Involvement of 5-hydroxytryptaminergic transmission for the Mesobuthus tamulus venom-induced depression of spinal reflexes in neonatal rat in vitro.
Mesobuthus tamulus (MBT) venom is shown to depress the spinal reflexes through a mechanism unrelated to the NMDA receptors. 5-Hydroxytryptamine (5-HT) is another excitatory transmitter in the spinal cord therefore, the present study was undertaken to examine the involvement of 5-HT in the venom-induced depression of reflexes. The experiments were performed on isolated hemisected spinal cords from 4 to 6-day-old rats. Stimulation of a dorsal root with supramaximal strength evoked monosynaptic reflex (MSR) and polysynaptic reflex (PSR) potentials in the corresponding segmental ventral root. MBT venom (0.3 microg/ml) depressed the spinal reflexes in a time-dependent manner and the maximal depression was seen at 10 min. The time to produce 50% depression (T-50) of MSR and PSR was 8.1+/-1.41 and 6.8+/-0.5 min, respectively. Pretreatment with pindolol (1 microM; 5-HT(1A/1B) receptor antagonist) blocked the reflexes up to 15 min. On the other hand, ketanserin (10 microM; 5-HT(2A/2C) receptor antagonist) or ondansetron (0.1 microM; 5-HT(3) receptor antagonist) blocked the venom-induced depression of MSR and PSR during entire exposure time (30 min). The 5-HT concentration of the cords exposed to venom (1.6+/-0.04 microg/g tissue) was significantly greater than the control group (0.98+/-0.08 microg/g tissue). The results indicate that venom-induced depression of spinal reflexes is mediated via 5-HTergic transmission involving 5-HT(1A/1B), 5-HT(2A/2C) and 5-HT(3) receptors.
Maurya
Amar N
AN
Department of Physiology, Institute of Medical Sciences, Banaras Hindu University, Varanasi, UP, India.
Deshpande
Shripad B
SB
D000818:Animals; D000831:Animals, Newborn; D009924:Organ Culture Techniques; D051381:Rats; D044263:Receptors, Serotonin, 5-HT1 / Q000187:drug effects / Q000378:metabolism; D044348:Receptors, Serotonin, 5-HT2 / Q000187:drug effects / Q000378:metabolism; D044406:Receptors, Serotonin, 5-HT3 / Q000187:drug effects / Q000378:metabolism; D012023:Reflex, Monosynaptic / Q000187:drug effects / Q000502:physiology*; D012604:Scorpion Venoms / Q000494:pharmacology*; D012701:Serotonin / Q000378:metabolism*; D012702:Serotonin Antagonists / Q000494:pharmacology; D013116:Spinal Cord / Q000187:drug effects / Q000502:physiology*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*
D044263:Receptors, Serotonin, 5-HT1; D044348:Receptors, Serotonin, 5-HT2; D044406:Receptors, Serotonin, 5-HT3; D012604:Scorpion Venoms; D012702:Serotonin Antagonists; D012701:Serotonin