ORIGINAL PAPER Octopamine modulates spermathecal muscle contractions in Locusta migratoria Received: 5 October 2001 / Revised: 12 August 2002 / Accepted: 5 November 2002 / Published online: 20 December 2002 Ó Springer-Verlag 2002 Abstract Octopamine was identified in the spermathe- cal tissue of Locusta migratoria using HPLC and immunohistochemical techniques. Octopamine-like immunoreactive unpaired median neurons were identified in the VIIth and VIIIth (terminal) abdominal ganglia and octopamine-like immunoreactive axons were present in the ventral ovipositor nerve (branches from this nerve innervate the spermatheca). Stimulatory actions of octo- pamine on myogenic and neurogenic contractions were observed. Dose-dependent increases in the frequency of myogenic contractions and the amplitude of neurogenic contractions were elicited by the application of octopa- mine to the spermathecal muscle. Non-sustained basal tension increases were noted in some preparations, al- though these were not found to be dose-dependent. SchistoFLRFamide (PDVDHVFLRFamide) inhibited octopamine-induced contractions by a maximum of about 30%. In the presence of 3-isobutyl-1-methyl- xanthine, octopamine increased cAMP levels in all regions of the spermathecal. The largest increase in cAMP content was found in the spermathecal sac, followed by the straight duct and coil duct. Phentolamine blocked octo- pamine-induced increases in cAMP levels and abolished the actions of octopamine on myogenic contractions. Keywords Octopamine Æ Spermatheca Æ cAMP Æ SchistoFLRFamide Æ Locusta Abbreviations DUM dorsal unpaired median Æ IBMX 3-isobutyl-1-methylxanthine Æ VOM ventral ovipositor nerve Æ VUM ventral unpaired median Æ cAMP cyclic adenosine 3Õ,5Õ monophosphate Introduction The spermatheca of the female locust, situated dorsal to the oviducts, is a repository for spermatozoa deposited by the male during mating. The spermatheca consists of the spermathecal sac (receptaculum seminis) at the anterior end, followed by the coil duct, anterior straight duct and the posterior straight duct which leads into the genital chamber where fertilization occurs (see Fig. 1; Clark and Lange 2000). Spermatozoa movement through the spermatheca to the genital chamber is dependent on spermathecal contractions, as has been demonstrated in Chelymorpha alternans (Rodrı´guez 1994), Anthonomus grandis (Villavaso 1975) and in Tel- eogryllus commodus (Sugawara1989). The contractions of the spermatheca of Locusta migratoria are at least partially controlled by neural input (Clark and Lange 2000). The spermatheca is innervated bilaterally by motor neurons situated in the VIIIth (terminal) ab- dominal ganglion and dorsal unpaired median (DUM) neurons located in the terminal and VIIth abdominal ganglia. Axons project through the VIIIth sternal nerve to the ventral ovipositor nerve (VON), from which nerve branches innervate the spermatheca (see Fig. 1; Clark and Lange 2000). During egg-laying the coordination of spermathecal muscle movements with those of the ovi- ducts may be essential for successful fertilization. Numerous studies have examined the neurochemicals involved in the control of lateral and common oviduct contractions. These neurochemicals include proctolin (Lange et al. 1986), serotonin (Orchard and Lange 1985), the FMRFamide-related peptides (FaRPs) (Lange et al. 1991; Peeff et al. 1994) and octopamine (Orchard and Lange 1985; Lange and Tsang 1993). Most of these neurochemicals have also been associated with the spermatheca of L. migratoria (Lange 1993; Clark and Lange 2002a, 2002b; J. Clark and A.B. Lange, unpublished observations). Proctolin and serotonin have stimulatory actions on contractions of both the locust oviduct (Orchard and Lange 1985; Lange et al. 1986) J Comp Physiol A (2003) 189: 105–114 DOI 10.1007/s00359-002-0375-x J. Clark Æ A.B. Lange J. Clark Æ A.B. Lange (&) Department of Zoology, University of Toronto at Mississauga, Mississauga, Ontario, L5L 1C6, Canada E-mail: alange@utm.utoronto.ca Tel.: +1-905-828-3898 Fax: +1-905-828-3792