Original Articles
Neural Processing of Craniovascular Pain: A Synthesis of the Central Structures Involved in Migraine
Peter J. Goadsby, M.D., Ph.D., Alessandro S. Zagami, M.D. and Geoffrey A. Lambert, Ph.D.
Institute of Neurological Sciences, The Prince Henry and Prince of Wales Hospitals, Little Bay, Sydney, NSW 2036, Australia. This paper is the winner of the 1991 Harold G. Wolff Lecture Award. Reprint requests to: Dr. P.J. Goadsby, Department of Neurelogy, Clinical Sciences Building, The Prince Henry Hospital, Little Bay, Sydney NSW 2036, Australia. Accepted for Publication: March 30, 1991. SYNOPSIS
In order to determine the anatomical distribution of cells concerned with relaying craniovascular nociception, local cerebral glucose utilization was determined by the 2-deoxyglucose method in tissue autoradiographs of the a-chloralose anesthetized cat. The superior sagittal sinus was carefully lifted from the brain by sectioning the dura laterally and the falx inferiorly and suspending the sinus across two platinum hook electrodes for stimulation. The sinus was stimulated electrically and its effect on caudal brainstem, upper cervical spinal cord and diencephalic metabolic activity determined. Stimulation of the sinus caused increased metabolic activity in the trigeminal nucleus caudalis, in the cervical dorsal horn and in a discrete area in the dorsolateral spinal cord at the second cervical segment. Metabolic activity was also increased in the ventrobasal thalamus, specifically in the ventroposteromedial (188%) nuclear group, in the medial nucleus of the posterior complex (70%) and the intralaminar complex (49%). There was no change in the surrounding thalamus, lateral geniculate nucleus or overlying cerebral cortex. These increases in 2-deoxy-glucose utilisation were blocked by bilateral trigeminal ganglion ablation. The dorsolateral area activated in the spinal cord corresponds to a hitherto unrecognised group of cells in or near the lateral cervical nucleus that may form an important relay for craniovascular nociception. Further electrophysiological studies with glass coated tungsten microelectrodes have characterised the cells in these regions of the thalamus to be responsible for relaying nociceptive information. An understanding of the connections and properties of the neurons that subserve craniovascular pain is an essential prerequisite to understanding the complex pathophysiology of migraine. (Headache 31:365-371, 1991) INTRODUCTION
In this paper the central structures that process craniovascular pain will be outlined. Essential to a complete description and understanding of the pathophysiology of migraine is the identification and characterization of the brain regions that transduce the pain. Clinically it is clear that the trigeminal system is involved in migraine, but where in the central nervous system do vascular nociceptive afferents synapse and then pass to cortical attention? Migraine is a painful episodic headache that is often characterized by a throbbing pain.1 Stimulation of the cranial vessels, such as the superior sagittal sinus (SSS), is certainly painful in man.2 The dural nerves that innervate the cranial vessels largely consist of small diameter myelinated and unmyelinated fibers that almost certainly subserve a nociceptive function.3,4 The trigeminal ganglion contains the cell bodies of the bipolar neurons that innervate the large cerebral arteries and dura.5 Moreover, these nerves contain powerful vasodilator neuropeptides, such as substance P6 and calcitonin generelated peptide (CGRP),7 that can be released when the trigeminal ganglion is stimulated either in man or cat.8 Importantly electrical stimulation of the SSS in the cat leads to both marked changes in cerebral blood flow9 and elevated cranial levels of CGRP.10 In contrast, electrical stimulation of the tooth pulp in the cat does not cause release of vasoactive peptides (unpublished observations). Most recently it has been shown that in the acute attack of migraine with or without aura CGRP is elevated in the cranial circulation.11 These studies have therefore used stimulation of the SSS as a model for excitation of craniovascular pain pathways that in many respects mimics many of the changes seen in cerebrovascular physiology and pharmacology during the attack in man. The method allowed a reproducible activation of these systems so that central pain pathways from the cranial vessels could be mapped with a functional marker (2-deoxyglucose) and characterized electrophysiologically. METHODS
Adult male or female cats were anesthetized by induction with halothane and then with a-chloralose 60 mg/kg, intra-peritoneal) and additionally for the electrophysiological experiments with urethan (500 mg/kg, intra-peritoneal). The animals were intubated, placed in a stereotaxic device, paralyzed and ventilated. End-expiratory CO2 was continuously monitored and adjusted to within physiological limits by
altering the respirator pump volume. The femoral artery and vein were cannulated with polyethylene catheters for monitoring blood pressure and heart rate and administration of drugs and fluids. Core temperature was monitored by a rectal thermistor and controlled with a heating blanket. The level of anesthesia was monitored by cardiovascular responses to pain, with supplemental anesthesia being administered (a-chloralose, 10mg/kg, intravenously) as required. Surgery and stimulation. The preparation for electrical stimulation of the SSS is described in detail elsewhere.9 Briefly, a midline circular craniotomy was performed. Two parallel longitudinal incisions were made in the dura and a third in the falx to suspend the dura/falx/sinus complex over a hook electrode. A bath of mineral oil constrained by dental acrylic was fashioned to prevent the SSS from drying out and to electrically isolate it from surrounding structures. In some of the electrophysiological studies a second smaller craniotomy was carried out over the temporo-parietal region to expose the middle meningeal artery. It was gently mobilized, protected with mineral oil and stimulated by silver ball electrodes. Both the SSS and middle meningeal artery were stimulated by a stimulus isolation unit (Grass Instruments, SIU5A) driven by a S88 (Grass Instruments) stimulator that delivered single shocks (20-120V, 250msec duration) at a rate of 0.2Hz. Local cerebral glucose utilization. Local cerebral glucose utilization was measured using the 2-deoxy-glucose technique of Sokoloff and colleagues12 as applied in this laboratory.13 Briefly, a 30-35s pulse of 2-deoxy-D-[114C]-glucose (2-DG) was administered intravenously and accompanied by timed sampling over the ensuing 45 mins. At the end of this time the animal was rapidly killed with a bolus of KCI and the brain removed and frozen. The brain was sliced in a freezing microtome and sections apposed to sensitive film for 10-14 days and then developed. The relationship of the tissue radioactivity to 2-DG utilization was calculated using a lumped constant of 0.411, the radioactivity of the timed arterial and corresponding plasma glucose concentrations. Regions of interest in the high spinal cord, medulla, diencephalon and cortex were then identified and metabolic activity determined with quantitative densitometry. Sections were later stained with thionin for histological correlation. Electrophysiological studies. Extracellular recordings were made with glass coated tungsten micro-electrodes plated with platinum. These electrodes had a resistance of 200Kohm at 1Khz. Single unit responses to electrical stimulation of the SSS, middle meningeal artery or face were made. The responses were amplified, displayed on an oscilloscope and recorded on tape for later examination. Post-stimulus time (PoST) histograms were constructed on-line by a Z-80 or 80286/80287 based microcomputer system and stored on disk. Latencies were calculated by measuring the onset of the stimulus to the leading edge of the PoST histogram interval. Chemical and mechanical stimulation. The SSS or middle meningeal artery (MMA) was stimulated mechanically by displacing the vessels in an upward or lateral direction using a loop of silk thread. In some experiments the effects of local applied drugs were tested by removal of the mineral oil, washing the vessel with isotonic saline warmed to 37°C and applying small cotton wool pellets soaked with the drug to the vessel. Bradykinin triacetate (5x10-4M) was made fresh in isotonic saline for each experiment. Capsaicin (1%) was prepared by dissolving the substance in 10% Tween 80 in paraffin oil, or in a Tween/paraffin mixture (vehicle)14 and applying it again with cotton pellets. Receptive field identification. Receptive fields were sought on the face and their type ascertained according to the criteria of Hu and colleagues.15 Units that responded only to noxious stimulation (pinch, crush with serrated forceps or deep pressure) were consisdered nociceptive specific (NS) while units which responded to non-noxious stimuli (brush, stroke, light touch) but showed greater responses to noxious stimuli were classified as wide dynamic range (WDR). Units only responding to these non-noxious stimuli were classified as low threshold mechanoreceptive (LTM). Data were analyzed for the metabolic studies using a single way ANOVA with Dunnett's test16,17 and for electrophysiological studies with either a Student t test or Mann-Whitney U test.18 To localize recording sites electrode placements were verified by making 20-25mA DC current lesions of 30s duration. Sites were then reconstructed after brain section and thionin staining by reference to a standard atlas.19 RESULTS
Cardiovascular (blood pressure and heart rate) and respiratory data were within normal limits for all the animals that are included in this analysis. In total 11 animals were studied for the glucose utilization study (4 controls, 4 SSS stimulated and 3 with SSS stimulation after bilateral trigeminal ganglia ablation). In the electrophysiological studies 18 cats were studied yielding a total of 81 units in the thalamus. Metabolic Mapping. Electrical stimulation of the SSS increased glucose utilization in the C2 region of the spinal cord. This increase was most prominent in the dorsolateral area of the white matter (DLA) near a group of cells that have been labelled as the lateral cervical nucleus.20 Changes were seen bilaterally as the SSS is a midline structure. Glucose utilization increased from a control level of 10±2 to 78±11 mmol/100g/min during stimulation (p
Neural Processing of Craniovascular Pain: A Synthesis of the Central Structures Involved in Migraine
Peter J. Goadsby, M.D., Ph.D., Alessandro S. Zagami, M.D. and Geoffrey A. Lambert, Ph.D.
Institute of Neurological Sciences, The Prince Henry and Prince of Wales Hospitals, Little Bay, Sydney, NSW 2036, Australia. This paper is the winner of the 1991 Harold G. Wolff Lecture Award. Reprint requests to: Dr. P.J. Goadsby, Department of Neurelogy, Clinical Sciences Building, The Prince Henry Hospital, Little Bay, Sydney NSW 2036, Australia. Accepted for Publication: March 30, 1991. SYNOPSIS
In order to determine the anatomical distribution of cells concerned with relaying craniovascular nociception, local cerebral glucose utilization was determined by the 2-deoxyglucose method in tissue autoradiographs of the a-chloralose anesthetized cat. The superior sagittal sinus was carefully lifted from the brain by sectioning the dura laterally and the falx inferiorly and suspending the sinus across two platinum hook electrodes for stimulation. The sinus was stimulated electrically and its effect on caudal brainstem, upper cervical spinal cord and diencephalic metabolic activity determined. Stimulation of the sinus caused increased metabolic activity in the trigeminal nucleus caudalis, in the cervical dorsal horn and in a discrete area in the dorsolateral spinal cord at the second cervical segment. Metabolic activity was also increased in the ventrobasal thalamus, specifically in the ventroposteromedial (188%) nuclear group, in the medial nucleus of the posterior complex (70%) and the intralaminar complex (49%). There was no change in the surrounding thalamus, lateral geniculate nucleus or overlying cerebral cortex. These increases in 2-deoxy-glucose utilisation were blocked by bilateral trigeminal ganglion ablation. The dorsolateral area activated in the spinal cord corresponds to a hitherto unrecognised group of cells in or near the lateral cervical nucleus that may form an important relay for craniovascular nociception. Further electrophysiological studies with glass coated tungsten microelectrodes have characterised the cells in these regions of the thalamus to be responsible for relaying nociceptive information. An understanding of the connections and properties of the neurons that subserve craniovascular pain is an essential prerequisite to understanding the complex pathophysiology of migraine. (Headache 31:365-371, 1991) INTRODUCTION
In this paper the central structures that process craniovascular pain will be outlined. Essential to a complete description and understanding of the pathophysiology of migraine is the identification and characterization of the brain regions that transduce the pain. Clinically it is clear that the trigeminal system is involved in migraine, but where in the central nervous system do vascular nociceptive afferents synapse and then pass to cortical attention? Migraine is a painful episodic headache that is often characterized by a throbbing pain.1 Stimulation of the cranial vessels, such as the superior sagittal sinus (SSS), is certainly painful in man.2 The dural nerves that innervate the cranial vessels largely consist of small diameter myelinated and unmyelinated fibers that almost certainly subserve a nociceptive function.3,4 The trigeminal ganglion contains the cell bodies of the bipolar neurons that innervate the large cerebral arteries and dura.5 Moreover, these nerves contain powerful vasodilator neuropeptides, such as substance P6 and calcitonin generelated peptide (CGRP),7 that can be released when the trigeminal ganglion is stimulated either in man or cat.8 Importantly electrical stimulation of the SSS in the cat leads to both marked changes in cerebral blood flow9 and elevated cranial levels of CGRP.10 In contrast, electrical stimulation of the tooth pulp in the cat does not cause release of vasoactive peptides (unpublished observations). Most recently it has been shown that in the acute attack of migraine with or without aura CGRP is elevated in the cranial circulation.11 These studies have therefore used stimulation of the SSS as a model for excitation of craniovascular pain pathways that in many respects mimics many of the changes seen in cerebrovascular physiology and pharmacology during the attack in man. The method allowed a reproducible activation of these systems so that central pain pathways from the cranial vessels could be mapped with a functional marker (2-deoxyglucose) and characterized electrophysiologically. METHODS
Adult male or female cats were anesthetized by induction with halothane and then with a-chloralose 60 mg/kg, intra-peritoneal) and additionally for the electrophysiological experiments with urethan (500 mg/kg, intra-peritoneal). The animals were intubated, placed in a stereotaxic device, paralyzed and ventilated. End-expiratory CO2 was continuously monitored and adjusted to within physiological limits by
altering the respirator pump volume. The femoral artery and vein were cannulated with polyethylene catheters for monitoring blood pressure and heart rate and administration of drugs and fluids. Core temperature was monitored by a rectal thermistor and controlled with a heating blanket. The level of anesthesia was monitored by cardiovascular responses to pain, with supplemental anesthesia being administered (a-chloralose, 10mg/kg, intravenously) as required. Surgery and stimulation. The preparation for electrical stimulation of the SSS is described in detail elsewhere.9 Briefly, a midline circular craniotomy was performed. Two parallel longitudinal incisions were made in the dura and a third in the falx to suspend the dura/falx/sinus complex over a hook electrode. A bath of mineral oil constrained by dental acrylic was fashioned to prevent the SSS from drying out and to electrically isolate it from surrounding structures. In some of the electrophysiological studies a second smaller craniotomy was carried out over the temporo-parietal region to expose the middle meningeal artery. It was gently mobilized, protected with mineral oil and stimulated by silver ball electrodes. Both the SSS and middle meningeal artery were stimulated by a stimulus isolation unit (Grass Instruments, SIU5A) driven by a S88 (Grass Instruments) stimulator that delivered single shocks (20-120V, 250msec duration) at a rate of 0.2Hz. Local cerebral glucose utilization. Local cerebral glucose utilization was measured using the 2-deoxy-glucose technique of Sokoloff and colleagues12 as applied in this laboratory.13 Briefly, a 30-35s pulse of 2-deoxy-D-[114C]-glucose (2-DG) was administered intravenously and accompanied by timed sampling over the ensuing 45 mins. At the end of this time the animal was rapidly killed with a bolus of KCI and the brain removed and frozen. The brain was sliced in a freezing microtome and sections apposed to sensitive film for 10-14 days and then developed. The relationship of the tissue radioactivity to 2-DG utilization was calculated using a lumped constant of 0.411, the radioactivity of the timed arterial and corresponding plasma glucose concentrations. Regions of interest in the high spinal cord, medulla, diencephalon and cortex were then identified and metabolic activity determined with quantitative densitometry. Sections were later stained with thionin for histological correlation. Electrophysiological studies. Extracellular recordings were made with glass coated tungsten micro-electrodes plated with platinum. These electrodes had a resistance of 200Kohm at 1Khz. Single unit responses to electrical stimulation of the SSS, middle meningeal artery or face were made. The responses were amplified, displayed on an oscilloscope and recorded on tape for later examination. Post-stimulus time (PoST) histograms were constructed on-line by a Z-80 or 80286/80287 based microcomputer system and stored on disk. Latencies were calculated by measuring the onset of the stimulus to the leading edge of the PoST histogram interval. Chemical and mechanical stimulation. The SSS or middle meningeal artery (MMA) was stimulated mechanically by displacing the vessels in an upward or lateral direction using a loop of silk thread. In some experiments the effects of local applied drugs were tested by removal of the mineral oil, washing the vessel with isotonic saline warmed to 37°C and applying small cotton wool pellets soaked with the drug to the vessel. Bradykinin triacetate (5x10-4M) was made fresh in isotonic saline for each experiment. Capsaicin (1%) was prepared by dissolving the substance in 10% Tween 80 in paraffin oil, or in a Tween/paraffin mixture (vehicle)14 and applying it again with cotton pellets. Receptive field identification. Receptive fields were sought on the face and their type ascertained according to the criteria of Hu and colleagues.15 Units that responded only to noxious stimulation (pinch, crush with serrated forceps or deep pressure) were consisdered nociceptive specific (NS) while units which responded to non-noxious stimuli (brush, stroke, light touch) but showed greater responses to noxious stimuli were classified as wide dynamic range (WDR). Units only responding to these non-noxious stimuli were classified as low threshold mechanoreceptive (LTM). Data were analyzed for the metabolic studies using a single way ANOVA with Dunnett's test16,17 and for electrophysiological studies with either a Student t test or Mann-Whitney U test.18 To localize recording sites electrode placements were verified by making 20-25mA DC current lesions of 30s duration. Sites were then reconstructed after brain section and thionin staining by reference to a standard atlas.19 RESULTS
Cardiovascular (blood pressure and heart rate) and respiratory data were within normal limits for all the animals that are included in this analysis. In total 11 animals were studied for the glucose utilization study (4 controls, 4 SSS stimulated and 3 with SSS stimulation after bilateral trigeminal ganglia ablation). In the electrophysiological studies 18 cats were studied yielding a total of 81 units in the thalamus. Metabolic Mapping. Electrical stimulation of the SSS increased glucose utilization in the C2 region of the spinal cord. This increase was most prominent in the dorsolateral area of the white matter (DLA) near a group of cells that have been labelled as the lateral cervical nucleus.20 Changes were seen bilaterally as the SSS is a midline structure. Glucose utilization increased from a control level of 10±2 to 78±11 mmol/100g/min during stimulation (p
