Neurotransmitter Interactions in the Stomatogastric System of the Spiny Lobster: One Peptide Alters the Response of a Central Pattern Generator to a Second Peptide

Abstract

Two of the peptides found in the stomatogastric nervous system of the spiny lobster, Panulirus interruptus, interacted to modulate the activity of the cardiac sac motor pattern. In the isolated stomatogastric ganglion, red-pigment-concentrating hormone (RPCH), but not proctolin, activated the bursting activity in the inferior ventricular (IV) neurons that drives the cardiac sac pattern. The cardiac sac pattern normally ceased within 15 min after the end of RPCH superfusion. However, when proctolin was applied within a few minutes of that time, it was likewise able to induce cardiac sac activity. Similarly, proctolin applied together with subthreshold RPCH induced cardiac sac bursting. The amplitude of the excitatory postsynaptic potentials from the IV neurons to the cardiac sac dilator neuron CD2 (1 of the 2 major motor neurons in the cardiac sac system) was potentiated in the presence of both proctolin and RPCH. The potentiation in RPCH was much greater than in proctolin alone. However, the potentiation in proctolin after RPCH was equivalent to that recorded in RPCH alone. Although we do not yet understand the mechanisms for these interactions of the two modulators, this study provides an example of one factor that can determine the "state" of the system that is critical in determining the effect of a modulator that is "state dependent," and it provides evidence for yet another level of flexibility in the motor output of this system.

Modulation of Oscillator Interactions in the Crab Stomatogastric Ganglion by Crustacean Cardioactive Peptide

“…However, it is possible that in the animal, other modulatory substances could act synergistically with CCAP, and that the effective CCAP thresholds and actions could be conditioned by other circulating or neurally delivered modulatory substances. This kind of enhancement of the action of one peptide by another is seen in Dickinson et al (1997), demonstrating the enhancement of synaptic potentials in the stomatogastric nervous system. We show here that CCAP alters both the motor patterns produced by the STG and the gain of the motor neuron to movement transfer function.…”

Inter-animal variability in the effects of C-type allatostatin on the cardiac neuromuscular system in the lobster Homarus americanus

“…For example, octopamine exerts an antagonistic effect on serotonin modulation at the neuromuscular junction in crayfish and crabs; when applied together, the increase in synaptic potential amplitude that is evoked by serotonin is decreased, regardless of whether octopamine increases or decreases the same post-synaptic potential when applied alone (Djokaj et al, 2001). Interactions among peptide neuromodulators have likewise been documented: in the spiny lobster (Panulirus interruptus), previous application of red pigment concentrating hormone (RPCH) results in a qualitative change in the response of the cardiac sac pattern generator to proctolin (Dickinson et al, 1997). The lobster heart is modulated by a myriad of substances, so numerous possibilities for such metamodulation exist.…”

“…In the spiny lobster stomatogastric system, for example, the modulatory effects of one neuropeptide (proctolin) can be dramatically altered by interactions with a second peptide (red pigment concentrating hormone) (Dickinson et al, 1997). Similarly, the modulatory effects of octopamine in the moth Manduca sexta are altered by exposure to 20-hydroxyecdysone, a phenomenon described as metamodulation (Mesce, 2002).…”

Octopamine Modulates the Axons of Modulatory Projection Neurons

“…Red pigment concentrating hormone and proctolin likewise act on both anterior and STG sites to influence the STG motor patterns (Dickinson et al, 1993(Dickinson et al, , 1997.…”