strychnine and Nerve-Degeneration

During the past decade, converging lines of evidence have linked the abnormal release or leak of excitatory amino acids to the neurodegeneration associated with a wide range of pathologies including cerebral ischemias, Huntington's disease, and AIDS dementia (Coyle and Robinson, 1987; Lipton, 1994; Meldrum, 1994). Pharmacological studies indicate that activation of both ionotropic and metabotropic glutamate receptors can substantially contribute to excitotoxic cell damage (Choi, 1992; Pizzi et al., 1993; Sheardown et al., 1993; Xue et al., 1994). Based on these findings, therapeutic strategies based on blunting or blocking glutamatergic transmission may be useful in treating a variety of neurodegenerative disorders.

Topics: AIDS Dementia Complex; Amino Acids; Amino Acids, Cyclic; Animals; Brain Ischemia; Humans; Huntington Disease; Nerve Degeneration; Neurons; Neuroprotective Agents; Receptors, Glycine; Receptors, N-Methyl-D-Aspartate; Strychnine

Inhibitory GABAergic and glycinergic neurotransmission in the spinal cord play a central role in the regulation of neuronal excitability, by maintaining a balance with the glutamate-mediated excitatory transmission. Glutamatergic agonists infusion in the spinal cord induce motor neuron death by excitotoxicity, leading to motor deficits and paralysis, but little is known on the effect of the blockade of inhibitory transmission. In this work we studied the effects of GABAergic and glycinergic blockade, by means of microdialysis perfusion (acute administration) and osmotic minipumps infusion (chronic administration) of GABA and glycine receptors antagonists directly in the lumbar spinal cord. We show that acute glycinergic blockade with strychnine or GABAergic blockade with bicuculline had no significant effects on motor activity and on motor neuron survival. However, chronic bicuculline infusion, but not strychnine, induced ipsilateral gait alterations, phalange flaccidity and significant motor neuron loss, and these effects were prevented by AMPA receptor blockade with CNQX but not by NMDA receptor blockade with MK801. In addition, we demonstrate that the chronic infusion of bicuculline enhanced the excitotoxic effect of AMPA, causing faster bilateral paralysis and increasing motor neuron loss. These findings indicate a relevant role of GABAergic inhibitory circuits in the regulation of motor neuron excitability and suggest that their alterations may be involved in the neurodegeneration processes characteristic of motor neuron diseases such as amyotrophic lateral sclerosis.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Atrophy; Bicuculline; Dizocilpine Maleate; Drug Interactions; GABA Antagonists; Gait; Male; Motor Activity; Motor Neurons; Muscle Hypotonia; Nerve Degeneration; Rats; Receptors, Glycine; Spinal Cord; Strychnine

The role of the neutral amino acid glycine in excitotoxic neuronal injury is unclear. Glycine coactivates glutamate N-methyl-D-aspartate (NMDA) receptors by binding to a distinct recognition site on the NR1 subunit. Purely excitatory glycine receptors composed of NR1 and NR3/NR4 NMDA receptor subunits have recently been described, raising the possibility of excitotoxic effects mediated by glycine alone. We have previously shown that exposure to high concentrations of glycine causes extensive neurotoxicity in organotypic hippocampal slice cultures by activation of NMDA receptors. In the present study, we investigated further properties of in vitro glycine-mediated toxicity. Agonists of the glycine recognition site of NMDA receptors (D-serine and D-alanine) did not have any toxic effect in hippocampal cultures, whereas competitive blockade of the glycine site by 7-chlorokynurenic acid was neuroprotective. Stimulation (taurine, beta-alanine) or inhibition (strychnine) of the inhibitory strychnine-sensitive glycine receptors did not produce any neurotoxicity. The toxic effects of high-dose glycine were comparable in extent to those produced by the excitatory amino acid glutamate in our model. When combined with sublethal hypoxia/hypoglycemia, the threshold of glycine toxicity was decreased to less than 1 mM, which corresponds to the range of concentrations of excitatory amino acids measured during in vivo cerebral ischemia. Taken together, these results further support the assumption of an active role of glycine in excitotoxic neuronal injury.

Topics: Alanine; Animals; Animals, Newborn; Brain Ischemia; Dose-Response Relationship, Drug; Drug Resistance; Glutamic Acid; Glycine; Hippocampus; Kynurenic Acid; Nerve Degeneration; Neurons; Neuroprotective Agents; Neurotoxins; Organ Culture Techniques; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Strychnine; Taurine

Using quantitative autoradiography, the strychnine-sensitive glycine site and strychnine-insensitive glycine site of the N-methyl-D-aspartate receptor were analyzed in the cervical segment of the spinal cord of the wobbler mouse, which is a purported model of human motor neuron diseases. Significantly increased density of the strychnine-sensitive site was found in the lamina II-inner (+17%) and laminae III & IV (+17%) of wobbler mice. The strychnine-insensitive site was also increased in lamina I & II-outer (+15%), lamina II-inner (+15%), laminae III & IV (+48%), laminae V-VIII (+43%) and lamina X (+26%) of wobbler mice. However, no significant differences were observed for the both sites in the ventral horn where motor neurons are located. These findings suggest that both inhibitory and excitatory-associated glycinergic dysfunctions are involved in the wobbler mouse motor neuron disease.

Topics: Animals; Disease Models, Animal; Female; Glycine; Male; Mice; Mice, Neurologic Mutants; Motor Neurons; Nerve Degeneration; Receptors, Glycine; Spinal Cord; Strychnine

Previous studies indicate that tuberculoventral and cartwheel cells in the dorsal cochlear nucleus as well as a group of stellate cells in the ventral cochlear nucleus are likely to be glycinergic. To test whether these neurons contain higher levels of free glycine than cells that are probably not glycinergic, immunocytochemical studies with antibodies against glycine conjugates were undertaken on slices of the murine cochlear nuclear complex. Present results show that the cell bodies of all three groups of neurons are immunolabeled. However, the somatic labeling of the tuberculoventral and cartwheel cells can be modulated by experimental conditions. In slices fixed immediately after cutting, many cell bodies in the deep layer of the dorsal cochlear nucleus (DCN), presumably tuberculoventral neurons, are labeled. As a slice is incubated in vitro, cell bodies in the deep layer of the DCN lose their glycine-like immunoreactivity. After 7 hours in vitro, labeled cells are absent in the deep DCN, but the immunoreactivity can be regained by electrically stimulating the auditory nerve for 20 minutes. The loss of immunoreactivity is prevented by electrical stimulation, by axotomy, and by inclusion of 0.8 microM tetrodotoxin, or 1 microM strychnine, or 50 microM colchicine or 50 microM beta-lumicolchicine in the bathing saline. Cartwheel cells retain their immunoreactivity during incubation in vitro without electrical stimulation, but lose it under two conditions. One is following a cut across the ventral cochlear nucleus (VCN) that severs most of their granule cell input, and the other is the inclusion of tetrodotoxin in the bathing saline. The labeling of cell bodies in the ventral cochlear nucleus and of puncta and processes is not changed by any of these experimental manipulations.

Topics: Animals; Brain Chemistry; Cochlear Nucleus; Colchicine; Electric Stimulation; Glycine; Immunohistochemistry; Mice; Mice, Inbred CBA; Mice, Inbred ICR; Nerve Degeneration; Neurons; Strychnine; Tetrodotoxin; Vestibulocochlear Nerve

The lumbar and cervical spinal dorsal horns of adult rats with a chronic (8 days) constriction injury of the sciatic nerve on one side (and a sham operation on the other) were examined for signs of transsynaptic degeneration. The incidence of neurons with signs of degeneration (pyknosis and hyperchromatosis; 'dark neurons') was significantly increased in the lumbar dorsal horn on both sides. The ipsilateral lumbar increase was significantly greater than the contralateral increase. There was no increase in the incidence of dark neurons in the cervical dorsal horns of the same rats. The distribution of lumbar dark neurons was similar bilaterally. The majority of the dark neurons were found in the sciatic nerve's territory in laminae I-II. A second group of rats received the same surgery but in addition received a series of 7 daily subconvulsive doses of strychnine. Dark neurons were again found bilaterally (with ipsilateral predominance) in the sciatic nerve's territory in lumbar laminae I-II, but the incidence was significantly greater than that found in the group that did not receive strychnine. The same result was obtained in a third group of strychnine-treated rats when the sham operation was omitted. Thus the appearance of contralateral dark neurons is not dependent on unintentional nerve damage created by the sham procedure. An additional group of rats was sacrificed 8 days after receiving a unilateral sciatic nerve transection, a contralateral sham operation, and the 7 daily strychnine injections. There was no increase in the incidence of dark neurons in any of these rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Constriction; Denervation; Male; Nerve Degeneration; Neurons; Oligodendroglia; Rats; Rats, Inbred Strains; Reference Values; Sciatic Nerve; Spinal Cord; Strychnine; Synapses; Time Factors

A painful peripheral neuropathy was produced by loosely tying constrictive ligatures around the sciatic nerve of rats. Eight days after the nerve injury and after a series of injections a subconvulsive dose of strychnine, the animals were sacrificed and the spinal cord dorsal horn was examined for signs of transsynaptic degeneration. The presence of strychnine-enhanced transsynaptic degeneration was apparent from the presence of many pyknotic and hyperchromatic neurons (dark neurons). The dark neurons were seen in laminae I-IV bilaterally, but they were significantly more frequent ipsilateral to the nerve injury. The majority of the dark neurons were found within the medial two-thirds of laminae I-II; this region corresponds to the intraspinal territory of the sciatic nerve's small diameter afferents. The results suggest that a peripheral nerve injury that produces neuropathic pain induces morphological alterations of intraspinal somatosensory circuitry.

Topics: Animals; Male; Nerve Degeneration; Pain; Peripheral Nervous System Diseases; Rats; Rats, Inbred Strains; Strychnine

Adult rats underwent unilateral transection of the inferior alveolar nerve and subsequent intraperitoneal injection of strychnine (1 mg/kg, 3-23 days) at various posttransectional intervals. When they were sacrificed at 18-30 days posttransectionally, many pyknotic neuronal cell bodies were observed in plastic embedded toluidine blue-stained 1 micron-thick sections of the medullary dorsal horn. They were mostly found in the dorsal part of the dorsal horn ipsilateral to the neurotomy and were more abundant in laminae I/II than in laminae III/IV. Similar pyknotic neurons were found after 1 or 2 days of L-allylglycine administration (55.7 mg/kg/day) at a posttransectional interval of 20 days. Unlike those observed after strychnine treatment, the pyknotic neurons after L-allylglycine treatment were evenly distributed throughout laminae I-IV of the dorsal half of the medullary dorsal horn. Twenty-three days of bicuculline (2 mg/kg/day) or picrotoxin (0.5 mg/kg/day) treatment at an interval of 7 days did not yield pyknotic neurons. The results are discussed in the light of intrinsic synaptic circuitry of the dorsal horn.

Topics: Allylglycine; Animals; Bicuculline; Glycine; Male; Mandibular Nerve; Medulla Oblongata; Nerve Degeneration; Picrotoxin; Rats; Rats, Inbred Strains; Strychnine

Following transection of a nerve, strychnine (1 mg/kg per day) was intraperitoneally injected for 3-23 days at various post-transectional intervals and the medullary and spinal dorsal horns were histologically examined. Strychnine-enhanced transsynaptic destruction was seen when the inferior alveolar nerve was transected and the proximal stump was left in situ in the mandibular canal. Pyknotic neuronal cell bodies were observed in the dorsal half of the medullary dorsal horn ipsilateral to the nerve transection, an area which is known to receive dense innervation from the ipsilateral inferior alveolar nerve. Three days of strychnine treatment revealed pyknotic cells when the experiment was terminated between 18 and 30 days postoperatively. A longer period of strychnine treatment had a tendency to produce more pyknotic cells. Transection of neither mental, lingual, auriculotemporal nor infraorbital nerve induced strychnine-enhanced transsynaptic destruction in the medullary and spinal dorsal horns which are known to receive primary input from the severed nerves. Strychnine-enhanced transsynaptic destruction following transection of the inferior alveolar nerve was effectively prevented by placing the proximal stump outside the mandibular canal.

Topics: Animals; Male; Mandible; Mandibular Nerve; Nerve Degeneration; Neurons; Rats; Rats, Inbred Strains; Spinal Cord; Strychnine; Synapses; Time Factors; Trigeminal Nerve

The effects of systemic administration of strychnine (1 mg/kg), picrotoxin (0.5 mg/kg) and bicuculline (2 mg/kg) on acute transsynaptic destruction of medullary dorsal horn neurons following transection of the inferior alveolar nerve were assessed in rats. Single intraperitoneal injections of the above drugs were given without, 1 min before or 1 min after the nerve transection. The effect of transection without drug administration was also examined. Eighteen hours after nerve transection without drug, approximately 7 dark neurons were found in a single toluidine blue stained 1 micron section of the rostral medullary dorsal horn ipsilateral to the nerve transection. Administration of the drugs 1 min before the nerve transection significantly increased the number of dark neurons in a single section to about 17 (strychnine), 46 (picrotoxin) and 20 (bicuculline). These dark neurons were found mainly in the dorsal half of medullary dorsal horn. Delivery of any of the drugs 1 min after the nerve transection did not increase the number of dark neurons. The data thus indicate that the transneuronal effect of transection of the nerve was enhanced by antagonism of glycinergic and GABAergic inhibition of dorsal horn neurons. In view of the short latency and duration of transsynaptic destructive activity, a massive injury discharge of primary afferent neurons and the subsequent release of excitatory neurotransmitters appear to be the direct cause of convulsant-enhanced rapid transsynaptic destruction which follows the peripheral nerve transection.

Topics: Animals; Bicuculline; Nerve Degeneration; Neurons; Peripheral Nerve Injuries; Peripheral Nerves; Picrotoxin; Rats; Rats, Inbred Strains; Strychnine

Topics: Animals; Brain Stem; Male; Mandibular Nerve; Nerve Degeneration; Neural Pathways; Neurons; Rats; Rats, Inbred Strains; Strychnine

The effect of topical application of axonal transport blockers to the transected peripheral nerve was assessed by quantitating the strychnine-enhanced transsynaptic degeneration following transection of the inferior alveolar nerve in adult rats. Systemic administration of strychnine (1 mg/kg/day) for 7 days at the postoperational interval of 23 days proved to be suitable for quantitating the transsynaptic degeneration at the light microscopic level. When the proximal stump of transected nerve was treated with 2% colchicine immediately after transection, 5.8 +/- 6.8 dark neurons in a single section of the medullary dorsal horn, ipsilateral to the nerve transection, were observed. Following similar treatment with 0.4% vinblastine and 0.2% vincristine, 24.4 +/- 10.5 and 9.4 +/- 7.0 dark neurons were seen, respectively. When compared with 43.0 +/- 9.4 dark neurons, which were seen in animals without alkaloid treatment, colchicine, vinblastine and vincristine significantly reduced the transsynaptic degeneration by 86, 43, and 78%, respectively. Possible mechanisms involved in prevention of transsynaptic degeneration by the alkaloids are discussed.

Topics: Administration, Topical; Alkaloids; Animals; Colchicine; Male; Medulla Oblongata; Nerve Degeneration; Peripheral Nerves; Rats; Rats, Inbred Strains; Strychnine; Time Factors; Vinblastine; Vincristine

The effects of the convulsants strychnine, bicuculline, picrotoxin and L-allylglycine on the transsynaptic destruction of medullary dorsal horn neurons were examined following transection of the inferior alveolar nerve in adult rats. Strychnine and L-allylglycine enhanced the transsynaptic effect of nerve transection and caused degeneration of many dorsal horn neurons, while bicuculline and picrotoxin did not. The removal of glycinergic and GABAergic postsynaptic inhibition appears to enhance the transsynaptic destructive activity which follows the peripheral nerve transection.

Topics: Allylglycine; Animals; Bicuculline; Glycine; Mandibular Nerve; Medulla Oblongata; Nerve Degeneration; Neurons; Picrotoxin; Rats; Rats, Inbred Strains; Strychnine; Synapses

Loss of motor neurons is the primary pathological hallmark of amyotrophic lateral sclerosis. Drug and neurotransmitter receptors are neuronal markers and can be indicators of neuronal connectivity. Knowledge of alterations in receptors in amyotrophic lateral sclerosis should contribute to our understanding of normal spinal cord neurotransmitter systems as well as of the pathophysiology of amyotrophic lateral sclerosis. We therefore used a sensitive, light microscopic in vitro labeling receptor autoradiographic technique to map and quantitate muscarinic cholinergic, glycinergic, and benzodiazepine receptors in three levels of spinal cord from six patients with amyotrophic lateral sclerosis and six age- and sex-matched control patients. In control tissues, the receptor distributions were similar in the three levels of spinal cord and also similar to those found in previous studies with animals. In amyotrophic lateral sclerosis, major reductions in receptor densities were noted in Rexed layer IX, the region containing motor neurons. Reductions were noted in other laminae as well, particularly for muscarinic receptors. The changes in muscarinic receptors were caused solely by changes in high-affinity agonist sites. Reductions in glycine and muscarinic receptors were highly correlated with the degree of motor neuron loss found in the amyotrophic lateral sclerosis patients. The findings in this study point out the usefulness of this receptor mapping technique in understanding the changes in neuronal populations that occur in the degenerative neurological diseases.

Topics: Adult; Aged; Amyotrophic Lateral Sclerosis; Autoradiography; Female; Flunitrazepam; Humans; Male; Middle Aged; Motor Neurons; N-Methylscopolamine; Nerve Degeneration; Neurotransmitter Agents; Receptors, Cell Surface; Receptors, GABA-A; Receptors, Glycine; Receptors, Muscarinic; Receptors, Neurotransmitter; Scopolamine Derivatives; Spinal Cord; Strychnine

1. Monosynaptic i.p.s.p.s were produced in spinal motoneurones of the cat by stimulation of a pool of interneurones following chronic degeneration of descending tracts and primary afferent fibres in the lumbosacral cord.2. Monosynaptic i.p.s.p.s so evoked by supramaximal stimuli often showed a fluctuation in amplitude with occasional failures of response.3. When two successive stimuli were applied at a short interval, the mean amplitude of the second i.p.s.p.s was greater than that of the first. This facilitation was associated with a decrease in the number of failures, a decrease in the coefficient of variation of the amplitude distribution and an increase in the probability of occurrences of large i.p.s.p.s.4. A statistical analysis of the i.p.s.p. amplitude fluctuation showed that the monosynaptic i.p.s.p. is composed of discrete unit potentials evoked with a certain probability in a manner described by a binomial law.5. The application of strychnine decreased the mean amplitude of i.p.s.p.s with little change in the coefficient of variation of the i.p.s.p. amplitude distribution.6. It is concluded that the release of inhibitory transmitter occurs in quantal steps and that strychnine blocks primarily the post-synaptic receptors for the inhibitory transmitter.

Topics: Animals; Cats; Electric Stimulation; Electrophysiology; Evoked Potentials; Factor Analysis, Statistical; Interneurons; Lumbosacral Region; Motor Neurons; Nerve Degeneration; Neural Inhibition; Spinal Cord; Strychnine; Synapses; Synaptic Transmission

Topics: Animals; Auditory Cortex; Auditory Perception; Brain; Corpus Callosum; Dogs; Dominance, Cerebral; Ear; Electroencephalography; Memory, Short-Term; Mesencephalon; Nerve Degeneration; Neural Pathways; Ocular Physiological Phenomena; Seizures; Strychnine; Visual Cortex; Visual Perception