The induction of heat shock protein gene expression in response to stress is critical for the ability of organisms to cope with and survive exposure to these stresses. However, most studies on HSF1-mediated induction of hsp70 gene expression have utilized immortalized cell lines and temperatures above the physiologically relevant range. For these reasons much less is known about the heat shock response as it occurs in mammalian cells within tissues in the intact organism. To gain insight into this area we determined the temperature thresholds for activation of HSF1 DNA binding in different mouse tissues. We have found that HSF1 DNA binding activity and hsp70 synthesis are induced in spleen cells at significantly lower temperatures relative to cells of other tissues, with a temperature threshold for activation (39°C) that is within the physiological range for fever. Furthermore, we found that the lowered temperature set point for induction of the stress response in spleen is specific to T-lymphocytes residing within this tissue and is not exhibited by B-lymphocytes. This lowered threshold is also observed in T-lymphocytes isolated from lymph nodes, suggesting that it is a general property of T-lymphocytes, and is seen in different mouse strains. Fever is an early event in the immune response to infection, and thus activation of the cellular stress response in T-lymphocytes by fever temperatures could serve as a way to give these cells enough time to express hsps in anticipation of their function in the coming immune response. The induced hsps likely protect these cells from the stressful conditions that can exist during the immune response, for example increasing their protection against stress-induced apoptosis.When cells are exposed to elevated temperature, they respond by rapidly increasing the expression of heat shock proteins (hsps), which act to protect essential cellular functions from the adverse effects of increased temperature (1-5). This phenomenon, known as the cellular stress response, is mediated by a transcriptional regulatory protein called heat shock factor 1 (HSF1), 1 which exhibits heat-inducible DNA binding activity. Upon exposure of cells to elevated temperature, HSF1 is converted from an inactive monomeric form to a trimeric DNA-binding form, which then interacts with specific sequences in the promoters of hsp genes and induces their transcription (5-11).Fever represents a physiological example of elevated temperature in an organism. Our previous studies analyzing HSF1 activation in a limited set of mouse tissues in response to whole body hyperthermia at different temperatures revealed that the threshold temperature for HSF1 activation can vary between tissues. The temperature threshold for activation of HSF1 DNA binding in male germ cells is 35°C, consistent with the known temperature sensitivity of this cell type (12). However, in the somatic testis cell types and liver cells of these heat-treated mice, HSF1 DNA binding was not activated until a temperature of ϳ42°C was reached (12,13). Th...

Ruffner, Marvin E., Stuart I. Cromarty, and Robin L. Cooper. Depression of synaptic efficacy in high-and low-output Drosophila neuromuscular junctions by the molting hormone (20-HE). J. Neurophysiol. 81: 788 -794, 1999. The molt-related steroid hormone, 20-hydroxyecdysone (20-HE), was applied to muscles 6 and 7 of third instar larval of Drosophila melanogaster neuromuscular junction preparations to examine if rapid, nongenomic responses could be observed as was shown recently to occur in crustacean neuromuscular junctions. At a dose of 10 M, the excitatory junction potentials were reduced in amplitude within minutes. To elucidate the site of action of the hormone, focal-macropatch recordings of synaptic currents were obtained over the neuromuscular junctions. The results showed that the high-output (Is) and the low-output (Ib) motor nerve terminals, which innervate muscles 6 and 7, released fewer synaptic vesicles for each stimulation while exposed to 20-HE. Because the size and shape of synaptic currents from spontaneous releases did not change, the effects of the 20-HE are presynaptic. The rapid effects of this hormone may account in part for the quiescent behavior associated with molts among insects and crustaceans. I N T R O D U C T I O NHormones have essential roles in developmental changes in the life of the fruit fly Drosophila melanogaster, from the instar stages to the pupa and to the adult forms. Hormones associated with developmental changes during metamorphosis are known as ecdysteroids, one of which is 20-hydroxyecdysone (20-HE), currently regarded as the active form of ecdysone (Riddford 1985;Steel and Davey 1985). This particular group of hormones is important in causing the behavioral and physical changes that occur during the development stages of each molt (Truman 1996). In D. melanogaster, the highest levels of ecdysteroid are measured during the third instar larva to prepupal formation and in the pupa stage preceding the adult stage (White et al. 1997). It has been shown that motor neurons in the hawkmoth, Manduca sexta, undergo various responses such as apoptosis, regression, and regrowth during various stages of development where levels of ecdysteroids are also high (Truman and Reiss 1995). Thus it has been observed that steroids show both physiological and anatomic effects on neurons (Jacobs and Weeks 1990; Levine and Weeks 1996;Thummel 1996).It has been established that the actions of ecdysteroids described to date within these insects indicate a steroidbased genomic effect (Levine and Weeks 1996;Segraves 1994;Thummel 1996). Currently there is a vast amount of knowledge showing the genomic action of various steroids and hormones on gene expression in insects. Besides the generalized steroidal effects, such as those reported for estradiol, aldosterone, vitamin D3, and cortisol, within mammalian systems, there is substantial documentation of nongenomic effects by direct binding to membrane-bound receptors that result in rapid action of cellular processes. These nongenomic cellular processes...

Cooper, Robin L. and Marvin E. Ruffner. Depression of synap-cortisol in mammalian systems, there is now substantial doctic efficacy at intermolt in crayfish neuromuscular junctions by 20-umentation that nongenomic, membrane-bound steroid rehydroxyecdysone, a molting hormone. J. Neurophysiol. 79: 1931-ceptors can mediate rapid action of cellular processes such as 1941, 1998. This report demonstrates that ecdysteroids can reduce inositol tri-phosphate (IP 3 ) release, increased flux of calcium synaptic transmission at an intermolt stage of a crustacean tonic from internal stores, higher levels of guanosine 3,5-cyclic neuromuscular junction by acting at a presynaptic site. The steroid monophosphate (cGMP) and adenosine 3,5-cyclic monomolting hormone, 20-hydroxyecdysone (20-HE), appears to act phosphate (cAMP), and direct activation of a Na / /H / antithrough a rapid, nongenomic mechanism that decreases the probaporter (Wehling 1995).bility of synaptic vesicle release and reduces the number of releaseStudies investigating the nongenomic actions of molt-resites. Quantal analysis revealed that fewer vesicles were released for a given stimulus when 20-HE was present, and this in turn lated compounds among crustaceans and insects are sparse. accounted for the reduced synaptic efficacy. Reduced synaptic ef-Behavioral changes occur in crustaceans in preparation for ficacy produced smaller evoked postsynaptic currents and smaller and immediately after molting, but these mechanisms are excitatory postsynaptic potentials (EPSPs) across the muscle fiber not fully understood. There is an indication that the moltmembrane. The reduction in EPSPs was observed among muscle related hormone may induce the behaviors associated with fibers that were innervated by high-or low-output terminals. The this period (Cromarty 1995). The present study shows that behavior of crustaceans/crayfish during the molt cycle, when 20-in neuromuscular preparations in which the axon had been HE is high, may be explained by the reduction in synaptic transmissevered from its cell body, ecdysone elicited a rapid re- nounced reduction in the size of the excitatory postsynaptic potentials (EPSPs) recorded in the muscle. To determine if During molting, a crustacean sheds its exoskeleton and 20-HE caused differential release of the neurotransmitter, replaces it with one large enough in which to grow. The evoked as well as spontaneous synaptic currents were reecdysteroid hormones play an important role in directing corded for subsequent quantal analysis of synaptic efficacy. the preparation of the animal for the premolt and molt. To Quantal analysis allowed assessment of changes caused by characterize the restructuring of the motor neurons and mus-addition of particular neuromodulators to the electrophysiocles during metamorphosis, extensive experimental use has logical characteristics of both pre-and postsynaptic cells. been made of members of another arthropod subphylum, For example, a difference in the rate of spontaneous release Insecta: Drosophila, and the ...

Natural grasslands are one of the most threatened ecosystems in North America. Conservation efforts are often hampered by exotic plant invasions in existing remnant natural grasslands. Tall fescue [Schedonorus phoenix(Scop.) Holub.] is an introduced cool-season (C3) forage/turf grass which readily invades natural grasslands in Kentucky and neighboring states. Our study objectives were to (1) compare the efficacy and application timing effect of clethodim to that of imazapic to selectively remove tall fescue from natural grasslands and (2) evaluate the response of the nontarget grassland plant community (i.e., native grass and forb canopy cover) following herbicide treatments. Clethodim and imazapic treatments consisted of early (April 4, 2001) and late (April 20, 2001) applications, and these were applied at 0.23 and 0.21 kg ai ha−1, respectively. Both herbicides reduced tall fescue cover (P ≤ 0.05); herbicide application timing had no effect on herbicide efficacy to control tall fescue. Native grass cover was higher (P ≤ 0.05) in all herbicide-treated plots compared to the untreated controls, except for the late clethodim-treated plots. All herbicide treatments increased forb abundance compared to controls. Spring applications of clethodim were equally effective to those of imazapic at controlling tall fescue in natural grasslands. Imazapic released native grasses better than clethodim, whereas clethodim was better at increasing forb abundance. Furthermore, early clethodim treatments had fewer nontarget effects on native C4grasses compared to late clethodim treatments. Overall, clethodim shows promise as a beneficial management tool for tall fescue control in C4-dominated natural grasslands.

Conservation and restoration efforts of native grasslands are being hindered by invasive, exotic plants. Exotic bluestem grasses (Bothriochloa and Dichanthium spp.) have become increasingly invasive throughout the rangelands of the central and southern Great Plains, United States. Accordingly, the aim of this study was to evaluate the efficacy of glyphosate, imazapyr, and imazapyr + glyphosate treatments with or without disking to remove exotic bluestems from a south Texas coastal prairie. We evaluated three different control regimens: 1) herbicide treatments only, 2) herbicide treatments followed by two diskings (H + D), and 3) disking followed by herbicide treatments (D + H). Percent exotic bluestem, native grass, and forb cover were visually estimated at 0 (pre-treatment: May 2006), 20, 52, and 104 wk after treatment (WAT). The herbicide-only and H + D regimens were ineffective at controlling exotic bluestems. However, exotic bluestem cover in herbicide-treated plots of the D + H regimen was significantly lower (P # 0.05) compared to control plots and most treatment plots of the herbicide-only and H + D regimens up to 52 WAT. Control regimens did not notably facilitate an increase in native grass cover from pre-treatment levels, but native grass cover remained the highest, and increased the most, in some imazapyr-treated plots of the herbicide-only and D + H regimens, respectively. In the H + D and D + H regimens, disking resulted in a flush of forb cover (up to 50%) at 52 WAT; yet forb cover was # 5% in these plots by 104 WAT. Exotic bluestem cover recovered back to, or was greater than, pretreatment levels among most treatment plots across all three control regimens at 104 WAT. This study suggests that follow-up control measures are needed to suppress the re-invasion of exotic bluestems after initial control efforts. Additional studies are needed to evaluate other strategies to control exotic bluestems in rangelands of the central and southern United States. Resumen Los esfuerzos de conservación y reforestación de pastizales nativos han sido obstaculizados por plantas invasivas y tóxicas. El pasto exótico bluestem grasses (Bothriochloa and Dichanthium spp.) se ha vuelto cada vez mas invasivo en los pastizales del centro y el sur de las Grandes Planicies de Estados Unidos, por consiguiente, el objetivo de este estudio fue evaluar la eficiencia de tratamientos a base de glyphosate, imazapyr, y imazapyr + glyphosate con o sin arado de disco para remover los plantas exóticas de bluestem de un pastizal de las planicies de las costas de Texas. Evaluamos tres diferentes regímenes de control: 1) aplicación únicamente de herbicida; 2) aplicación de herbicida seguidos por las rastra de discos dos veces (H + D); y 3) rastra de discos seguido de la aplicación de herbicida (D + H). El porcentaje del pasto exótico bluestem, gramíneas nativas y cobertura herbácea fue estimado visualmente como 0 (pre-tratamiento: Mayo 2006), 20, 52, and 104 semanas después de la aplicación de los tratamientos (WAT). Los tratamientos solo he...