Temperature dependent modulation of lobster neuromuscular properties by serotonin.
In cold-blooded species the efficacy of neuromuscular function depends both on the thermal environmental of the animal's habitat and on the concentrations of modulatory hormones circulating within the animal's body. The goal of this study is to examine how temperature variation within an ecologically relevant range affects neuromuscular function and its modulation by the neurohormone serotonin (5-HT) in Homarus americanus, a lobster species that inhabits a broad thermal range in the wild. The synaptic strength of the excitatory and inhibitory motoneurons innervating the lobster dactyl opener muscle depends on temperature, with the strongest neurally evoked muscle movements being elicited at cold (<5 degrees C) temperatures. However, whereas neurally evoked contractions can be elicited over the entire temperature range from 2 to >20 degrees C, neurally evoked relaxations of resting muscle tension are effective only at colder temperatures at which the inhibitory junction potentials are hyperpolarizing in polarity. 5-HT has two effects on inhibitory synaptic signals: it potentiates their amplitude and also shifts the temperature at which they reverse polarity by approximately +7 degrees C. Thus 5-HT both potentiates neurally evoked relaxations of the muscle and increases the temperature range over which neurally evoked muscle relaxations can be elicited. Neurally evoked contractions are maximally potentiated by 5-HT at warm (18 degrees C) temperatures; however, 5-HT enhances excitatory junction potentials in a temperature-independent manner. Finally, 5-HT strongly increases resting muscle tension at the coldest extent of the temperature range tested (2 degrees C) but is ineffective at 22 degrees C. These data demonstrate that 5-HT elicits several temperature-dependent physiological changes in the passive and active responses of muscle to neural input. The overall effect of 5-HT is to increase the temperature range over which neurally evoked motor movements can be elicited in this neuromuscular system.
Hamilton
Jonna L
JL
Department of Neuroscience, University of Virginia Health Science Center, Charlottesville, VA 22908-0230, USA.
Edwards
Claire R
CR
Holt
Stephen R
SR
Worden
Mary Kate
MK
D000818:Animals; D001831:Body Temperature / Q000187:drug effects*; D005071:Evoked Potentials / Q000187:drug effects; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D053444:Inhibitory Postsynaptic Potentials / Q000187:drug effects; D017774:Long-Term Potentiation / Q000187:drug effects; D018485:Muscle Fibers, Skeletal / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D009129:Muscle Tonus / Q000187:drug effects; D008121:Nephropidae / Q000187:drug effects* / Q000502:physiology*; D009469:Neuromuscular Junction / Q000187:drug effects* / Q000378:metabolism*; D012701:Serotonin / Q000494:pharmacology*
D012701:Serotonin