Muscle Response to Changing Neuronal Input in the Lobster(Panulirus Interruptus)Stomatogastric System: Slow Muscle Properties Can Transform Rhythmic Input into Tonic Output

Abstract

Slow, non-twitch muscles are widespread in lower vertebrates and invertebrates and are often assumed to be primarily involved in posture or slow motor patterns. However, in several preparations, including some well known invertebrate "model" preparations, slow muscles are driven by rapid, rhythmic inputs. The response of slow muscles to such inputs is little understood. We are investigating this issue with a slow stomatogastric muscle (cpv1b) driven by a relatively rapid, rhythmic neural pattern. A simple model suggests that as cycle period decreases, slow muscle contractions show increasing intercontraction temporal summation and at steady state consist of phasic contractions overlying a tonic contracture. We identify five components of these contractions: total, average, tonic, and phasic amplitudes, and percent phasic (phasic amplitude divided by total amplitude). cpv1b muscle contractions induced by spontaneous rhythmic neural input in vitro consist of phasic and tonic components. Nerve stimulation at varying cycle periods and constant duty cycle shows that a tonic component is always present, and at short periods the muscle transforms rhythmic input into almost completely tonic output. Varying spike frequency, spike number, and cycle period show that frequency codes total, average, and tonic amplitudes, number codes phasic amplitude, and period codes percent phasic. These data suggest that tonic contraction may be a property of slow muscles driven by rapid, rhythmic input, and in these cases it is necessary to identify the various contraction components and their neural coding. Furthermore, the parameters that code these components are interdependent, and control of slow muscle contraction is thus likely complex.

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

“…This contrasts with the effects of A-ASTs, which have been shown to modulate muscle contraction both pre-and postsynaptically (Jorge-Rivera and Marder, 1997;Kreissl et al, 1999). Although there were no direct effects of C-AST on muscle contraction, we found that C-AST's ability to decrease contraction amplitude was in fact due to an indirect effect at the neuromuscular junction; namely, a decrease in facilitation resulting from the decreased cycle frequency, as has been seen in other studies of this system (Mahadevan et al, 2004) as well as other crustacean neuromuscular systems (Jorge-Rivera et al, 1998;Mercier and Wilkins, 1984;Morris and Hooper, 1998). Interestingly, because C-AST consistently decreased cycle frequency in all lobsters, a decrease in facilitation was certainly also present in the preparations in which contraction amplitude increased.…”

Neural Control of Unloaded Leg Posture and of Leg Swing in Stick Insect, Cockroach, and Mouse Differs from That in Larger Animals

“…The consequences of motor neuron activity therefore cannot be understood without understanding this transformation (see Chiel and Beer, 1997, for a full discussion of this issue). Work on the pyloric muscles of the lobster stomatogastric system well demonstrates this issue (Morris and Hooper, 1998;Morris et al, 2000;Thuma et al, 2003). Pyloric motor neurons fire bursts of action potentials approximately once per second.…”

Functional consequences of activity-dependent synaptic enhancement at a crustacean neuromuscular junction

“…Synaptic integration has been studied extensively in crustaceans, particularly at the neuromuscular junction (Atwood, 1976;Atwood and Wojtowicz, 1986;Bittner, 1968;Bykhovskaia et al, 2004;Dudel and Kuffler, 1961;JorgeRivera and Marder, 1997;Jorge-Rivera et al, 1998;Katz et al, 1993;Morris and Hooper, 1997;Morris and Hooper, 1998;Morris and Hooper, 2001;Msghina et al, 1998). STG motor neurons provide the large gastric mill muscle fibers with a number of spatially separated synaptic sites, which ensures that the entire muscle fiber receives depolarizing inputs and contracts as a whole.…”