Decreased availability of metabolic fuels suppresses estrous behavior in Syrian hamsters.

The availability of oxidizable metabolic fuels affects reproductive physiology and behaviors in female mammals. In Syrian hamsters, 48 h of food deprivation is sufficient to suppress secretion of gonadotropins and ovarian steroids and to prevent the occurrence of ovulation and estrous behavior. These experiments attempted to determine whether the deprivation-induced suppression of lordosis is entirely due to the disruption of ovarian steroid secretion or whether there are also changes in behavioral responsiveness to estradiol and/or progesterone (P). Estrous behavior was induced in ovariectomized hamsters with sequential injections of 5 micrograms of estradiol benzoate (EB) and 200 micrograms P. Food deprivation for 48 h, either before or just after EB treatment, significantly suppressed the amount of time females spent in lordosis during a 5-min test with a sexually experienced male. Treatment with an inhibitor of glycolysis (2-deoxy-D-glucose) in combination with an inhibitor of fatty acid oxidation (methyl palmoxirate) for 48 h mimicked the effects of food deprivation and suppressed the amount of time spent in lordosis after treatment with EB+P. Given alone, neither metabolic inhibitor had an effect on lordosis. These findings indicate that suppression of hamster estrous behavior by metabolic fuel deprivation is at least in part due to a reduced responsiveness to estradiol and/or progesterone. Furthermore, estrous behavior is responsive to metabolic fuels in general. This is unlike hamster ovulatory cycles, which are primarily responsive to glucose availability.

Effect of ovarian regression and molt on plasma concentrations of thymosin beta 4 in domestic hens (Gallus domesticus).

Molt induced by infusion of a gonadotropin-releasing hormone agonist (GnRH-A, ([D-leu6,Pro9]-GnRH N-ethylamide]) or feed withdrawal (FW) has been used as a model to study interactions between ovarian activity and thymosin beta 4 during molting in domestic hens. Thirty-three laying hens were divided into three groups: 1, controls, 2, GnRH-A infusion induced molt (GnRH-A), or 3, FW induced molt. All groups had reduced daylength. Blood was sampled weekly and assayed for concentrations of thymosin beta 4 and progesterone (P4). Plasma P4 concentrations were significantly depressed in both treatment groups compared to controls, indicating ovarian regression. Plasma P4 concentrations had returned to control values in the GnRH-A group by 28 d after the start of treatment, while P4 was still depressed in the FW group at day 42 when the experiment ended. Plasma concentrations of thymosin beta 4 were elevated relative to controls from day 7 through day 14 in the GnRH-A group and from day 7 until day 28 in the FW group. It is concluded that plasma concentrations of thymosin beta 4 are elevated during molting in domestic hens, but the elevation is not attributable to depressed P4 concentrations.

Molt induced by gonadotropin-releasing hormone agonist as a model for studying endocrine mechanisms of molting in laying hens.

Molt induced by infusion of a gonadotropin-releasing hormone agonist (GnRH-A, ([D-Leu6,Pro9]-GnRH N-ethylamide]) has been used as a model for studying the endocrine mechanisms of molting. Molt induced by GnRH-A was also compared with that induced by feed withdrawal (FW). Thirty-three laying hens were divided into three groups: 1) sham infused (controls), 2) molted by GnRH-A infusion (GnRH-A), or 3) molted by FW. All groups had reduced day length. Birds were weighed and blood was sampled twice per week. Plasma was assayed for thyroxine (T4), triiodothyronine (T3), and progesterone (P4); egg production was recorded. A separate group of GnRH-A molted (n = 8) and control (n = 4) hens were killed during the molt and liver, ovary, and oviduct were weighed. Plasma T4 concentrations were elevated (P less than .01), whereas plasma T3 did not change and plasma P4 decreased (P less than .05) in the GnRH-A group compared with the control group. Plasma T4 was higher (P less than .05) in the GnRH-A group than in the FW group, whereas plasma T3 was higher (P less than .05) in the FW group than in the GnRH-A group. Plasma P4 concentrations declined to similar low levels in the GnRH-A and FW groups. The GnRH-A caused weight loss (P less than .05) from the ovary, oviduct, and liver. The GnRH-A-molted hens lost less BW (P less than .001) and were out of lay for 12 days less than FW-molted hens. Postmolt rates of lay were not significantly different for the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Genetic variation of Venezuelan equine encephalitis virus strains of the ID variety in Colombia.

To determine the degree of genetic variation within one serologic group of Venezuelan equine encephalitis virus and the relatedness of viruses with different epidemiologic backgrounds isolated within the same country, virion RNA from 16 isolates belonging to subtype I were compared by RNase T1 oligonucleotide fingerprinting. RNA fingerprints of 12 enzootic isolates showed a large degree of heterogeneity, even though they were serologically indistinguishable. A reference enzootic strain from Colombia showed more genetic relatedness to three epizootic strains isolated in the same country, than to its own serogroup prototype strain isolated in Panama. Thus, genetic relatedness within Venezuelan equine encephalitis strains in Colombia seems to be a function of geography rather than epidemiology.

Monoclonal antibodies define antigenic variation in the ID variety of Venezuelan equine encephalitis virus.

Three monoclonal antibodies were generated that are specific for the E2 glycoprotein of Venezuelan equine encephalitis (VEE) virus and have useful reactivities in an enzyme-linked immunosorbent assay (ELISA). Antibody 1A1B-9 distinguished between the IC (epizootic) and ID (enzootic) varieties of VEE virus by ELISA. Clone 7A1A-1 antibody distinguished the Panamanian prototype virus (3880) from Colombian ID isolates by a 500-fold difference in titer by endpoint ELISA, and it detected antigenic variation in ID isolates from southern Colombia and Ecuador. Antibody 7A3A-4 defined a cryptic antigenic site on the latter two isolates. These monoclonal antibodies complement others in identifying VEE isolates by a simple ELISA.

Vector competence of Culex (Melanoconion) taeniopus for allopatric and epizootic Venezuelan equine encephalomyelitis viruses.

The vector competence of Culex (Melanoconion) taeniopus was examined in the laboratory for "enzootic" allopatric and "epizootic" strains of Venezuelan equine encephalomyelitis viruses of hemagglutination inhibition subtypes I, II, III, and IV. Following bloodmeals from viremic hamsters, and extrinsic incubation of 20-22 days, mosquitoes were allowed to refeed for transmission attempts. Infection rates never exceeded 50% with oral doses of less than 10(4) chick embryo cell culture plaque forming units (CECPFU), and approached 100% only after ingestion of greater than or equal to 10(5.5) PFU. Transmission was achieved for some "epizootic" subtype IABC and "enzootic" subtype ID strains after bloodmeals containing greater than or equal to 10(3.4) CECPFU; subtypes II, III, and IV were never transmitted despite oral doses up to 10(5.0) CECPFU. These data contrast sharply with those reported previously for sympatric "enzootic" subtype IE Middle American Venezuelan encephalitis viruses.

Decreased granulosa cell luteinizing hormone sensitivity and altered thecal estradiol concentration in the aged hen, Gallus domesticus.

Few studies have examined the effect of age on the ovulation cycle of the hen. Our aim was to determine if changes in the ovary account for the decrease in egg production with age. Young hens (28-38 wk of age) laying at least 20 eggs per sequence and old hens (53-63 wk of age) laying 3-6 eggs per sequence were used. We determined luteinizing hormone (LH) sensitivity of the ovary of young and old hens by measuring LH stimulable adenylyl cyclase (AC) activity of the granulosa layer. We also measured theca- and granulosa-layer weights and steroid concentrations of these layers and of the serum in young and old hens. Mean basal AC activity (pg/min/mg protein) for the largest (F1) and second largest (F2) follicles from young and old hens did not differ. A significant dose-response relationship to LH was present in all groups, and AC responsiveness to increasing doses of LH was greater in the F1 and F2 follicles of young hens than in the same follicles of old hens. The F4 and F5 follicles of young hens had a significantly greater estradiol (E2) concentration (pg/mg theca protein) compared to old hens, while the E2 concentration in the F2 follicle was greater in old hens. The theca layer of the F1 follicle of old hens weighed significantly more than that of young hens, whereas the theca layer of the F3, F4 and F5 follicles from young hens weighed more than those of old hens.(ABSTRACT TRUNCATED AT 250 WORDS)

Ecologic observations of Venezuelan encephalitis virus in vertebrates and isolations of Nepuyo and Patois viruses from sentinel hamsters at Pacific and Atlantic habitats in Guatemala, 1968-1980.

La Avellana and Puerto Barrios, two enzootic foci of Venezuelan encephalitis (VE) virus on the Pacific and Caribbean lowlands (respectively) of Guatemala have been studied over a 13-year period. Data from sentinel hamsters and guinea pigs and wild and domestic vertebrates are reported. VE virus strains were isolated from hamsters each period they were exposed during the rainy seasons 1968-1980 and at the end of the dry season 1974. Rates of isolation of VE virus ranged from 0.2%-5.7% hamster/days/exposure. All strains tested were free of epizootic virions. Although virus was isolated from sentinel guinea pigs, their deaths were not attributable to infection with VE virus. Antibody titers in 26 of 28 terrestrial mammals bled at La Avellana in 1971 were higher to enzootic than to epizootic VE strains. Thirty-seven percent of 109 residents of Puerto Barrios had antibody to VE virus. In 13 of 20 tested, antibodies were engendered by the enzootic strain. Nepuyo and Patois viruses were isolated from sentinel hamsters at both La Avellana and Puerto Barrios.

Comparative ability of chicken and mammalian LHRH to release LH from rooster pituitary cells in vitro.

Biological properties of homogeneous solutions of chicken (c) and mammalian (m) LHRH were compared by their ability to release LH, in vitro, from a rooster pituitary cell incubation system. Homogeneity of the two LHRH species was confirmed by High Performance Liquid Chromatography (HPLC) using linear gradients of acetonitrile and phosphate buffer. A clear HPLC separation of [Gln8]-LHRH ( cLHRH ) and [Arg8]-LHRH ( mLHRH ) was obtained, with the former having a consistently longer retention time than the latter. cLHRH cause a greater (p less than .025) in vitro release of LH at low doses (less than 1 ng/2 X 10(5) live pituitary cells), but not at high doses (greater than 10 ng/2 X 10(5) live pituitary cells), than that caused by mLHRH . Our results indicate that rooster pituitary cells are significantly more sensitive to low doses of cLHRH than to similar doses of mLHRH , when assessed by their ability to release LH in vitro.

Primary viraemia responses of herons to experimental infection with Murray Valley encephalitis, Kunjin and Japanese encephalitis viruses.

Rufous night herons, Pacific herons, little egrets and intermediate egrets were experimentally infected with Murray Valley encephalitis, Kunjin or Japanese encephalitis viruses. Viraemias of at least one day's duration were detected in all birds except two intermediate egrets inoculated with a very low dose of Kunjin virus and one rufous night heron inoculated with Japanese encephalitis virus. there was usually a viraemia of 3 to 5 days' duration commencing on the first or second day and continuing until day 5 or 6 and rarely until day 7. Maximum titres tended to be higher in young birds, up to 2-5 months of age (10(4)-10(5) mouse LD50/ml), than in older birds more than 8 months of age (10(3)-10(4) mouse LD50/ml). Significant differences in maximum viraemia titres were not observed in the different species or between Murray Valley encephalitis and Kunjin viruses. Japanese encephalitis viraemias were significantly lower, but this was probably due to the high mouse brain passage level of the strain used. The onset of viraemia was earlier in intermediate egrets than in rufous night herons inoculated with similar doses of Murray Valley encephalitis virus, but no difference in the susceptibility to infection was observed. With Kunjin virus there was a significant difference in the susceptibility of intermediate egrets and rufous night herons, with rufous night herons being more susceptible to infection with low doses of virus. This difference in threshold of infection, if it extends to other species with both Kunjin and Murray Valley encephalitis viruses, may, in part, be an explanation for the greater incidence of natural infections observed in rufous night herons compared with other species and orders of water birds.

Primary antibody responses of herons to experimental infection with Murray Valley encephalitis and Kunjin viruses.

Antibody responses of rufous night herons (Nycticorax caledonicus) and little egrets (Egretta garzetta) following infection with Murray Valley encephalitis and Kunjin viruses were determined. Haemagglutinin-inhibiting antibodies were first detected on day 5 or 6 after inoculation and increased rapidly, reaching maximum titres of 320 to 2560 between 10 and 20 days after inoculation. Titres declined 20-320 between 60 and 120 days after inoculation, then tended to remain stationary. Titres were 2- to 8-fold higher to infecting virus than heterologous virus. Neutralizing antibody development paralleled that of HI antibodies with titres maintained at a higher level for longer periods; however, they did eventually decline to low levels. Following MVE virus infection IgM (19S), HI antibodies were 80-100% of HI antibodies detectable on day 6 or 7 after inoculation and declined rapidly, becoming undetectable by 20 days after inoculation. With Kunjin virus infections, IgM HI antibodies represented 90-100% of HI antibodies detectable on day 6 or 7 after inoculation. Significant levels of IgM HI antibodies were still detectable 20 days after inoculation (5-30% of total HI antibodies) and, in some birds, even at 27 days after inoculation (up to 10%), IgG (7S) HI antibodies were low or undetectable on day 6 or 7 after inoculation, then increased rapidly with rapidly rising HI antibody titres. The specificity of IgM and IgG antibodies and unfractionated sera was determined by testing against Murray Valley encephalitis, Kunjin, Japanese encephalitis and West Nile virus haemagglutinating antigens. It was possible to determine with which virus a bird had been infected from the pattern of cross-reaction with these antigens. These results should provide a rational basis for the interpretation of serological results from naturally infected birds.

Enfermedad humana causada por el virus Nepuyo, un bunyavirus de mesoamerica transmitido por mosquitos. / Human diseases caused by Nepuyo virus, mosquito-borne bunyavirus of Middle America

En el curso de estudios sobre el virus de la encefalitis venezolana realizados en La Avellana, departamento de Santa Rosa, en la costa del Pacifico de Guatemala se contrajeron dos infecciones por virus Nepuyo, un bunyavirus del complejo del grupo C de la zona neotropical. Un caso se presento en agosto de 1972 y el otro en agosto de 1977. En ambos casos aparecio una enfermedad febril leve, parecida al dengue, con viremia, comienzo subito, cefalea, mialgias y postracion. Se encontraron anticuerpos inhibidores de la hemaglutinacion y neutralizantes, pero no anticuerpos fijadores del complemento. Probablemente los vectores selvaticos sean mosquitos del complejo Culex (Melanoconion), mientras que como huespedes vertebrados amplificadores de los arbovirus del grupo C actuan roedores, marsupiales y seres humanos. En todo caso, convendria realizar estudios ecologicos detallados

Studies of Venezuelan encephalitis in migrating birds in relation to possible transport of virus from South to Central America.

All of 13 species of northward migrating shorebirds and 7 species of songbirds captured on the Pacific coast of Guatemala during April and May of 1974--1976 were susceptible to infection with small doses of either an epizootic or an enzootic strain of Venezuelan encephalitis (VE) virus. They produce moderate to high levels of viremia for 2--4 days post-inoculation; levels high enough to infect both epizootic and enzootic vector mosquitoes. Viremias were often sufficient even on the 3rd day after inoculation, a time that might represent the end of a migratory flight, assuming that the physiological state of the birds after capture reflected that during migratory flight. Birds of many taxa react similarly to infection with strains of VE virus, and have the potential for being moderately to highly effective amplifying hosts. However, whether northward migrating birds could have been the agents for the introduction of the epizootic Ecuadorian strain that initiated the middle-American epizootic of 1969--1971 is less clear. Data are not available for the extent, rates or routes of migration between the region of Ecuador and Central America, but the best information on the real speed of migration from elsewhere indicates that even warblers that fly more slowly than shorebirds could make the flight in 72 hours or less. Still, that there are geographically segregated subtypes of VE virus suggests that avian transport has been of minimal importance over long time spans. The role of inactivated vaccines in the middle-American epizootic remains an open question.

Venezuelan encephalitis virus infection in neotropical bats. I. Natural infection in a Guatemalan enzootic focus.

A serological survey of 939 Neotropical bats of 22 species from an enzootic focus of Venezuelan encephalitis (VE) virus on the Pacific lowlands of Guatemala during 1971--1975 revealed VE virus specific antibodies in seven species, three belonging to the genus Artibeus. VE virus was isolated from the blood of one Uroderma bilobatum. Antibody frequency was considerably lower in bats than in terrestrial mammals, and tended to vary within any given species from locality to locality and from year to year. At the village of La Avellana where VE virus was most active, antibody rates in the two best-sampled Artibeus species were 0.14 in 1971, 0.11 in 1972, 0.03 in 1973, and 0.11 in 1975. The positive rate of 0.10 over all years at La Avellana for the genus Artibeus suggests that these and possibly other bats regularly are infected by VE virus, and may possibly serve as alternate hosts to maintain virus circulation if most terrestrial animals become immune.