Cellular Neuronal Control of Molluscan Heart

Bivalve and gastropod molluscs undergo large changes in externalenvironmental conditions, as well as in internal state. Cardiacresponses to these changing conditions have been recorded ina variety of species. There is a general tendency for heartrate, and presumably cardiac output, to increase in responseto situations that would increase the load on respiratory andexcretory systems. Changes in molluscan heart function in manycases appear not to be mediated directly by cardiac nerves,but rather by such indirect mechanisms as changes in blood constituentsor mechanical, hemodynamic effects on heart muscle. Three typesof cardiac response in Aplysia have been shown to be mediated,at least in part, by the heart regulator nerves. The neural circuits that regulate heart rate in Aplysia andin Helix have been partially described in cellular detail. InMercenaria, Aplysia and other molluscan species there is evidencethat cyclic adenosine monophosphate has a role in mediatingthe excitatory effects of serotonin on heart muscle. There appearsto be, in fact, a general tendency in the Aplysia nervous systemfor neurons that exert tonic, modulatory effects within neuralnetworks that control a variety of behaviors to use serotoninfor a transmitter. In each case there is evidence to suggestthat changes in cyclic adenosine monophosphate levels may mediatesome of the modulatory effects of serotonin.     

Pollen as a marker for migration of Helicoverpa armigera and H. punctigera (Lepidoptera: Noctuidae) from western Queensland

Abstract Pollen carried on the probosces of Helicoverpa punctigera (Wallengren) and H. armigera (Hübner) trapped in western Queensland and in cropping areas of eastern Australia in September 1989 and 1990 was identified by scanning electron microscopy. Ninety-five per cent of moths carried pollen. A total of 19 morphological pollen species’, representing 14 plant families, was found. Up to six pollen species were found on individual moths, and 61% carried more than one. Pollen from plants unsuitable for larval survival was common. Pollen loads generally reflected the abundance of locally flowering plants, but there were exceptions which suggested migration. Pollen of Ptilotus (Amaranthaceae), Velleia (Goodeniaceae) and Eremophila (Myoporaceae), and the Asteraceae (Tubuliflorae) were found on moths trapped in the east. These plants either did not occur in the areas where the moths were caught, or did not flower there at the time the moths were caught. However, they were abundant in possible source areas such as western Queensland. Among moths caught in eastern regions, 30% of H. punctigera and 18% of H. armigera carried pollen from such plants. The value and limitations of moth-borne pollen as a marker for migration are discussed.     

Electrical Events Correlated with Contractile Vacuole Activity in the Suctorian, Heliophrya

SYNOPSIS. The surface membrane potentials of suctorian genus Heliophrya were studied with intracellular electrodes. Resting membrane potentials averaged -32 mV, and spontaneous depolarizing potentials occurring at apparently random intervals and having a variety of waveforms were routinely observed. Such spontaneous potentials were correlated in time with visually monitored contractile vacuole activity. Individual contractile vacuoles had unique, although somewhat variable, electrical signatures. In the presence of an intracellular electrode all vacuoles contracted independently, but at approximately the same frequency. The amplitude of the electrical potentials increased when the membrane was hyperpolarized and decreased when it was depolarized. The sign of such potentials reversed at between -10 mV and the zero membrane potential. A 20% decrease in the membrane resistance was measured at the peak of the spontaneous depolarizing potentials.     

Dynamics of Cell Redifferentiation in Dictyostelium mucoroides

During migration of a D. mucoroides slug, prespore cells at the immediate edge of the prespore-prestalk junction advance into the prestalk region in approximately 1.5 min. Redifferentiation of the prespore into prestalk cells occurs during this period. Evidence that the cells redifferentiated required autoradiographic, electron microscopic, and staining techniques. These methods determined that glycoprotein synthesis declined; prespore vesicles, the organelles found specifically in prespore cells, were degraded; and staining was reduced during this developmental transition into prestalk cells.     

Use of Implanted Radiotransmitters to Estimate Survival of Greater Sage-Grouse Chicks

ABSTRACT Reduced chick survival has been implicated in declines of greater sage-grouse (Centrocercus urophasianus) populations. Because monitoring survival of unmarked sage-grouse chicks is difficult, radiotelemetry may be an effective technique to estimate survival rates, identify causes of mortality, and collect ecological data. Previous studies have used subcutaneous implants to attach radiotransmitters to hatchlings of several species of birds with precocial young. Previous researchers who used subcutaneous implants in free-ranging populations removed chicks from the capture location and implanted transmitters at an alternate site. Because logistics precluded removing newly hatched greater sage-grouse chicks from the field, we evaluated a method for implanting transmitters at capture locations. We captured 288 chicks from 52 broods and monitored 286 radiomarked chicks daily for 28 days following capture during May and June 2001–2002. Two (>1%) chicks died during surgery and we did not radiomark them. At the end of the monitoring period, 26 chicks were alive and 212 were dead. Most (98%, 207/212) radiomarked chick mortality occurred < 21 days posthatch and predation (82%, 174/212) was the primary cause of death. Necropsies of 22 radiomarked chicks did not indicate inflammation or infection from implants, and they were not implicated in the death of any chicks. Fate of 48 chicks was unknown because of transmitter loss (n = 16), radio failure (n = 29), and brood mixing (n = 3). Overall, the 28-day chick survival rate was 0.220 (SE = 0.028). We found that mortalities related to the implant procedure and transmitter loss were similar to rates reported by previous researchers who removed chicks from capture sites and implanted transmitters at an alternate location. Subcutaneous implants may be a useful method for attaching transmitters to newly hatched sage-grouse chicks to estimate survival rates, identify causes of mortality, and collect ecological data.     

Serological investigations of cell adhesion in the slime molds,Dictyostelium discoideum,Dictyostelium purpureum,and Polysphondylium violaceum

1. Antibodies to slime molds were produced by injecting D. discoideum and D. purpureum amebas from 48 hour cultures into rabbits. 2. Anti-D. discoideum and anti-D. purpureum sera caused agglutination of homologous amebas from 24 to 26 hour cultures, agglutination of certain heterologous amebas from 30 to 36 hour cultures, and agglutination of all heterologous amebas from 43 to 48 hour cultures. 3. The data show that new surface antigens are formed in cultures after 26 hours and it is suggested that the new antigens are concerned with cell adhesion. 4. The probable role of surface antigens in the interaction of cells of different species of slime molds was discussed.