Serotonin modulation of caudal photoreceptor in crayfish.
The sixth abdominal ganglion (6th AG) of the crayfish contains two photosensitive neurons. This caudal photoreceptor (CPR) displays spontaneous electrical activity and phasic-tonic responses to light pulses. In this paper, we analyzed the presence of serotonin in the 6th AG and its effects in the modulation of the activity of CPR. In the first part of our study, we identified serotonergic neurons in the 6th AG by immunostaining using an antibody against serotonin. Next, we quantified the serotonin contents in the 6th AG by using liquid chromatography. Finally, we searched for serotonergic modulation of the CPR electrical activity by using conventional extracellular recordings. We found 13 immunopositive neurons located in the ventral side of the 6th AG. The mean diameter of their somata was 23+/-9 microm. In addition, there was immunopositive staining in neuropilar fibers and varicosities. The contents of serotonin and its precursors in the 6th AG varied along the 24-h cycle. Its maximum value was reached by midday. Topic application of serotonin to ganglia kept in darkness increased the CPR spontaneous firing rate and reduced its light responsiveness. Both effects were dose-dependent within ED(50) approximately 1 microM and were blocked by the 5-HT antagonist methysergide. These observations support the role of serotonin as a neurotransmitter or neuromodulator in the CPR of the two species of crayfish Procambarus clarkii and Cherax quadricarinatus.
Rodríguez-Sosa
Leonardo
L
División de Estudios de Posgrado e Investigación, Facultad de Medicina. Universidad Nacional Autónoma de México. C.U. 04510, México, D.F. México. Electronic address: lrsosa@servidor.unam.mx.
Calderón-Rosete
Gabina
G
División de Estudios de Posgrado e Investigación, Facultad de Medicina. Universidad Nacional Autónoma de México. C.U. 04510, México, D.F. México.
Villalobos
Mercedes Graciela Porras
MGP
División de Estudios de Posgrado e Investigación, Facultad de Medicina. Universidad Nacional Autónoma de México. C.U. 04510, México, D.F. México.
Mendoza Zamora
Elena
E
División de Estudios de Posgrado e Investigación, Facultad de Medicina. Universidad Nacional Autónoma de México. C.U. 04510, México, D.F. México.
González
Víctor Anaya
VA
División de Estudios de Posgrado e Investigación, Facultad de Medicina. Universidad Nacional Autónoma de México. C.U. 04510, México, D.F. México.
D000005:Abdomen; D000818:Animals; D000906:Antibodies / Q000276:immunology; D003400:Astacoidea / Q000187:drug effects / Q000502:physiology*; D004594:Electrophysiology; D005260:Female; D017952:Ganglia, Invertebrate / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008784:Methysergide / Q000494:pharmacology; D017956:Photoreceptor Cells, Invertebrate / Q000187:drug effects / Q000502:physiology*; D012701:Serotonin / Q000494:pharmacology / Q000502:physiology*
D000906:Antibodies; D012701:Serotonin; D008784:Methysergide