ISSN:
1573-6830
Keywords:
dopamine
;
motoneuron
;
muscle
;
neuromuscular
;
neurotransmitter
;
gill
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Summary 1. Three neurons in the abdominal ganglion ofAplysia elicit gill movements similar to those observed when dopamine is added to a gill perfusate. One, which we designate L9, produces contractions of all medial and lateral external pinnule muscles, the circular and longitudinal muscles of the afferent vessel, and the circular muscles of the efferent vessel. The others produce identical contractions in anterior portions (L9-a) or posterior (L9-p) portions of the gill. These contractions are similar to, but less pronounced than, those produced by the motoneuron, L7. 2. Clear population excitatory junction potentials (EJPs) can be recorded extracellularly from the gill when other gill motoneurons, L7 and LDG1, are activated. However, EJPs are observed only occasionally upon activation of the L9 neurons. Nonetheless, with averaging techniques L9 EJPs are measurable and their latencies, times to peak, and durations are similar to those of L7 and LDG1. These observations suggest that the L9 cells are true gill motoneurons. 3. The contrations induced by activation of the L9 cells, but not those induced by L7 or LDG1, are blocked by ergometrine and fluphenazine. Since these drugs are thought to act exclusively on dopamine receptors and since L9-induced movements are similar to dopamine-induced movements, it is suggested that the L9 neurons are dopaminergic motoneurons. 4. Dopamine is known to modulate muscle contractions induced by activation of various gill motoneurons. However, the L9 neurons do not appear to produce such modulation directly. Even though an increased response of other motoneurons was occasionally observed after L9 stimulation, it was always preceded by a small additional contraction, which may reflect release of dopamine from an independent, peripheral storage site. 5. While considerable dopamine is present in ganglia and nerve trunks to the gill, no identified neuronal cell bodies, including L9 and other gill motoneurons, contained detectable dopamine. Because our electrophysiological, pharmacological, and histochemical data are all consistent with the L9 cells being dopaminergic, we suggest that dopamine may be synthesized in the axons and nerve terminals of L9 cells but not in their cell bodies.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00710851
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