Search

Identifying hazards and assessing associated risks can be a considerable challenge for researchers in universities and colleges. Neglecting risk management is generally one of the factors leading t...

The University of California Center for Laboratory Safety (Center) organized a laboratory safety workshop held on March 15–16, 2012 at the National Academy of Sciences’ Beckman Center in Irvine, California. The participants were a diverse group of 69 people who shared an interest in improving lab safety in a way that will be embraced by those who supervise and perform lab research ( Appendix A ). Participants were from academia, private industry, national laboratories as well as local and federal government. They were laboratory researchers from the physical sciences, engineering, and the biomedical and life sciences, and health and safety professionals. Through a series of talks, panel discussions, and breakout sessions, the workshop allowed for dialogue between all participants on the many topics under the umbrella of lab safety. One of the primary aims of the Center is to develop and optimize lab safety practices based on evidence from research, and to make the outcomes from that research broadly and readily accessible to the research and health and safety communities through peer-reviewed publications. In order to achieve this, the Center is looking to build productive collaborations and begin the process of developing research programs in lab safety. The workshop was a first step in this process.

To investigate the extent of gender bias in the volunteerism of small-group leaders amongst first-year medical students, and whether bias could be eliminated with special instructions to the students.The gender of leaders in small-group sessions in a real academic setting was monitored under two conditions: control conditions, in which basic instructions were provided to participants, and intervention conditions, in which the same basic instructions were provided plus a brief "pep talk" on the importance of experiencing a leadership role in a safe environment. During the small-group sessions, an observer noted the gender and names of group leaders for later analysis. After a class debriefing, a subset of leaders and nonleaders from both the control and intervention groups were invited to be interviewed about their perceptions of the small-group experience. Interviews were tape recorded and transcribed for analysis.In 2007-2008 and 2008-2009, disproportionately fewer women than men volunteered to become small-group leaders under control conditions. This gender bias was eliminated under intervention conditions. The interviews illustrated how a subtle change in instructions helped some female students take on a leadership role.Gender bias in leadership in the small-group setting amongst medical students-even when women make up half of the class-may persist without targeted intervention. The authors suggest that frequent and consistent intervention during medical school could be an important factor in encouraging women to identify themselves as leaders, promoting confidence to consider leadership roles in medicine.

Bisphenol-A (BPA) is a synthetic estrogen and monomer component of polycarbonate plastics and epoxy resins that are widely used in the production of food and beverage containers. It leaches into our food and drink at concentrations shown to have biological consequences. Here we show that exposure to low levels of BPA accelerated early embryonic development within 24 h of exposure, attenuated body growth, and advanced the times of hatching and reproductive maturation in medaka fish (Oryzias latipes). The acceleration in embryonic development and time to hatch were blocked by the thyroid-hormone receptor (TH-R) antagonist amiodarone, suggesting that BPA alters global developmental timing through a thyroid-hormone pathway. Our results are likely to have broad implications regarding the effects of plastic-derived contaminants on embryonic and reproductive development.

Earlier work showed that cell bodies and neurites of the peptidergic bag cell neurons of Aplysia californica contain mRNA for egg-laying hormone. The purpose of the present study was to determine if egg-laying hormone synthesis and prohormone processing is similar in the pleurovisceral connective nerves (containing neurites of bag cell neurons) and the bag cell neuron clusters (containing both cell bodies and neurites of bag cell neurons). Initial experiments confirmed by RT-PCR and sequencing that egg-laying hormone mRNA was present in the pleurovisceral connective nerves. To investigate possible regional differences in translation of mRNA and prohormone processing, clusters were separated from connective nerves and newly synthesized egg-laying hormone-immunoreactive proteins were analyzed. Results showed that synthesis and processing of prohormone occurred in both the clusters and isolated connective nerves; however, the relative abundance of prohormone, processing intermediates, and egg-laying hormone was different. Pulse-chase experiments showed that prohormone was processed more slowly in the connective nerves than in the clusters. These results show that mRNA in isolated neural processes of neuroendocrine cells can be translated, and that the cellular machinery for protein synthesis is present, but processing of the ELH prohormone is significantly compromised.

Understanding the physiological basis of environmental regulation of reproduction at the cellular level has been difficult or unfeasible in vertebrate species because of the highly complex and diffuse nature of vertebrate neuroendocrine systems. This is not the case with the simple nervous system of mollusks in which reproductive neuroendocrine cells are often readily identifiable in living tissue. Given that there are mollusks that are seasonal breeders, that the neuroendocrine cells controlling reproduction have been identified in several molluskan species, that these neurons are conducive to cell physiological analysis, and that basic features of cell biology have been highly conserved between mammals and mollusks, it seems that the mollusk would provide an excellent model system to investigate cell-physiological events that mediate effects of environmental signals on reproduction. The purpose of this review is to explore this idea in three species in which the topic of the neural basis of seasonal reproduction has been studied: the giant garden slug Limax maximus, the freshwater pond snail Lymnaea stagnalis, and the marine snail Aplysia californica.

1. Despite the considerable progress made in understanding the role of electrical activity in triggering secretion, the developmental relationships between excitability and secretion are not well understood. The well-characterized bag cell neurons of Aplysia provide an advantageous system in which to investigate developmental interactions of these two key properties of neurons. 2. A prolonged afterdischarge triggers egg laying hormone (ELH) secretion in mature bag cell neurons. To investigate secretion in the developmental framework of excitability, we first examined whether immature neurons, which are incapable of the mature form of excitability (afterdischarge), contain ELH and whether this hormone is packaged in vesicles. We used immunoelectron microscopy to compare vesicular localization of ELH and to compare the size and density of ELH-containing vesicles in neurons from adult and juvenile Aplysia. This comparison revealed that immature neurons contain ELH in vesicles in the size range of secretory vesicles. However, they lack a class of large vesicles (> 250 nm in diameter) that is characteristic of mature neurons. 3. To investigate whether the ELH contained in immature bag cell neurons could be secreted in response to electrical activity, we used the potassium channel blocker tetraethylammonium (TEA) combined with nerve stimulation to depolarize neurons from both juvenile animals (ovotestes do not contain eggs) and from adult Aplysia (ovotestes contain eggs). Using radioimmunoassay, we have found that the duration and amount of ELH secreted from bag cell neurons from juvenile Aplysia in response to TEA does not depend on whether or not the cells can be induced to afterdischarge, and the amount and duration of ELH secreted from bag cell neurons of juvenile Aplysia (whether or not they afterdischarged) differed from those secreted by adult neurons. However, by normalizing for body size, we found that the final estimated hemolymph concentration of ELH would be similar in juvenile and adult animals. 4. We investigated the potential functional significance of secretion of bag cell hormones in juvenile Aplysia by attempting to bypass the bag cell neurons and directly activate downstream elements with extract from adult bag cell neurons (BCE), known to contain ELH and other peptides. We found that juvenile Aplysia exhibit at least one component of egg-laying behavior, cessation of locomotion, in response to BCE during a developmental period (as measured by weight) in which they normally would possess neurons incapable of afterdischarge. Thus developmental regulation of excitability in the bag cell neurons may prevent inappropriate hormone release and subsequent premature expression of reproductive behaviors.

This study examined whether or not the reproductive response of female sheep to photoperiod varies with seasonal reproductive state. The specific objective was to test the hypothesis that the reproductive response to a long-day pattern of melatonin varies with the reproductive state of the ewe. The response examined was the synchronization of reproductive neuroendocrine induction (rise in serum luteinizing hormone, or LH) following nocturnal infusion of melatonin into pinealectomized ewes for 35 consecutive nights. This infusion restored a pattern of circulating melatonin similar to that in pineal-intact ewes maintained in a long photoperiod (LD 16:8). The ewes had been pinealectomized and without melatonin replacement for 16-25 months prior to the study. They were in differing reproductive states at the start of the infusion, as their endogenous reproductive rhythm had become desynchronized among individuals and with respect to time of year. Noninfused pinealectomized ewes served as controls. Regardless of the reproductive state at the start of the 35-day infusion of the long-day pattern of melatonin, all treated ewes exhibited the same reproductive neuroendocrine response after the infusion was ended. This consisted of a synchronized rise in LH some 6-8 weeks after the infusion was terminated, the maintenance of a high level of serum LH for some 15 weeks, and a subsequent precipitous fall in LH to a very low level. These results provide evidence that a long-day pattern of melatonin can synchronize reproductive neuroendocrine induction in the ewe, regardless of reproductive condition, and thus do not support the hypothesis that this response differs with seasonal reproductive state.

For over 20 years, the bag cell neurons of the marine mollusk Aplysia have been used to investigate second-messenger pathways that mediate effects of synaptic stimulation on ion currents and membrane excitability, presumably leading to exocytotic release of the neuropeptide egg-laying hormone (ELH). It is widely cited that a train of action potentials, called an afterdischarge, is necessary for activating cellular events leading to ELH secretion. Using a combination of electrophysiology, optical imaging of calcium signaling, and radioimmunoassay of ELH secretion, we show that an afterdischarge is not required for ELH secretion. Electrical stimulation that failed to produce afterdischarges but did lead to prolonged membrane depolarization and a rise in intracellular calcium concentration was sufficient to stimulate significant ELH release.

The role of Ca2+ from extracellular and intracellular sources in stimulating neurosecretion was investigated in four experiments using neuroendocrine bag cells of the marine mollusk Aplysia. (i) Bag cells were treated with either an extracellular calcium chelator (BAPTA) or Co(2+)-substitution within 30 s after onset of an electrical afterdischarge to prevent influx of Ca2+ from extracellular fluid. These treatments shortened the duration of the afterdischarge, but did not significantly affect the overall pattern or total amount of egg laying hormone (ELH) secretion, suggesting that extracellular Ca2+ is not required for maintenance of ELH release. (ii) Substitution of Ba2+ for Ca2+ has previously been shown to support bag cell afterdischarges that trigger transient elevations in intracellular Ca2+. We showed that this treatment also stimulates ELH secretion, suggesting that Ca2+ release from intracellular stores can stimulate ELH secretion. (iii) To raise intracellular Ca2+ levels in the absence of an afterdischarge, the calcium ionophore X537A was used to transport Ca2+ across plasma and organelle membranes. When this treatment was combined with extracellular calcium chelators so that the only source of Ca2+ was from intracellular compartments, ELH secretion was stimulated. Taken together, these findings are consistent with the hypothesis that release of Ca2+ from intracellular stores is sufficient to stimulate ELH secretion.

The rate of translation of egg-laying hormone (ELH) in Aplysia californica bag cell neurons rises after an afterdischarge (AD), the physiological trigger for egg-laying1. We found that the 5′ untranslated region (5′ UTR) of ELH possessed an internal ribosomal entry site (IRES), and that an AD was accompanied by a switch to cap-independent, IRES-mediated translation, indicating that the use of a cellular IRES can be regulated by physiological activity. Furthermore, the AD caused dephosphorylation of the initiation factor eIF4E, which was sufficient to increase use of the ELH IRES, showing that dephosphorylation of eIF4E can trigger a switch to IRES-mediated translation.

The 24-hour pattern of melatonin secretion was determined in 5 Suffolk ewes during extended exposure to a long day length to assess whether the eventual loss of response (photorefractoriness) to inhibitory long days resulted from an alteration in the circadian secretion of melatonin. Determinations of the secretory profile of melatonin were made once in short days (8 h light/day) before the switch to long days, and 11 times throughout the 250-day period of exposure to long days (16 h light/day). Samples were obtained hourly for 24 or 48 h. Reproductive state was assessed by response to estradiol-negative feedback, monitored as serum LH in ovariectomized ewes bearing estradiol implants. The characteristic secretory pattern of melatonin (low during the day, high at night), the duration of the melatonin elevation, and its phase relative to the light/dark cycle did not change as ewes became refractory to the inhibitory effects of long days. These results are consonant with the hypothesis that refractoriness of the ewe to inhibitory day length does not result from an alteration of the circadian rhythm of melatonin secretion.

Two experiments were performed to test the importance of both pituitary and neural sites of action of estradiol in inducing the surge of luteinizing hormone (LH) in the ewe. Both experiments were conducted using an animal model in which pulsatile secretion of gonadotropin-releasing hormone (GnRH) and endogenous secretion of ovarian steroids were eliminated by ovariectomy during seasonal anestrus and treatment with Silastic implants which maintained a luteal-phase level of serum progesterone. The hormonal requirements for the surge were then evaluated by systematic application of GnRH and estradiol signals using pulsatile infusion pumps (for GnRH) and Silastic implants (for estradiol). In experiment 1, the circulating level of estradiol and frequency of GnRH pulses were increased either abruptly or progressively (i.e. mimicking the changes in the estrous cycle between luteolysis and just before the LH surge). Abrupt increments led to an LH surge in all ewes; progressive rises to the same absolute levels did not. However, sudden application of a further large increase in GnRH upon the progressive rise elicited an LH surge in every instance. In experiment 2, a GnRH pulse pattern known to be effective in inducing the LH surge was applied under conditions of differing estradiol concentration: no estradiol, basal estradiol, basal rising to peak estradiol. The GnRH signal elicited high-amplitude surges of LH only in the presence of a peak estradiol concentration. Our findings are consistent with the conclusion that two actions are required for a rise in estradiol to elicit a full-amplitude surge of LH in the ewe: an action on the brain to evoke a sudden increase in GnRH release and an action on the pituitary to maximize its response to GnRH.