Abstract
The entomotoxic potential of Manilkara rufula crude extract (CEMR) and its aqueous (AFMR) and methanolic (MFMR) fractions were evaluated against Nauphoeta cinerea cockroaches. The results point out to a direct modulation of octopaminergic and cholinergic pathways in insect nervous system. CEMR induced an anti-acetylcholinesterase (AChE) effect in cockroach brain homogenates. CEMR significantly decreased the cockroach heart rate in semi-isolated heart preparations. CEMR also caused a broad disturbance in the insect behavior by reducing the exploratory activity. The decreased antennae and leg grooming activities, by different doses of CEMR, mimicked those of phentolamine activity, a selective octopaminergic receptor antagonist. The lethargy induced by CEMR was accompanied by neuromuscular failure and by a decrease of sensilla spontaneous neural compound action potentials (SNCAP) firing in in vivo and ex vivo cockroach muscle-nerve preparations, respectively. AFMR was more effective in promoting neuromuscular paralysis than its methanolic counterpart, in the same dose. These data validate the entomotoxic activity of M. rufula. The phentolamine-like modulation induced in cockroaches is the result of a potential direct inhibition of octopaminergic receptors, combined to an anti-AChE activity. In addition, the modulation of CEMR on octopaminergic and cholinergic pathways is probably the result of a synergism between AFMR and MFMR chemical compounds. Further phytochemical investigation followed by a bio-guiding protocol will improve the molecular aspects of M. rufula pharmacology and toxicology to insects.
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