Histamine excites groups III and IV afferents from the cat knee joint depending on their resting activity

The effect of histamine on the sensory activity of primary afferents was studied in normal and acutely inflamed cat knee joints. A subpopulation of groups III and IV articular afferents could be activated by close-arterial bolus injections of histamine: units with a high resting activity (about 100/min) were particular sensitive to histamine and were excited even by 3.3 fg histamine. The lower the resting discharges of groups III and IV units both from normal and acutely inflamed joints, the higher the dose of histamine (up to 3.3 or 33 microg) necessary to excite the nerve fibres. Thirty-seven of 39 units without any resting activity were completely insensitive to histamine. In contrast to its clear excitatory effect, histamine caused only minor changes in the responses to joint movements. Movement-evoked activity remained unchanged in 22 of 28 units, 1 unit was sensitized and 5 units showed reduced activity after histamine (3.3 microg). The present results support the notion that histamine may participate in the mediation of pain from injured or inflamed tissue. It is remarkable that histamine has a profound excitatory action on a proportion of both groups III and IV articular afferents without changing their sensitivity to joint movements.

Sensitisation of group III articular afferents to mechanical stimuli by substance P

OBJECTIVE

To examine the excitatory and sensitising effects of substance P (SP) on articular afferents in normal and acutely inflamed cat knee joints.

MATERIALS AND METHODS

In anesthetised cats recordings were made from 15 group III (conduction velocity 2.5-20 m/s) and 25 group IV afferent units (conduction velocity < 2.5 m/s) of the medial articular nerve of normal and acutely inflamed knee joints. SP (10 and 100 microg) was administered close-arterially.

RESULTS

SP at doses of 10 microg and 100 microg activated less than 50% of both group III and group IV units. The proportion of SP-positive units was significantly higher in inflamed (10 of 21) than in normal joints (2 of 18). SP induced activity in initially silent units or increased ongoing activity after latencies varying from 2 s to 5 min. The SP-evoked activity had an irregular pattern, a variable duration, and was not related to the dose injected. Bolus injections of SP (100 microg) sensitised group III articular afferents but not group IV units to noxious movements of the joint, regardless whether the units were from normal or acutely inflamed joints. The responses to innocuous movements were not influenced by SP. Group III units, initially not activated by any movement, displayed vigorous discharges to noxious movements after close-arterial SP. In 3 group III units tested, the SP-induced augmentation of responses to noxious movements was not mimicked by close-arterial injection of histamine (3.3 microg).

CONCLUSIONS

It is concluded that SP contributes to the sensitisation of a subpopulation of high-threshold articular afferents. Thus this neuronal mediator released peripherally in response to an injury or acute inflammation causes considerable changes in the mechanosensitivity of this subpopulation of nociceptive joint afferents.

Participation of NK1 receptors in nociceptin-induced modulation of rat knee joint mechanosensitivity

Nociceptin is known to act peripherally in the rat knee joint to modulate articular mechanosensitivity and it has been postulated that neurokinin-1 (NK1) receptors may be involved in this process. To test this hypothesis, single unit extracellular recordings were made from knee joint primary afferents in response to normal and extreme rotation of the joint. Afferent firing rate was assessed following close intraarterial injection of the NK1 antagonist RP67580 followed by administration of 20 nmol nociceptin. With both normal and hyper-rotation of the knee, nociceptin was unable to elicit its usual mechanomodulatory effect such that afferent activity was not significantly different from control (P = 0.7572 and P = 0.9182 for normal and hyper-rotation of the joint, respectively). These data indicate that nociceptin-induced mechanosensitivity changes in the rat knee depend upon NK1 receptor activation possibly through secondary release of substance P.

Swelling-activated calcium signalling in cultured mouse primary sensory neurons

The effects of hypo-osmotic membrane stretch on intracellular calcium concentration ([Ca(2+)](i)), cell volume and cellular excitability were investigated in cultured mouse primary sensory trigeminal neurons. Hypotonic solutions (15--45%) led to rapid cell swelling in all neurons. Swelling was accompanied by dose-dependent elevations in [Ca(2+)](i) in a large fraction of neurons. Responses could be classified into three categories. (i) In 57% of the neurons [Ca(2+)](i) responses had a slow rise time and were generally of small amplitude. (ii) In 21% of the neurons, responses had a faster rise and were larger in amplitude. (iii) The remaining cells (22%) did not show [Ca(2+)](i) responses to hypo-osmotic stretch. Slow and fast [Ca(2+)](i) changes were observed in trigeminal neurons of different sizes with variable responses to capsaicin (0.5 microM). The swelling-induced [Ca(2+)](i) responses were not abolished after depletion of intracellular Ca2+ stores with cyclopiazonic acid or preincubation in thapsigargin, but were suppressed in the absence of external Ca(2+). They were strongly attenuated by extracellular nickel and gadolinium. Hypotonic stimulation led to a decrease in input resistance and to membrane potential depolarization. Under voltage-clamp, the [Ca(2+)](i) elevation produced by hypotonic stimulation was accompanied by the development of an inward current and a conductance increase. The time course and amplitude of the [Ca(2+)](i) response to hypo-osmotic stimulation showed a close correlation with electrophysiological properties of the neurons. Fast [Ca(2+)](i) responses were characteristic of trigeminal neurons with short duration action potentials and marked inward rectification. These findings suggest that hypo-osmotic stimulation activates several Ca(2+)-influx pathways, including Gd(3+)-sensitive stretch-activated ion channels, in a large fraction of trigeminal ganglion neurons. Opening of voltage-gated Ca(2+) channels also contributes to the response. The pattern and rate of Ca(2+) influx may be correlated with functional subtypes of sensory neurons.

Peripheral modulation of rat knee joint afferent mechanosensitivity by nociceptin/orphanin FQ

The peripheral effects of nociceptin were examined in normal and acutely inflamed rat knee joints by analyzing single unit recordings from articular primary afferents in response to normal and extreme rotation of the knee. Bolus close intraarterial injection of nociceptin (0.01, 1 and 100 microM) caused a sensitization of normal and inflamed knee joint afferents in response to movements in the normal working range of the joint. When the joint was hyper-rotated, nociceptin had no significant effect on afferent discharge rate in normal knees, however, in inflamed joints the top dose of the neuropeptide caused a decrease in articular mechanosensitivity. These findings suggest that nociceptin seems to be involved in the control of peripheral nociceptive mechanisms, although the behaviour of the peptide is dependent upon the inflammatory status of the tissue.

Involvement of nitric oxide in the modulation of dural arterial blood flow in the rat

1. Nitric oxide (NO) has been proposed to be a key molecule in the pathogenesis of migraine pain and other headaches that are linked to vascular disorders. Several lines of evidence indicate that the meningeal vascularization is crucially involved in the generation of these headaches. In an experimental model in the rat a dominating role of calcitonin gene-related peptide (CGRP) in causing neurogenic vasodilatation and increased blood flow has been shown. The aim of the present study was to clarify the role of NO in this model with regard to the meningeal blood flow. 2. The blood flow in and around the medial meningeal artery (dural arterial flow) was recorded in the exposed parietal dura mater encephali of barbiturate anaesthetized rats using laser Doppler flowmetry. Local electrical stimulation of the dura mater (pulses of 0.5 ms delivered at 7.5 - 17.5 V and 5 or 10 Hz for 30 s) caused temporary increases in dural arterial flow for about 1 min that reached peaks of 1.6 - 2.6 times the basal flow. The effects of NO synthase (NOS) inhibitors on the basal flow and the electrically evoked increases in flow were examined. 3. Systemic (i. v.) administration of N(omega)-nitro-L-arginine methyl ester (L-NAME) at cumulative doses of 10 and 50 mg kg(-1) lowered the basal flow to 87 and 72%, respectively, of the control and reduced the evoked increases in blood flow to 82 and 44% on an average. Both these effects could partly be reversed by 300 mg kg(-1) L-arginine. The systemic arterial pressure was increased by L-NAME at both doses. Injection of the stereoisomer D-NAME at same doses did not change basal flow and evoked increases in flow. 4. 4. Topical application of L-NAME (10(-4) - 10(-2) M) was effective only at the highest concentration, which caused lowering of the basal blood flow to 78% of the control; the evoked increases in flow were not changed. Topical application of 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine (AMT), a specific inhibitor of the inducible NOS, at concentrations of 10(-4) - 10(-2) M lowered the basal flow to 89, 87.5 and 85%, respectively, but did not significantly change the evoked flow increases. Same concentrations of 7-nitroindazole monosodium salt (7-NINA), a specific inhibitor of the neuronal NOS, had no significant effects on basal flow and evoked increases in flow. 5. It is concluded that NO is involved in the maintenance of the basal level of dural arterial blood flow as well as in the electrically evoked flow increases, which have been shown to be mainly mediated by CGRP released from dural afferent fibres. The most important source of NO is probably the endothelium of dural arterial vessels. The synergistic effect of NO and CGRP on the stimulated blood flow may be in part due to a NO mediated facilitation of the CGRP release.

Somatostatin reduces the meningeal arterial blood flow in the rat

The effect of somatostatin (SOM) on neurogenic increases in meningeal blood flow was examined in barbiturate anaesthetized rats. The parietal skull was trepanized and the blood flow in the medial meningeal artery was monitored using a laser Doppler flowmeter with needle probes. Electrical stimulation (pulses of 8-10 V at 5-10 Hz for 30 s) close to the superior sagittal sinus evoked reproducible increases in blood flow. These increases were reduced by topical applications of SOM at concentrations of 10(-5)-10(-3) M in a dose-dependent manner. The effect was most pronounced within 10 min after application of SOM followed by a recovery of the flow responses. We conclude that stimulus-evoked increases in dural arterial flow, which are most likely caused by afferent activation and can be regarded as an element of neurogenic inflammation, are reduced by anti-inflammatory peptides such as SOM.

Presynaptic inhibition in the vertebrate spinal cord revisited

The present review examines the experimental evidence supporting the existence of central mechanisms able to modulate the synaptic effectiveness of sensory fibers ending in the spinal cord of vertebrates. The first section covers work on the mode of operation and the synaptic mechanisms of presynaptic inhibition, in particular of the presynaptic control involving axo-axonic synapses made by GABAergic interneurons with the terminal arborizations of the afferent fibers. This includes reviewing of the ionic mechanisms involved in the generation of primary afferent depolarization (PAD) by GABAergic synapses, the ultrastructural basis underlying the generation of PAD, the relationship between PAD and presynaptic inhibition, the conduction of action potentials in the terminal arborizations of the afferent fibers, and the modeling of the presynaptic inhibitory synapse. The second section of the review deals with the functional organization of presynaptic inhibition. This includes the segmental and descending presynaptic control of the synaptic effectiveness of group-I and group-II muscle afferents, the evidence dealing with the local character of PAD as well as the differential inhibition of PAD in selected collaterals of individual muscle-spindle afferents by cutaneous and descending inputs. This section also examines observations on the presynaptic modulation of large cutaneous afferents, including the modulation of the synaptic effectiveness of thin myelinated and unmyelinated cutaneous fibers and of visceral afferents, as well as the presynaptic control of the synaptic actions of interneurons and descending tract neurons. The third section deals with the changes in PAD occurring during sleep and fictive locomotion in higher vertebrates and with the changes of presynaptic inhibition in humans during the execution of a variety of voluntary movements. In the final section, we examine the non-synaptic presynaptic modulation of transmitter release, including the possibility that the intraspinal endings of primary afferents also release colocalized peptides in a similar way as in the periphery. The outcome of the studies presently reviewed is that intraspinal terminals of sensory fibers are not hard-wired conductors of the information generated in their peripheral sensory receptors, but dynamic systems that convey information that can be selectively addressed by central mechanisms to specific neuronal targets. This central control of information flow in peripheral afferents appears to play an important role in the generation of integrated movements and processing of sensory information, including nociceptive information.

Examination of colocalization of calcitonin gene-related peptide- and substance P-like immunoreactivity in the knee joint of the dog

It is generally assumed that the majority of substance P (SP)-containing afferents are also immunoreactive for calcitonin gene-related peptide (CGRP). In order to determine whether this is also the case in articular afferents where the contents of these peptides are low, we carried out a double labeling study using Fast Blue (FB) as a retrograde tracer injected into the center of the knee joint cavity of the dog together with immunohistochemistry for SP and CGRP. After 7-36 days of survival, dorsal root ganglia (DRGs, L4-S1) were removed. Labeled cells were found mainly (94%) in L5 - 6 DRGs, and SP- and CGRP-like immunoreactivity was found in about 17 and 29% of FB-labeled cells, respectively. The coexistence of SP and CGRP was observed in 10.4% of articular afferents and only 62.7% of SP-positive articular neurons contained CGRP, a much lower ratio than in other afferents of the dog such as testicular afferents. Our data suggest that these peptides are not always released together and that they do not always work together in the joint under normal conditions.

Positron emission tomography reveals changes in global and regional cerebral blood flow during noxious stimulation of normal and inflamed elbow joints in anesthetized cats

In cats the global (gCBF) as well as the regional cerebral blood flow (rCBF) and blood pressure were measured before, during, and after noxious inward and outward rotations of normal and inflamed elbow joints. The animals were anesthetized with halothane and immobilized by gallamine triethiodide. The gCBF as well as the rCBF were measured using positron emission tomography (PET) with a camera specifically designed for use in small animals. Slow intravenous bolus injections of 15O-labeled water were followed by 3-min acquisition of regional radioactivity starting at the time of injection. In all experiments the gCBF as well as the blood pressure were increased by noxious inward-outward rotations of the normal and of the inflamed joint, whereas the blood pressure and the rCBF remained unchanged during bolus injections under control conditions (without any joint movement). Movements of the inflamed joint evoked significantly greater increases in blood pressure and gCBF than corresponding ones of the normal joint. These increases in gCBF were paralleled by increases in rCBF along the complete anterior to posterior axis of the brain. Again, the increases in rCBF were larger, more extensive and more uniform following the stimulation of the inflamed joint relative to the results obtained with stimulation of the normal joint. No significant laterality was seen, but when an atlas-based region of interest (ROI) analysis was carried out and when the individual variations in rCBF were removed with two-way ANOVA, significant differences were disclosed in rCBF between the stimulated condition and the resting condition in a large number of brain regions. In particular, noxious rotation of the normal (right) elbow joint induced a significant increase in rCBF over the cerebral cortex and in the right thalamus and hippocampus. The same stimulation of the (left) inflamed joint induced a significant increase in rCBF throughout the brain; the biggest increase being over the right posterior cortex. It is concluded that under the conditions of the present experiments the generally accepted autoregulation of the cerebral blood flow is not fully functioning, and various factors that may be responsible for this failure (which obscures rCBF differences) are discussed. The more pronounced increases in rCBF when moving inflamed joints instead of normal ones is thought to be a direct consequence of the peripheral sensitization of the articular nociceptors and the consequent central hyperexcitability induced in the articular nociceptive pathways.

Calcitonin gene-related peptide- and substance P-like immunoreactive fibers in the spermatic nerve and testis of the dog

In order to determine if calcitonin gene-related peptide (CGRP) and substance P (SP) coexist in peripheral spermatic nerve fibers, we carried out a double-staining immunofluorescence study using confocal microscopy and fluorescence microscopy. CGRP- and SP-like immunoreactivity (LI) coexisted in the spermatic nerve trunk and in the single fibers running along the surface of the testis. The great majority of the SP-containing fibers also held CGRP-LI, although some fibers contained CGRP-LI without SP-LI. These observations are consistent with previous observations on testicular dorsal root ganglion neurons. Additionally, we carried out an immunogold silver staining for CGRP and found CGRP-containing nerve bundles, single nerve fibers and their nerve terminals. Some CGRP-containing nerve terminals were located very superficially in the tunica albuginea (<5 microm from the surface).

Quantification of cat's articular afferents containing calcitonin gene-related peptide or substance P innervating normal and acutely inflamed knee joints

In cats with an acute (32 h) unilateral knee joint inflammation the proportion of calcitonin gene-related peptide-(CGRP) and substance P-(SP) immunoreactive articular afferents, retrogradely labelled by Fast Blue (FB), were determined using immunohistochemistry. The proportion of neurons containing CGRP was significantly higher on the inflamed side (52%) than on the contralateral side (39%) and in controls (42%). However, the proportion of SP-immunoreactive articular perikarya on the inflamed side (26%) did not differ from the contralateral side (24%) and the control cats (22%). These data indicate that acute inflammation induces the synthesis of CGRP but not of SP in joint afferents.

Effects of the 5-HT1 receptor agonists, sumatriptan and CP 93,129, on dural arterial flow in the rat

The blood flow in and around the medial meningeal artery (dural arterial flow) was recorded in the exposed parietal dura mater encephali of the anesthetized rat using laser Doppler flowmetry. Local electrical stimulation of the dura mater (pulses of 0.5 ms delivered at 7.5-17.5 V and 5 or 10 Hz for 30 s) caused temporary increases in dural arterial flow. The effects of the 5-HT1 receptor agonists sumatriptan and CP 93,129 on the basal flow and the electrically evoked increases in flow were examined. Topical administration of undiluted sumatriptan (12 mg/ml) lowered the basal and the evoked flow by 20% on average. Systemic (i.v.) administration of sumatriptan (0.24, 0.72 and 3.6 mumol/kg) caused a short-lasting reduction of the evoked flow increases only at the higher doses while the basal flow was not significantly altered. Systemic administration of CP 93, 129 (0.46 and 4.6 mumol/kg) caused no significant changes of the basal and the evoked flow. At a dose of 23 mumol/kg CP 93,129 lowered the basal flow by 20% and the evoked flow by 30% for 20 min. The systemic arterial pressure was not significantly altered by sumatriptan and CP 93,129 within the whole range of doses. It is suggested that sumatriptan and CP 93,129 at high doses exert inhibitory effects on those fine afferent nerve fibers which release the calcitonin gene-related peptide, since this neuropeptide mediates the evoked increases in dural arterial flow.

Morphine microinjected into the nucleus tractus solitarius and rostral ventrolateral medullary nucleus enhances somatosympathetic A- and C- reflexes in anesthetized rats

The modulatory effects of morphine microinjected into localized areas of the brainstem on somatosympathetic A- and C-reflexes were examined in urethane-anesthetized rats. Somatosympathetic A- and C-reflexes were elicited in a branch of the inferior cardiac nerve by electrical stimulation of myelinated (A) and unmyelinated (C) afferent fibers in the tibial nerve. Morphine (0.002-0.2 microgram/50 nl) was microinjected into the rostral, intermediate and caudal parts of the nucleus tractus solitarius (NTS), the rostral ventrolateral medullary nucleus (RVLM), the caudal ventrolateral medullary nucleus (CVLM), the locus coeruleus (LC), the raphe magnus (RM), the periaqueductal gray (PAG), and the accumbens nucleus (Acb). Microinjections of morphine (0.2 microgram) into the intermediate and caudal NTS produced significant augmentations of the A- and C-reflexes, C-reflexes being more markedly enhanced than A-reflexes. Microinjection of morphine (0.2 microgram) into the RVLM produced a prominent increase in the C-reflex, the threshold dose for a significant increase being 0.02 microgram morphine. Microinjection of morphine up to 0.2 micrograms/50 nl into the other areas mentioned above had no significant effect on either reflex component. All opiate-induced increases of the reflex discharges could be reversed by intravenous application of naloxone (2 mg/ kg). The reflex augmentation induced by microinjection of morphine into the NTS may be caused by suppressing inhibitory baroreceptor information or by enhancing excitatory chemoreceptor information in the NTS. Augmentation of the C-reflex induced by microinjection of morphine into the RVLM may be caused by facilitating C-reflex pathways or by suppressing inhibitory neural circuits involved in the C-reflex within the RVLM.

Parallel organization of proprioceptive inputs from joint receptors to cortical somatosensory areas I and II in the cat

1. Studies in monkeys indicate that proprioceptive and tactile inputs are conveyed from the thalamus to the primary somatosensory cortex (SI) and thence to the secondary somatosensory area (SII) in a serial scheme. In contrast, in the cat, tactile information is conveyed in parallel from the thalamus to SI and SII. The present study, in the cat, employed reversible inactivation of SI to determine whether proprioceptive inputs to SII from joint receptors depend on an indirect serial path via SI or are conveyed over a direct path from the thalamus. 2. SI and SII foci for knee joint inputs were determined with evoked potential mapping. Reversible inactivation of the SI focus by cooling had no effect on the amplitude, latency or time course of SII potentials evoked by joint inputs. There was also no consistent effect on the response levels of individual SII neurones examined during SI inactivation. Furthermore, there was no attenuation of the later components of the responses, and therefore no evidence that these depended on an indirect path to SII via SI. 3. Results demonstrate that proprioceptive inputs project directly from thalamus to SII over a pathway organized in parallel with that to SI, in contrast to the serial scheme reported for proprioceptive processing in primates.

A new combination of methods for the localization, identification, and three-dimensional reconstruction of the sensory endings of articular afferents characterized by electrophysiology

A combination of methods is described to identify and reconstruct corpuscular and non-corpuscular sensory endings of group II and group III nerve fibers following functional examination by electrophysiology. Afferent units activated by electrical stimulation of the medial articular nerve of the cat's knee were analyzed by single fiber recordings and characterized by their responsiveness to mechanical stimuli. The receptive fields of the units were closely demarcated by fine needles when the responses elicited by insertion of the needles were being recorded. After fixation, the tissue around the demarcated field was dissected and histologically processed. Series of semithin sections were cut from the embedded tissue blocks containing the receptive fields. Corpuscular endings of group II fibers and peripheral myelinated group III nerve fibers, presumably corresponding to the characterized units, were identified by light microscopy of semithin sections and localized within the demarcated area. Non-corpuscular endings were identified by electron microscopy of ultrathin sections cut in alternation with, or after re-embedding of, semithin sections. Morphometric analysis of ultrathin section series allowed the measurement of parameters such as the mean axon diameter and the organelle content of the sensory endings. The methods described are appropriate for collecting data that correlate the structural and functional characteristics of sensory endings in deep tissues.

Calcitonin gene related peptide released from dural nerve fibers mediates increase of meningeal blood flow in the rat

The parietal dura mater encephali of the rat was shown by immunohistochemistry to be densely innervated by calcitonin gene related peptide (CGRP) immunoreactive nerve fibers spreading around the medial meningeal artery and its branches. Electrical stimulation of the dural surface (10-20 V, 5-10 Hz, 10-30 min) caused a depletion of CGRP-immunopositive fibers, suggesting a release of CGRP. The dural blood flow around branches of the medial meningeal artery was also monitored with a laser Doppler flowmeter. Short periods (30 s) of electrical stimulation with parameters that presumably released CGRP form nerve fibers caused a repeatable and constant increase of the blood flow for 1-2 min. This evoked increase could dose dependently be inhibited by topical application of the CGRP antagonist hCGRP8-37. Accordingly, administration of hCGRP increased the basal blood flow. We conclude that stimulation of trigeminal afferents innervating the dura mater releases CGRP from peptidergic afferent terminals, thereby causing vasodilatation and increasing the meningeal blood flow, an important element of neurogenic inflammation.

Modulation of somatocardiac sympathetic reflexes mediated by opioid receptors at the spinal and brainstem level

Modulation of somatosympathetic reflexes at the spinal cord and the brainstem was studied by administering opioid receptor agonists into the intrathecal space of the lumbar spinal cord and into the subarachnoid space of the cisterna magna in rats anesthetized with alpha-chloralose and urethane. Somatocardiac sympathetic A- and C-reflexes were elicited by electrical stimulation of myelinated (A) and unmyelinated (C) afferent fibers of the tibial nerve, respectively. Intrathecal administration of the mu-opioid receptor agonist DAMGO selectively depressed the C-reflex in a dose-dependent manner (minimum effective dose 10 ng), whereas the intrathecal injection of the delta-opioid receptor agonist DPDPE and the kappa-opioid receptor agonist U-50,488H only at doses of 10 micrograms and 100 micrograms, respectively, led to a significant depression of the C-reflex. Injection of DAMGO into the cisterna magna enhanced both A- and C-reflexes in a dose-dependent manner (minimum effective dose 1 ng). The administration of neither DPDPE nor U-50,488H into the cisterna magna affected A- or C-reflexes. It is concluded that the activation of mu-opioid receptors is mainly or exclusively responsible for suppressing somatosympathetic C-reflexes at the spinal cord and for enhancing them at the brainstem.

Somatostatin-like immunoreactivity in primary afferents of the medial articular nerve and colocalization with substance P in the cat

The proportion of somatostatin-containing dorsal root ganglion cells innervating the knee joint of the cat via the medial articular nerve was determined by using retrograde labeling with fast blue and immunohistochemistry. Immunoreactivity was found in 8.6% of labeled cell bodies. In colchicine-treated ganglia, the proportion increased to 16.8%. Only small and intermediate-sized perikarya showed somatostatin-like immunoreactivity, indicating that this neuropeptide is synthesized predominantly in primary afferent units with unmyelinated sensory axons but may also be present in primary afferents with thinly myelinated sensory fibers. Colchicine treatment had no influence on the cell size distribution. Colocalization of somatostatin with substance P was determined by comparing the proportions of immunopositive dorsal root ganglion cells after incubation with antibodies against substance P or somatostatin or with a mixture of both. Substance P-like immunoreactivity was found in 18.1% (untreated ganglia) and 19.6% (colchicine treated ganglia) of the labeled neurons. After incubation with a mixed antibody solution, 18.2% of joint afferents in untreated and 19.9% of the cells in colchicine-treated ganglia were immunopositive. Comparing this result with the results obtained using somatostatin and substance P antibodies alone, one can calculate that both neuropeptides are colocalized in about 17% of the cat's knee joint afferents. About 3% of the neurons contain only substance P, whereas almost none of the neurons contain only somatostatin. Based on this fact, one can assume that both neuropeptides are coreleased in peripheral tissue as well as in the central nervous system.

Increase of meningeal blood flow after electrical stimulation of rat dura mater encephali: mediation by calcitonin gene-related peptide

1. The dura mater encephali of the rat was exposed and the blood flow around branches of the medial meningeal artery was monitored with a laser Doppler flowmeter. Changes in the meningeal blood flow (MBF) following electrical stimulation of the dura mater at a parasagittal site were registered. The effects of human calcitonin gene-related peptide (h-alpha CGRP) and the CGRP antagonist (h-alpha CGRP8-37) on the MBF were tested. 2. Electrical stimulation with rectangular pulses of 0.5 ms, 10-20 V, 5-10 Hz and a duration of 30 s caused an increase of the MBF in 14 out of 16 rats tested. The increases were dependent on stimulus strength and frequency. 3. The increase in MBF was inhibited in a dose-dependent manner by topical application of 0.1 ml of h-alpha CGRP8-37 at concentrations of 10(-7) - 10(-5) M. The highest dose abolished the increase in MBF. 4. Topical administration of 0.1 ml of h-alpha CGRP at a concentration of 10(-4) M increased the basal MBF by 15% on average. 5. It is suggested that the increase in MBF following electrical stimulation of the dura mater is mediated by the release of CGRP. The contribution of the dural afferent and sympathetic and parasympathetic efferent nerve fibres to this response are discussed.