Role of the amygdaloid cholecystokinin (CCK)/gastrin-2 receptors and terminal networks in the modulation of anxiety in the rat. Effects of CCK-4 and CCK-8S on anxiety-like behaviour and [3H]GABA release.

The amygdala plays a key role in fear and anxiety. The intercalated islands are clusters of glutamate-responsive GABAergic neurons rich in cholecystokinin (CCK)-2 receptors which control the trafficking of nerve impulses from the cerebral cortex to the central nucleus of amygdala. In this study, the nature of the CCK-glutamate-GABA interactions within the rat rostral amygdala, and their relevance for anxiety, were studied. CCK/gastrin-like immunoreactive nerve terminals were found to be mainly restricted to the paracapsular intercalated islands and the rostrolateral part of the main intercalated island. Behaviourally, the bilateral microinjection of CCK-4 (0.043-4.3 pmol/side) or CCK-8S (4.3 pmol/side) into the rostrolateral amygdala reduced the open-arm exploration in the elevated plus-maze without affecting locomotion. In contrast, neither CCK-4 nor CCK-8S (0.043-4.3 pmol/side) had any effects in the shock-probe burying test as compared with their saline-treated controls. Biochemically, CCK-4 (0.3 and 1.5 microm), unlike CCK-8S, enhanced significantly the K(+)-stimulated release of [(3)H]GABA from amygdala slices. These effects were fully prevented by prior superfusion of the slices with either the selective CCK-2 receptor antagonist CR2945 (3 microm), or 6,7-dinitroquinoxaline-2,3(1H,4H)-dione (DNQX), 10 microm, a glutamatergic (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/kainate receptor antagonist. It is suggested that CCK modulates glutamate-GABA mechanisms by acting on CCK-2 receptors via volume transmission occurring at the level of the basolateral amygdaloid nucleus and/or by synaptic or perisynaptic volume transmission in the region of the rostrolateral main and paracapsular intercalated islands, resulting in subsequent disinhibition of the central amygdaloid nucleus and anxiety or panic-like behaviour.

The nerve supply of the lumbar intervertebral disc.

The anatomical studies, basic to our understanding of lumbar spine innervation through the sinu-vertebral nerves, are reviewed. Research in the 1980s suggested that pain sensation was conducted in part via the sympathetic system. These sensory pathways have now been clarified using sophisticated experimental and histochemical techniques confirming a dual pattern. One route enters the adjacent dorsal root segmentally, whereas the other supply is non-segmental ascending through the paravertebral sympathetic chain with re-entry through the thoracolumbar white rami communicantes. Sensory nerve endings in the degenerative lumbar disc penetrate deep into the disrupted nucleus pulposus, insensitive in the normal lumbar spine. Complex as well as free nerve endings would appear to contribute to pain transmission. The nature and mechanism of discogenic pain is still speculative but there is growing evidence to support a 'visceral pain' hypothesis, unique in the muscloskeletal system. This mechanism is open to 'peripheral sensitisation' and possibly 'central sensitisation' as a potential cause of chronic back pain.

Relationship between plasma norepinephrine at peak exercise and 123I-MIBG imaging of the heart and lower limbs in heart failure.

BACKGROUND: Past studies suggested that plasma norepinephrine during exercise originates in sympathetic nerve endings and that the main origin differs among pathophysiological conditions. AIMS: This study investigated the most important site of sympathetic terminals as an origin of plasma norepinephrine during exercise in patients with heart failure using (123)I- metaiodobenzylguanidine (MIBG) scintigraphy. METHODS AND RESULTS: Twenty patients with organic heart disease underwent exercise testing and (123)I-MIBG scintigraphy. Systemic (123)I-MIBG uptake was measured 4 hours after (123)I-MIBG injection, and the heart-to-brain (H/B) and lower limb-to-brain ratios (L/B) were calculated. Plasma norepinephrine concentration was measured at rest and at peak exercise. Subjects were divided into two groups: those with preserved left ventricular ejection fraction (LVEF> or =45%, n=8) and those with reduced LVEF (<45%, n=12). Plasma norepinephrine at rest did not correlate with H/B or L/B. In the preserved LVEF group, plasma norepinephrine at peak exercise was correlated with H/B (r=0.722), but not with L/B. In the reduced LVEF group, the norepinephrine response to peak exercise correlated with L/B (r=0.642), but not with H/B. CONCLUSION: The present findings suggest that norepinephrine concentration is regulated by sympathetic terminal function of working muscles in patients with impaired LVEF and by that of the heart in patients with preserved LVEF.

Motor nerve ending disorder in myasthenia gravis.

Mild myasthenia gravis patients were compared with normals with respect to the capacity of their motor nerve endings (MNEs) to generate a neostigmine-induced postactivation repetition (PAR). Dose-response analyses of PAR recorded from muscle electrically and by contractile measurement disclose a loss of this pharmacologic responsiveness in myasthenia. Since mild myasthenics transmitted nerve impulse trains of 20 to 200 Hz, as did normals, it was evident that PAR is transmitted insofar as it can be generated by MNEs. The dose-response analyses support this. These data indicate an MNE disorder in the disease.

Neonatal inflammation and primary afferent terminal plasticity in the rat dorsal horn.

Abnormal or excessive activity related to pain and injury in early life may alter normal synaptic development and lead to changes in somatosensory processing. The aim of the current study was to define the critical factors that determine long-term plasticity in spinal cord afferent terminals following neonatal inflammation. Hindpaw inflammation was produced in neonatal rat pups with 5 or 25 microl 2% carrageenan, and 5 or 25 microl complete Freund's adjuvant (CFA). All groups displayed a clear inflammatory response that recovered in 2 weeks in all but the 25 microl CFA group, who had persistent chronic inflammation confirmed by histological examination of the paw at 8 weeks. The 25 microl CFA group was also the only group that displayed a significant expansion of the sciatic and saphenous nerve terminal field in lamina II of the dorsal horn at 8 weeks, using wheat-germ agglutinin-horse radish peroxidase transganglionic labelling. This effect was not accompanied by changes in dorsal root ganglion (DRG) cell number, expression of activating transcription factor 3 (ATF3), or alterations in calcitonin gene related peptide (CGRP) or isolectin B4 binding; and was not mimicked by partial nerve damage. No long-term change in mechanical or thermal behavioural sensory thresholds was seen in any group. Lower dose CFA caused an acute, reversible expansion of terminal fields in lamina II in neonatal animals, while CFA did not produce this effect in adults. The duration and effect of neonatal inflammation is therefore dependent on the type and volume of inflammatory agent used. The expansion of afferent terminals in lamina II following neonatal CFA inflammation is maintained into adulthood if the inflammation is also maintained, as seen following 25 microl CFA. This effect is not seen in adult animals, emphasising the plasticity of the nervous system early in development.

Peripheral CGRP release as a marker for neurogenic inflammation: a model system for the study of neuropeptide secretion in rat paw skin.

The local release of pro-inflammatory neuropeptides in the periphery has been associated with the development of neurogenic inflammation. However, there is an increasing number of reports demonstrating tissue-dependent differences regarding the mechanisms engaged by these neuropeptides to initiate and maintain the inflammatory response in the target tissue. Since skin is often involved in tissue injury, the present studies were designed to develop a model for assessing cutaneous peptide secretion as a marker for neurogenic inflammation in skin tissue. Calcitonin gene-related peptide (CGRP), as one of several neuropeptides known to be involved in neurogenic inflammation, was chosen to study capsaicin-induced effects on peripheral neurosecretion. The corial surface of the hairy skin of a rat hindlimb was superfused in vitro, and the basal and capsaicin-evoked peripheral release of immunoreactive CGRP (iCGRP) was measured using a radioimmunoassay. The main objectives of these studies were to characterize the various properties of this release including dose-dependency, exocytosis and receptor-mediation as well as the effects of acute and long-term capsaicin desensitization. Capsaicin significantly and dose-dependently increased the release of iCGRP at concentrations ranging from 3 to 300 microM. Omission of calcium ions or treatment with the competitive capsaicin receptor antagonist capsazepine completely inhibited the capsaicin-induced iCGRP release. Superfusion of the skin with 100 microM capsaicin following a conditioning stimulation with capsaicin at concentrations ranging from 0.3 to 100 microM led to an acute, dose-dependent desensitization of the CGRP response. In addition, chronic desensitization following the neonatal injection of capsaicin completely abolished the acute iCGRP response to capsaicin. The method described here should prove to be a valuable tool for the evaluation of the processes regulating the peripheral, cutaneous release of pro-inflammatory neuropeptides. This strategy, therefore, may lead to a better understanding of the mechanisms involved in the development and maintenance of neurogenic inflammation, particularly in the skin.

Cardiac positron emission tomography imaging with [11C]hydroxyephedrine, a specific tracer for sympathetic nerve endings, and its functional correlates in congestive heart failure.

The integrative mechanisms of autonomic dysfunction in congestive heart failure (CHF) remain poorly understood. We sought to study cardiac retention of [11C]hydroxyephedrine (HED), a specific tracer for sympathetic presynaptic innervation, and its functional correlates in CHF. Thirty patients with mild to moderate heart failure underwent resting cardiac HED positron emission tomography imaging, spectrum analysis testing of systolic pressure and heart rate variability in the resting supine and 70 degrees head-up tilt positions, and testing of baroreflex sensitivity. Compared with control subjects, global myocardial HED retention index was reduced by 30% (p <0.01) in patients with CHF. The HED retention index did not correlate significantly with heart rate variability. However, it correlated with baroreflex sensitivity at rest (r = 0.43, p = 0.05) and with systolic pressure low-frequency (0.03 to 0.15 Hz) variability at head-up tilt (r = 0.76, p <0.01), as well as with low-frequency systolic pressure variability response from baseline to tilt (r = 0.75, p <0.01). We conclude that cardiac HED retention is reduced in patients with CHF. This correlates with blunted vascular sympathetic effector responses during posture-induced reflex activation and baroreflex control of heart rate, suggesting an interdependence between cardiac presynaptic innervation abnormalities and neural mechanisms important to blood pressure maintenance in CHF.

Effects of moderate hypothermia on in situ cardiac sympathetic nerve endings.

Although hypothermia is known to alter neuronal control of circulation, it has been uncertain whether clinically used hypothermia (moderate hypothermia) affects in situ cardiac sympathetic nerve endings. We examined the effects of moderate hypothermia on cardiac sympathetic nerve ending function in anesthetized cats. By use of a cardiac dialysis technique, we implanted dialysis probes in the midwall of the left ventricle and monitored dialysate norepinephrine (NE) levels as an index of NE output from cardiac sympathetic nerve endings. Hypothermia (27.0+/-0.5 degrees C) induced decreases in dialysate NE levels. Dialysate NE levels did not return to the control level at normothermia after rewarming. Dialysate NE response to inferior vena cava occlusion was attenuated at hypothermia but restored at normothermia after rewarming. Dialysate NE response to high K(+) (100 mM) was attenuated at hypothermia and was not restored at normothermia after rewarming. Hypothermia induced increases in dialysate dihydroxyphenylglycol (DHPG) levels. There were no differences in desipramine (neuronal NE uptake blocker, 10 microM) induced increment in dialysate NE level among control, hypothermia, and normothermia after rewarming. However, hypothermia induced an increase in DHPG/NE ratio. These data suggest that hypothermia impairs vesicle NE mobilization rather than membrane NE uptake. We conclude that moderate hypothermia suppresses exocytotic NE release via central mediated reflex and regional depolarization.

Functional immunohistochemistry of neuropeptides and nitric oxide synthase in the nerve fibers of the supratentorial dura mater in an experimental migraine model.

The supratentorial cerebral dura of the albino rat is equipped with a rich sensory innervation both in the connective tissue and around blood vessels, which includes nociceptive axons and their terminals; these display intense calcitonin gene-related peptide (CGRP) immunoreactivity. Stereotactic electrical stimulation of the trigeminal (Gasserian) ganglion, regarded as an experimental migraine model, caused marked increase and disintegration of club-like perivascular CGRP-immunopositive nerve endings in the dura mater and induced an apparent increase in the lengths of CGRP-immunoreactive axons. Intravenous administration of sumatriptan or eletriptan, prior to electrical stimulation, prevented disintegration of perivascular terminals and induced accumulation of CGRP in terminal and preterminal portions of peripheral sensory axons. Consequently, immunopositive terminals and varicosities increased in size; accumulation of axoplasmic organelles resulted in the "hollow" appearence of numerous varicosities. Since triptans exert their anti-migraine effect by virtue of agonist action on 5-HT(1D/B) receptors, we suggest that these drugs prevent the release of CGRP from perivascular nerve terminals in the dura mater by an action at 5-HT(1D/B) receptors. Nitroglycerine (NitroPOHL), given subcutaneously to rats, induces increased beading of nitric oxide synthase (NOS)-immunoreactive nerve fibers in the supratentorial cerebral dura mater, and an apparent increase in the number of NOS-immunoreactive nerve fibers in the dural areas supplied by the anterior and middle meningeal arteries, and the sinus sagittalis superior. Structural alterations of nitroxidergic axons innervating blood vessels of the dura mater support the idea that nitric oxide (NO) is involved in the induction of headache, a well-known side effect of coronary dilator agents.

Enhanced neural regeneration from transected vagus nerve terminal in diabetic mice in vitro.

This study examined the effect of diabetes on neural regeneration in vitro. Nodose ganglia (NG) with vagal nerve fibers, dissected from streptozotocin-induced diabetic and normal C57BL/6J mice were embedded in collagen gel. After 3 and 7 days in culture, the numbers of regenerating neurites from transected nerve terminals of NG in diabetic mice were significantly greater than those in controls. Although many studies have revealed diabetes-associated impairment in neural regeneration, the results in the present study suggest that experimental diabetes could induce the potential to enhance regenerative capability of vagal sensory nerves after axotomy.

Centrifugal activity in afferent C-fibers influences the spontaneous afferent barrage generated in nerve-end neuromas.

We have investigated the effect of a prolonged, low-frequency impulse barrage on the spontaneous afferent discharge that originates in experimental nerve-end neuromas in the rat sciatic nerve. Centrifugal activity in afferent A-fibers did not affect electrogenesis in the neuroma. When C-fibers were recruited, however, over half of the axons tested were either suppressed or excited. We suggest that these effects resulted from the stimulation-evoked release of neuroactive peptides or related substances from the cut ends of afferent C-fibers.

Neuroprotection of mild hypothermia: differential effects.

To estimate whether mild hypothermia during repetitive hypoxia provides a neuroprotective effect on brain tissue, hippocampal slice preparations were subjected to repetitive hypoxic episodes under different temperature conditions. Slices of guinea pig hippocampus (n=40) were placed at the interface of artificial cerebrospinal fluid (aCSF) and gas (normoxia: 95% O2, 5% CO2; hypoxia: 95% N2, 5% CO2). Evoked potentials (EP) and direct current (DC) potentials were recorded from hippocampal CA1 region. Slices were subjected to two repetitive hypoxic episodes under the following temperature conditions: (A) 34 degrees C/34 degrees C, (B) 30 degrees C/30 degrees C and (C) 34 degrees C/30 degrees C. Hypoxic phases lasted until an anoxic terminal negativity (ATN) occurred. The recovery after first hypoxia lasted 30 min. Tissue function was assessed regarding the latency of ATN and the recovery of evoked potentials. The ATN latencies with protocol A (n = 25) for the first and second hypoxia were 5.9+/-1.3 min (mean+/-S.E.M., 1st hypoxia) and 2.4+/-0.9 min (2nd hypoxia), with protocol B the latencies (n = 7) were significantly longer: 25.2+/-7.1 min and 15.6+/-7.7 min. With protocol C (n=8), the latencies were 5.6+/-1.8 and 3.3+/-0.5 min. No differences were seen in the recovery of the EPs with protocols A-C. Our results suggest that a mild hypothermia is only neuroprotective if applied from an initial hypoxia onwards.

Neuropathic pain behavior in rats depends on the afferent input from nerve-end neuroma including histamine-sensitive C-fibers.

Sciatic and saphenous neurectomy in rats produces nerve-end neuromas, known to be a source of afferent input. Concurrently rats self-injure the denervated hindpaw ('autotomy'), a behavior related to neuropathic pain in humans. Here we show that surgical resection of the neuromas in various groups of rats, each at a different postoperative time (days 22, 33, 48) suppress autotomy. This recalls the pain relief in humans following resection of painful neuromas. We also show that daily injections of astemizole, a peripheral anti-histamine which blocks histamine H1-receptors, suppress autotomy. Since mostly C-fibers in rat neuroma are sensitive to histamine, these results corroborate the suggestion that autotomy is driven by afferent neuroma input, mainly in histamine-sensitive C-fibers.

Sensory innervation of soft tissues of the lumbar spine in the rat.

The purpose of this study was to investigate neurophysiologically and anatomically the soft tissues of the dorsal compartment of the lumbar spine in order to understand better their possible role in low back pain. The focus was primarily on the lumbar facet joint and supraspinous ligament of the Sprague-Dawley rat. Microdissection of the dorsal ramus and electrophysiological and neuroanatomical studies of the dorsal ramus and its terminations in paravertebral tissue revealed that (a) there are mechanosensitive, slowly adapting fibers in the rat lumbar facet joint capsule; (b) there are slowly adapting, mechanosensitive units in the rat supraspinous ligaments that respond to tensile loading; both types of mechanosensitive units have high threshold; (c) mechanical stimulation of these tissues sometimes elicits afterdischarges lasting several minutes; (d) many extracellular recordings from the medial branch of the dorsal ramus appear to be reflex activity to mechanical stimulation; (e) silver impregnation of the rat joint capsule reveals individual axons, very few of which were encapsulated, suggesting that they terminate in free nerve endings; and (f) the nerves of the rat facet joint capsule contain 68, 160, and 200 kdalton polypeptide subunits of neurofilament protein (NFP). These results indicate that neurons of lumbar facet joint capsules and ligaments in the back are sensitive to mechanical strain and that the higher threshold neurons may serve a nociceptive (pain) function.

Neural mechanisms of lumbar pain.

This article discusses neuroanatomic and neurophysiologic bases for low back pain. Evidence for the existence of pain generators in facet, disc, muscle, nerve roots, and dorsal root ganglia are discussed. Mechanisms that may explain the persistence of pain, including neurogenic and non-neurogenic inflammation and central sensitization, are also presented.

Evaluation of somatosensory pathway by short latency evoked potentials in patients with end-stage renal disease maintained on hemodialysis.

Somatosensory evoked potentials and peripheral nerve conduction velocity were studied on 10 patients with end-stage renal failure maintained on hemodialysis treatment. None of the patients had symptomatic neuropathy and the only abnormal finding on neurological examination was absent ankle jerk in 7 of the 10 patients. Nerve conduction velocities and intercomponent conduction times of the somatosensory evoked potential were determined using electrical stimulation of nerve trunks and mechanical stimulation of the finger. Nerve ending conduction times was determined using a combination of the two stimuli and found to be abnormal in 8 patients. All 10 patients had slowed sensory conduction velocities at some segment of the tested peripheral nerve. Intercomponent time differences in the somatosensory evoked potentials could not be defined in the majority of our patients due to the absence of many of the components, making it impossible to distinguish whether the changes in somatosensory evoked potentials were due to impaired peripheral input, or to changes in the somatosensory pathway.

The painful consequences of peripheral injury.

Peripheral damage is immediately assessed by the central nervous system by way of a gate control system so that the sensory outcome depends not only on the fact of the injury and the injury signals but also on other convergent impulses from the periphery and on descending controls from brain to spinal cord. However peripheral injury, particularly when nerves are affected, sets off a chain of slow reactions which start in the area of damage but spread centrally. There are the local inflammatory reactions which change the sensitivity of nerves or of sprouts growing from cut nerves. There are changes which move over the entire length of the damaged axon changing the dorsal root ganglia and the terminals of afferents within the spinal cord. The arrival of injury produced impulses in the spinal cord triggers changes with a latency of many minutes which persist for hours even if no further impulses arrive. These increases of excitability and expansion of receptive fields which are triggered by C fibres may be the basis of the secondary hyperalgesias and reflex changes associated with injury.

Treatment of end-neuromas, neuromas-in-continuity and scarred nerves of the digits by proximal relocation.

This paper reports the results of treatment by proximal relocation of 104 painful nerves in 57 digits in 48 patients. These included 86 digital nerves and 18 terminal branches of the superficial radial nerve and the dorsal branch of the ulnar nerve. Eighty-three were end-neuromas and 14 were neuromas-in-continuity, of which nine followed nerve repair and five occurred following a closed crush injury. Seven were painful as a result of tethering in scarred tissue. Eighty nerves (77%) required a single relocation and 24 (23%) required more than one operation. Ninety-eight per cent of nerve relocations achieved complete pain relief at the primary site. One patient had mild pain on pressure at the primary site after relocation of two nerves from this site. Over 90% of the nerves had no spontaneous pain, pain on movement or hypersensitivity of the overlying skin at the final site of relocation. However, the incidence of mild or no pain on direct pressure at the site of nerve relocation was lower at 83% as relocated nerves, although traumatized less often at the sites chosen for relocation, can still be painful on direct pressure.

Psychological, physiological, and pharmacological management of pain.

It has been the intent of the authors to impress upon the clinician the multifaceted nature of the human pain experience. We have sought to create an understanding of the emotional nature of pain. The treatment of pain as a pure sensation without directing attention to its behavioral and psychological aspects will generally lead to failure in understanding and ultimately in treating this ubiquitous problem in our profession. The use of drugs alone will have only a minor effect on the treatment of pain. Knowledge of environmental control and an understanding and empathetic approach to the patient in pain or in stress will carry the dentist a long way toward his goal of dental treatment without pain or emotional upset.

Capsaicin treatment inhibits osteopenia and heat hyperalgesia induced by chronic constriction injury to the sciatic nerve in rats.

Chronic constriction injury (CCI) to the rat sciatic nerve results in osteopenia in the affected hind limb. One possible mechanism for this osteopenia is neurogenic inflammation, in which neuropeptides, represented by substance P (SP), are involved. We attempted to determine whether capsaicin treatment, which can deplete SP from nerve terminals, is effective in inhibiting osteopenia induced by CCI. Capsaicin (total dose, 125 mg/kg) or the vehicle alone was given intraperitoneally to adult rats 2 days before (Experiment 1) and 7 days after (Experiment 2) CCI surgery. Paw withdrawal latency (PWL) was measured prior to and every week for 5 weeks after surgery. Bone mineral density (BMD) and the number of osteoclasts in tibial bones were determined 5 weeks after surgery. In rats treated with the vehicle, BMD on the CCI side was decreased significantly, while the number of osteoclasts was significantly increased in both experiments. Capsaicin treatment either before or 1 week after surgery inhibited the decreases in BMD as well as the increase in the number of osteoclasts on the CCI side. PWL for the CCI side in the vehicle group was significantly shorter than for the sham side in both experiments. However, capsaicin treatment before surgery resolved heat hyperalgesia in Experiment 1, while in Experiment 2, even though heat hyperalgesia developed on the CCI side, it was resolved by capsaicin treatment. The results of the present study show that capsaicin inhibits the development of osteopenia as well as heat hyperalgesia induced by CCI. They also support our hypothesis that neurogenic SP release is involved in the pathogenesis of bony changes induced by CCI.