Evidence of 5-hydroxytryptamine synthesis in the follicles of Sepia officinalis and direct involvement in the control of egg-laying

At the beginning of egg-laying, in the cuttlefish Sepia officinalis, the oo cytes accumulated in the proximal oviduct are released into the mantle cavi ty by the contractions of the oviduct before being encapsulated and fertili sed. A bioassay based on the recording of the contractile activity of the d istal oviduct was performed to characterise the molecule(s) inhibiting the oviducal motility and then responsible for the storage of the oocytes befor e mating. From 200 full-grown oocytes, a factor lowering the oviducal contr actions was purified and isolated by means of HPLC. ESI-MS as well as elect rochemical detection following HPLC fractionation allowed identification of the 5-hydroxytryptamine in the pure fraction. The inhibition of the oviduc al contractions by 5-HT was dose dependent with a threshold near 10(-7) M. An immunoenzymatic assay showed that 5-HT appeared in the follicles at the beginning of vitellogenesis and reached a maximum level in the full-grown o ocytes. In vitro experiments revealed that 5-HT is synthesised by the folli cular cells and the full-grown oocytes, before being released to target pro ximal oviduct. Thus 5-HT could be one of the molecules involved in the accu mulation of oocytes in the oviduct before mating. (C) 2000 Wiley-Liss, Inc.