Dk. Okimoto et Mh. Stetson, Presence of an intrapineal circadian oscillator in the teleostean family poeciliidae, GEN C ENDOC, 114(2), 1999, pp. 304-312
In most fish, rhythmic melatonin production is controlled by circadian osci
llators located within the pineal (=pineal clocks) that are reset daily by
the ambient light:dark (LD) cycle. However, one question that has yet to be
addressed concerns the phylogenetic distribution of the pineal clock withi
n fish families. We tested whether a pineal clock identified in the sailfin
molly (Poecilia velifera) in an earlier study is also present in some othe
r representatives of the teleostean family Poeciliidae; Isolated pineals fr
om adults belonging to the genus Poscilia (P. velifera albino, I! reticulat
a, and P. sphenops), genus Xiphophorus (X. helleri and X. maculatus), and g
enus Limia (L. vittata)were obtained and cultured under LD and/or continuou
s darkness (DD) at constant temperature (27 degrees C); With one exception,
free-running rhythms in melatonin release with circadian periodicities ran
ging from 19.5 to 27.4 h (n = 26) were detected in isolated pineals from al
l paeciliid representatives tested under DD exposure. In addition, rhythmic
melatonin production was also observed in isolated pineals of some represe
ntatives tested from all three genera under LD exposure, suggesting the pro
perty of direct photosensitivity. Taken together, these data suggest that a
circadian oscillator residing in the pineal of the sailfin molly also appe
ars to be: present: in all of the poeciliid representatives tested in our s
ystem, supporting the notion that the presence of a pineal clock occurs at
the family level of taxonomic organization. (C) 1999 Academic Press.