Browsing by Author "Mandal, Maloy B"
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Item Ca2+ -free medium enhances the magnitude of slow peak in compound action potential of frog sciatic nerve in vitro.(2004-01-28) Mandal, Maloy B; Deshpande, Shripad BThe present investigation was carried out to know the effect of Ca2+ on different peaks of compound action potential (CAP) representing the fibers having different conduction velocity. CAP was recorded from a thin bundle of nerve fibers obtained from desheathed frog sciatic nerve. Suction electrodes were used for stimulating and recording purposes. In Ca2+ -free amphibian Ringer, two distinct peaks (Peak-I and Peak-II) were observed. The threshold, conduction velocity (CV), amplitude and duration of Peak-I were 0.32 +/- 0.02 V, 56 +/- 3.0 m/sec, 2.1 +/- 0.2 mV and 0.75 +/- 0.1 ms, respectively. The Peak-II exhibited ten times greater threshold, eight times slower CV, three times lower amplitude and four times greater duration as compared to Peak-I. Addition of 2 mM Ca2+ in the bathing medium did not alter CAP parameters of Peak-I excepting 25% reduction in CV. But, in Peak-II there was 70-75% reduction in area and amplitude. The concentration-attenuation relation of Peak-II to various concentrations of Ca2+ was nonlinear and 50% depression occurred at 0.35 mM of Ca2+. Washing with Ca2+ -free solution with or without Mg2+ (2 mM)/verapamil (10 microM) could not reverse the Ca2+ -induced changes in Peak-II. Washing with Ca2+ -free solution containing EDTA restored 70% of the response. The results indicate that Ca2+ differentially influence fast and slow conducting fibers as the activity of slow conducting fibers is greatly suppressed by external calcium.Item In Vitro Study of Acetylcholine and Histamine Induced Contractions in Colon and Rectum of Adult and Neonate Rats.(2013-04) Singh, Shuchita; Mandal, Maloy BContractile mechanisms of different parts of the gut in adult and neonate may not be identical due to developmental processes. The present study was undertaken to investigate acetylcholine (ACh) and histamine induced contractile responses of colon and rectum in adult and neonatal albino rats. Contractile responses were recorded from isolated in vitro preparations. The dose-response curve for ACh (0.001-100 μM) revealed dose dependent increase in contractile responses. A significantly (P<0.05) greater contractile responses (g/g wet tissue) was observed in rectum as compared to colon. Atropine pretreatment significantly blocked ACh responses in both rectum and colon. The blockade was higher in adult preparations. The dose-response study for histamine (0.001-100 μM) did not show any significant difference between rectum and colon. Histamine (100 μM) induced contractions were significantly (P<0.05) increased after pretreatment with pheniramine (100 μM) in adult rectum. This potentiating response of pheniramine was absent in neonate rectum. Such effect was also not seen in colon of both adult and neonate. The present investigation indicates that the contractile responses induced by ACh are similar in both adult and neonate, excepting that the blocking effect of atropine in colon was more pronounced in adult as compared to neonate. Further, the results also indicated different mechanism of histamine action in adults and neonates as evidenced by the significant enhancement of contractions by pheniramine only in adult rectum. Therefore, the present results indicate the existence of a different cholinergic and histaminergic activity in adult and neonate as well as in rectal and colonic tissue.Item In vivo and in vitro bradycardia induced by local anesthetics is potentiated by calcium channel blockers.(2009-04) Mandal, Maloy B; Sahu, Manoj K; Mandal, Sanchayan; Gupta, P KThe present study examined the interactions of local anesthetics (LA) and calcium channel blockers (CCBs) on rhythmicity of heart using in vivo and in vitro experiments. ECG recordings were made from the anesthetized rats for in vivo preparations and spontaneously beating isolated rat right atrial potential for the in vitro experiments. The in vivo experiments with LA showed dose-dependent bradycardia with lignocaine (LIG, 100-500 μg/kg) and bupivacaine (BUP, 10-100 μg/kg). BUP was 4-5 times more potent than LIG. Verapamil (VML) and diltiazem (DTZ), CCBs also produced dose (10-100 μg/kg) -dependent bradycardia. However, none of them affected the PR/QT interval or QRS complex. Further, LA-induced bradycardia was potentiated by CCBs. In addition, flattening of P-wave in ECG was observed with doses (10-25 μg/kg) of LA in the presence of CCBs. Similarly, the in vitro experiments demonstrated a concentration-dependent decrease in atrial rate by BUP or VML. The BUP-induced decrease was potentiated in the presence of VML. Thus, the results suggest that CCBs potentiate the LA-induced bradycardia by involving pacemaker activity. Further, the flattening of P-wave in ECG serves as an early indicator of the cardiotoxicity produced by these drugs.Item Ptychodiscus brevis toxin decreases the spontaneous activity of rat right atria involving muscarinic receptors and potassium channels.(2008-04-10) Singh, Jitendra N; Mandal, Maloy B; Deshpande, Shripad BMarine dinoflagellate Ptychodiscus brevis toxin (PbTx), is known to produce toxic effects on cardiovascular system. The present experiments were conducted to evaluate the effect of synthetic phosphorus containing Ptychodiscus brevis toxin on spontaneously beating right atrium in vitro. The PbTx (0.84-84 microM) decreased the rate and force of right atrial contractions in a concentration-dependent manner. Ethanol, a vehicle present in highest concentration of PbTx, had no effect on atrial rate or force of contraction. Pretreatment with atropine blocked the PbTx-induced decrease in atrial rate and force of contraction. The tetraethylammonium, a potassium channel blocker, blocked the PbTx-induced decrease in atrial rate and force, where as, L-type of calcium channel blocker, nifedipine blocked the PbTx-induced force of contraction but not the rate changes. The results indicate that the PbTx decreased the atrial rate and force of contraction via cholinergic receptors involving K+ channel.Item Sleep duration of an individual has adverse influence on auditory episodic memory.(2007-10-15) Nepal, Desh Bandhu; Kumar, Tushant; Mandal, Maloy B; Deshpande, Shripad BThe present study evaluated the influence of habitual sleep duration on episodic memory in a wakeful state. Episodic memory was assessed for auditory and visual processing pathways. A total of 96 medical students (53 male and 43 female, between the age group 18-23 years) accustomed to different sleep durations volunteered in the tests. The tests included auditory free recall of 10 common words, pictorial free recall of 10 pictures and recognition of 10 miniature animal replicas with 10 distracters. There was no gender-related difference in the visual and the auditory memory scores. The visual episodic memory scores were similar in persons sleeping longer or shorter duration. On the other hand auditory memory scores were significantly lower in persons accustomed to >10 h sleep. The results indicate the importance of sleep duration on episodic memory processing of learned material even during wakeful state specially which involves auditory system.