Possible regeneration of rat medial frontal cortex following neonatal frontal lesions

The experiments described here show that the cavity left by midline frontal cortex removals at 10 days of age (P10) fills in with neural tissue. Similar changes are not found at earlier and later ages. This neuronal filling is blocked by prior pretreatment by administration of Bromodeoxyuridine (BrdU) on embryonic day 13. Administration of BrdU following the P10 lesion does not interfere with regrowth. Subsequent immunohistochemical staining for BrdU demonstrates the regrown area to be composed of newly generated cells. which include pyramidal and nonpyramidal neurons. Injections of a retrograde tracer into the striatum or posterior parietal cortex shows that the new neurons have connections similar to those of undamaged brains. The regrowth of this tissue is correlated with recovery of function in a test of forelimb use. Thus, the mammalian brain, during some privileged postnatal stages of growth. is capable of extensive reorganization that includes regeneration of lost neurons. These results are discussed in relation to the proximity of the lesion to the stem cells in the lateral ventricle and their postnatal migrational activities.     

Exacerbation of methamphetamine-induced neurochemical deficits by melatonin

Methamphetamine (METH), administered in large, repeated doses, compromises the dopaminergic and serotonergic systems as indicated by prolonged suppression of tyrosine hydroxylase and tryptophan hydroxylase activity and concurrent decreases in the content of dopamine and 5-hydroxytryptamine. Because dopamine is necessary for these dopaminergic and serotonergic deficits we postulated that dopamine and/or its reactive metabolites are responsible for these degenerative alterations. Because we previously demonstrated that in vitro reducing conditions reverse the decrease in tryptophan hydroxylase activity, we reasoned that melatonin, a purported endogenous antioxidant, may alter this response. Rats were treated with METH and/or melatonin and trytophan hydroxylase activity and 5-hydroxytryptamine content were assessed; tyrosine hydroxylase activity and dopamine content were also measured. Not only did melatonin not prevent METH-induced deficits in serotonergic and dopaminergic parameters, but coadministration of melatonin with METH actually enhanced most of the monoaminergic effects of METH. This enhancing effect could not be attributed to alteration of body temperature. Because METH abuse causes insomnia and melatonin is promoted in some countries for insomnia, the implications of the interaction between these two drugs could be clinically important.     

Behavioral and electrophysiological responses of Arhopalus tristis to burnt pine and other stimuli

The exotic longhorn beetle Arhopalus tristisis a pest of pines, particularly those damaged by fire, and a major export quarantine issue in New Zealand. Actinograph recordings of caged individuals showed that males and females were most active from dusk to midnight. Olfactometer experiments indicated that females moved upwind toward odors from burnt pine (80%, N= 75), compared to unburnt pine (20%). Oviposition choice tests showed that eggs were predominantly laid on burnt logs (79%, N= 20), compared to unburnt logs. Beetles were trapped by funnel traps baited with burnt (mean catch per trap 7.8) and unburnt (mean catch 4.1 per trap) pine bark from inside a screen cage (4 × 3 m), while unbaited traps had a mean catch 0.1 beetles (N= 8 replicates). The treatment of burnt pine bark with a 1:1:2 mixture of green leaf volatiles (E)-2-hexen-1-ol and (E)-2-hexenal) in mineral oil as a repellent reduced trap catch by fivefold in a similar experiment (mean catches of 1.2 beetles per trap to burnt pine bark plus repellent treatment and 6.2 beetles per trap to burnt pine bark alone). The treatment of burnt pine bark with this solution also reduced oviposition by 98.5% (mean eggs per log of 11.1 on burnt pine and 0.3 on burnt pine plus repellent), indicating that oviposition cues have the potential to be significantly disrupted. The electrophysiological responses of adult beetles were recorded to a range of odorants. Normalized responses to monoterpenes known to occur in Pinus radiataranged from about 20 to about 150, with -terpineol giving the greatest responses in both sexes. Green leaf volatiles also gave high responses. The potential exists to improve the management of this insect using chemical cues in various ways.     

Properties of ATP receptor-mediated synaptic transmission in the rat medial habenula

The properties of central ATP-mediated synaptic currents were studied using whole-cell patch-clamp recording in rat medial habenula slices. Release was shown to be calcium dependent with a Hill coefficient of approximately 2. The voltage dependence of synaptic current amplitudes was approximately linear. Some reduction of the synaptic current amplitudes was observed at 10 mM extracellular calcium, suggesting calcium block/permeability of the channels. This was confirmed by observation of current-voltage reversal potentials in different calcium concentrations. We estimate that the channels underlying half the synapses showed a negligible calcium permeability. In the other four out of eight synapses the results suggest a very high calcium permeability with an estimated PCa/PCs of > 10. Thus, at -70 mV, in 1 mM calcium, more than 15% of the ATP-mediated synaptic current is estimated to be carried by calcium, but only at synapses with calcium-permeable channels. Net current through these synaptic channels is also controlled by the voltage dependence of synaptic current decay time constants (increasing e-fold for 158 mV depolarization) and by a strong dependence of transmitter release on the frequency of stimulation of the presynaptic neurone, with failure rates increasing 3-fold as stimulation rates were increased from 1 to 10 Hz.     

Evaluation of issues relating to the carcinogen risk assessment of chromium

Important issues in the carcinogenic risk assessment of chromium compounds are whether both trivalent and hexavalent chromium compounds are carcinogenic, the role of solubility in the carcinogenic response, and the carcinogenicity of ingested chromium. Hexavalent chromium compounds are carcinogenic to animals via several routes of exposure, while trivalent chromium compounds, although they demonstrate evidence of genotoxicity, have not been shown in animal studies to be carcinogenic. Workers in chromate production plants, where the risk of lung cancer is elevated, are exposed to both trivalent and hexavalent chromium compounds. A cancer unit risk estimate for Wistar rats exposed to a hexavalent chromium aerosol (sodium dichromate) is less than the risk estimate for workers in chromate production. If this difference is biologically real, a possible explanation may be that trivalent compounds also have a carcinogenic effect. For hexavalent chromium compounds, it is contended that only sparingly soluble hexavalent chromium compounds are carcinogenic. Recent evidence, however, indicates that highly soluble hexavalent chromium compounds are also carcinogenic. Animal ingestion studies have not found trivalent chromium compounds to be carcinogenic by ingestion; hexavalent compounds have not been studied. Research by EPA to address the issue of valence state and solubility with respect to carcinogenicity is currently being conducted.     

Blast-related fracture patterns: a forensic biomechanical approach

Improved protective measures and medical care has increased the survivability from battlefield injuries. In an attempt to reduce the debilitating consequences of blast injury, understanding and mitigating the effects of explosion on the extremities is key. In this study, forensic biomechanical analyses have been applied to determine mechanisms of injury after the traumatic event. The aims of this study were (i) to determine which effects of the explosion are responsible for combat casualty extremity bone injury in two distinct environments, namely open, free-field (open group), and in vehicle or in cover (enclosed group), and (ii) to determine whether patterns of combat casualty bone injury differed between environments. Medical records of casualties admitted to a military hospital in Afghanistan were reviewed over a six-month period. Explosive injuries have been sub-divided traditionally into primary, secondary and tertiary effects. All radiographs were independently reviewed by a military radiologist, a team of military orthopaedic surgeons and a team of academic biomechanists, in order to determine ‘zones of injury’ (ZoIs), and their related mechanisms. Sixty-two combat casualties with 115 ZoIs were identified. Thirty-four casualties in the open group sustained 56 ZoIs; 28 casualties in the enclosed group sustained 59 ZoIs. There was no statistical difference in mean ZoIs per casualty between groups (p = 0.54). There was a higher proportion of lower limb injuries in the enclosed group compared with the open group (p < 0.05). Of the casualties in the open group, 1 ZoI was owing to the primary effects of blast, 10 owing to a combination of primary and secondary blast effects, 23 owing to secondary blast effects and 24 owing to tertiary blast effects. In contrast, tertiary blast effects predominated in the enclosed group, accounting for 96 per cent of ZoIs. These data clearly demonstrate two distinct injury groups based upon the casualties'' environment. The enclosed environment appears to attenuate the primary and secondary effects of the explosion. However, tertiary blast effects were the predominant mechanism of injury, with severe axial loading to the lower extremity being a characteristic of the fractures seen. The development of future mitigation strategies must focus on reducing all explosion-related injury mechanisms. Integral to this process is an urgent requirement to better understand the behaviour of bone in this unique environment.     

The interaction between design and occupier behaviour in the safety of new homes

The design of new homes includes many safety features intended to protect occupiers from injury or ill health within the home, however the effectiveness of these primary intervention measures is likely to be affected by user behaviour. This study examined the interaction between user activity and dwelling design and how this might affect health and safety. It aimed to identify how people use features within new homes and how this may limit the protection afforded by building design, codes and regulations. Forty, home-based, semi-structured, in-depth interviews and home inspections were conducted with individuals recently inhabiting a new home. A range of behaviours were reported in relation to building features including fire doors, pipes and cables, and loft access, which may lead to increased risk of injury or ill-health. For example, occupiers described interfering with the self-closing mechanisms on fire doors and drilling into walls without considering the location of services. They also reported knowingly engaging in unsafe behaviour when accessing the loft, increasing their risk of falls. The accounts suggest that designers and builders need to give greater consideration to how occupier behaviour interacts with building features so that improvements in both design and occupier education can lead to improved health and safety.     

Context cues as mediators: II. Four-stage paradigms.

Tested the effect of colors as context cues acting as mediators using 90 undergraduates. The mediation paradigms were 4-stage stimulus equivalence, response equivalence, and chaining. The results provide equivocal support for a mediation hypothesis. The present results are compared with those of a previous investigation of 3-stage paradigms, which suggested that context cues could function as mediators. (French summary) (PsycINFO Database Record (c) 2010 APA, all rights reserved)