Journal of Insect Physiology 47 2001 277–285 www.elsevier.comlocatejinsphys
Crustacean cardioactive peptide is a modulator of oviduct contractions in Locusta migratoria
Andrew Donini
a,
, Hans-Ju¨rgen Agricola
b
, Angela B. Lange
a
a
Department of Zoology, University of Toronto at Mississauga, 3359, Mississauga Road North, Mississauga, Ontario, L5L 1C6, Canada
b
Biologisch-Pharmazeutische Fakulta¨t, Friederich-Schiller Universita¨t, Erberstr. 1, D-07743, Jena, Germany Received 10 March 2000; accepted 1 July 2000
Abstract
Crustacean cardioactive peptide CCAP stimulates the contractions of locust oviducts. CCAP increased the basal tonus and increased the frequency and amplitude of phasic contractions, as well as the amplitude of neurally-evoked oviduct contractions in
a dose-dependent manner. Oviducts from Vth instar larvae and adult locusts aged 10 days or less, were more sensitive to CCAP than oviducts from adult locusts aged 12 days or more. This may be indicative of a differential expression of number or subtypes
of CCAP receptors on the oviducts at different ages, and may be related to reproductive functions or to functions of CCAP on the oviducts during ecdysis. The oviducts appear more sensitive to CCAP when compared with previously published reports of CCAP
actions on the hindgut. CCAP actions on the amplitude of neurally-evoked contractions of the oviducts are similar to those of proctolin, however, the oviducts are more sensitive to CCAP. No CCAP-like immunoreactive structures were discovered in the
nerves innervating the oviducts, or on the oviducts themselves, confirming the previously published suggestion Dircksen et al., 1991 that CCAP acts as a neurohormone at the oviducts. Cells showing CCAP-like immunoreactivity were discovered in the fat
body associated with the oviducts and represent a potential source of CCAP, along with CCAP released from the transverse nerve and perivisceral organs.
2001 Elsevier Science Ltd. All rights reserved.
Keywords: Crustacean cardioactive peptide; Locusta migratoria; Oviducts; Neurohormone; Muscle contraction
1. Introduction
The walls of the lateral and common oviducts of the African migratory locust, Locusta migratoria, are com-
posed of muscle layers Lange et al., 1984. The individ- ual cells which make up the muscle are electrically
coupled and have the ability to undergo spontaneous depolarizations Orchard and Lange, 1986. As a result,
the oviducts of the locust can contract rhythmically even when isolated from the central nervous system. The ovi-
ducts also receive innervation arising from the VIIth abdominal ganglion via a branch of the sternal nerve,
termed the oviducal nerve, which forms connections onto the lower lateral oviducts and the anterior common
oviduct Lange and Orchard, 1984a. Both the myogenic and the neurally-evoked contractions of the locust ovi-
Corresponding author. Tel.: +
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E-mail address: adoninicredit.erin.utoronto.ca A. Donini.
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ducts can be modulated by neurochemicals acting as neurohormones andor neurotransmitters Lange, 1992.
A number of neurochemicals, including neuropeptides such as proctolin, SchistoFLRFamide, locustatackykin-
ins and locustamyotropins have been found to modulate oviduct contractions in the locust Lange et al. 1986,
1991; Schoofs et al., 1990a,b,c,d; Kwok et al., 1999. The biogenic amine, octopamine, and the amino acid
glutamate are also capable of modulating the muscular activity of the oviducts in the locust Lange and
Orchard, 1984b.
Proctolin stimulates the oviduct visceral muscle, lead- ing to a dose-dependent increase in basal tonus and an
increase in the overall myogenic activity of the oviducts Lange et al., 1986. Application of proctolin to the ovi-
ducts, while stimulating the oviducal nerves, results in a dose-dependent increase in tonus and amplitude of the
neurally-evoked contractions, coupled with an increase in the rate of post-contraction relaxation Noronha and
Lange, 1997. Axons possessing proctolin-like immuno- reactivity have been found in the oviducal nerves, with
278 A. Donini et al. Journal of Insect Physiology 47 2001 277–285
cell bodies present in the VIIth abdominal ganglion Lange et al., 1986. Studies suggest that proctolin acts
as a co-transmitter, modulating the contractions elicited by a more conventional transmitter such as glutamate
Orchard and Lange, 1986; Lange et al., 1986; Noronha and Lange, 1997.
A SchistoFLRFamide-like peptide and the biogenic amine octopamine are both present in the innervated
regions of the oviducts Lange et al., 1991. Physiologi- cal experiments demonstrate that SchistoFLRFamide
inhibits contractions of the oviducts, resulting in a reduction of basal tonus and a decrease in the frequency
and amplitude of phasic contractions Lange et al., 1991. Similarly, the biogenic amine, octopamine,
inhibits contractions of the oviduct muscle, decreasing basal tonus and the amplitude of phasic contractions, as
well as decreasing the amplitude of neurally-evoked con- tractions Lange and Orchard, 1984b; Orchard and
Lange, 1988.
In this study we identify the crustacean cardioactive peptide CCAP as a potent modulator of locust oviduct
contractions. CCAP is a member of a family of cardioac- celeratory peptides designated as such because of their
ability to stimulate the heart. CCAP was originally iso- lated and sequenced from neurohaemal structures, the
pericardial organs, of the shorecrab Carcinus maenas Stangier et al., 1987. It is a cyclic nonapeptide Pro–
Phe–Cys–Asn–Ala–Phe–Thr–Gly–Cys-amide and has been shown to stimulate an increase in the amplitude
and the frequency of contractions of the crayfish heart Stangier et al., 1987. Release experiments reveal that
CCAP immunoreactive CCAP–IR material can be released from the pericardial organs with high potassium
saline in a calcium-dependent manner Stangier et al., 1988. Further studies reveal an extensive network of
CCAP–IR neurons in the central nervous system of Car- cinus maenas, suggesting that the peptide may also func-
tion as a neurotransmitter Dircksen and Keller, 1988. It has been reported that CCAP is an enhancer of crayfish
hindgut contractions Stangier et al., 1989.
CCAP has since been discovered in insects, including the
tobacco hawkmoth,
Manduca sexta
and the
migratory locust, Locusta migratoria Cheung et al., 1992; Stangier et al., 1989. In Manduca sexta, CCAP
has been shown to increase the heartrate and more recently CCAP has been implicated in the onset of ecdy-
sis Cheung et al., 1992; Gammie and Truman, 1999. In the brain and nervous system of Locusta migratoria,
an extensive network of CCAP–IR cells and fibers exists Dircksen and Homberg, 1995; Dircksen et al., 1991.
CCAP has been shown to stimulate hindgut contractions of Locusta migratoria Stangier et al., 1989 and has
been reported to stimulate primarily the amplitude of the heart beat as opposed to the rate, as well as exerting
myotropic effects on the oviducts in Locusta migratoria see Dircksen et al., 1991. From immunocytochemical
studies, Dircksen et al. 1991 have reported that there is no CCAP–IR innervation to either the hindgut or the
oviduct, and thus concluded that CCAP must act as a neurohormone at these tissues.
In the present study we have characterized the effects of CCAP on the oviducts of Locusta migratoria. Dose–
response curves for CCAP on spontaneous and neurally- evoked contractions of locust oviducts were constructed
with the aid of physiological and neurophysiological techniques. Immunohistochemical studies were perfor-
med to examine for the likely source of CCAP acting on the oviducts.
2. Materials and methods
