Development of Amblyospora campbelli (Microsporida: Amblyosporidae) in the Mosquito Culiseta incidens (Thomson)

The complete life cycle of Amblyospora campbelli (Kellen and Wills, 1962) (Microsporida: Amblyosporidae) requires a two-host system involving the mosquito host, Culiseta incidens (Thomson), and an obligatory intermediate copepod host. The parasite has dimorphic spore development producing meiospores (haploid condition) and binucleated spores (diploid condition), either as an exclusive infection or simultaneously (within females only). This is the 1st known report of concurrent spore development within an adult mosquito host, and, therefore, shows the Amblyospora campbelli system to be uniquely different from other Amblyospora spp. cycles previously described. The significance of dimorphic spore development is discussed. In females, diplokaryotic meronts may invade oenocytes, causing a benign-type of infection. A blood-meal is required to initiate sporulation of the binucleate spore. The binucleate spore contains the sporoplasm involved in transovarial transmission. A 2nd sporulation sequence, primarily in adipose tissue, may involve both males and females. In this sequence, repeated merogonic division greatly increased the density of diplokaryotic meronts and generally involved most of the body of the host. Production of meiospores, unlike that for the binucleate spore, appeared to be spontaneous (i.e. no obligatory blood meal). Survivorship of male and female larval mosquitoes was nearly equal. Adult females spread the parasite in three ways: transovarial, transovum, and by meiospore deposition.     

Population dynamics of Gyrodactylus sp. (Monogenea) infecting the sand goby in the Oslo Fjord, Norway

Prevalence and abundance of Gyrodactylus sp. on the 1993 year-class of sand gobies Pomatoschistus minutus in the Oslo Fjord, Norway, decreased slightly during the cold months, increased as temperature increased in spring, reaching a peak in June, then decreased significantly, corresponding with a decline in the number of hosts from August. Abundance and, especially, prevalence increased again in September, and decreased in late autumn. Death of the most heavily infected hosts, and/or host resistance might be responsible for the decline in parasite numbers on post-spawners in summer. The young of the year (1994 year-class) were probably infected shortly after they commenced benthic life in July, and prevalence and abundance increased significantly throughout late summer and autumn. Parasite abundance on males was significantly higher than on females at the height of the breeding season in June, but significantly lower at the end of the breeding season in July. Two-thirds of the parasites infected the gills, oral cavity and pharynx. The proportion of parasites on the body, head and fins increased on both sexes, but significantly more so on males, during the breeding season of the host, when parasite intensity was highest. Possible routes of transmission of the parasite are discussed.     

The Sec1 Family: A Novel Family of Proteins Involved in Synaptic Transmission and General Secretion

Abstract: The Sec1 family, a novel family of proteins involved in synaptic transmission and general secretion, is described. To date, 14 members of this family have been identified: four yeast proteins, Sec1, Sly1, Slp1/Vps33, and Vps45/Stt10; three nematode proteins, Unc-18 and the homologues of Sly1 and Slp1; the Drosophila Rop; and six mammalian proteins, the rat Munc-18/n-Sec1/rbSec1A and rbSec1B, the mouse Munc-18b/muSec1 and Munc-18c, and the bovine Munc-18 and mSec1. The mammalian proteins share 44–63% sequence identity with the nematode Unc-18 and Drosophila Rop proteins and 20–29% with the yeast proteins and their nematode homologues. The Sec1 proteins are mostly hydrophilic and lack a transmembrane domain. Nevertheless, Sec1 proteins are found as membrane-bound proteins. Some of them are also found as soluble, cytoplasmic proteins. Binding of the rat brain Sec1 to the presynaptic membrane may be due to strong interaction with syntaxin, an integral component of this membrane. The rat brain Sec1 is also bound to Cdk5, a neural cyclin-dependent kinase. The Sec1 proteins play a positive role in exocytosis. Loss of function mutations in SEC1 , SLY1 , or SLP1 result in blocking of protein transport between distinct yeast subcellular compartments. Inactivation of unc-18 and rop results in inhibition of neurotransmitter release and, in the case of rop , inhibition of general secretion as well. In addition, studies of Rop and n-Sec1 indicate that they also play a negative role in synaptic transmission, mediated by their interaction with syntaxin. A working model addressing the dual regulative role of the Sec1 proteins in secretion is presented.     

Nicotinic Autoreceptors Mediating Enhancement of Acetylcholine Release Become Operative in Conditions of "Impaired" Cholinergic Presynaptic Function

Abstract: The existence in the mammalian CNS of release-inhibiting muscarinic autoreceptors is well established. In contrast, few reports have focused on nicotinic autoreceptors mediating enhancement of acetylcholine (ACh) release. Moreover, it is unclear under what conditions the function of one type of autoreceptor prevails over that of the other. Rat cerebrocortex slices, prelabeled with [³H]choline, were stimulated electrically at 3 or 0.1 Hz. The release of [³H]ACh evoked at both frequencies was inhibited by oxotremorine, a muscarinic receptor agonist, and stimulated by atropine, a muscarinic antagonist. Nicotine, ineffective at 3 Hz, enhanced [³H]ACh release at 0.1 Hz; mecamylamine, a nicotinic antagonist, had no effect at 3 Hz but inhibited [³H]ACh release at 0.1 Hz. The cholinesterase inhibitor neostigmine decreased [³H]ACh release at 3 Hz but not at 0.1 Hz; in the presence of atropine, neostigmine potentiated [³H]ACh release, an effect blocked by mecamylamine. In synaptosomes depolarized with 15 mM KCI, ACh inhibited [³H]ACh release; this inhibition was reversed to an enhancement when the external [Ca²⁺] was lowered. The same occurred when, at 1.2 mM Ca²⁺, external [K⁺] was decreased. Oxotremorine still inhibited [³H]ACh release at 0.1 mM Ca²⁺. When muscarinic receptors were inactivated with atropine, the K⁺ (15 mM)-evoked release of [³H]ACh (at 0.1 mM Ca²⁺) was potently enhanced by ACh acting at nicotinic receptors (EC₅₀? 0.6 µM). In conclusion, synaptic ACh concentration does not seem to determine whether muscarinic or nicotinic autoreceptors are activated. Although muscarinic autoreceptors prevail under normal conditions, nicotinic autoreceptors appear to become responsive to endogenous ACh and to exogenous nicotinic agents under conditions mimicking impairment of ACh release. Our data may explain in part the reported efficacy of cholinesterase inhibitors (and nicotinic agonists) in Alzheimer's disease.     

SUBOPTIMAL VIRULENCE OF AN INSECT-PARASITIC NEMATODE

Recent considerations of parasite virulence have focused on the adverse effects that parasites can have on the survival of their hosts. Many parasites, however, reduce host fitness by an equally deleterious but different means, by causing partial or complete sterility of their hosts. A model of optimal parasite virulence is developed in which a quantity of host resources can be allocated to either host or parasite reproduction. Increases in parasite reproduction thus cause reductions in host fertility. The model shows that under a wide variety of ecological conditions, such parasites should completely sterilize their hosts. Only when opportunities for horizontal transmission are very limited should the parasites appropriate less than all of a host's reproductive resources. Field and laboratory evidence shows that the nematode parasite Howardula aoronymphium is relatively avirulent to one of its principal host species, Drosophila falleni, whereas it is much more virulent to D. putrida and D. neotestacea, suggesting that there may be substantial vertical transmission in D. falleni. However, epidemiological studies in the field and laboratory assays of host specificity strongly suggest that the three host species share a single parasite pool in natural populations, indicating that parasites in all three host species experience high levels of horizontal transmission. Thus, the low virulence of H. aoronymphium to D. falleni is not consistent with the model of optimal parasite virulence. It is proposed that this suboptimal virulence in D. falleni is a consequence of populations of H. aoronymphium being selected to exploit simultaneously several different host species. As a result, virulence may not be optimal in any one host. One must, therefore, consider the full range of host species in assessing a parasite's virulence.     

Conformational transmission in ATP synthase during catalysis: Search for large structural changes

Escherichia coli ATP synthase has eight subunits and functions through transmission of conformational changes between subunits. Defective mutation at Gly-149 was suppressed by the second mutations at the outer surface of the subunit, indicating that the defect by the first mutation was suppressed by the second mutation through long range conformation transmission. Extensive mutant/pseudorevertant studies revealed that / and / subunits interactions are important for the energy coupling between catalysis and H⁺ translocation. In addition, long range interaction between amino and carboxyl terminal regions of the subunit has a critical role(s) for energy coupling. These results suggest that the dynamic conformation change and its transmission are essential for ATP synthase.     

Alfalfa mosaic and cucumber mosaic virus infection in chickpea and lentil: incidence and seed transmission

Samples collected in 1994 and 1995 from commercial crops of chickpeas and lentils growing in the agricultural region of south-west Western Australia were tested for infection with alfalfa mosaic (AMV) and cucumber mosaic (CMV) viruses, and for members of the family Potyviridae using enzyme-linked immunosorbent assay (ELISA). In 1994 no virus was detected in the 21 chickpea crops tested but in 1995, out of 42 crops, AMV was found in two and CMV in seven. With lentils, AMV and/or CMV was found in three out of 14 crops in 1994 and 4 out of 13 in 1995, both viruses being detected in two crops in each year. Similar tests on samples from chickpea and lentil crops and plots growing at experimental sites, revealed more frequent infection with both viruses. No potyvirus infection was found in chickpeas or lentils in agricultural areas either in commercial crops or at experimental sites. However, bean yellow mosaic virus (BYMV) was detected along with AMV and CMV in irrigated plots of chickpeas and lentils at a site in Perth. When samples of seed from infected crops or plots of chickpeas and lentils were germinated and leaves or roots of seedlings tested for virus infection by ELISA, AMV and CMV were found to be seed-borne in both while BYMV was seed-borne in lentils. The rates of transmission found through seed of chickpea to seedlings were 0.1–1% with AMV and 0.1–2% with CMV. Seed transmission rates with lentil were 0.1–5% for AMV, 0.1–1% for CMV and 0.8% for BYMV. Individual seed samples of lentil and chickpea sometimes contained both AMV and CMV. With both species, infection with AMV and CMV was sometimes found in commercial seed stocks or seed stocks from multiplication crops of advanced selections nearing release as new cultivars. Seed-borne virus infection has important practical implications, as virus sources can be re-introduced every year to chickpea and lentil crops or plots through sowing infected seed stocks leading to spread of infection by aphid vectors, losses in grain yield and further contamination of seed stocks.     

Octopamine mediates rapid stimulation of protein kinase A in the antennal lobe of honeybees

In the honeybee octopamine mediates mechanisms of arousal that interfere with the appetitive proboscis extension response to food-indicating chemosensory stimuli. This study demonstrates that injections of octopamine or cyclic adenosine monophosphate (cAMP) into the primary chemosensory neuropil of the honeybee, the antennal lobe, evokes a rapid and transient activation of cAMP-dependent protein kinase (PKA). Other monoamines detectable in the antennal lobe, dopamine and serotonin, do not affect the level of PKA activity. Stimulation of the bees' antenna with the appetitive stimulus water or sucrose solution in vivo also causes a short-term activation of PKA in the antennal lobe. The increased PKA activity can be detected immediately (0.5 s) after stimulation but reverts to the basal level within 3 s. This effect can be abolished by monoamine depletion with reserpine. Since octopamine is the only monoamine that stimulates PKA, it appears to mediate the PKA activation after sucrose stimulus and may contribute to the processing of this chemosensory input. © 1995 John Wiley & Sons, Inc.     

Modulation of ion currents and regulation of transmitter release in short-term synaptic plasticity: The rise and fall of the action potential

Up and down-regulation of calcium and potassium conductances are associated with several forms of short-term synaptic modulation. Detailed investigation of synaptic plasticity in the marine gastropodAplysia, and in other mollusks, indicates that synaptic transmission can be influenced in a number of ways by modulatory neurotransmitters acting through several second-messenger cascades. Modulation at the synapse itself occurs by means of the regulation of calcium current as well as through effects on processes directly involved in transmitter mobilization and exocytosis. Modulation of potassium current plays a major role in controlling neuronal excitability and may contribute to a lesser extent to the regulation of transmitter release through actions on the resting potential and on action potential configuration.     

Modelling the effect of treatment and behavioral change in HIV transmission dynamics

In this paper we analyze a model for the HIV-infection transmission in a male homosexual population. In the model we consider two types of infected individuals. Those that are infected but do not know their serological status and/or are not under any sort of clinical /therapeutical treatment, and those who are. The two groups of infectives differ in their incubation time, contact rate with susceptible individuals, and probability of disease transmission. The aim of this article is to study the roles played by detection and changes in sexual behavior in the incidence and prevalence of HIV. The analytical results show that there exists a unique endemic equilibrium which is globally asymptotically stable under a range of parameter values whenever a detection /treatment rate and an indirect measure of the level of infection risk are sufficiently large. However, any level of detection/ treatment rate coupled with a decrease of the transmission probability lowers the incidence rate and prevalence level in the population. In general, only significant reductions in the transmission probability (achieved through, for example, the adoption of safe sexual practices) can contain effectively the spread of the disease.