Oviduct Contractions Research Articles

Signal transduction pathways regulating the contraction of an insect visceral muscle

This review examines the signal transduction pathways which regulate the contraction of an insect visceral muscle, namely the oviduct of the locust, Locusta migratoria. Detailed studies based upon neurophysiology, neurochemistry, and neuropharmacology have defined the neural control over contraction of locust oviducts. The identification of a variety of neuroactive chemicals which are associated with the innervation of this muscle, including peptides, an amine, and an amino acid, has allowed examination of second messenger systems which lead to an intricate control over muscle contraction. Thus, it is known that these neuroactive chemicals are involved with G-proteins, membrane lipid systems, cyclic nucleotides, calcium, and calmodulin as well as protein phosphorylation, thereby allowing these extracellular neuroactive chemicals to initiate and modulate contractile events within the individual muscle cells. Each of these systems is reviewed in the context of locust oviduct contraction and the possibilities of cross-talk regulation between these second messengers discussed. © 1996 Wiley-Liss, Inc.

Signal transduction pathways regulating the contraction of an insect visceral muscle

This review examines the signal transduction pathways which regulate the contraction of an insect visceral muscle, namely the oviduct of the locust, Locusta migratoria. Detailed studies based upon neurophysiology, neurochemistry, and neuropharmacology have defined the neural control over contraction of locust oviducts. The identification of a variety of neuroactive chemicals which are associated with the innervation of this muscle, including peptides, an amine, and an amino acid, has allowed examination of second messenger systems which lead to an intricate control over muscle contraction. Thus, it is known that these neuroactive chemicals are involved with G-proteins, membrane lipid systems, cyclic nucleotides, calcium, and calmodulin as well as protein phosphorylation, thereby allowing these extracellular neuroactive chemicals to initiate and modulate contractile events within the individual muscle cells. Each of these systems is reviewed in the context of locust oviduct contraction and the possibilities of cross-talk regulation between these second messengers discussed. © 1996 Wiley-Liss, Inc.

Non-linear dynamics of neurochemical modulation of mosquito oviduct and hindgut contractions.

Microphysiological techniques and computer-based methods of data acquisition and analysis were used to investigate the dynamics of neurochemical action on spontaneous contractions of continuously perfused oviducts and hindguts isolated from female mosquitoes (Aedes aegypti). Proctolin, leucomyosuppressin (LMS), serotonin and octopamine, which are known to modulate insect muscle contractions, and a mosquito neuropeptide, Aedes Head Peptide I (Aea-HP-I), which inhibits host-seeking behavior, were tested in the bioassays. LMS depressed contractile activity in oviducts at concentrations above 10(-12) mol l-1, but hindguts did not respond to concentrations below 10(-6) mol l-1. Hindgut contractions spontaneously restarted in 10(-6) mol l-1 LMS, but only washing out LMS restored activity in oviducts. LMS changed the amplitude of the oviduct contractions, but the dynamics of contraction remained steady. Following recovery of contractions in LMS, hindgut tissues contracted with a more regular pattern. Serotonin and octopamine had an identical action on oviduct and hindgut tissues. At concentrations greater than 10(-8) mol l-1, serotonin eliminated the refractory period between contractions and thus increased the contraction frequency of oviducts. Though the contractions appeared chaotic, state-series analysis proved that serotonin-treated oviducts contracted rhythmically. Above 10(-6) mol l-1, serotonin extinguished normal hindgut peristalsis and induced regular fluttering of the anteriormost portion of the hindgut, an effect possibly related to diuresis following the blood meal. Proctolin failed to stimulate both oviduct and hindgut contractions at concentrations up to 10(-6) mol l-1, but at 10(-8) mol l-1 induced contractions of cricket hindgut preparations. Aea-HP-I had no effect on either tissue at 10(-6) mol l-1 or lower concentrations. State-series analysis, based on simple manipulations of experimental data, permitted direct observation of the dynamics of oviduct and hindgut contractile activity.

Pseudodipeptide analogs of the pyrokinin/PBAN (FXPRLa) insect neuropeptide family containing carbocyclic Pro-mimetic conformational components

Three N-terminal amino acid residues of the C-terminal core pentapeptide Phe-X-Pro-Arg-Leu-NH 2 (X = Gly, Ser, Thr, Val) of the pryokinin/PBAN insect neuropeptide family were replaced by nonpeptide moieties. To reestablish some of the conformational properties lost upon removal of the peptide bonds and Pro of the three amino acid residue block, carbocyclic Pro-mimetic components were incorporated into pseudodipeptide analogs. The most active analog contained a trans- dl-1,2-cyclopentanedicarboxyl carbocyclic component and proved to be over 3 orders of magnitude more potent than a simple, straight chain pseudodipeptide analog and approached the potency of the pentapeptide core in a cockroach hindgut myotropic bioassay. The pseudodipeptide analog retains a critical carbonyl residue which can participate in a hydrogen bond that stabilizes a β-turn conformation in the active core region of the pyrokinin/PBAN peptides. This study demonstrates that knowledge of active conformation can be used to enhance the biological potency of pseudopeptide mimetic analogs of insect neuropeptides. The analogs represent a milestone in the development of pseudopeptide and nonpeptide mimetic analogs of this peptide family, which has been associated with such critical physiological processes as hindgut and oviduct contraction, pheromone biosynthesis, diapause induction, and induction of melanization and reddish coloration in a variety of insects. Mimetic analogs are potentially valuable tools to insect neuroendocrinologists studying these physiological processes and/or engaged in the development of future pest management strategies.

Binding affinity and physiological activity of some HVFLRFamide analogues on the oviducts of the locust, Locusta migratoria

SchistoFLRFamide (PDVDHVFLRFamide) is an insect neuropeptide which inhibits spontaneous and induced contractions of locust oviduct. The active core for inhibition lies within the sequence HVFLRFamide, whereas the core for binding lies within the sequence VFLRFamide. This latter peptide shows activity reversal, possessing minor stimulatory activity. The bioassay and receptor binding assay were employed to define the relationship between the binding affinity and biological activity of HVFLRFamide analogues on the oviduct of Locusta migratoria. Each amino acid in the sequence VFLRFamide was substituted with a structurally similar or dissimilar amino acid to yield a group of HVFLRFamide analogues. These analogues were tested for their binding affinity to receptors in locust oviduct membrane and for their biological effects on contractions of the isolated locust oviduct. The results indicate that (1) with the His residue in position 1, no activity reversal is achieved, the analogues are either inhibitory or possess no biological activity; (2) the C-terminal RFamide group is critical for binding affinity and biological activity of the analogues and (3) substitution of Arg 5 or Phe 6 with structurally similar amino acids Lys 5 or Tyr 6 results in two high-affinity antagonists, while substitution of Val 2 with Leu 2 or Ala 2 results in high-affinity agonists.

Isolation of Ala 1-proctolin, the first natural analogue of proctolin, from the brain of the Colorado potato beetle

Methanolic head and brain extracts of the Colorado potato beetle contain several myotropins, active in the Locusta oviduct motility assay. Reversed phase high performance liquid chromatography (RP HPLC) gave evidence for the presence of three myotropic factors, with retention times close to that of proctolin. Both strongly stimulated the frequency, amplitude and tonus of the myogenic oviduct contractions. Gas phase sequencing and FAB-MS revealed that, besides proctolin (Arg-Tyr-Leu-Pro-Thr), two natural proctolin analogues were present. The first one is Ala-Tyr-Leu-Pro-Thr and is designed as Ala 1-proctolin. The threshold concentration for biological activity of Ala 1-proctolin was 10 −7 M, compared to 10 −10 M for proctolin itself. Ala 1-proctolin is the first identified biological analogue of proctolin. The full nature of the first amino acid of a third proctolin-analogue ( x-Tyr-Leu-Pro-Thr) is probably a modified amino acid of which the identity could as yet not be revealed. Our results suggest the existence of a family of proctolin-like peptides.

Mode of action of an inhibitory neuropeptide SchistoFLRFamide on the locust oviduct visceral muscle

The possible mode of action of an inhibitory neuropeptide SchistoFLRFamide (PDVDHVFLRFamide) on locust oviduct visceral muscle was studied by examining its ability to inhibit calcium ionophore A23187-, caffeine- or phorbol ester-induced oviduct contractions. A23187-induced muscle contractions included two components: one which required the influx of extracellular Ca 2+ through Ca 2+ channels (blocked by cobalt ions), the other not blocked by cobalt ions. SchistoFLRFamide inhibited the cobalt-sensitive components, but not the latter. Caffeine induced two phases of contractions, a phasic contraction which was probably due to the release of intracellular Ca 2+ and a tonic contraction which required the influx of extracellular Ca 2+. SchistoFLRFamide inhibited the tonic contraction in a dose-dependent manner but did not influence the phasic contraction. The phorbol 12-myristate 13-acetate-induced muscle contraction required the presence of extracellular Ca 2+, with Ca 2+ probably entering through ligand-gated channels, but the contraction was not inhibited by SchistoFLRFamide. Based upon these results, it appears that SchistoFLRFamide inhibits muscle contraction by preventing the accumulation of free intracellular Ca 2+ from extracellular stores. SchistoFLRFamide is incapable of inhibiting contraction induced by the release of intracellular stores of Ca 2+. It is possible that SchistoFLRFamide closes or blocks voltage-gated and some ligand-gated Ca 2+ channels in the plasma membrane.

The motor innervation of the oviducts and central generation of the oviductal contractions in two orthopteran species (Calliptamus sp. and Decticus albifrons)

The oviducts of the female Decticus albifrons (Orthoptera: Tettigonidae) are innervated by six bilaterally paired neurones, while those of the female Calliptamus sp. (Orthoptera: Catantopidae) are innervated by three bilaterally paired neurones, located in the seventh abdominal ganglion. Using intracellular recording and staining, five of the six oviductal neurones of D. albifrons and the three oviductal neurones of Calliptamus sp. were physiologically and morphologically identified. All three oviductal neurones of Calliptamus sp. have a motor function. In D. albifrons, however, there is evidence for motor function in only three of the five identified oviductal neurones that appear to participate in the generation of the oviductal contractions. The remaining two identified neurones of D. albifrons have a branching pattern similar to that of motor neurones, but their physiological characteristics, large overshooting soma action potentials (30­40 mV) with a long afterhyperpolarising phase, are similar to those of the oviductal unpaired median neurones, which are known to modulate the oviductal contractions. The oviductal muscle exhibits two different modes of contractions: (a) fast and slow myogenic contractions, the fast contractions being produced by spontaneous potentials (30­40 mV) generated by some oviductal muscle fibres; and (b) neurogenic contractions caused by the rhythmic spiking of the oviductal motor neurones. This motor pattern is produced by the oviductal central pattern generator, a neural network residing in the last two abdominal ganglia (seventh and terminal abdominal ganglia) of the species examined here. When isolated both anteriorly and posteriorly, the seventh abdominal ganglion generates rhythmic oviductal contractions of lower frequency and amplitude than those recorded when the connectives between the genital ganglia are intact. The oviductal pattern generator is activated through release from descending inhibition, which originates, in Calliptamus sp., from the compound metathoracic ganglion (fused metathoracic and first three abdominal neuromeres) and in, D. albifrons, from the first free abdominal ganglion (fused second and third abdominal neuromeres).

Calmodulin mediates contraction of the oviducts of Locusta migratoria

Calmodulin (CaM) is a multifunctional calcium binding protein which is an essential mediator in the contraction of mammalian smooth muscle. In the present study, evidence is provided that CaM is important in mediating insect visceral muscle contraction. Calmodulin is present in the oviducts of the locust, Locusta migratoria, at c. 55 ng/mg protein, 2.7 times that found in the external ventral protractor of the VIIth abdominal segment, a skeletal muscle. The calmodulin inhibitors trifluoperazine (TFP) and N-(6-aminohexyl)-5-chloro-l-naphthalenesulfonamide (W7) inhibited proctolin-induced contractions in a dose-dependent manner. The effective dose for 50% inhibition (ED 50) of contraction for TFP was 1.6×10 −4 M and for W7 was 3.0×10 −4 M. High potassium-induced contractions were also inhibited dose-dependently by TFP and W7 with ED 50s of 1.8×10 −4 M and 5.1×10 −4 M, respectively. The protein kinase C (PKC) inhibitor chelerythrine had no effect on either proctolin- or high potassium-induced contractions of the locust oviduct indicating that TFP and W7 were not simply antagonizing PKC in producing their inhibitory effects. At least 15 calmodulin binding proteins (CaMBPs) were visualized in the locust oviduct muscle after probing SDS polyacrylamide gels with 35S-VU-1 CaM. Furthermore the binding of CaM to proteins in the gel was inhibited in a dose-dependent manner in the presence of either TFP or W7 paralleling the physiological inhibition of contraction. These results indicate that the contraction of the locust oviducal muscle is, at least in part, mediated by calmodulin, possibly through a CaMBP such as myosin light chain kinase, similar to the process of contraction in smooth muscles of vertebrates.

Isolation, sequence, and bioactivity of FMRFamide-related peptides from the locust ventral nerve cord

The ventral nerve cord of the locust, Locusta migratoria, was examined for the presence of FMRFamide-related peptides (FaRPs). RP-HPLC coupled to an RIA specific for extended-RFamides revealed the presence of several FaRPs eluting at different percentages of acetonitrile. The sequences of five of these peptides were determined. Two sequences are identical to the two peptides previously sequenced from brain and retrocerebral complex of Locusta. These two peptides (PDVDHVFLRFamide and ADVGHVFLRFamide) were inhibitory when tested on locust oviduct contractions. The other peptides are novel with sequences of GQERNFLRFamide, AXXRNFIRFamide, and AFIRFamide. The synthesized peptides were stimulatory when tested on locust oviduct contractions, increasing the frequency and amplitude of spontaneous contractions and resulting in a basal contraction.

Isolation, sequence, and bioactivity of PDVDHVFLRFamide and ADVGHVFLRFamide peptides from the locust central nervous system

The brain and the retrocerebral complex of the locust, Locusta migratoria, were examined for the presence of FMRFamide-related peptides (FaRPs) using an RIA specific for -RFamide. RP-HPLC of these extracts using both C18 and phenyl columns revealed the presence of several FaRPs eluting at different percentages of acetonitrile. The sequences of two peptides were determined. One sequence is identical to the previously described SchistoFLRFamide (PDVDHVFLRFamide), whereas a second peptide is novel and differs from SchistoFLRFamide in positions 1 and 4 (ADVGHVFLRFamide). The bioactivity of these native and synthetic FaRPs on locust oviduct contractions has been examined. Both peptides showed inhibitory activity on the locust oviduct. Truncated versions of PDVDHVFLRFamide revealed that the essential features for inhibition lay in the sequence HVFLRFamide.

The effect of proctolin analogues and other peptides on locust oviduct muscle contractions

The locust oviduct bioassay system was used to assess the ability of a variety of peptides to induce oviducal contractions. Proctolin analogues were three orders of magnitude less potent than proctolin. Proctolin supra-analogue and Arg-Tyr-Leu-Ala-Thr demonstrated high activity. Perhaps the most significant finding was the discrepancy between the high binding capacity of the proctolin analogue Arg-Tyr-Ser-Pro-Thr and its relatively low myotropic activity. This observation argues for a crucial role for the leucine residue in activating the proctolin receptor. Several other myotropic peptides were tested for their effect on oviduct contractions. FMRFamide caused contractions at doses several orders of magnitude higher than proctolin. The FLRFamide leucomyosuppressin inhibited proctolin-induced contractions. In addition, myomodulin and catch relaxing peptide caused oviducal contractions at low concentrations. The enkephalins had no effect when applied alone but potentiated proctolin-induced oviduct contractions. The mechanism of the potentiation is not known. The data argue for the presence of several binding sites on the oviduct membrane.

Isolation, identification and synthesis of PDVDHFLRFamide (SchistoFLRFamide) in Locusta migratoria and its association with the male accessory glands, the salivary glands, the heart, and the oviduct

An amidated decapeptide, exhibiting strong inhibitory activity of spontaneous visceral muscle movements, was isolated from 9000 brain-corpora cardiaca-corpora allata-subesophageal ganglion complexes of the migratory locust, Locusta migratoria. During the process of HPLC purifications, the biological activity of the fractions was monitored using the isolated hindgut of the cockroach Leucophaea maderae. The primary structure of this myotropic peptide is Pro-Asp-Val-Asp-His-Val-Phe-Leu-Arg-Phe-NH 2 and is identical to SchistoFLRFamide isolated from the grasshopper, Schistocerca gregaria. It shares the carboxy-terminal sequence FLRFamide with several identified peptides from different phyla. At this moment, six decapeptides isolated from different insect species are identical at 7 of the 10 amino acid residues (X-D-V-X-H-X-FLRFamide). The cockroach, fly, and locust peptides differ only by the N- terminal amino acid residue. Synthetic SchistoFLRFamide showed biological as well as chemical characteristics indistinguishable from the native peptide. It provoked a decrease in frequency and amplitude of contractions of the locust oviduct. By means of a polyclonal antiserum directed against the carboxy terminal of SchistoFLRFamide, we demonstrated that the male accessory glands, the heart, the oviduct, and the salivary glands were innervated by axons containing SchistoFLRFamide-like immunoreactivity. Administration of SchistoFLRFamide elicited an immediate effect on the basal membrane potential of the opalescent tubule gland cells.

Biochemical and physiological effects of octopamine and selected octopamine agonists on the oviducts of Locusta migratoria

The effects of octopamine and some selected octopamine agonists on neurally-evoked contrations and cyclic AMP levels of the lateral oviducts of the locust, Locusta migratoria, have been examined. Octopamine caused reversible, dose-dependent decreases in both the basal tonus and amplitude of neurally-evoked contractions of the lateral oviducts, and inhibited myogenic contractions. The 2-aminooxazoline, Ac6 [2-(4-chloro- o-toluidino)-2-oxazoline], and the substituted phenyliminoimidazolidines (PIIs), NC5 (2,6-diethyl-PII) and NC7 (2-methyl-4-chloro-PII), were each capable of eliciting similar responses to octopamine on neurally-evoked contractions. The vertebrate α-adrenergic receptor antagonist phentolamine blocked the physiological effects of all agonists tested. The effect of these agonists on cyclic AMP levels was also examined. Octopamine and the three agonists were able to increase the cyclic AMP content of the lateral oviducts in a dose-dependent manner. The increases in cyclic AMP were inhibited in the presence of various vertebrate receptor antagonists. The results of this study indicate that AC6, NC5, and NC7 all act as agonists to the octopamine 2-like receptors present on locust oviduct and confirm previous studies for the agonistic properties of these agents.

The effects of FMRFamide-related peptides on an insect ( Locusta migratoria) visceral muscle

We have examined the effects of a number of FMRFamide-related peptides on the contraction of locust oviducts. SchistoFLRFamide (PDVDHVFLRFa) and leucomyosuppressin (pQDVDHVFLRFa) both decrease the amplitude and frequency of myogenic contractions and reduce basal tension. Leucomyosuppressin also reduces the amplitude of proctolin-induced contractions, an effect previously shown for SchistoFLRFamide. In contrast to these inhibitory effects, other FMRFamide-related peptides stimulate contractions of locust oviduct. Thus, removal of the amide, as in SchistoFLRF, shortening of the peptide, as in FLRFamide and FMRF, or altering the N-terminal extension, as in YGGFMRFamide or TNRNFLRFamide, result in peptides which stimulate contraction, although at concentrations which are quite high. The requirements for inhibition lie in a C-terminal amidation and a specific N-terminal extension similar to PDVDHV or pQDVDHV. The results suggest the presence of at least two receptor types for FMRFamide-related peptides. One receptor type leads to inhibition of contraction whereas the other leads to stimulation of contraction. The direct neural control of locust oviducts and neurohormonal control by FMRFamide-related peptides is discussed.

The Identification of Motor and Unpaired Median Neurones Innervating the Locust Oviduct

ABSTRACT The different classes of neurones supplying the locust oviduct were individually identified by intracellular recording and staining. We could thus show that different regions of the oviduct are innervated by different sets of neurones. Three motor neurones (oviductal neurones 1–3, OVN1-3) supply the oviduct via nerve N2B of the seventh abdominal ganglion. Whereas all three motor neurones innervate the junctional area of the lateral and the common oviduct (OVNI, 2 and 3), the lateral oviduct is innervated by only one motor neurone (OVN2) and the common oviduct by two motor neurones (OVNI and 2). The cell bodies of all three motor neurones lie ventrally, near the origin of the sternal root, and their neuropilar branches are confined to the seventh abdominal ganglion. The neuropilar branches of OVNI and 2 extend mainly in the ipsilateral half of the ganglion; those of OVN3 reside exclusively in the contralateral half. The oviductal motor neurones, produce a phasic motor pattern, the oviductal rhythm, which causes neurogenic contractions of the junctional area and the common oviduct. These contractions serve to retain eggs in the lateral oviduct. The oviduct is also supplied by a large number (16–20) of median neurones with bilateral axons. All of these appear to innervate the lateral oviduct, but only two project to the junctional area and the common oviduct. The cell bodies of the median neurones are situated in the seventh abdominal ganglion and are arranged in two groups: a posterior group made up of 10–12 cells and an anterior group with 6–8 cells. Their primary neurites run towards the centre of the ganglion in the dorsal plane, where they bifurcate, sending a secondary neurite through each oviductal nerve. Their neuropilar branches are confined to the seventh abdominal ganglion, but some also possess thin axon collaterals projecting to the terminal abdominal ganglion. The anterior and posterior median neurones show considerable differences in their branching pattern within the ganglion. The posterior cells are all likely to be neurones of the well-known DUM cell group, but the anterior median cells probably represent a different class of neurone. Posterior median neurones support overshooting soma action potentials of 60–80 mV amplitude, with a characteristic undershoot of 6–15 mV. Orthodromic stimulation of these neurones results in a reduction of the amplitude and frequency of the oviductal contractions, suggesting that they have a modulatory role.

Isolation, identification and synthesis of Lom-AG-myotropin II, a novel peptide in the male accessory reproductive glands of Locusta migratoria

The male accessory glands of Locusta contain factors which stimulate oviduct contraction. From an extract of 4400 gland masses, a myotropic peptide (Lom-AG-myotropin II) was isolated by HPLC. Sequencing revealed the following sequence: Ala-His-Arg-Phe-Ala-Ala-Glu-Asp-Phe-Gly-Ala-Leu-Asp-Thr-Ala. Chemical synthesis confirmed that this peptide is active in the acid form instead of the amide form as other presently known myotropic peptides. The sequence does not resemble that of any peptide isolated from Locusta or other insects. The myotropin is active on the oviduct of Locusta migratoria but not on the oviduct of Leucophaea maderae. The myotropic activity can be detected on the hindgut of both insects but at much higher peptide concentrations.

Influence of ova within rat oviducts on spontaneous motility and on prostaglandin production

The present study was performed in order to explore the influence of ova present within rat oviducts on: a) tubal spontaneous motility and b) oviduct prostaglandin production. It was found that the isometric developed tension (IDT) of tubes isolated from proestrous rats (preovulatory oviducts) was significantly higher (P < 0.01) than the IDT of tubes from rats at estrus and at metestrus (postovulatory oviducts). After flushing the oviducts with KRB solution (i.e., after removing existing ova) the IDT of the oviducts obtained from estrous rats increased significantly (P < 0.01), whereas the IDT of tubes isolated from proestrous rats (i.e., preparations without ova) was not modified. On the other hand, isolated tubes containing their corresponding ova released into the suspending solution significantly more PGE 1 than PGE 2 or PGF 2α (P < 0.005). It was particulary interesting to find that after flushing the oviducts, tissue production of PGE 1, PGE 2 and PGF 2α was similar. Finally, when dose response curves for PGE 1 and for PGE 2 on the spontaneous contractions of oviducts isolated from rats at proestrus, estrus and metestrus were constructed, both PGs evoked an inhibitory inotropic action. The ED 50 for PGE 1 in tubes from estrous rats was significantly smaller (P < 0.01) than that for metestrous animals but significantly greater (P < 0.01) than that observed in oviducts from proestrous rats. The ED 50 for PGE 2 did not change in the different tested periods of the sex cycle. Results reported herein suggest the possibility that the ova present within rat oviducts, may influence their own transport along the tubes by modifying the amount of prostaglandins produced by the oviducts or via their own prostaglandin synthesis.

Proctolin in the innervation of the locust mandibular closer muscle modulates contractions through the elevation of inositol trisphosphate

Extracts of the locust (Locusta migratoria) mandibular closer muscle separated on reverse-phase HPLC and tested for bio-activity on the locust oviduct contain a bio-active substance that coelutes with authentic proctolin. Furthermore, the effect on oviduct contractions of this compound is indistinguishable from that of authentic proctolin. Antiserum to proctolin stains numerous axons with beaded endings that run along the fibres of the closer muscles and, in addition, the antiserum stains a number of cell bodies in the suboesophageal ganglion, some of which have axons in the mandibular nerve that innervates the mandibular musculature. The function of proctolin appears to be modulatory as its presence significantly increases the amplitude of neurally evoked contractions of the closer muscle. This effect can be mimicked by the addition of inositol 1,4,5-trisphosphate (IP3) to preparations in which the muscles have been permeabilized with dimethyl sulfoxide. The involvement of this second messenger is further implicated as we also show that proctolin produces a large, significant increase in the IP3 content of homogenized muscle.

Fertility Following Intrauterine Insemination Near the Time of Oviposition

The fate and fertility of semen deposited immediately following oviposition in the vicinity of the uterovaginal sperm host glands (USHG) was evaluated and compared with the semen deposited in the vagina. Intrauterine insemination of hens immediately after oviposition provided excellent fertility over a 2-wk period, compared to semen deposited in the vagina; also, 89% of the eggs laid within 25 h following intrauterine insemination were fertile, versus 33% following intravaginal insemination. Thus, spermatozoa deposited in the vicinity of the USHG immediately following oviposition (to simulate a release of spermatozoa from this region) can be transported to the infundibulum and effectively fertilize the next ovum ovulated.While some spermatozoa deposited in the uterus are transported to the infundibulum, the bulk of those retained in the oviduct populate the USHG. Thus, oviductal contractions immediately following oviposition do not adversely influence either the retention of spermatozoa or their incorporation into the USHG if the spermatozoa are placed on the uterine side of the uterovaginal junction.