Neural and hormonal control of muscular activity of the spermatheca in the locust, Locusta migratoria

The Male Reproductive System of the Kissing Bug, Rhodnius prolixus Stål, 1859 (Hemiptera: Reduviidae: Triatominae): Arrangements of the Muscles and the Myoactivity of the Selected Neuropeptides

The gross anatomy of the male reproductive structures and their associated musculature are described in the blood-gorging vector of Chagas disease, Rhodnius prolixus. The male reproductive system is composed of muscular tissues each performing contractions that aid in the movement of sperm out of the testis into the vas deferens, seminal vesicle and then into the ejaculatory duct, along with proteins and lipids from the transparent and opaque accessory glands. Phalloidin staining shows the various patterns of muscle fiber layers, from thin circular to more complex crisscross patterns, implying subtle differences in the form of the contractions and movement of each of the structures, allowing for waves of contractions or twisting patterns. The transcripts for the receptors for proctolin, myosuppressin (RhoprMS) and for the extended FMRFamides are expressed in the various regions of the reproductive system, and the nerve processes extending over the reproductive structures are positive for FMRFamide-like immunoreactivity, as are neurosecretory cells lying on the nerves. Proctolin and AKDNFIRFamide are strong stimulators for the frequency of the contractions, and RhoprMS can inhibit the proctolin-induced contractions. Taken together, this work implicates these two families of peptides in coordinating the male reproductive structures for the successful transfer of sperm and the associated accessory gland fluid to the female during copulation.

Nutritional and Physiological Regulation of Glassy-Winged Sharpshooter Oogenesis

The glassy-winged sharpshooter (Homalodisca vitripennis (Germar); Hemiptera: Cicadellidae: Cicadellinae) is an invasive insect that transmits the plant pathogenic bacterium Xylella fastidiosa Wells et al. (Xanthomonadales: Xanthomonadacae). While adult glassy-winged sharpshooter must feed to produce eggs, the role of nutritional status on initiating oogenesis is poorly understood. To determine the effects of glassy-winged sharpshooter nutrition on nymphal development, oogenesis, and fecundity, glassy-winged sharpshooter were reared on cowpea, sunflower, sorghum, and a mixture of the three plant species. Adults emerging from cowpea, sunflower, or plant mixture treatments had shorter development times, attained larger size, and had greater estimated lipid reserves than females reared on sorghum. In choice tests, nymphs avoided sorghum and preferentially fed on cowpea and sunflower. Adult females provisioned with a single plant species during the nymphal stage were provided with either the same host plant species or a mixture of host plant species (cowpea, sunflower, sorghum) for a 9-wk oviposition period, with 37% of females initiating oogenesis. Ovipositing females had greater juvenile hormone and octopamine levels than reproductively inactive females, although topical application of the juvenile hormone analog Methoprene did not promote oogenesis. Across nymphal diets, reproductively active females produced more eggs when held on plant mixtures than on single plant species. In choice tests, adult females were observed most frequently on cowpea, although most eggs were deposited on sorghum, the host least preferred by nymphs. Results suggest that fecundity is largely determined by the quality of the adult diet, although the stimulus that initiates oogenesis does not appear to be related to nutrition.

She's got nerve: roles of octopamine in insect female reproduction

The biogenic monoamine octopamine (OA) is a crucial regulator of invertebrate physiology and behavior. Since its discovery in the 1950s in octopus salivary glands, OA has been implicated in many biological processes among diverse invertebrate lineages. It can act as a neurotransmitter, neuromodulator and neurohormone in a variety of biological contexts, and can mediate processes including feeding, sleep, locomotion, flight, learning, memory, and aggression. Here, we focus on the roles of OA in female reproduction in insects. OA is produced in the octopaminergic neurons that innervate the female reproductive tract (RT). It exerts its effects by binding to receptors throughout the RT to generate tissue- and region-specific outcomes. OA signaling regulates oogenesis, ovulation, sperm storage, and reproductive behaviors in response to the female's internal state and external conditions. Mating profoundly changes a female's physiology and behavior. The female's OA signaling system interacts with, and is modified by, male molecules transferred during mating to elicit a subset of the post-mating changes. Since the role of OA in female reproduction is best characterized in the fruit fly Drosophila melanogaster, we focus our discussion on this species but include discussion of OA in other insect species whenever relevant. We conclude by proposing areas for future research to further the understanding of OA's involvement in female reproduction in insects.

Peptide hormones regulate the physiological functions of reproductive organs in Tenebrio molitor males

In insects, the majority of studies have been conducted on the hormonal regulation of female reproduction. Thus far, little is known about the regulation of male reproductive physiology, especially by peptide hormones. We report here, for the first time in insects, the effects of three peptides, Neb-colloostatin (SIVPLGLPVPIGPIVVGPR), Neb-TMOF (NPTNLH) and Lepde-NPF-I (ARGPQLRLRFa), on various aspects of reproduction in male Tenebrio molitor beetles. All three tested peptides increased the soluble protein concentration in the testes and the dry mass of the beetle's testes. They also significantly changed the protein profiles of the testes. Injection of these peptides also significantly changed the number of sperm cells in the testes. However, the observed effects were age specific. The most prominent changes were observed in 4-day-old males. Neb-colloostatin and Neb-TMOF decreased the number of sperm cells, whereas Lepde-NPF-I increased the number of spermatocytes. Moreover, in vitro experiments revealed that Neb-TMOF and Lepde-NPF-I increased the contractility of the ejaculatory duct of T. molitor males. The results obtained suggest that different reproductive processes in males might be regulated by complex mechanisms.

The octopamine receptor octß2R is essential for ovulation and fertilization in the fruit fly Drosophila melanogaster

The biogenic monoamine octopamine is essential for ovulation and fertilization in insects. Release of this hormone from neurons in the thoracoabdominal ganglion triggers ovulation and sperm release from the spermathecae. Here we show that the effects of octopamine on ovulation are mediated by at least two different octopamine receptors. In addition to the Oamb receptor that is present in the epithelium of the oviduct, the octß2R receptor is essential for ovulation and fertilization. Octß2R is widely expressed in the female reproductive tract. Most prominent is expression in the oviduct muscle and the spermathecae. Animals deficient in expression of the receptor show a severe egg-laying defect. The corresponding females have a much larger ovary that is caused by egg retention in the ovary. Moreover, the very few laid eggs are not fertilized, indicating problems in the process of sperm delivery. We assume that octß2R acts in a similar way as ß2-adrenoreceptors in smooth muscles, were activation of this receptor induces an increase in cAMP levels that lead to relaxation of the muscle. Taken together, our findings show that octopaminergic control of ovulation and fertilization is more complex than anticipated and that various receptors located in different cells act together to enable a well-orchestrated activity of the female reproductive system in response to copulation.

Myoinhibitors controlling oviduct contraction within the female blood-gorging insect, Rhodnius prolixus

Muscle activity can be regulated by stimulatory and inhibitory neuropeptides allowing for contraction and relaxation. There are various families of neuropeptides that can be classified as inhibitors of insect muscle contraction. This study focuses on Rhodnius prolixus and three neuropeptide families that have been shown to be myoinhibitors in insects: A-type allatostatins, myoinhibiting peptides (B-type allatostatins) and myosuppressins. FGLa/AST-like immunoreactive axons and blebs were found on the anterior of the dorsal vessel and on the abdominal nerves. FGLa/AST-like immunoreactive axons were also seen in the trunk nerves and on the bursa. The effects of RhoprAST-2 (FGLa/AST or A-type allatostatins) and RhoprMIP-4 (MIP/AST or B-type allatostatins) were similar, producing dose-dependent inhibition of R. prolixus spontaneous oviduct contractions with a maximum of 70% inhibition and an EC50 at approximately 10(-8)M. The myosuppressin of R. prolixus (RhoprMS) has an unusual FMRFamide C-terminal motif (pQDIDHVFMRFa) as compared to myosuppressins from other insects. Quantitative PCR results show that the RhoprMS receptor transcript is present in adult female oviducts; however, RhoprMS does not have an inhibitory effect on R. prolixus oviduct contractions, but does have a dose-dependent inhibitory effect on the spontaneous contraction of Locusta migratoria oviducts. SchistoFLRFamide, the myosuppressin of Schistocerca gregaria and L. migratoria, also does not inhibit R. prolixus oviduct contractions. This implies that FGLa/ASTs and MIP/ASTs may play a role in regulating egg movement within the oviducts, and that the myosuppressin although myoinhibitory on other muscles in R. prolixus, does not inhibit the contractions of R. prolixus oviducts and may play another role in the reproductive system.

Neuropeptidergic regulation of reproduction in insects

Successful animal reproduction depends on multiple physiological and behavioral processes that take place in a timely and orderly manner in both mating partners. It is not only necessary that all relevant processes are well coordinated, they also need to be adjusted to external factors of abiotic and biotic nature (e.g. population density, mating partner availability). Therefore, it is not surprising that several hormonal factors play a crucial role in the regulation of animal reproductive physiology. In insects (the largest class of animals on planet Earth), lipophilic hormones, such as ecdysteroids and juvenile hormones, as well as several neuropeptides take part in this complex regulation. While some peptides can affect reproduction via an indirect action (e.g. by influencing secretion of juvenile hormone), others exert their regulatory activity by directly targeting the reproductive system. In addition to insect peptides with proven activities, several others were suggested to also play a role in the regulation of reproductive physiology. Because of the long evolutionary history of many insect orders, it is not always clear to what extent functional data obtained in a given species can be extrapolated to other insect taxa. In this paper, we will review the current knowledge concerning the neuropeptidergic regulation of insect reproduction and situate it in a more general physiological context.

Sperm storage by spermatodoses in the spermatheca of Trioza alacris (Flor, 1861) hemiptera, psylloidea, triozidae: a structural and ultrastructural study

Female insects generally store sperm received during mating in specific organs of their reproductive tract, i.e., the spermathecae, which keep the sperm alive for a long time until fertilization occurs. We investigated spermatheca morphology and ultrastructure in the psylloidean insect Trioza alacris (Flor,1861) in which spheroidal sperm packets that we refer to as 'spermatodoses' are found after mating. The ectoderm-derived epithelium of the sac-shaped spermatheca that has a proximal neck, consists of large secretory and flat cuticle-forming cells. Secretory cells are characterized by a wide extracellular cavity, bordered by microvilli, in which electron-dense secretion accumulates before discharge into the spermathecal lumen. The cuticle-forming cells produce the cuticular intima of the organ and a peculiar specialized apical structure, through which secretion flows into the lumen. At mating, the male transfers bundles of sperm cells embedded in seminal fluid into the spermathecal neck. Sperm cells proceed towards the spermathecal sac lumen, where they are progressively compacted and surrounded with an envelope that also encloses secretions of both male and female origin. We describe the formation of these sperm containing structures and document the contribution of the female secretion to spermatodose or female-determined spermatophore construction. We also discuss the choice of the term 'spermatodose' for T. alacris and suggest it be used to refer to sperm masses constructed in the female reproductive organs, at least when they involve the contribution of female secretion.

Evidence of a central pattern generator regulating spermathecal muscle activity in Locusta migratoria and its coordination with oviposition

Electrophysiological recordings were conducted to determine the control of spermathecal contractions during oviposition of interrupted egg-laying locusts, Locusta migratoria. Following transection of the central nervous system below the metathoracic ganglion, rhythmic patterned bursting was detected by extracellular recordings of the nerve N2B2 that innervates the muscles of the spermatheca. Subsequent transections at more posterior regions of the ventral nerve cord revealed more robust rhythmic bursting in N2B2. This rhythmic bursting pattern was found to be coordinated with bursting in the ventral opener nerve (N2B1) that innervates the ventral opener muscle. This muscle controls the ventral ovipositor valves. Electromyographic recordings from the spermathecal muscle and ventral opener muscle confirmed a rhythmic bursting pattern resulting in an increase in muscle activity. Taken together, the results indicate that there is probably a central pattern generator (CPG), which is regulated by descending inhibition, that controls the spermathecal muscle activity. This CPG appears to be located within the VIIth and VIIIth abdominal ganglia, and was found to integrate with the CPG that regulates oviposition digging in locusts. These results provide further insight into the intricate coordination and control of reproductive tissues underlying reproductive behaviours in locusts.

Characterization of a novel octopamine receptor expressed in the surf clam Spisula solidissima

We have cloned and sequenced a cDNA from the surf clam (Spisula solidissima, a pelecypod mollusc) that encodes an octopamine receptor which we have named Spi-OAR. The sequence of Spi-OAR shares many similarities with two Aplysia and three Drosophila octopamine receptors belonging to a sub-group of beta-adrenergic-like octopamine receptors. Using an expression vector and transient transfections of Spi-OAR into HEK 293 cells, we observed an increase of cAMP upon addition of octopamine and, to a lesser extent, of tyramine, but not after addition of dopamine, serotonin, or histamine. Using a battery of known agonists and antagonists for octopamine receptors, we observed a rather unique pharmacological profile for Spi-OAR through measurements of cAMP. Spi-OAR exhibited some constitutive activity in HEK 293 cells and no Ca(2+) responses could be detected following addition of octopamine to Spi-OAR-transfected cells. RT-PCR analysis revealed ubiquitous expression of Spi-OAR mRNA in all adult tissues, oocytes and early embryos examined. While addition of serotonin to isolated clam oocytes resulted in meiotic activation, similar additions of octopamine had no effect, suggesting that its potential role in clam reproductive physiology differs significantly from that of serotonin. This work identifies Spi-OAR as a novel mollusc octopamine receptor closely related to other invertebrate beta-adrenergic-like octopamine receptors, with possible reproductive and other physiological functions. This initial characterization of Spi-OAR makes possible further investigations and comparisons with more studied and familiar insect or gastropod mollusc octopamine receptors.

The female reproductive system and control of oviposition in Locusta migratoria migratorioidesThe present review is the first of a series of occasional review articles that have been invited by the Editors and will feature the broad range of disciplines and expertise represented in our Editorial Advisory Board

The spermatheca acts as a repository for sperm deposited by the male and, in the African migratory locust ( Locusta migratoria migratorioides (Fairmaire and Reiche, 1849)), is situated dorsal to the lateral and common oviducts. In the locust, eggs mature in the ovaries and are ovulated into the lateral oviducts where they are held until a suitable oviposition site is found. At that time, a hole is dug in the soil by the locust and, aided by muscular contractions of the upper lateral oviducts, the eggs are propelled through the common oviduct and genital chamber and deposited in a pod in the soil. Contractions of the spermathecal sac lead to sperm release, resulting in fertilization of eggs in the genital chamber. Coordination of digging and of the oviducts and spermatheca is clearly critical to the production of viable eggs. The muscles responsible for digging and both reproductive structures are under central neuronal control, incorporating neurons that express an array of neuropeptide and amine phenotypes. Many of the phenotypes are common to both reproductive tissues. A neural loop ensures the coordinated release of sperm when an egg passes into the genital chamber. This review will discuss our understanding of the neural control of these reproductive tissues and their coordination with digging.

Tyramine: from octopamine precursor to neuroactive chemical in insects

It is well acknowledged that tyramine acts as the biosynthetic intermediate precursor for octopamine. This fact has biased the interpretation of biological effects of tyramine towards an artifact of it being a partial agonist on octopamine receptors. Over recent years there has been an accumulation of evidence to show that tyramine is in fact a neuroactive chemical in its own right, with diverse physiological/behavioral roles. In addition, tyramine plays a unique role in a non-neuronal tissue, namely the Malpighian tubules. This review examines this evidence, taking into account the criteria that need to be satisfied in order to claim neuroactive chemical status. Thus, the evidence points to tyramine being synthesized by, and present in, neurons; capable of being released from neurons; removed by high affinity plasma membrane transporters; acting upon specific tyramine receptors; and producing physiological/behavioral effects that can be blocked by antagonists. This composite evidence is strong, although the final proof still awaits analysis on a uniquely identifiable tyraminergic neuron as has been possible with octopamine.

Tyramine as a possible neurotransmitter/neuromodulator at the spermatheca of the African migratory locust, Locusta migratoria

Tyramine-like immunoreactivity was identified in neurons of the VIIIth abdominal ganglion and in axons projecting to the spermatheca of adult females of Locusta migratoria. Tyramine-like immunoreactive processes were also found throughout all regions of the spermatheca and tyramine-like immunoreactive bipolar or multipolar neurons were present on the spermathecal sac. HPLC coupled with electrochemical detection revealed more tyramine than octopamine present in spermathecal tissue. Electrical stimulation of the ventral ovipositor nerve resulted in a significant increase in calcium-dependent release of tyramine from the spermatheca. Both tyramine and octopamine increase the frequency and basal tonus of spermathecal contractions in a dose-dependent manner, with octopamine having a lower threshold. When tyramine is applied along with a half maximal octopamine dose, there is an additive effect on contractions of the spermatheca with slight synergistic effects at lower doses of tyramine. High concentrations of tyramine (10(-4)M) stimulated increases in cyclic AMP levels of the spermatheca; an effect blocked by phentolamine. Phentolamine has a higher affinity (and thus a lower IC(50) value congruent with 5.6 x 10(-8)M) than yohimbine (IC(50) congruent with 1.1 x 10(-4)M) in reducing tyramine-induced spermathecal contractions. Taken together, these results suggest that tyramine may be a co-transmitter with octopamine at the spermatheca, with both neuroactive chemicals acting on an octopamine receptor.