Respiratory pumping in Aplysia fasciata as part of an integrated defensive response to increases and decreases in seawater concentration

Abstract

Much of the neural circuitry controlling respiratory pumping in Aplysia has been well characterized, but the function of this movement is incompletely understood. To gain insight into possible functions of respiratory pumping, responses were examined for a 40 min exposure to two stimuli that modulate the movement: 1) increase and 2) decrease in seawater concentration. Thresholds were present for both stimuli to affect respiratory pumping. Above threshold, there were graded increases in the number of pumps elicited. There were decrements in respiratory pump frequency as a function of time exposed to the stimulus. Increased respiratory pumping did not contribute to volume regulation in response to exposure to altered seawaters, but was associated with increased defensive responses, such as escape locomotion (swimming) and inking. In addition, head shock, a well-established noxious stimulus, elicited temporal patterns of respiratory pumping similar to those elicited by altered seawaters. The data indicate that in our experimental conditions, respiratory pumping is elicited as part of an integrated defensive response to noxious seawaters.

Separate Effects of a Classical Conditioning Procedure on Respiratory Pumping, Swimming, and Inking inAplysia fasciata

“…Previous studies in our laboratory showed that increases and decreases in seawater concentration (Levy et al 1993), as well as an increase in seawater pCO 2 that is measured by a decrease in pH (Levy et al 1989), elicit increases in the rate of respiratory pumping in A. fasciata. A number of observations supported the conclusion that respiratory pumping in response to these stimuli does not have a respiratory or a volume regulatory function but, rather, is a defensive response (Levy et al 1993). First, the temporal patterning of respiratory pumping in response to these altered seawaters is similar to that in response to a noxious stimulus, head shock (Levy et al 1993).…”

“…First, the temporal patterning of respiratory pumping in response to these altered seawaters is similar to that in response to a noxious stimulus, head shock (Levy et al 1993). Second, surgical procedures that block the increased respiratory pumping in response to changes in seawater concentration increase the ability of an animal to maintain its volume rather than decreasing it (Levy and Susswein 1993;Levy et al 1993). Third, respiratory pumping in response to an increased pCO 2 is associated with a decrease in oxygen consumption rather than with an increase (Levy et al 1989).…”

“…A number of observations supported the conclusion that respiratory pumping in response to these stimuli does not have a respiratory or a volume regulatory function but, rather, is a defensive response (Levy et al 1993). First, the temporal patterning of respiratory pumping in response to these altered seawaters is similar to that in response to a noxious stimulus, head shock (Levy et al 1993). Second, surgical procedures that block the increased respiratory pumping in response to changes in seawater concentration increase the ability of an animal to maintain its volume rather than decreasing it (Levy and Susswein 1993;Levy et al 1993).…”

“…Third, respiratory pumping in response to an increased pCO 2 is associated with a decrease in oxygen consumption rather than with an increase (Levy et al 1989). Fourth, increases and decreases in seawater concentration also elicit escape locomotion and inking, bona fide defensive responses (Levy et al 1993). Fifth, a classical conditioning procedure in which a noxious stimulus (head shock) is paired with a subthreshold exposure to an altered seawater causes a pairing-specific increase in respiratory pumping in response to these stimuli an hour following the pairing (Levy and Susswein 1990;Levy et al 1994b).…”

“…In this paper we examine whether a training procedure that leads to pairing-specific increases in respiratory pumping when animals are stimulated with an altered seawater conditioned stimulus (CS) also causes increases in other defensive responses, such as swimming and inking. Previous studies have suggested that somewhat different neural pathways, which use different neurotransmitters, may be activated in response to a variety of altered seawaters that can modulate respiratory pumping (Levy and Susswein 1993). For this reason, it was of interest to determine the effects of training on a number of different altered seawaters.…”