Modification of leech behavior following foraging for artificial blood

Abstract

In this study we examined whether the foraging for artificial blood affected the behavioral responsiveness of leeches to electrical stimulation of the body wall. After foraging for artificial blood, electrical stimulation of the posterior end of the leech significantly increased the percentage of stimulation trials that elicited locomotory activity--swimming and crawling--compared to the behaviors elicited when leeches did not forage or foraged for normal saline. On the other hand, shortening always dominated the behavioral profile of the leech to anterior stimulation even after foraging for artificial blood. In intact anterior end-isolated nerve cord preparations, we also found that application of artificial blood to the intact anterior end was sufficient to modify motor responsiveness to DP nerve stimulation. Full strength artificial blood had an overall negative effect on the likelihood of DP nerve stimulation initiating swimming and on the average length of elicited swim episodes compared to when pond water surrounded the anterior end. Application of a 10% solution of artificial blood to the anterior end led to an increase in the likelihood of DP nerve stimulation eliciting swimming.

Decision Points: The Factors Influencing the Decision to Feed in the Medicinal Leech

“…Hungry H. verbana use both visual (Dickinson and Lent, 1984) and mechanical (Young et al, 1981) cues from water waves to determine whether prey is present and which direction to move. Chemical cues also promote swimming during foraging behavior (Brodfuehrer et al, 2006). Once contact is made with a potential host, both thermal and chemical cues govern the decision to feed.…”

“…This diversity in serotonin action can in some cases be explained by whether serotonin is applied to the brain or within specific regions within the segmental ganglia (Crisp and Mesce, 2003; Calviño and Szczupak, 2008). Additionally, we do not know which sensory neurons activate these serotonergic neurons, although it is likely that the lip chemoreceptors (Elliott, 1986, 1987) are a major source because the suppression of other behaviors is observed during the exploration of a potential food item even before the leech begins to feed (Gaudry and Kristan, 2009) and when full strength artificial blood is presented at ambient temperature to the lip of head-intact isolated nerve cord preparations (Brodfuehrer et al, 2006). Furthermore, chemosensory stimulation is known to activate some of the serotonergic neurons (Groome et al, 1995; Zhang et al, 2000).…”

Contextual modulation of behavioral choice

“…The presence of food can bias the choice of behavioral response: the likelihood of large tail flips (which move the animal further from the food) decreases when food is present, as does the activity of medial giant interneurons (which receive tactile and visual inputs) that drive the tail flip response. Medicinal leeches ignore mechanosensory stimulation that would normally elicit locomotion behaviors in the presence of artificial blood [30]. Pinching the tail of a marine slug ( Aplyisa californica ) can elicit either feeding or locomotory behavior, and serotonergic neurons sensitive to food modulate the choice between these two behaviors [31].…”

“…The medicinal leech has a clear behavioral hierarchy, with feeding taking precedence over all other behaviors [43]. Following up the earlier study by Brodfuehrer et al, (2006) [30] showing decreased responsiveness to touch in the presence of artificial blood, Gaudry and Kristan [44••] found that when a leech is actively engaged in feeding on blood, serotonin presynaptically inhibits the connections between mechanosensory neurons and interneurons that mediate other behaviors such as swimming, crawling, shortening and bending (Figure 2A). This inhibition, which makes the leech able to maintain feeding and be unresponsive to even intense mechanosensory sensation, was observed behaviorally in sanguivorous (bloodsucking) species, but not carnivorous species [45].…”

Activation of two forms of locomotion by a previously identified trigger interneuron for swimming in the medicinal leech

“…The identification of multifunctional projection interneurons raises the question as to how the same activity pattern in these interneurons can encode the initiation process of multiple behaviors. It is generally thought that the behavior elicited depends on the integration of multiple factors such as sensory cues, hormone or neuromodulator levels, and behavorial state (Brodfuehrer et al 2006;Hedwig 2000;Libersat and Pflueger 2004;Matsuura et al 2002;Watson and Ritzman 1994).…”