title: Octopamine enhances neuromuscular transmission in developing and adult moths, Manduca sexta.
abstract: The effect of octopamine on neuromuscular transmission was examined in developing and adult Manduca sexta. Intracellular recordings were made from the dorsal longitudinal muscle (DLM), superfused with solutions containing DL-octopamine or other amines. In untreated adult moths and pharate adults nearly ready to enclose (stage Day 19), stimulation of the motor nerve evokes a large excitatory junction potential (EJP), an active membrane response, and a twitch. In adults and Day 19 animals DL-octopamine (10(-7) to 10(-4)M) has no effect on the amplitude and rise-time of the electrical response in normal saline, but 10(-6) to 10(-4) M DL-octopamine increases the amplitude of the excitatory junction potential recorded in saline containing one-third the normal calcium concentration. Immature (Day 16) muscle, which normally produces only small EJPs following stimulation of its motor nerve, responds to 10(-6) to 10(-4) M DL-octopamine by an increase in the EJP above threshold for an active membrane response and a contraction. When the muscle has developed sufficiently to spike and contract in response to nerve stimulation in the absence of exogenous octopamine (Days 17 and 18), application of DL-octopamine increases the maximum rate at which the muscle contracts in response to each stimulus in a train (designated the maximum following frequency, MFF). The threshold dose for an effect on the MFF of Day 18 immature moths is less than 10(-10) M. At this stage 10(-8) M DL-octopamine increases the MFF four-fold. The effect on the MFF is dose-dependent over the range 10(-10) M to 10(-6) M. The biogenic amines DL-epinephrine, DL-norepinephrine, tyramine, DL-phenylethanolamine, 2-phenylethylamine, and dopamine, applied at concentrations of 10(-8) or 10(-4) M, do not change the MFF. Both DL-synephrine (10(-8) M) and serotonin (10(-7) M) mimic the action of 10(-10) M DL-octopamine on the MFF. The action of DL-octopamine (10(-7) M) is blocked by phentolamine (10(-4)M) but not by propranolol (10(-4)M). The octopamine content of hemolymph was determined with a radioenzymtic assay. The concentration of octopamine in the hemolymph increases 3.6-fold, from 5 X 10(-8) M on Day 18 (duration of adult development is 19 days) to 1.85 X 10(-7) M one day following eclosion.(ABSTRACT TRUNCATED AT 400 WORDS)
authors.forename: L W
authors.initials: LW
authors.lastname: Klaassen
authors.forename: A E
authors.initials: AE
authors.lastname: Kammer
mesh_terms: D000818:Animals; D005426:Flight, Animal; D006458:Hemolymph / Q000378:metabolism; D007915:Lepidoptera / Q000502:physiology*; D009036:Moths / Q000502:physiology*; D024510:Muscle Development; D009132:Muscles / Q000187:drug effects / Q000502:physiology; D009469:Neuromuscular Junction / Q000187:drug effects*; D009655:Octopamine / Q000378:metabolism / Q000494:pharmacology*; D011941:Receptors, Adrenergic / Q000378:metabolism; D017982:Receptors, Biogenic Amine; D013565:Sympatholytics / Q000494:pharmacology; D009435:Synaptic Transmission / Q000187:drug effects*
chemical_list: D011941:Receptors, Adrenergic; D017982:Receptors, Biogenic Amine; D013565:Sympatholytics; C027604:norsynephrine receptor; D009655:Octopamine