Pain Pathways in General, and the importance of this snail:
The two broad categories of nerve fibers responsible for nociception in the human and other mammals are known as the A-Delta Nociceptor and the C-Fiber Nociceptor. These fibers are responsible for two painful phenomena familiar to most humans known as the "first pain" and the "second pain." The first pain occurs immediately after physical trauma, such as stubbing the toe. Characterized by a sharp localized pain, the first pain allows the mammal to locate the injured area of the body immediately. The second pain occurs moments after and is often perceived as a dull burning pain. This pain remains for a longer time period than the first pain and offers the animal "incentive" to immobilize the injured body part and to allow sufficient time for it to heal.
In an article titled "Mechanosensory Neurons Innervating Aplysia Siphon Encode Noxious Stimuli and Display Nociceptive Sensitization" (The Journal of Neuroscience, Vol. 17, No.1, Jan. 1, 1997, pp. 459-469), Paul A. Illich and Edgar T. Walters (University of Texas-Houston Medical School) demonstrated similarities between the vertebrate A-Delta nociceptors and the nociceptive nerve fibers of the aquatic snail Aplysia californica. According to Illich and Walters, properties of the A. californica nociceptors included a relatively high frequency of peak responses (greater than 30 Hz.), relatively large RFs, and lack of activation by most chemical activators which would normally activate C polymodal nociceptors. These characteristics, in addition to the display of sensitization, meet the accepted criteria for the A-Delta nociceptor which has been described in the vertebrate.
Given the degree of similarity between vertebrate nociceptors and the nociceptors of A. californica, I believe it of benefit to pursue studies illucidating similarities between nociceptors of a related snail (H. aspersa) and the nociceptors of the vertebrate. The H. aspersa snail is easily maintained in a terrestrial environment consisting of several clear plastic ventilated rectangular containers, a constant temperature, 12:12 inverse light:dark cycles, and is allowed ad libitum access to food which is maintained in a shallow rectangular glass dish located in the center of the terraria. The H. aspersa snail requires far less maintenance than snails which require an aquatic environment.