CONICET | Buscador de Institutos y Recursos Humanos

Leeches crawl on solid surfaces by successive elongation and contraction of its body, anchored on the front and rear suckers. These movements would exert mechanical forces on the skin, innervated by three types of mechanosensory neurons. Because activation of the mechanoreceptors elicit a series of defensive behaviors, the mechanosensory signals could perturb the rhythmic displacement.Recordings of low threshold tactile (T) mechanosensory neurons in isolated midbody ganglia during dopamine-elicited fictive crawlings (crawling) show that T cells receive inhibitory signals in phase with the activation of the motoneurons that cause the contraction. The inhibition is probably due to the activation of a synaptically-driven chloride conductance. Because the study was produced in the absence of the periphery this inhibition must be originated by the nervous system, probably downstream of the central pattern generator.To confirm that inhibition of T cells is necessary to the smooth occurrence of crawling we analyzed the effect of exciting these neurons during the contraction phase and during the elongation phase. The results show that activation of T cells interrupts the burst of the motoneuron that controls contraction, but has no effect during elongation.We interpret that the circuit that controls crawling sends an efference copy to the sensory neurons, to counteract the discharge caused by he mechanical forces exerted during contraction.