Quantitative Assessment of Muscle Activity and Joint Load in Braced and Unbraced Osteoarthritis Knee by External Strain Gauge Sensor.

OBJECTIVES: Altered biomechanics leads to the development of degenerative joint disease. The joint pressure and dynamic loading varies during activities of daily living. The study was undertaken to assess the muscle activation pattern of the medial and lateral knee compartments (tibiofemoral joint) during gait in osteoarthritis subjects without and with knee brace undergoing either exercise therapy or balance therapy. The joint load was assessed by the strain gauge transducer and the weight shift pattern is taken as an indicator for the muscle activation pattern. METHODS: In a prospective design study on 57 male subjects diagnosed osteoarthritis knee with Kellagren-Lawrennce scale walked barefooted with and without designed offloader knee brace on a level surface for three minutes. The subjects were allocated in two different study groups i.e. Conventional (exercise therapy) (Control Group, n=31) and Structured Neuromuscular Postural Training (SNPT) group (Balance therapy) (Study Group, n=26). The subjects were sub grouped as pre-elderly (40-60 Years) and elderly (>61 years) group in both. The quantitative assessment of muscle activity and joint loading with and without knee brace was done using designed strain gauge sensor instrument. The pressure changes of strain gauges of muscles around the knee joint viz. vastus medialis (VM), vastus lateralis (VL), semi membranosus/tendinosus (Medial Hamstring) (MH), Biceps Femoris (Lateral Hamstring) (LH), gastro-soleus (GS) and tibialis anterior (TA) muscles during normal gait were observed at baseline and 6 weeks follow up after undergoing exercise therapy or balance therapy treatment as per allocation of study groups. The digital values from MATLAB were recorded and analyzed. RESULTS: At the end of 6 weeks conventional/SNPT (structured neuromuscular postural training) treatments, medial hamstring muscle activity showed significant difference (p<0.001) in pre-elderly subgroup, while significant difference was seen in vastus laterals (VL), medial hamstring (MH) (p<0.005) and lateral hamstring (LH) muscles (p<0.001) in elderly subgroup. Further, the muscle co-contraction has been higher for vastus medialis-medial hamstring (VM-MH) pair compared to vastus lateralis-lateral hamstring (VL-LH) pair without brace at baseline. The application of offloader valgus knee brace significantly increases VL-LH co-contractions in magnitude and decreases in VM-MH co-contractions at 6 weeks follow up. CONCLUSION: Muscle activity increased in medial hamstring both in pre-elderly and elderly subjects. While, Vastus Laterals and lateral hamstring showed increased activities in elderly subjects. Hence, balance training and the application of off loader knee brace will be helpful to redistribute the load on medial tibiofemoral compartment.

2-Deoxy-D-glucose reverses the Indian red scorpion venom-induced cardiopulmonary abnormalities in anesthetized rats.

Role of 2-Deoxy-D-glucose (2-DG) in reversing the Indian red scorpion (Mesobuthus tamulus concanesis Pocock, MBT) venom-induced toxicity was examined. Femoral arterial pressure, ECG and respiratory movements were recorded in urethane anesthetized rats. Plasma glucose and serum insulin levels were also estimated. Intravenous injection of 5 mg/kg MBT venom produced immediate decrease in mean arterial pressure, heart rate and respiratory frequency followed by an increase and subsequent progressive decrease. ECG pattern exhibited ischaemic changes. There was hyperinsulinemia after venom without corresponding decrease in plasma glucose. The animals died within 37 +/- 9 min and demonstrated significant increase in pulmonary water content. 2-DG pretreatment (0.5 g/kg, iv) improved the cardiopulmonary abnormalities induced by venom and the animals survived for nearly 120 min. There was no hyperinsulinemia and increased pulmonary water content in these animals. In insulin (2 IU/kg) treated rats, the MBT venom-induced cardiopulmonary abnormalities were attenuated and ECG abnormalities were reversed. The pulmonary water content in these animals exhibited a decreasing trend and the animals survived for 120 min. Repaglinide (10 microg/kg, iv) pretreatment failed to reverse the venom-induced cardiopulmonary changes including the increased pulmonary water content. The survival time was similar to venom only group. The present results reveal that 2-DG reverses the venom-induced cardiopulmonary toxicity probably by restoring insulin sensitivity.

2-Deoxy-D-glucose alters the cardio-respiratory parameters in anaesthetized rats.

2-Deoxy-D-Glucose (2-DG), a synthetic analogue of glucose, is used as an anticancer agent either alone or in combination with other tumor treatment protocols. The present study was conducted to identify the systemic effects of 2-DG on parameters of vital importance. The blood pressure, ECG and respiratory excursions were recorded in anesthetized adult rats. At the end (after 120 min) of experiments, the plasma glucose and serum insulin levels were estimated. Injection of 2-DG (0.5 g/kg) produced an immediate increase in mean arterial pressure (MAP) and respiratory rate. The increase in MAP continued throughout the period of observation (120 min) and the maximal increase was seen at 90 min (27%). Whereas, the respiratory rate decreased by 17% at 15 min which decreased further to 37% by 120 min. Heart rate also decreased after 2-DG in a time-dependent manner and 40% decrease was observed at 120 min. Administration of 2-DG increased the plasma glucose level significantly (30%) as compared to saline control group but did not increase the serum insulin level. The results indicate that 2-DG alters the cardio-respiratory parameters by mechanisms unrelated to plasma insulin activity.

Pathophysiological approach to the management of scorpion envenomation.

Indian red scorpion (Mesobuthus tamulus; MBT) produces lethal stings and is a matter of concern in certain parts of India. MBT envenomation produces multi-systemic involvement, thus presents difficulty in the management. Symptomatic treatment has been practiced earlier that failed to relieve the toxic effects of the venom. Therefore, present manuscript deals with pathophysiologically based approach in the management of toxicity considering the merits and the demerits of treatment protocols so as to evolve a consensus in the treatment strategies of scorpion envenomation.

Identification of a novel pulmonary oedema producing toxin from Indian red scorpion (Mesobuthus tamulus) venom.

The experiments were conducted to identify the toxin that produces pulmonary oedema in Mesobuthus tamulus (BT) envenomed animals. Crude BT venom was subjected to Sephadex gel filtration (G-75) and the fractions were screened for optical density (OD), neurotoxicity (prolongation of compound action potential in frog sciatic nerve) and lethality. All these parameters exhibited a peak between 54-94 ml eluates. Fractions of this peak were pooled (SP) and loaded on to carboxymethyl cellulose column. The column was then eluted with increasing buffer concentrations at constant pH and temperature. Eluates were screened for neurotoxicity and OD. Four peaks of neurotoxic activity (T1-T4) were detected. T2 and T3 were lethal whereas T1 and T4 were non-lethal. T2 exhibited mainly neurotoxicity and failed to augment phenyldiguanide (PDG)-induced reflex response or to produce pulmonary oedema. T3 was having minimal neurotoxic actions but augmented PDG-reflex and produced pulmonary oedema. The effects of T3 persisted even after dialysis with 8 kDa cut-off filter but not those of T2. The T3 effects resembled toxic manifestations of BT venom and were blocked by aprotinin pre-treatment. T3 demonstrated a band at approximately 100 kDa in SDS-PAGE. The results demonstrate the presence of a lethal, high molecular weight, pulmonary oedema producing toxin in BT venom.

Bisphenol A depresses monosynaptic and polysynaptic reflexes in neonatal rat spinal cord in vitro involving estrogen receptor-dependent NO-mediated mechanisms.

Bisphenol A (BPA), a toxic chemical from plastics, is known to produce locomotor abnormalities which may imply the alteration in synaptic activity at Ia-α motoneuron synapse also. However the effect of BPA on this synapse is not known. Therefore, this study was undertaken to examine the effect of BPA on reflexes originating at Ia-α motoneuron synapse in the spinal cord. The experiments were performed on isolated hemisected spinal cords from 4 to 6d rats. Stimulation of a dorsal root evoked segmental monosynaptic (MSR) and polysynaptic (PSR) reflex potentials in the corresponding ventral root. Nitrite content (indicator of NO activity) of cords was estimated in the presence of BPA with/without antagonists. Superfusion of BPA (3-100µM) depressed the reflexes in a concentration- and time-dependent manner. The depression was ∼20, ∼50 and ∼70% at 10, 30 and 100µM of BPA, respectively. The 50% depression occurred around 15min at 30µM of BPA. Pretreatment with estrogen receptor (ERα) antagonist, tamoxifen, blocked the BPA-induced depression of reflexes, whereas, 17ß-estradiol, ER agonist, did not depress the reflexes even up to 10µM. Further, pretreatment with Nω-Nitro-l-arginine methyl ester hydrochloride (l-NAME) or hemoglobin (Hb) blocked the BPA-induced depression of spinal reflexes. Nitric oxide (NO) donor sodium-nitroprusside depressed the MSR and PSR in a concentration-dependent manner. The nitrite concentration of the cords exposed to BPA was 733µM/gm of tissue (three times the saline group). Pretreatment with tamoxifen/l-NAME/Hb blocked the BPA-induced increase of nitrite levels. The present observations indicate that BPA depressed spinal synaptic transmission through ERα-dependent NO-mediated mechanisms. The altered synaptic activity may implicate for neurobehavioral locomotor abnormalities after exposure to BPA.

Temperature-dependence of reflex transmission in the neonatal rat spinal cord, in vitro: influence on strychnine- and bicuculline-sensitive inhibition.

The amplitude, latency and rise time of the monosynaptic reflex, recorded from the spinal cord of the neonatal rat in vitro, was temperature-dependent with optimal conditions occurring at 25 degrees C. The reflex was inhibited when conditioning stimuli were applied to an adjacent dorsal root at 1-150 msec before the monosynaptic reflex was evoked; the inhibition had both an early and a late phase. The early phase of inhibition occurred at conditioning-test intervals of 1-20 msec with peak inhibition occurring at 7 msec. Raising the temperature of the bath to 31 degrees C or exposing the cord to strychnine blocked the early phase of inhibition. The late phase of inhibition occurred at conditioning-test intervals greater than 20 msec, was unaffected by temperature and was blocked by bicuculline. The early phase of inhibition therefore appears to be postsynaptic in origin and mediated by glycine while the late component of inhibition may be presynaptic in origin and mediated by gamma-aminobutyric acid (GABA).

Involvement of N-methyl-D-aspartate receptors for the Ptychodiscus brevis toxin-induced depression of monosynaptic and polysynaptic reflexes in neonatal rat spinal cord in vitro.

The effects of Ptychodiscus brevis toxin (PbTx) on the Ia-alpha motoneuron synaptic transmission in neonatal rat spinal cord in vitro was examined. The stimulation of a dorsal root evoked monosynaptic (MSR) and polysynaptic reflex (PSR) potentials in the segmental ventral root in Mg2+-free medium. Superfusion with PbTx (2.8-84 microM) depressed the MSR and the PSR in a concentration-dependent manner. At 2.8 microM of PbTx, the depression of MSR and PSR was 24+/-8.3% and 37+/-9.7%, respectively. The maximal depression was seen at 84 microM of the toxin (78% for MSR and 96% for PSR). The concentration of toxin required to produce 50% depression was 28.3+/-6.4 microM for MSR and 5.5+/-1.1 microM for PSR. The PbTx (28 microM) did not alter the magnitude of the dorsal root or the ventral root potentials. Addition of MgSO4 (1.3 mM) or DL-2-amino-5-phosphonovaleric acid (APV; 10 microM) to the physiological solution abolished the PSR totally and decreased the MSR by about 30%. In both the conditions, the PbTx-induced depression of the MSR was attenuated significantly. The PbTx-induced depression was blocked completely in the presence of APV+6-cyano-7-nitroquinoxaline-2,3-dione (0.1 microM). NMDA (1 microM) by itself did not alter the magnitude of MSR or PSR but enhanced the PbTx-induced depression (28 microM) of PSR significantly. 7-Chlorokynurenic acid (3 microM; glycine(B) antagonist) did not block the PbTx-induced depression of MSR. D-serine (glycine(B) agonist) did not reverse the PbTx-induced depression of reflexes although it reversed the 7-chlorokynurenic acid-induced depression of PSR. The results indicate that the PbTx depressed the spinal reflexes without altering the magnitude of dorsal root or ventral root activity. The depression of the PSR involved NMDA receptors while that of the MSR involved NMDA and non-NMDA receptors. The PbTx actions did not involve the glycine(B) site of the NMDA receptor.

Astrocytes are more vulnerable than neurons to cellular Ca2+ overload induced by a mitochondrial toxin, 3-nitropropionic acid.

The differential effects of 3-nitropropionic acid on cultured neurons and astrocytes (of cortical and striatal origin) were examined by studying intracellular Ca2+ changes using imaging techniques with fura-2. The neurons and astrocytes whose intracellular Ca2+ concentration was recorded were identified later by immunocytochemical staining for microtubule-associated protein 2 and glial fibrillary acidic protein, respectively. 3-Nitropropionic acid (1.7 mM) irreversibly increased intracellular Ca2+ in astrocytes (27%) and, to a significantly smaller extent, in neurons (10%). The latency to onset of the intracellular Ca2+ increase was longer in neurons (45 min) than in astrocytes (29 min). Thus, a differential susceptibility of astrocytes and neurons was observed. The 3-nitropropionic acid-induced astrocytic and neuronal Ca2+ accumulations were both due to influx of Ca2+, as the increases were absent in Ca2+-free medium. An inhibitor of the Na+-Ca2+ exchanger (2',4'-dichlorobenzamil), greatly reduced the intracellular Ca2+ increase in astrocytes, but not in neurons. This indicates that the intracellular Ca2+ increase in astrocytes is primarily mediated by a reverse operation of the Na+-Ca2+ exchange system, whereas in neurons it is mediated by a different mechanism. In addition, we noted that astrocytic cell death occurred in 9% of cells at 60 min or more after the start of a 40 min perfusion with 3-nitropropionic acid, while only 4% of neurons died. In astrocytes, cell death was preceded by blebbing of the cell membrane, and by a sustained increase in intracellular Ca2+ followed by an abrupt further elevation occurring just before cellular collapse. The present results indicate that astrocytes are more vulnerable than neurons to 3-nitropropionic acid-induced cellular Ca2+ overload and toxicity, and hence support the hypothesis that, in part, 3-nitropropionic acid-induced neurotoxicity could be secondary to astrocytic cell death caused by Ca2+ overload.

Acute 3-nitropropionic acid intoxication induces striatal astrocytic cell death and dysfunction of the blood-brain barrier: involvement of dopamine toxicity.

Mechanisms underlying the selective vulnerability of the lateral striatal area to the toxic effects of 3-nitropropionic acid (3-NPA) were investigated in rats. A single exposure to 3-NPA (20 mg/kg, s.c.) induced no deficits in behavior and histology, but subsequent injection produced motor symptoms, catalepsy, lip smacking, abnormal gait, paddling, rolling, opisthotonos, tremor, recombence, somnolence and so on, in 30% of the animals within a few hours. Diffusion-weighted magnetic resonance imaging of the brains revealed an area of high signal intensity in the bilateral striata. By this stage (within a few hours), striatal astrocytes had become swollen and disintegrated. Extravasation of immunoglobulin G was detected, indicating blood-brain barrier (BBB) dysfunction. Electron microscopy revealed edema and disorganization of structures inside the astrocytic end-feet around the branches of the lateral striatal artery. Neurons were less vulnerable than astrocytes to the 3-NPA injury. Treatment of the rats with D2 receptor agonist prior to exposure to 3-NPA attenuated the behavioral abnormalities and histological damage whereas pretreatment with D2 antagonist exacerbated these changes. The concentrations of extracellular dopamine (DA) and dihydroxyphenyl acetic acid (DOPAC) were both increased in rats exposed to 3-NPA. In vitro imaging of astrocytes revealed a progressive increase in [Ca2+]i after superfusion with 3-NPA, and the 'ceiling' level was maintained even after extensive washing. DA superfusion also increased the astrocytic [Ca2+]i and this increase was reversible. Data indicate that 3-NPA-induced striatal damage was associated with astrocytic cell death and dysfunction of the BBB. Intracellular edema and extreme Ca2+ overload induced by the toxin were further aggravated by an increase in the level of DA activity. These factors acting either singly or in combination may trigger astrocyte destruction.

Estrogen protects against while testosterone exacerbates vulnerability of the lateral striatal artery to chemical hypoxia by 3-nitropropionic acid.

Gender differences in the vulnerability of the lateral striatal artery (1STR artery) to systemic intoxication with 3-nitropropionic acid (3-NPA, succinate dehydrogenase inhibitor) were studied. Subcutaneous injection of 3-NPA (20 mg/kg once a day for 2 days) induced striatal selective lesions in half of male rats associated with motor symptoms (rolling, paddling, recumbency, etc) while female rats were resistant. Lesions were located in the lateral striata and characterized by astroglial necrotic cell death, enhanced immunoreaction to factor VIII-related antigen, edema, extravasation of IgG and sometimes bleeding. The motor and histological disturbances were highly sex-dependent and modulated by changes in hormonal levels. Males were more susceptible than females. Castration had little effect but ovariectomy enhanced the vulnerability. Replacement therapy with testosterone increased while estradiol or tamoxifen suppressed the vulnerability in ovariectomized females. Investigation of the arterial architecture of the brain often revealed rectangular and acute angled branchings in the centrolateral striatum where the ISTR artery feeds. A parallel in vitro toxicity study demonstrated that an extreme Ca++ overload and a strong cellular swelling resulted in astrocytic cell death. Data suggest that 1STR artery and astrocytes are highly vulnerable to 3-NPA intoxication in males. The greater vulnerability of the ISTR artery may contribute to the pathogenesis of neurodegenerative diseases, striatal bleeding, etc. Protective effects of estrogen and tamoxifen may mediate gender differences often observed in these disorders and suggest their potential use as therapeutic agents for these disorders.

Thyrotropin-releasing hormone reverses the supersensitively depressed monosynaptic transmission by serotonin in 5,7-dihydroxytryptamine-treated neonatal rats in vitro.

The interaction of serotonin and thyrotropin-releasing hormone (TRH) on monosynaptic reflex (MSR) in isolated neonatal spinal cords was examined. Superfusion of serotonin (1-30 microM) in untreated cords, depressed the MSR in a dose-dependent manner. The depression was about 25% at 10 microM of serotonin, in either control or vehicle-treated groups. While for the same concentration of serotonin, the depression was 97 +/- 2.1% of the control in cords from 5,7 dihydroxytryptamine (5,7-DHT)-treated animals. The inhibition of the reflex seen in cords obtained from 5,7-DHT-treated animals could not be reversed by washing with normal physiological solution (> 60 min) or in presence of serotonin antagonists. TRH (0.03-1.0 microM) reversed the depression in a concentration-dependent manner and complete reversal could be seen with 1 microM of TRH. These observations indicate that, serotonin and TRH act dissimilarly on the spinal synaptic transmission though they are known to coexist in the descending bulbospinal tracts.

In vitro protection of 3-nitropropionic acid-induced toxicity of astrocytes by basic fibroblast growth factor and thrombin.

The protective action of basic fibroblast growth factor (bFGF) and thrombin on cultured cortical astrocytes in vitro to the toxic effects of 3-nitropropionic acid (3-NPA) was examined. 3-NPA produced concentration- and time-dependent astrocyte loss as indicated by decrease in the number of glial fibrillary acidic protein (GFAP) positive cells and increase in lactate dehydrogenase (LDH) level of the culture medium. The 3-NPA-induced cellular loss was apparent within 12 h and was maximal at 24 h. The presence of bFGF (10 ng/ml) by itself increased the number of astrocytes at various time intervals, and attenuated the 3-NPA-induced cell loss significantly at various concentrations (0.017-1.7 mM), in 24 and 48 h of exposure. Lower concentrations of thrombin (up to 1 nM) had no effect on the number of astrocytes but higher concentrations (10-100 nM) produced greater cell loss. Thrombin (1 nM) prevented the 3-NPA-induced decrease in GFAP positive cells at both 24 and 48 h intervals. This was further substantiated by the fact that thrombin as low as 0.01 nM attenuated the 3-NPA-induced increase of LDH activity at 24 and 48 h exposure times. But, with 1 nM of thrombin, the attenuation of the LDH activity was seen only at 24 h. The results indicate that 3-NPA produced acute astrocyte toxicity and was attenuated by bFGF and lower concentrations of thrombin.

Analogs of thyrotropin-releasing hormone in potentiating the spinal monosynaptic reflex in vitro.

The efficacy of thyrotropin-releasing hormone (TRH) and its analogs to potentiate the spinal monosynaptic reflex was studied in isolated cords. The analogs examined were L-pyro-2-aminoadipyl-histidyl-thizolidine-4-carboxyamide (MK-771); pyroglutamyl-histidyl-prolineamide (TRH); pyroglutamyl-L-histidyl-3,3'-dimethyl-prolineamide (RX77368); (3-methyl-His2)TRH(methyl-TRH); gamma-buturolactone-gamma-carbonyl-histidyl-prolineamide citrate (DN-1417); pyroglutamyl-histidyl-proline (TRH-free acid); and histidyl-proline-diketopiperazine (cyclo(His-Pro)). The TRH analogs potentiated the monosynaptic reflex in a dose-dependent manner and the maximal potentiation occurred at about 1 microM. TRH-free acid potentiated the monosynaptic reflex but the maximal potentiation occurred at 100 times the TRH concentration. Cyclo(His-Pro) was totally ineffective. The concentration required to potentiate the monosynaptic reflex by 50% of the maximal response (EC50) was taken as an index for comparing various analogs in relation to TRH. The EC50 values of the analogs did not differ significantly from each other. However, the ratio of the mean value of an analog to that of TRH was of the following order: MK-771 (N- and C-terminally altered) > or = TRH > or = DN-1417 (N-terminal) > or = methyl-TRH > or = RX77368 (C-terminal) >>> TRH-free acid. Cyclo(His-Pro) was ineffective.

Interaction of thyrotropin-releasing hormone and methysergide on the monosynaptic reflex in isolated mammalian spinal cord.

The interaction between thyrotropin-releasing hormone (TRH) and methysergide (MeSG) on reflex activity was examined in spinal cords from neonatal rats. MeSG depressed the monosynaptic reflex (MSR) by nearly 90% at 0.03 microM but had no effect on the dorsal root reflex at 0.003-3.0 microM. Neither spiperone, ketanserin, cyproheptadine nor ICS 205-930 (3-tropanyl-indole-3-carboxylate) depressed the MSR nor did they affect the potentiation elicited by TRH. TRH reversed the depression of the MSR by MeSG in a concentration-dependent manner without affecting the dorsal root reflex. MeSG-induced depression of the MSR was also reversed by 3,4-diaminopyridine which simultaneously increased the magnitude and duration of both reflexes. It appears that neither MeSG-induced depression nor TRH-induced potentiation of the MSR involves the spinal serotonergic system or blockade of K+ channels.

Indian red scorpion (Buthus tamulus) venom-induced augmentation of cardiac reflexes is mediated through the mechanisms involving kinins in urethane anaesthetized rats.

The mechanism underlying the action of Indian red scorpion (Buthus tamulus; BT) venom on cardiac reflexes was examined in urethane anaesthetized adult albino rats of either sex. Intravenous injection of phenyldiguanide (PDG) produced reflex hypotension, bradycardia and apnea lasting for > 60 s. The PDG-induced reflex responses (blood pressure, heart rate and respiration) were augmented greatly (magnitude and time period) after exposure to BT venom (100 microg/kg, i.v., for 30 min). However, there were no great alterations in resting blood pressure, heart rate and respiratory rate. Pretreatment with kallikrein kinin inhibitor (aprotinin; 6000 kallikrein inactivating unit, i.v.) blocked the BT venom-induced augmentation of PDG reflex response. Further, pretreatment with indomethacin (prostaglandin synthetase inhibitor; 10 mg/kg) and heparin (1000 units/kg) also blocked the venom-induced potentiation of the reflex. Captopril (15 mg/kg), an agent known to increase endogenous kinins, also augmented the PDG induced-reflex to the same extent as in BT envenomed rats. The captopril-induced augmentation of the reflex was blocked by aprotinin and heparin, but not by indomethacin. The results indicate that kinins and prostaglandins are involved in the BT venom-induced augmentation of the cardiac reflexes.

Toxicity of scorpion (Buthus tamulus) venom in mammals is influenced by the age and species.

The present study was undertaken to determine the toxicity of scorpion (Buthus tamulus) venom in young and adult rats, as well as in different species of adult animals (rats, mice and guinea-pigs). The median lethal dose (LD50; mg/kg s.c.) of scorpion venom in young and adult rats was 2.2 +/- 0.21 and 1.3 +/- 0.14, respectively. The LD50 value for mice (7.2 +/- 1.35) was significantly greater than adult rats or guinea-pigs (1.14 +/- 0.08). The LD50 dose for i.v. route in anaesthetized adult rats was 95 +/- 13.2 micrograms/kg weight, which is 13 times less than that required for s.c. route. The results show that the lethality of scorpion venom in mammals differs with the age and species of the animals.

Indian red scorpion (Buthus tamulus) venom-induced augmentation of cardiac reflexes is mediated through the involvement of peripheral 5-HT3 and central 5-HT1A receptor subtypes.

The present study was undertaken to identify 5-HT receptor subtypes involved in Buthus tamulus (BT) venom-induced augmentation of cardiac reflexes elicited by phenyldiguanide (PDG). Intravenous injection of PDG (10 microg/kg) produced parallel decrease in mean arterial pressure (MAP) and heart rate (HR) in urethane anaesthetized rats (r=0.82; p < 0.001). Injection of PDG (1-40 microg/kg, i.v.) produced concentration-dependent decrease in time-response area of the HR. After BT venom (20 microg/kg) the concentration-response curve was shifted to the left. Further, fall of MAP and HR in response to submaximal concentration of PDG (10 microg/kg) were augmented significantly. Pretreatment with 5-HT3 receptor antagonist (ondansetron; 10 microg/kg) intravenously, blocked the BT venom-induced augmentation of PDG reflex but spiperone (100 microg/kg; 5-HT1A/5-HT2 antagonist) or ketanserin (300 microg/kg; 5-HT2 antagonist) failed to do so. Afferent discharges elicited by PDG (10 microg/kg) in vagus nerve were doubled after exposure to BT venom. Ondansetron (100 microg/kg, i.v.) totally abolished the discharges after exposure to BT venom but not by spiperone or ketanserin. Intracerebroventricular injection of spiperone (100 microg/kg) but not ketanserin or ondansetron, blocked the BT venom-induced augmentation of PDG reflex. Results show that the BT venom-induced augmentation of reflex elicited by PDG is mediated through the involvement of 5-HT3 receptors peripherally and 5-HT1A type of receptors centrally.

Diisopropylfluorophosphate-induced depression of segmental monosynaptic transmission in neonatal rat spinal cord is also mediated by increased axonal activity.

Involvement of dorsal and ventral root activity for the depressant action of diisopropylfluorophosphate (DFP) on synaptic transmission was examined using in vitro spinal cord/root preparations. Superfusion of DFP produced a dose-dependent depression of monosynaptic reflex (MSR) and maximal depression of about 80% occurred at 1000 microM. The concentration to produce 50% of the maximal inhibition was about 100 microM of DFP. The DFP (100 microM)-induced depression of MSR was reversed by atropine (0.5 microM) but not by mecamylamine (0.5 microM). Contrary to the action on MSR, DFP potentiated the ventral root potential and 1st peak of dorsal root potential. The maximal potentiation was about 25% of control in both the root potentials at 100 microM of DFP. However, the second peak of dorsal root potential was slightly depressed (10-20% of control) by DFP (1-1000 microM). Further, the cords treated with DFP (100 microM) showed significant decrease in the cholinesterase (ChE) activity (27% of control). Results suggest that the DFP-induced depression was mediated at least by two different mechanisms, one through the inhibition of ChE activity and the other through the activation axonal activity having inhibitory inputs to the segmental synaptic transmission. These inputs mediate their action through muscarinic receptors.