.

Stellate ganglion innervation of the vertebro-basilar arterial system demonstrated in the rat with anterograde and retrograde WGA-HRP tracing☆

Stellate ganglia projections to cerebral arteries have been investigated with wheatgerm-agglutinated horseradish peroxidase (WGA-HRP). Injections of WGA-HRP into the stellate ganglia resulted in labelling of nerve fibres on the vertebral and basilar arteries, and their side branches. The innervation was bilateral, but with an ipsilateral predominance. After WGA-HRP application on the basilar artery, retrogradely labelled cells appeared in both stellate ganglia, but most numerously in the right ganglion (70-75%). Failure to detect stellate projections to cerebral arteries in 6-hydroxydopamine (6-OHDA)-pretreated animals indicates that these fibres are of noradrenergic sympathetic character. It is suggested that the stellate fibres follow the vertebral arteries towards the basilar artery and its branches.

Effect of Selective Lesions of Medullary Catecholamine Nuclei on Experimental Cerebral Vasospasm in the Rat

Intracisternal injection of blood in the rat induces an angiographically demonstrable, biphasic cerebral vasospasm of the vertebrobasilar system, with a maximal acute spasm at 10 min and a maximal late spasm at 2 days after the subarachnoid hemorrhage (SAH). Selective lesioning of the A1 nuclei in the medulla oblongata prior to the SAH prevents the development of the late spasm, but the acute spasm develops to the same extent as in sham-lesioned animals. Lesions of the medullary A2 nuclei not only prevent the development of both acute and late spasm, but give rise to a dilatation of the vertebrobasilar arteries at day 2 post-SAH. The study indicates that both the A1 and A2 nuclei participate in the development of vasospasm post-SAH. The contrasting patterns of spasm after A1 and A2 lesions suggest a different mechanism for acute and late spasm.

Subarachnoid Hemorrhage in the Rat: Cerebral Blood Flow and Glucose Metabolism after Selective Lesions of the Catecholamine Systems in the Brainstem

A double-isotope autoradiographic technique was used to evaluate CBF and glucose metabolism 2 days after a subarachnoid hemorrhage (SAH) in rats with lesions in the lower brainstem. Lesioning in the mesencephalon of the ascending catecholamine pathways from locus ceruleus and from the A1 and A2 nuclei, or lesioning in the medulla oblongata of the ascending fibers from A1 and A2, prevents the development of the global changes in flow and metabolism seen in normal animals post SAH. Also the focal low-flow areas with markedly elevated deoxyglucose uptake, which can develop in normal animals 2 days post SAH, were not seen in the lesioned animals after the SAH. The findings indicate that the A1 and A2 nuclei, which project to the hypothalamus–pituitary, are essential for the flow and metabolic changes after an SAH. The lesions per se did not change baseline flow and metabolism as compared with sham-lesioned animals.

Effect of selective lesions in the hypothalamic-pituitary region on the development of cerebral vasospasm following an experimental subarachnoid hemorrhage in the rat

Intracisternal injection of blood in the rat induced an angiographically demonstrable biphasic cerebral vasospasm with a maximal acute spasm at 10 min and a maximal late spasm at 2 days after the subarachnoid hemorrhage. Systemic administration of 6-hydroxydopamine, which destroys catecholamine fibers in the circumventricular areas characterized by the absence of a blood–brain barrier, prevented the development of both the acute and the late spasm. Isolation or removal of one of the circumventricular organs, the pituitary, from the brain via a stalk transection or a hypophysectomy did not affect the degree of vasospasm. Lesion of the median eminence, another region without a blood–brain barrier, prevented the development of both types of spasm. The median eminence receives projections from the A1 and A2 nuclei in the medulla oblongata. It is suggested that the projections of these nuclei to the internal layer of the median eminence underlie the development of spasm.

Cerebrovascular and metabolic changes during the delayed vasospasm following experimental subarachnoid hemorrhage in baboons, and treatment with a calcium antagonist.

A model has been designed in baboons for simulating the clinical situation during the late phase of vasospasm in patients with subarachnoid hemorrhage (SAH). A total amount of 14-33 ml autologous blood was injected into the cisternal system on 3 occasions in the course of 4 days. Neurological symptoms were seen, and the mortality rate was 29%. Angiography 3 days after the last injection showed arterial vasoconstriction amounting to 23% in the vertebro-basilar system, and 11% (right) and 18% (left) in the carotid system. Cerebral blood flow (CBF) measured by the intra-arterial 133Xe technique and the cerebral metabolic rate of oxygen (CMRO2) were reduced by 18% and 11%, respectively. The hypercapnic CBF response was significantly impaired, from a mean of 3.90 ml/100 g/min to 1.72 ml/100 g/min of flow increase for each mm Hg elevation of paCO2. Autoregulation, tested by administration of angiotensin II, was also significantly affected as evidenced by a pressure-dependent increment of CBF during hypertension in 5 out of 7 animals tested. The impaired autoregulation was reflected in the autoregulatory index, which in the whole group increased from 0.06 ml/100 g/min for each mm Hg increase in MABP in the pre-SAH animals to 0.29 ml/100 g/min per mm Hg post-SAH. Treatment with the calcium antagonist, nimodipine (0.5 microgram/kg/min i.v. during 45 min), enhanced CBF significantly by 17% before experimental SAH, whereas after SAH the effect was slight and did not reach statistical significance; CMRO2 was not significantly affected in either group. Intravenous nimodipine combined with hypertension resulted in a marked increase in the autoregulatory index to 1.58 ml/100 g/min per mm Hg in pre-SAH animals and a less pronounced increment to 0.58 ml/100 g/min per mm Hg following experimental SAH. The beneficial effect of nimodipine reported in SAH patients is therefore, in view of our findings, more likely due primarily to a protective mechanism at the cellular level than to an influence on the vascular bed.

The effect on the development of cerebral vasospasm in the rat of lesioning of the peripheral and central catecholamine systems.

An experimental SAH was produced in the rat by the intracisternal injection of blood. The animals were examined with bilateral vertebral angiography or autoradiographic CBF- and CMRgI-studies. A biphasic vasospasm was seen with a maximal acute spasm at ten minutes and a maximal late spasm at two days post SAH. On day two post SAH, CBF studies demonstrated focal low flow areas in the cortex and caudate-putamen. The CMRgI examinations revealed focal areas with deoxyglucose accumulation corresponding to the low flow areas, suggesting an anaerobic glycolysis. Adrenal demedullation did not change the degree of spasm. Cranial sympathectomy reduced the degree of late spasm by about 50%. Lesioning of the ascending CA pathways in the mesencephalon prior to the SAH, prevented the development of both the acute and the late spasm. It also prevented the development of the focal CBF and CMRgI changes.

Changes in contractile response and effect of a calcium antagonist, nimodipine, in isolated intracranial arteries of baboon following experimental subarachnoid hemorrhage☆

Isolated pial arteries from a previously well-characterized model of experimental subarachnoid hemorrhage (SAH) in baboon were tested for their contractile response to 5-hydroxytryptamine (5-HT), norepinephrine (NE), and prostaglandin F2 alpha (PGF2 alpha) and the effect of the calcium antagonist, nimodipine. Autologous blood was injected cisternally at three times with one-day intervals to a total amount of 11.5-29.5 ml (mean: 18.5 ml), and the animals were killed 7 days after the first injection. Untreated animals served as controls. The degree of maximum contraction (EAm) with 5-HT and NE in the control situation was for the three arteries tested in the order middle cerebral greater than anterior cerebral greater than basilar artery. Experimental SAH markedly increased EAm, by 190-370 percent above control values (depending on type of vessel) for 5-HT and 170-185 percent for NE. In addition, the sensitivity to 5-HT was significantly increased, as evidenced by a left-shift of the concentration-response curve. Previous exposure of the artery to 10(-6) M nimodipine reduced the contractile response of both amines to approximately half, the inhibition being slightly less pronounced post-SAH. When vessels were contracted beforehand with the amines or with PGF2 alpha, followed by administration of increasing amount of nimodipine (10(-9) M to 10(-6) M), a concentration-dependent relaxation was obtained by up to 60 percent of the original level. This relaxing effect was significantly less following SAH in the experiments with NE and PGF2 alpha compared to 5-HT; the contraction in the presence of 5-HT did not differ before and after experimental SAH. The experiments show that SAH markedly enhances the intrinsic activity for both 5-HT and NE. Nimodipine inhibits the contractile response less efficiently following experimental SAH. The difference in the responsiveness to 5-HT on the one hand, and to NE and PGF2 alpha on the other, could be due to differences in the blood-induced alterations of those calcium channels that are influenced by the calcium antagonist, nimodipine.

Late cerebral arterial spasm: The cerebrovascular response to hypercapnia, induced hypertension and the effect of Nimodipine on blood flow autoregulation in experimental subarachnoid hemorrhage in primates

1. Late cerebral arterial spasm was induced by repeated injections of autologous blood in a total amount of 14-33 ml into the basal cisterns of baboons to mimick subarachnoid hemorrhage (SAH). Regional cerebral blood flow (CBF), sagittal sinus pressure, cerebral arterial caliber from angiograms, and cerebral metabolic rate of oxygen (CMRO2) were measured before and after the experimental SAH to determine responses to hypercapnia and induced hypertension. The effect of the calcium antagonist, Nimodipine, on CBF autoregulation pre- and post-SAH was tested. 2. One week after the blood injections were started there was about 10-20% reduction, depending on territory measured, in the arterial diameter of the carotid and vertebral systems. This was associated with an 18% reduction in CBF and 9% decrease in the brain metabolism. 3. During hypercapnia before and after experimental SAH the flow increased with a mean of 3.7 and 1.8 ml, respectively, for each mm Hg elevation of PaCO2. In control animals, graded angiotensin-induced hypertension did not overtly affect CBF. Following SAH, the CBF autoregulation was impaired in 5 of 6 animals tested. 4. I.v. infusion of Nimodipine markedly curtailed the CBF autoregulation in pre-SAH animals and, to a somewhat slighter extent, also in post-SAH animals.