N no locomotive response to mechanical stimulation. Even so, a longitudinal incision, via the animal’s body, produced behind the brain and continued posteriorly along the midline for most of the animal’s length (therefore generating a L-shaped cut through the worm’s physique), didn’t avoid locomotory escape behavior, suggesting the presence of a diVuse sensory neural network (Koopowitz 1973). Presumably pin prick represents a noxious stimulus and hence the evoked behavior may very well be deemed asJ Comp Physiol A (2009) 195:1089Mollusca Nociceptors and nociceptive behavior have also been investigated in various species of Mollusca. For instance, the land snail, Cepaea nemoralis, responds to placement on a hotplate (0 ) with stereotypical lifting of your anterior portion from the extended foot. The expression of opioid receptors and endogenous ligands for these receptors is deemed fundamental in determining whether or not nociception can happen (Sneddon 2004). As a result, it can be fascinating to note that opiate agonists improved withdrawal latency, which may be blocked by the opiate receptor antagonist, naloxone (Kavaliers et al. 1983). The usage of 1 and two opioid receptor agonists also elevated response latency (Thomas et al. 1997) and immunohistochemical staining indicates the presence of endogenous -receptor agonists (Sakharov et al. 1993). The hot-plate test is really a common model for measuring nociception in rodents and opiates commonly raise the withdrawal latency even though Dynorphin A (1-8) medchemexpress strain diVerences in basal withdrawal latency plus the magnitude on the eVect of morphine do take place (Mogil et al. 1996). Therefore, the action of opioid receptor agonistsantagonists upon withdrawal latency supports the hypothesis that the foot lifting response in C. nemoralis is certainly a nocifensive behavior. Just about the most intensively studied Mollusca is the gastropod, Aplysia californica. The Wrst potentially nociceptive sensory neurons within a. californica, innervating the siphon and mantle, had been identiWed within the left E (LE) Landiolol Protocol cluster in the abdominal ganglion (Castellucci et al. 1970). Initial studies indicated that these had been low threshold mechanoreceptors (Byrne et al. 1974), but this was later shown to be due to sensitization induced by tightly pinning out the siphon (Illich and Walters 1997). In a “free siphon” model low-level tactile stimuli that evoked siphon withdrawal failed to activate LE cells. On the other hand, upon reaching activation threshold LE-cell activity elevated with stimulus strength and maximal activity occurred when crushing tearing stimuli, causing body wall damage, had been employed. These are qualities of nociceptors, cells tuned to detect noxious stimuli. A second group of sensory neurons would be the ventrocaudal (VC) cells of your pleural ganglia. Tactile stress towards the organism’s posterior generates graded responses in these cells, which adapt slowly to maintained stimulation. Despite the fact that responsive to weak stimuli, VC-cells respond most vigorously to pinching on the posterior, which simultaneously evokes “tail” withdrawal, suggestive that pinching is noxious and, as a result, that VC-cells are acting as nociceptors. Certainly electrical activation of a VC sensory neuron induced motor neuron activation and withdrawal of your “tail”, or far more properly the posterior, supporting this theory (Walters et al. 1983). This capability of VC-cells to respond to weak stimulation and most vigorously toT 20mV 200ms Ptouch 7gPN7g 21gFig. three Intracellular recordings from T-, P- and N-cells.