Persistent block of CA1 synaptic function by prolonged hypoxia

The effects of prolonged hypoxia were studied by field and intracellular recordings from hippocampal slices of the rat, kept submerged at 34 degrees C. When artificial cerebrospinal fluid contained 10 mM glucose, even very long exposures to hypoxia or 300 microM cyanide (21-25 min) did not block field excitatory postsynaptic potentials and population spikes irreversibly. By contrast, in the presence of 4 mM glucose, hypoxia lasting only 9-13 min-ending 2-3 min after the characteristic transient recovery ("hypoxic injury potential")-resulted in irreversible block of synaptic responses. Voltage-dependent sodium channels and N-methyl-D-aspartate receptors are involved, because irreversible block was prevented by tetrodotoxin (0.5 microM), kynurenate (2 mM) or DL-aminophosphonovalerate (50 microM), whereas 6,7-dinitroquinoxaline-2,3-dione (25 microM) suppressed only the transient recovery. The hypoxic suppression of afferent volleys in slices kept in 4 mM glucose was also prevented by kynurenate or aminophosphonovalerate. Intracellular recordings revealed opposite effects of hypoxia according to glucose concentration: in 10 mM glucose, mainly hyperpolarization; in 4 mM glucose, after a brief hyperpolarization, a major and usually irreversible depolarization. In the presence of kynurenate or tetrodotoxin, major depolarizations also occurred, but they were reversible. Thus, large depolarizations of hippocampal neurons do not necessarily lead to irreversible block of synaptic transmission: there is lasting damage only when hypoxia is combined with low glucose, presumably because a reduced supply of glycolytically generated ATP limits the Na+/K+ pump's ability to maintain or restore membrane potentials and thus prevent excessive activation of N-methyl-D-aspartate receptors.

Influence of visual and proprioceptive afferences on upper limb ataxia in patients with multiple sclerosis

Our objective was to investigate how cooling of the arm and vision influence pointing movements in healthy subjects and patients with cerebellar limb ataxia due to clinically proven multiple sclerosis. An infrared video motion analysis system was used to record the unrestricted, horizontal pointing movements toward a target under three different conditions involving a moving, stationary, or imaginary target; a visual, or acoustic trigger; and vision or memory guidance. All three tasks were performed before and after cooling the arm in ice water. Patients had more hypermetric and slower pointing movements than controls under all tested conditions. Patients also had significantly larger three-dimensional finger sway paths during the postural phase and larger movement angles of the wrist joint. Memory-guided movements were the most hypermetric recorded in both groups. Cooling of the limb had no effect on amplitude or peak velocity of the pointing movement in either group under all tested conditions, but significantly reduced the three-dimensional finger sway path during the postural phase in patients with limb ataxia. Cooling-induced reduction of the finger sway was largest in those patients with the largest finger sway before cooling. In conclusion, the cooling-induced reduction of the proprioceptive afferent inflow, most probably of group I spindle afferents, reduces postural tremor of patients with cerebellar dysfunction.

Reduced NO enhances the central gain of cardiac sympathetic afferent reflex in dogs with heart failure

The aim of the present study was to test the hypothesis that a decrease in central nitric oxide (NO) is involved in the enhancement of the central gain of the cardiac "sympathetic afferent" reflex (CSAR) in dogs with congestive heart failure (CHF). Thirteen dogs with pacing-induced CHF and sixteen sham dogs were anesthetized with alpha-chloralose and were baroreceptor denervated and vagotomized. The CSAR was evoked by stimulation of the left ventral ansa. A lateral cerebroventricular cannula was inserted to deliver sodium nitroprusside (SNP) and NG-nitro-L-arginine methyl ester (L-NAME). Arterial pressure, heart rate, and renal sympathetic nerve activity (RSNA) were recorded at baseline and during elicitation of the CSAR. We found that 1) the responses of RSNA to stimulation were augmented in dogs with CHF, 2) SNP depressed the increase in RSNA induced by the CSAR in CHF dogs but had no effect in sham dogs, and 3) L-NAME potentiated the CSAR-induced increase in RSNA in sham dogs but not in dogs with CHF. We conclude that reduced central NO is involved in the enhanced central gain of the CSAR in CHF dogs.

The sensory trigeminal system in birds: input, organization and effects of peripheral damage. A review

The primary sensory trigeminal system in birds comprises the mesencephalic trigeminal nucleus and the trigeminal ganglion with projections to the principal sensory nucleus (PrV) and the descending tract with its subnuclei. Other cranial nerves can contribute to PrV and the descending system that together form the somatosensory system of the head. There is also a proprioceptive component. The somatosensory system comprises a component serving tactile sense and a nociceptive component. The former processes information from many mechanoreceptors in beak and tongue; both PrV and subnuclei of the descending system are involved. The nociceptive component consists of small ganglion cells projecting presumably to layers I and II of the caudal subnucleus of the descending trigeminal system and cervical dorsal horn; this is the only trigeminal region showing immunoreactivity for substance P. The effects of amputation of the tips of the beak of chickens (debeaking) are estimated by fiber counts in electron microscopic preparations of the trigeminal branches innervating that area, and by cell counts in Nissl stained sections of the trigeminal ganglion. Our data indicate that debeaking causes a loss of exteroceptive units, but not of nociceptive units. Comparison of sections stained for the presence of substance P (immunohistochemistry) did not reveal a long-term effect on the nociceptive system suggestive of the occurrence of chronic pain.

[Local ice application in therapy of kinetic limb ataxia. Clinical assessment of positive treatment effects in patients with multiple sclerosis]

Upper limb ataxia is one of the most disabling symptoms of patients with multiple sclerosis (MS). There are some clinically tested therapeutic strategies, especially with regard to cerebellar tremor. But most of the methods used for treatment of limb ataxia in physiotherapy and occupational therapy are not systematically evaluated, e.g. the effect of local ice applications, as reported by MS patients and therapists, respectively. We investigated 21 MS patients before and in several steps 1 up to 45 min after cooling the most affected forearm. We used a series of 6 tests, including parts of neurological status and activities of daily living as well. At each step skin temperature and nerve conduction velocity were recorded. All tests were documented by video for later offline analysis. Standardized evaluation was done by the investigators and separately by an independent second team, both of them using numeric scales for quality of performance. After local cooling all patients showed a positive effect, especially a reduction of intentional tremor. In most cases this effect lasted 45 min, in some patients even longer. We presume that a decrease in the proprioceptive afferent inflow-induced by cooling-may be the probable cause of this reduction of cerebellar tremor. Patients can use ice applications as a method of treating themselves when a short-time reduction of intention tremor is required, e.g. for typing, signing or self-catheterization.

Ectopic impulse generation and autoexcitation in single myelinated afferent fibers in patients with peripheral neuropathy and positive sensory symptoms

Microneurographic studies were performed using cutaneous nerves of 8 patients with documented peripheral neuropathy who expressed positive sensory symptoms. Intraneural recordings in single myelinated fibers revealed: (i) ectopic generation of bursts of spontaneous action potentials; (ii) ectopic generation of ongoing repetitive discharges transiently interrupted by natural stimulation of the receptive field; and (iii) repetitive discharges triggered by a preceding action potential. These results provide direct evidence of a peripheral pathophysiological basis for spontaneous and stimulus-induced paresthesias and dysesthesias in patients with peripheral neuropathy.

Nontransmural laser treatment incompletely denervates canine myocardium

BACKGROUND

Clinical experience with transmyocardial laser revascularization (TMLR) has reproducibly demonstrated an improvement in angina class. Denervation has been implicated as a mechanism whereby this clinical effect may be achieved. Because endovascular techniques for TMLR are currently under development, we investigated the impact of nontransmural endoventricular laser treatment on cardiac nerves in a canine model.

METHODS AND RESULTS

Five mongrel dogs underwent creation of nontransmural endoventricular channels in the anterior left ventricle with a Holmium:YAG laser. Cardiac afferent nerve function was assessed in control and treatment regions by the epicardial application of bradykinin, a potent algesic, at initial thoracotomy before laser treatment, and at repeat thoracotomy 2 weeks later. The resulting central nervous system-mediated decrease in systemic mean arterial pressure seen in all animals at baseline was reduced by 90% at 2 weeks in the laser-treated territory but was preserved in controls. Immunoblot analysis of tissue samples taken from laser-treated regions demonstrated a 66% reduction in tyrosine hydroxylase, a sympathetic nerve-specific enzyme, as assessed by densitometry. Enzyme content was unchanged in control regions.

CONCLUSIONS

These data suggest that nontransmural endoventricular laser treatment only partially denervates the heart. This may have implications for the clinical efficacy of the endovascular approach in the relief of angina pectoris.

Anatomic and technical considerations in needle electromyography of the lumbar spine

Interpretation of the paraspinal needle electromyographic examination requires knowledge of complex and specialized anatomy and pathophysiological processes. The purpose of this article is to elucidate the anatomy and physiology of the lumbar paraspinal needle examination and apply this knowledge to accurate needle technique and rational clinical interpretation of the paraspinal examination.

Transsynaptic changes of neurons and associated microglial reaction in the spinal cord of rats following middle cerebral artery occlusion

This study investigated transsynaptic neuronal damage and microglial reaction in the spinal cord contralateral to focal cerebral ischaemia in rats induced by permanent occlusion of the right middle cerebral artery (MCA). Three and five days after MCA occlusion, some neurons in the dorsal horn of lumbar spinal cord underwent degeneration and they appeared to be engulfed by reactive microglia; on the other hand, the ventral horn neurons remained ultrastructurally intact. It is suggested that the neuronal degeneration in the dorsal horn was attributed to deafferentation of the local neurons following ischaemic lesion of the corticospinal neurons which are the main source of afferent inputs.

The effect of experimental spinal cord edema on the spinal evoked potential

Experimental spinal cord edema was successfully produced in the cat intumescentia cervicalis by the infusion method of Marmarou. The water content around the infusion site significantly increased to 75.9% from the normal value of 69.8% of white matter in the lateral column, with the infusion of 20 microliters of autoserum. The edema was observed for a length of ca.20 mm, spreading mainly longitudinally in the lateral column. The spinal evoked potential was measured four times on the course of infusion and the N1 peak latency at the end of infusion did not show any significant difference compared to the value before infusion. This model may contribute to basic understanding of pathophysiology of spinal cord edema by changing the nature and the volume of infusate, and the location of infusion, according to the experimental purpose.

An increase in the threshold of citric acid-induced cough during chest wall vibration in healthy humans

This study tested the hypothesis that the afferent input from the respiratory muscles may be involved in the neural mechanisms inducing cough responses. Coughing was evoked in conscious healthy humans by the inhalation of citric acid aerosol of several concentrations either during or not during chest wall vibration (100 Hz) at the right second intercostal space or during vibration of the right thigh. The mean threshold citric acid concentration to induce coughing was significantly higher during chest wall vibration (geometric mean, 131.8 mg/ml) than without vibration (75.9 mg/ml). Vibration after topical anesthesia of the chest wall skin did not significantly change the threshold concentration of citric acid. The threshold citric acid concentration during vibration of the right thigh did not significantly differ from that without vibration. We concluded that inputs from the chest wall afferent, presumably from the intercostal muscle or costovertebral joint, may have an inhibitory effect on the initiation of coughing at the higher neural structure in conscious humans.

Afferent receptors in the airways and cough

The roles of airway rapidly adapting receptors (RARs) and of C-fibre receptors in the induction of cough are reviewed. It is concluded that, while there is substantial evidence that irritant receptors in the laryngeal wall and RARs in the tracheobronchial mucosa can cause cough, the evidence for such a similar direct role for C-fibre receptors is tenuous. Indeed there is accumulating evidence that the C-fibre receptors may cause apnoea and rapid shallow breathing, and also reflexly inhibit cough. However the C-fibre receptors may release tachykinins when stimulated, and these in turn may cause plasma extravasation from mucosal postcapillary venules. RARs are excited by increases in interstitial liquid volume, so C-fibre receptors may indirectly enhance cough via the RARs.

In-phase chest wall vibration decreases dyspnea during arm elevation in chronic obstructive pulmonary disease patients

In-phase chest wall vibration (IPV) is known to decrease dyspnea in patients with chronic obstructive pulmonary disease (COPD) at rest and during leg exercise. In the present study, the effects of IPV (100 Hz) on dyspnea and arm fatigue during upper extremity activity were studied in 9 patients with COPD (mean FEV1, 0.95 l). Dyspnea and arm fatigue (modified Borg scale) and ventilatory variables were measured during arm elevation (AE) with weights lifted straight above the head with and without IPV. Mean dyspnea during AE was 3.3 without IPV and 2.1 with IPV (p<0.05), but, arm fatigue, oxygen saturation and end-tidal FCO2 were not affected by IPV. Minute ventilation during AE was significantly increased with IPV in 5 of 9 patients. The results suggest that IPV decreases dyspnea during AE.

Postherpetic neuralgia: irritable nociceptors and deafferentation

Postherpetic neuralgia (PHN) is a common and often devastatingly painful condition. It is also one of the most extensively investigated of the neuropathic pains. Patients with PHN have been studied using quantitative testing of primary afferent function, skin biopsies, and controlled treatment trials. Together with insights drawn from an extensive and growing literature on experimental models of neuropathic pain these patient studies have provided a preliminary glimpse of the pain-generating mechanisms in PHN. It is clear that both peripheral and central pathophysiological mechanisms contribute to PHN pain. Some PHN patients have abnormal sensitization of unmyelinated cutaneous nociceptors (irritable nociceptors). Such patients characteristically have minimal sensory loss. Other patients have pain associated with small fiber deafferentation. In such patients pain and temperature sensation are profoundly impaired but light moving mechanical stimuli can often produce severe pain (allodynia). In these patients, allodynia may be due to the formation of new connections between nonnociceptive large diameter primary afferents and central pain transmission neurons. Other deafferentation patients have severe spontaneous pain without hyperalgesia or allodynia and presumably have lost both large and small diameter fibers. In this group the pain is likely due to increased spontaneous activity in deafferented central neurons and/or reorganization of central connections. These three types of mechanism may coexist in individual patients and each offers the possibility for developing new therapeutic interventions.

Cytokines and fever. Mechanisms and sites of action

The cytokines interleukin (IL)-1, IL-6, and tumor necrosis factor (TNF)-alpha induce increases in body temperature via direct and indirect actions on the brain and are believed to act as endogenous pyrogens. We studied the mechanisms of action of these cytokines on fever in rats. Local administration of lipopolysaccharide (LPS) into a subcutaneous air pouch elicits marked fever, accompanied by increases in the levels of TNF-alpha, IL-1, and IL-6 in the pouch, but only IL-6 in the plasma. Thus, TNF-alpha and IL-1 probably act locally to stimulate the release of a secondary circulating mediator(s) (e.g., IL-6) that can interact with the brain. Neural afferents have also been implicated in relaying messages to the brain. Pyrogenic responses are reportedly attenuated by subdi-aphragmatic vagotomy; however, we failed to observe inhibition of fever in vagotomized rats injected with either LPS or a pyrogenic dose of IL-1, although behavioral responses are abolished.

Glutamate antagonism during secondary deafferentation enhances cognition and axo-dendritic integrity after traumatic brain injury

The combination of central fluid percussion traumatic brain injury (TBI) followed 24 h later by a bilateral entorhinal cortical deafferentation (BEC) produces profound cognitive morbidity. We recently showed that MK-801 given prior to TBI in this insult improved spatial memory for up to 15 days. In the present study we examine whether MK-801 treatment of the BEC component in the combined insult model affects cognitive recovery. Two strategies for drug treatment were tested. Fifteen minutes prior to the BEC lesion in the combined insult, rats were given i.p. doses of either 3 mg/kg (acute group) or 1 mg/kg (chronic group) MK-801. The acute group received no further injections, whereas the chronic group received 1 mg/kg MK-801 i.p. twice a day for 2 days post-BEC lesion. Two additional groups of animals received BEC lesion alone and either acute or chronic MK-801 treatment identical with the combined insult cases. Each group was then assessed for spatial memory deficits with the Morris water maze at days 11-15 and 60-64 postinjury. Both acute and chronic MK-801 treatment in the combined insult group significantly reduced spatial memory deficits at 15 days postinjury relative to untreated injured cases (P < .01). This reduction appeared more robust at 15 days and persisted for up to 64 days in the chronically treated group (P < .05). By contrast, neither acute nor chronic MK-801 treatment affected memory performance with the BEC insult alone. Immunocytochemical localization of parvalbumin showed that chronic administration of MK-801 in the combined insult cases attenuated the injury-induced dendritic atrophy of inhibitory neurons in the dentate gyrus and area CA1. Synaptophysin immunobinding revealed that chronic MK-801 treatment of the BEC component of the combined insult normalized the distribution of presynaptic terminals within the dentate gyrus. These results suggest that cognitive deficits produced by head trauma involving both neuroexcitation and deafferentation can be attenuated with chronic application of glutamatergic antagonists during the period of deafferentation injury and that this attenuation is correlated with axo-dendritic integrity.

Signal transduction in activation of ischemically sensitive abdominal visceral afferents: role of PKC

Abdominal ischemia reflexly activates the cardiovascular system by stimulating abdominal visceral afferent nerve endings. Whereas many ischemic metabolites responsible for activating these nerves have been identified (e.g., bradykinin), their precise mechanism of action is unclear. Protein kinase C (PKC) is an important part of the signal transduction process underlying the action of metabolites such as bradykinin and is a regulator of neuronal activity. Therefore, we hypothesized that PKC contributes to stimulation of ischemically sensitive abdominal visceral afferents. Single-unit activity was recorded from the right thoracic sympathetic chain of anesthetized cats. Exogenous activation of PKC using phorbol 12, 13-dibutyrate (PDBu, 5 microg/kg ia) increased the impulse activity of ischemically sensitive C-fiber afferents from 0.04 +/- 0.01 to 0. 67 +/- 0.23 impulses/s (n = 11; P < 0.05). The influence of endogenous activation of PKC also was evaluated during 10 min of mesenteric ischemia. Inhibition of PKC using PKC-(19-36) (20 microg/kg iv) reduced ischemia-induced increases in afferent activity from 0.46 +/- 0.11 to 0.19 +/- 0.08 impulses/s (n = 7, P < 0.05). Moreover, PKC-(19-36) (20 microg/kg iv) reduced the response of ischemically sensitive C fibers to bradykinin (0.5-1.0 microg/kg ia) from 1.18 +/- 0.20 to 0.66 +/- 0.14 impulses/s (n = 13, P < 0. 05). These results indicate that PKC contributes to activation of abdominal visceral afferents during ischemia and specifically to part of the bradykinin-induced activation of these afferents.

Management of displaced lateral orbital wall fractures associated with visual and ocular motility disturbances

Impacted fractures of the lateral orbital wall are a type of orbital blow-in fracture that may be accompanied by decreased visual acuity and ocular motility limitations. Eleven patients who suffered this injury triad were retrospectively reviewed to determine the nature of the ophthalmologic injuries and the effect of fracture reduction on recovery of ophthalmologic functions. Two patients with decreased visual acuity owing to trauma to the globe recovered to subjective pretrauma levels following surgery. Nine patients were thought to have a traumatic optic neuropathy with varying degrees of visual loss. Patients with an injury to the intraorbital portion of the optic nerve and a presurgical visual acuity of 20/400 or better recovered to subjective pretrauma levels. Those with visual acuity of less than 20/400 or an injury to the intracanalicular portion of the nerve had responses ranging from no improvement to objective improvement with large field defects. Ocular motility improved in all patients, many in the immediate postsurgical period consistent with removal of a mechanical restriction. No patients had worsening of ophthalmologic deficits as a result of manipulation of fracture fragments. Our experience suggests that early surgical intervention facilitates recovery of vision and eye movement. The traumatic optic neuropathy that accompanies this fracture is distinct from the indirect type of optic nerve injury that may respond to steroids, and the ophthalmoplegia is distinct from the usual traumatic superior orbital fissure syndrome that resolves spontaneously. An understanding of the impacted lateral orbital wall fracture and its ophthalmologic implications is essential for any surgeon who desires to manage craniomaxillofacial injuries.

P2X receptor-mediated excitation of nociceptive afferents in the normal and arthritic rat knee joint

1. We tested the hypothesis that functional P2X receptors are present on peripheral terminals of primary afferent articular nociceptors in the rat knee joint. Neural activity was recorded extracellularly from the medial articular nerve innervating the knee joint in rats anaesthetized with pentobarbitone. 2. The selective P2X receptor agonist, alphabeta methylene ATP (alphabetameATP), and the endogenous ligand, ATP, caused a rapid short-lasting excitation of a sub-population of C and Adelta nociceptive afferent nerves innervating normal knee joints when injected intra-arterially or intra-articularly, and this effect was antagonized by the non-selective P2 receptor antagonist PPADS. 3. Induction of a chronic (14-21 days) unilateral inflammatory arthritis of the knee joint using locally injected Freund's adjuvant neither increased or decreased responsiveness of joint nociceptors to alphabetameATP or ATP. 4. Our results support the hypothesis that alphabetameATP-sensitive P2X receptors are expressed on peripheral nociceptive afferents in the rat knee joint suggesting that they may be involved in the initiation of nociception and pain.

Relative afferent pupillary defects in patients with Leber hereditary optic neuropathy and unilateral visual loss

PURPOSE

It has been suggested that the pupillary light reaction is relatively preserved in the affected eyes of patients with Leber hereditary optic neuropathy (LHON). To test the hypothesis that visual-pupillomotor dissociation exists in LHON, we performed a retrospective study to evaluate the magnitude of the relative afferent pupillary defect (RAPD) in patients who had experienced monocular visual loss. We also compared the size of the measured RAPD with the size of the RAPD that would be expected on the basis of documented visual field loss.

METHODS

We identified a cohort of patients with LHON and monocular visual loss, whose pupillary reactions had been quantified using neutral density filters. From a review of the case records, we determined whether an RAPD was present, as well as the magnitude of the documented RAPDs. We also calculated the expected size of the RAPD for each patient, using previously established templates that correlated the size of the RAPD with the degree of visual field loss.

RESULTS

An RAPD was identified in all 10 patients in this study. There was no significant difference between the size of the measured and predicted RAPD, nor did the size of the RAPD correlate with visual acuity or the time interval between the onset of visual loss and evaluation.

CONCLUSION

The results of this study do not support the hypothesis that visual-pupillomotor dissociation is a common feature of LHON.

Activity-dependent regulation of dopamine content in the olfactory bulbs of naris-occluded rats

Several lines of evidence strongly suggest that reduced olfactory nerve activity results in decreased bulb dopamine content. In the present study, high performance liquid chromatography with electrochemical detection was used to assess catecholamine levels in bulbs from postnatal day 60 rats that had undergone either unilateral naris cautery or a sham surgery on day 30. Thirty days of odor deprivation dramatically reduced dopamine and dihydroxyphenylacetic acid levels in functionally-deprived bulbs (ipsilateral to occluded nares) as compared to contralateral controls, while norepinephrine and dihydroxyphenylglycol levels were unchanged. The loss of dopamine was more severe in medial as compared to lateral aspects of experimental bulbs, while the loss of dihydroxyphenylacetic acid was similar on the two sides. To test directly the hypothesis that afferent activity regulates dopamine and dihydroxyphenylacetic acid content, 1 h of high frequency tetanic nerve stimulation was provided to the rostral-medial olfactory nerve layer in deprived olfactory bulbs, and catecholamine levels were assessed from 6 to 192 h later. Partial and temporary recovery of dopamine was observed in medial aspects of the bulb when rats were examined 96 h later, while consistent recovery of dihydroxyphenylacetic acid content was not apparent. These data corroborate evidence that olfactory nerve activity is a potent regulator of bulb dopamine and indicate that continued afferent input is necessary to maintain dopamine levels.

Steps toward recovery of function after hemilabyrinthectomy in frogs

Removal of the labyrinthine organs on one side results in a number of severe postural and dynamic reflex deficits. Over time some of these behavioral deficits normalize again. At a chronic stage the brain of frogs exhibits a number of changes in vestibular and propriospinal circuits on the operated side that were studied in vitro. The onset of changes in the vestibular nuclear complex was delayed, became evident only after head posture had recovered by more than 50%, and was independent of the presence or absence of a degeneration of vestibular nerve afferent fibers. The time course of changes measured in the isolated spinal cord paralleled the time course of normalization of head and body posture. Results obtained after selective lesions of individual labyrinthine nerve branches show that unilateral inactivation of utricular afferent inputs is a necessary and sufficient condition to provoke postural deficits and propriospinal changes similar to those after the removal of all labyrinthine organs. The presence of multiple synaptic changes at distributed anatomic sites over different periods of time suggests that different parts of the central nervous system are involved in the normalization of different manifestations of the vestibular lesion syndrome.