A pair of statocysts are located in the periganglionic connective tissue of the pedal ganglia of the opisthobranch mollusc Pleurobranchaea japonica. Lightand electron-microscopic observations show that the sensory epithelium of the statocyst consists of 13 diskshaped hair cells. Each hair cell sends a single axon to the cerebral ganglion through the static nerve. Neurotransmitters in the hair cells were examined by means of immunocytochemistry. Our results show that the 13 sensory hair cells include two SCPB-, three FMRFamide-, and eight histamine-like immunoreactive cells. One hair cell contains a transmitter substance other than SCPB-, FMRFamide, histamine, serotonin, or GABA. One of the two SCPB-like immunoreactive cells, located in the ventral region of the statocyst, is the largest cell in the statocyst. The other, located in the anterodorsal region, shows co-immunoreactivity to both SCPB and FMRFamide antisera. Among the three FMRFamide-like immunoreactive hair cells, one is located in the posteroventral region, separated from the other two, which are adjacent to each other in the anterodorsal region. All the eight histaminelike immunoreactive hair cells are adjacent to one another, occupying the remainder of a triangular pyramidshaped region. These immunoreactive cells are symmetrically placed in the right and left statocysts. This mosaic arrangement was identical among specimens. Thus the static nerve may code information about position or movement of the statoliths, with the use of different transmitters in the mosaic arrangement of the hair cells.

A pair of statocysts are located in the periganglionic connective tissue of the pedal ganglia of the opisthobranch mollusc Pleurobranchaea japonica. Light- and electron-microscopic observations show that the sensory epithelium of the statocyst consists of 13 disk-shaped hair cells. Each hair cell sends a single axon to the cerebral ganglion through the static nerve. Neurotransmitters in the hair cells were examined by means of immunocytochemistry. Our results show that the 13 sensory hair cells include two SCPB-, three FMRFamide-, and eight histamine-like immunoreactive cells. One hair cell contains a transmitter substance other than SCPB-, FMRFamide, histamine, serotonin, or GABA. One of the two SCPB-like immunoreactive cells, located in the ventral region of the statocyst, is the largest cell in the statocyst. The other, located in the anterodorsal region, shows co-immunoreactivity to both SCPB and FMRFamide antisera. Among the three FMRFamide-like immunoreactive hair cells, one is located in the posteroventral region, separated from the other two, which are adjacent to each other in the anterodorsal region. All the eight histamine-like immunoreactive hair cells are adjacent to one another, occupying the remainder of a triangular pyramid-shaped region. These immunoreactive cells are symmetrically placed in the right and left statocysts. This mosaic arrangement was identical among specimens. Thus the static nerve may code information about position or movement of the statoliths, with the use of different transmitters in the mosaic arrangement of the hair cells.

In crustacean neurogenic hearts, the myocardium contracts under the tight control of rhythmically active neurons of the cardiac ganglion located inside the heart. We demonstrated that the myocardium of Bathynomus doederleini was sensitive to glutamate, quisqualate, and kainate, and that the tension of myocardial cells developed in a dose-dependent manner. The threshold concentrations were 10(-5) M for quisqualate, 10(-4) M for glutamate, and 3 x 10(-4) M for kainate. Concanavalin A, known to prevent desensitization of glutamate receptors at crustacean neuromuscular junctions, augmented excitatory junctional potentials evoked by the cardiac ganglionic neurons in myocardial cells. Using a high performance liquid chromatography (HPLC), we analyzed glutamate in extracts of the cardiac ganglion and myocardium. We obtained values for glutamate concentrations, 8741.2 +/- 184.2 and 678.2 +/- 10.7 pmol/mg, respectively. Although we attempted to measure monoamines in the extracts by HPLC, these were not detected at measurable (more than 1 fmol per 10-microL sample) levels. In conclusion, myocardial cells in isopod crustaceans were suggested to receive glutamatergic motor innervation.

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