Ontogenetic and regional morphologic variations in the turkey ulna diaphysis: implications for functional adaptation of cortical bone

This study examines relationships between bone morphology and mechanically mediated strain/fluid-flow patterns in an avian species. Using mid-diaphyseal transverse sections of domestic turkey ulnae (from 11 subadults and 11 adults), we quantified developmental changes in predominant collagen fiber orientation (CFO), mineral content (%ash), and microstructure in cortical octants or quadrants (i.e., %ash). Geometric parameters were examined using whole mid-diaphyseal cross-sections. The ulna undergoes habitual bending and torsion, and demonstrates nonuniform matrix fluid-flow patterns, and high circumferential strain gradients along the neutral axis (cranial-caudal) region at mid-diaphysis. The current results showed significant porosity differences: 1) greater osteocyte lacuna densities (N.Lac/Ar) (i.e., "non-vascular porosity") in the caudal and cranial cortices in both groups, 2) greater N.Lac/Ar in the pericortex vs. endocortex in mature bones, and 3) greater nonlacunar porosity (i.e., "vascular porosity") in the endocortex vs. pericortex in mature bones. Vascular and nonvascular porosities were not correlated. There were no secondary osteons in subadults. In adults, the highest secondary osteon population densities and lowest %ash occurred in the ventral-caudal, caudal, and cranial cortices, where shear strains, circumferential strain gradients, and fluid displacements are highest. Changes in thickness of the caudal cortex explained the largest proportion of the age-related increase in cranial-caudal breadth; the thickness of other cortices (dorsal, ventral, and cranial) exhibited smaller changes. Only subadult bones exhibited CFO patterns corresponding to habitual tension (ventral) and compression (dorsal). These CFO variations may be adaptations for differential mechanical requirements in "strain-mode-specific" loading. The more uniform oblique-to-transverse CFO patterns in adult bones may represent adaptations for shear strains produced by torsional loading, which is presumably more prevalent in adults. The micro- and ultrastructural heterogeneities may influence strain and fluid-flow dynamics, which are considered proximate signals in bone adaptation.

Suppression of integrin activation by activated Ras or Raf does not correlate with bulk activation of ERK MAP kinase

The rapid modulation of ligand-binding affinity ("activation") is a central property of the integrin family of cell adhesion receptors. The Ras family of small GTP-binding proteins and their downstream effectors are key players in regulating integrin activation. H-Ras can suppress integrin activation in fibroblasts via its downstream effector kinase, Raf-1. In contrast, to H-Ras, a closely related small GTP-binding protein R-Ras has the opposite activity, and promotes integrin activation. To gain insight into the regulation of integrin activation by Ras GTPases, we created a series of H-Ras/R-Ras chimeras. We found that a 35-amino acid stretch of H-Ras was required for full suppressive activity. Furthermore, the suppressive chimeras were weak activators of the ERK1/2 MAP kinase pathway, suggesting that the suppression of integrin activation may be independent of the activation of the bulk of ERK MAP kinase. Additional data demonstrating that the ability of H-Ras or Raf-1 to suppress integrin activation was unaffected by inhibition of bulk ERK1/2 MAP kinase activation supported this hypothesis. Thus, the suppression of integrin activation is a Raf kinase induced regulatory event that can be mediated independently of bulk activation of the ERK MAP-kinase pathway.

R-Ras C-terminal sequences are sufficient to confer R-Ras specificity to H-Ras

Activated versions of the similar GTPases, H-Ras and R-Ras, have differing effects on biological phenotypes: Activated H-Ras strongly transforms many fibroblast cell lines causing dramatic changes in cell shape and cytoskeletal organization. In contrast, R-Ras transforms fewer cell lines and the transformed cells display only some of the morphological changes associated with H-Ras transformation. H-Ras cells can survive in the absence of serum whereas R-Ras cells seem to die by an apoptotic-like mechanism in response to removal of serum. H-Ras can suppress integrin activation and R-Ras specifically antagonizes this effect. To map sequences responsible for these differences we have generated and investigated a panel of H-Ras and R-Ras chimeras. We found that the C-terminal 53 amino acids of R-Ras were necessary and sufficient to specify the contrasting biological properties of R-Ras with respect to focus morphology, reactive oxygen species (ROS) production and reversal of H-Ras-induced integrin suppression. Surprisingly, we found chimeras in which the focus formation and integrin-mediated phenotypes were separated, suggesting that different effectors could be involved in mediating these responses. An integrin profile of H-Ras and R-Ras cell pools showed no significant differences; both activated H-Ras and R-Ras expressing cells were found to have reduced beta(1) activity, suggesting that the activity state of the beta(1) subunit is not sufficient to direct an H-Ras transformed cell morphology.

Integrin activation controls metastasis in human breast cancer

Metastasis is the primary cause of death in human breast cancer. Metastasis to bone, lungs, liver, and brain involves dissemination of breast cancer cells via the bloodstream and requires adhesion within the vasculature. Blood cell adhesion within the vasculature depends on integrins, a family of transmembrane adhesion receptors, and is regulated by integrin activation. Here we show that integrin alpha v beta 3 supports breast cancer cell attachment under blood flow conditions in an activation-dependent manner. Integrin alpha v beta 3 was found in two distinct functional states in human breast cancer cells. The activated, but not the nonactivated, state supported tumor cell arrest during blood flow through interaction with platelets. Importantly, activated alpha v beta 3 was expressed by freshly isolated metastatic human breast cancer cells and variants of the MDA-MB 435 human breast cancer cell line, derived from mammary fat pad tumors or distant metastases in severe combined immunodeficient mice. Expression of constitutively activated mutant alpha v beta 3(D723R), but not alpha v beta 3(WT), in MDA-MB 435 cells strongly promoted metastasis in the mouse model. Thus breast cancer cells can exhibit a platelet-interactive and metastatic phenotype that is controlled by the activation of integrin alpha v beta 3. Consequently, alterations within tumors that lead to the aberrant control of integrin activation are expected to adversely affect the course of human breast cancer.

The effector loop and prenylation site of R-Ras are involved in the regulation of integrin function

The closely related small GTP-binding proteins H-Ras and R-Ras have opposing effects on the regulation of integrin cell adhesion receptors. To gain insight into the properties of R-Ras with respect to the regulation of integrin function and interactions with downstream effectors we performed an analysis of R-Ras variants containing mutations in the effector binding domain and C-terminal prenylation site. We found that the activation of the downstream effector PI 3-kinase was sensitive to mutations in the effector binding domain, as was the binding to the effectors, Ral-GDS, Raf-1 and the novel effector Nore1. Furthermore, specific mutations in the effector binding loop and C-terminal prenylation motif impaired the ability of R-Ras to regulate integrin function in CHO cells. However, the ability of the R-Ras effector loop mutants to bind, and activate known effectors did not correlate with their ability to regulate integrin function. Thus, the known R-Ras effectors are not critical for regulating integrin activation, at least in CHO cells. Consequently, these studies provide insight into the structural basis of the interactions between R-Ras and its candidate effectors and suggest the existence of novel mechanisms through which this GTPase could regulate cell adhesion.

Death effector domain protein PEA-15 potentiates Ras activation of extracellular signal receptor-activated kinase by an adhesion-independent mechanism

PEA-15 is a small, death effector-domain (DED)-containing protein that was recently demonstrated to inhibit tumor necrosis factor-alpha-induced apoptosis and to reverse the inhibition of integrin activation due to H-Ras. This led us to investigate the involvement of PEA-15 in Ras signaling. Surprisingly, PEA-15 activates the extracellular signal receptor-activated kinase (ERK) mitogen-activated protein kinase pathway in a Ras-dependent manner. PEA-15 expression in Chinese hamster ovary cells resulted in an increased mitogen-activated protein kinase kinase and ERK activity. Furthermore, PEA-15 expression leads to an increase in Ras guanosine 5'-triphosphate loading. PEA-15 bypasses the anchorage dependence of ERK activation. Finally, the effects of PEA-15 on integrin signaling are separate from those on ERK activation. Heretofore, all known DEDs functioned in the regulation of apoptosis. In contrast, the DED of PEA-15 is essential for its capacity to activate ERK. The ability of PEA-15 to simultaneously inhibit apoptosis and potentiate Ras-to-Erk signaling may be of importance for oncogenic processes.

Neuroprotective strategies for basal ganglia degeneration: Parkinson's and Huntington's diseases

There are three main mechanisms of neuronal cell death which may act separately or cooperatively to cause neurodegeneration. This lethal triplet of metabolic compromise, excitotoxicity, and oxidative stress causes neuronal cell death that is both necrotic and apoptotic in nature. Aspects of each of these three mechanisms are believed to play a role in the neurodegeneration that occurs in both Parkinson's and Huntington's diseases. Strategies to rescue or protect injured neurons usually involve promoting neuronal growth and function or interfering with neurotoxic processes. Considerable research has been done on testing a large array of neuroprotective agents using animal models which mimic these disorders. Some of these approaches have progressed to the clinical arena. Here, we review neuroprotective strategies which have been found to successfully ameliorate the neurodegeneration associated with Parkinson's and Huntington's diseases. First, we will give an overview of the mechanisms of cell death and the background of Parkinson's and Huntington's diseases. Then we will elaborate on a range of neuroprotective strategies, including neurotrophic factors, anti-excitotoxins, antioxidants, bioenergetic supplements, anti-apoptotics, immunosuppressants, and cell transplantation techniques. Most of these approaches hold promise as potential therapies in the treatment of these disorders.

A note on the effects of contact frequency and time of day of boar exposure on the efficacy of the boar effect

Sixty-four Large White/Landrace crossbred gilts were used in this study, 16 gilts being allocated to each of four treatments to compare the effects on puberty attainment of exposure to boar contact either 0, 1 or 2 times daily. The once-daily exposure occurred in either the morning or the afternoon (AM vs. PM). Treatments were of 20-min duration starting at a mean gilt age of 160 days and continuing for 60 days. Boar exposure significantly increased the proportion of gilts attaining puberty within 60 days of the commencement of treatments (P < 0.05) compared with gilts not receiving boar contact. Gilts receiving boar exposure twice daily attained puberty significantly earlier than did gilts in the two treatment groups (AM and PM, respectively) given a single daily boar exposure period (mean gilt ages at puberty 176.4 vs. 192.7 and 189.2 days of age, respectively, P < 0.05). It is concluded that (a) twice-daily boar contact enhances the efficacy of the boar effect in gilts above that seen with a single daily boar exposure period and (b) this enhanced response of the gilt is due to the frequency of boar contact and not to the time of day at which the contact occurs.

The IGF-I amino-terminal tripeptide glycine-proline-glutamate (GPE) is neuroprotective to striatum in the quinolinic acid lesion animal model of Huntington's disease

Huntington's disease is an incurable genetic neurological disorder characterized by the relatively selective degeneration of the striatum. Lesioning of the striatum in rodents using the excitatory amino acid agonist, quinolinic acid (QA), effectively mimics the human neuropathology seen in Huntington's disease. Using this animal model of Huntington's disease, we investigated the ability of the insulin-like growth factor-I (IGF-I) amino-terminal tripeptide glycine-proline-glutamate (GPE) to protect striatal neurons from degeneration. Adult rats received a single unilateral intrastriatal injection of QA (100 nmol) and then daily injection of either vehicle or GPE (0.3 microgram/microliter/day) into the striatum for 7 days. QA at this dose resulted in a partial lesioning of the striatum after 7 days to approximately 50% of cells of unlesioned levels in vehicle-treated animals. The major striatal neuronal phenotype, GABAergic projection neurons, were identified by immunocytochemical labeling of either glutamate decarboxylase 67 (GAD(67)) or the calcium binding protein calbindin in alternate sections. Treatment with GPE for 7 days reversed the loss in projection neurons when assessed by counts of calbindin-stained cells; however, these rescued cells did not regain immunologically detectable levels of GAD(67). GPE also significantly reversed the phenotypic degeneration of cholinergic interneurons identified by immunolabeling for choline acetyltransferase (ChAT) and NADPH diaphorase interneurons identified histochemically. GPE treatment failed to rescue the calcium binding protein interneuron populations of parvalbumin and calretinin neurons. These findings reveal that exogenous administration of GPE selectively prevents excitotoxin induced phenotypic degeneration of striatal projection neurons and cholinergic and NADPH diaphorase interneurons in an animal model of Huntington's disease.

Expression of the activin axis and neuronal rescue effects of recombinant activin A following hypoxic-ischemic brain injury in the infant rat

Neurotrophic factors are induced in the brain in response to injury and may restrict the extent of neuronal loss and facilitate recovery. We have previously reported a strong neuronal induction of activin betaA subunit mRNA expression after a hypoxic-ischemic (HI) injury in the rat brain. Here, we further extended our studies to examine a role for the activin inhibitory binding protein, follistatin after injury and also to determine the potential of activin as a neuronal rescue agent. Ribonuclease protection assay (RPA) was used to quantify the time course of the mRNA expression of activin betaA subunit and follistatin, following a 60-min HI brain injury. Activin betaA subunit mRNA level increased in the contralateral hemisphere 5 h after injury and returned to normal at 10 h post injury. In contrast, follistatin mRNA levels decreased in the same hemisphere at 5 and 10 h after injury. The effect of intracerebroventrically (i. c.v.) administered recombinant human activin A or its antagonist, inhibin A, on neuronal death after a 15-min HI brain injury was determined for a number of brain regions. One microgram activin A (n=23) reduced the neuronal loss in the hippocampal CA1/2 region, dorsolateral striatum but not in the parietal cortex. In contrast, 1 microg of inhibin A (n=18) did not have a significant effect on the extent of neuronal loss in any of the affected regions. This pattern of neuroprotection was consistent with the distribution of immunoreactivity for the activin receptor type II subunit. These results demonstrate that activin A, but not its functional antagonist inhibin A, can enhance the survival of injured hippocampal and striatal neurons. Since follistatin is thought to exert a neutralising effect on activin A activity, the down-regulation of follistatin expression post injury may be allowing activin A to become more accessible to neurons after injury. Overall, these results suggest a role of the activin axis in modulating the survival of specific populations of injured neurons.

Administration of recombinant human Activin-A has powerful neurotrophic effects on select striatal phenotypes in the quinolinic acid lesion model of Huntington's disease

Huntington disease is characterized by the selective loss of striatal neurons, particularly of medium-sized spiny glutamate decarboxylase67 staining/GABAergic projection neurons which co-contain the calcium binding protein calbindin. Lesioning of the adult rat striatum by intrastriatal injection of the N-methyl-D-aspartate receptor agonist quinolinic acid (100 nmol) results in a pattern of striatal neuropathology seven days later that resembles that seen in the Huntington brain. Using this animal model of human Huntington's disease we investigated the effect of daily intrastriatal infusion of the nerve cell survival molecule ActivinA (single bolus dose of 0.73 microg daily for seven days) on the quinolinic acid-induced degeneration of various striatal neuronal phenotypes. By seven days, unilateral intrastriatal infusion of quinolinic acid produced a partial but significant loss (P < 0.01) in the number of striatal neurons immunoreactive for glutamate decarboxylase (to 51.0+/-5.8% of unlesioned levels), calbindin (to 58.7+/-5.1%), choline acetyltransferase (to 68.6+/-6.1%), NADPH-diaphorase (to 47.4+/-5.4%), parvalbumin (to 58.8+/-4.1%) and calretinin (to 60.6+/-8.6%) in adult rats that were administered intrastriatal phosphate-buffered saline for seven days following quinolinic acid. In contrast, in rats that received intrastriatal recombinant human ActivinA once daily for seven days following quinolinic acid, phenotypic degeneration was significantly attenuated in several populations of striatal neurons. Treatment with ActivinA had the most potent protective effect on the striatal cholinergic interneuron population almost completely preventing the lesion induced decline in choline acetyltransferase expression (to 95.1+/-5.8% of unlesioned levels, P < 0.01). ActivinA also conferred a significant protective effect on parvalbumin (to 87.5+/-7.7%, P < 0.01) and NADPH-diaphorase (to 77.5+/-7.5%, P < 0.01) interneuron populations but failed to prevent the phenotypic degeneration of calretinin neurons (to 56.6+/-5.5%). Glutamate decarboxylase67 and calbindin-staining nerve cells represent largely overlapping populations and both identify striatal GABAergic projection neurons. We found that ActivinA significantly attenuated the loss in the numbers of neurons staining for calbindin (to 79.7+/-6.6%, P < 0.05) but not glutamate decarboxylase67 (to 61.1+/-5.9%) at seven days following quinolinic acid lesioning. Taken together these results suggest that exogenous administration of ActivinA can rescue both striatal interneurons (labelled with choline acetyltransferase, parvalbumin, NADPH-diaphorase) and striatal projection neurons (labelled by calbindin) from excitotoxic lesioning with quinolinic acid. Longer-term studies will be required to determine whether these surviving calbindin-expressing projection neurons recover their ability to express the glutamate decarboxylase67/GABAergic phenotype. These results therefore suggest that treatment with ActivinA may help to prevent the degeneration of vulnerable striatal neuronal populations in Huntington's disease.

The small GTP-binding protein R-Ras can influence integrin activation by antagonizing a Ras/Raf-initiated integrin suppression pathway

The rapid modulation of ligand-binding affinity ("activation") is a central property of the integrin family of cell adhesion receptors. The small GTP-binding protein Ras and its downstream effector kinase Raf-1 suppress integrin activation. In this study we explored the relationship between Ras and the closely related small GTP-binding protein R-Ras in modulating the integrin affinity state. We found that R-Ras does not seem to be a direct activator of integrins in Chinese hamster ovary cells. However, we observed that GTP-bound R-Ras strongly antagonizes the Ras/Raf-initiated integrin suppression pathway. Furthermore, this reversal of the Ras/Raf suppressor pathway does not seem to be via a competition between Ras and R-Ras for common downstream effectors or via an inhibition of Ras/Raf-induced MAP kinase activation. Thus, R-Ras and Ras may act in concert to regulate integrin affinity via the activation of distinct downstream effectors.

Genetic and pharmacological analyses of Syk function in alphaIIbbeta3 signaling in platelets

Agonists induce inside-out alphaIIbbeta3 signaling resulting in fibrinogen binding and platelet aggregation. These in turn trigger outside-in signaling resulting in further platelet stimulation. Because the Syk tyrosine kinase is activated during both phases of integrin signaling, we evaluated its role in alphaIIbbeta3 function in murine platelets rendered null for Syk by gene targeting and in human platelets incubated with piceatannol, a tyrosine kinase inhibitor reportedly selective for Syk. Both Syk null murine platelets and piceatannol-treated human platelets exhibited a partial, but statistically significant defect in activation of alphaIIbbeta3 by adenine diphosphate (ADP) +/- epinephrine as assessed by fibrinogen binding. Syk null platelets adhered normally to immobilized fibrinogen, and mice with these platelets exhibited normal tail bleeding times. In contrast, piceatannol treatment of human platelets completely inhibited platelet adhesion to immobilized fibrinogen. The discrepancy in extent of integrin dysfunction between murine and human platelet models may be due to lack of specificity of piceatannol, because this compound inhibited the activity of Src and FAK as well as Syk and also reduced tyrosine phosphorylation of multiple platelet proteins. These results provide genetic evidence that Syk plays a role in alphaIIbbeta3 signaling in platelets and pharmacological evidence that, although piceatannol also inhibits alphaIIbbeta3 signaling, it does so by inhibtion of multiple protein tyrosine kinases.

Activity and injury-dependent expression of inducible transcription factors, growth factors and apoptosis-related genes within the central nervous system

This review primarily discusses work that has been performed in our laboratories and that of our direct collaborators and therefore does not represent an exhaustive review of the current literature. Our aim is to further discuss the role that gene expression plays in neuronal plasticity and pathology. In the first part of this review we examine activity-dependent changes in the expression of inducible transcription factors (ITFs) and neurotrophins with long-term potentiation (LTP) and kindling. This work has identified particular ITFs (Krox-20 and Krox-24) and neurotrophin systems (particularly the brain-derived neurotrophic factor (BDNF)/tyrosine receptor kinase-B, Trk-B system) that may be involved in stabilizing long-lasting LTP (i.e. LTP3). We also show that changes in the expression of other ITFs (Fos, Jun-D and Krox-20) and the BDNF/trkB neurotrophin system may play a central role in the development of hippocampal kindling, an animal model of human temporal lobe epilepsy. In the next part of this review we examine changes in gene expression after neuronal injuries (ischemia, prolonged seizure activity and focal brain injury) and after nerve transection (axotomy). We identify apoptosis-related genes (p53, c-Jun, Bax) whose delayed expression selectively increases in degenerating neurons, further suggesting that some forms of neuronal death may involve apoptosis. Moreover, since overexpression of the tumour-suppressor gene p53 induces apoptosis in a wide variety of dividing cell types we speculate that it may perform the same function in post-mitotic neurons following brain injuries. Additionally, we show that neuronal injury is associated with rapid, transient, activity-dependent expression of neurotrophins (BDNF and activinA) in neurons, contrasting with a delayed and more persistent injury-induced expression of certain growth factors (IGF-1 and TGFbeta) in glia. In this section we also describe results linking ITFs and neurotrophic factor expression. Firstly, we show that while BDNF and trkB are induced as immediate-early genes following injury, the injury-induced expression of activinA and trkC may be regulated by ITFs. We also discuss whether loss of retrograde transport of neurotrophic factors such as nerve growth factor following nerve transection triggers the selective and prolonged expression of c-Jun in axotomized neurons and whether c-Jun is responsible for regeneration or degeneration of these axotomized neurons. In the last section we further examine the role that gene expression may play in memory formation, epileptogenesis and neuronal degeneration, lastly speculating whether the expression of various growth factors after brain injury represents an endogenous neuroprotective response of the brain to injury. Here we discuss our results which show that pharmacological enhancement of this response with exogenous application of IGF-1 or TGF-beta reduces neuronal loss after brain injury.

The death effector domain of PEA-15 is involved in its regulation of integrin activation

Increased integrin ligand binding affinity (activation) is triggered by intracellular signaling events. A Ras-initiated mitogen-activated protein kinase pathway suppresses integrin activation in fibroblasts. We used expression cloning to isolate cDNAs that prevent Ras suppression of integrin activation. Here, we report that PEA-15, a small death effector domain (DED)-containing protein, blocks Ras suppression. PEA-15 does not block the capacity of Ras to activate the ERK mitogen-activated protein kinase pathway. Instead, it inhibits suppression via a pathway blocked by a dominant-negative form of the distinct small GTPase, R-Ras. Heretofore, all known DEDs functioned in the regulation of apoptosis. In contrast, the DED of PEA-15 is essential for its capacity to reverse suppression of integrin activation. Thus, certain DED-containing proteins can regulate integrin activation as opposed to apoptotic protease cascades.

Integrin affinity modulation

Integrin cell-adhesion receptors mediate interactions between cells and the extracellular matrix. Dynamic regulation of integrin adhesive function is termed 'activation' or 'inside-out' signalling. Activation is key to integrin function in processes as diverse as cell migration, the organization of the extracellular matrix and platelet aggregation. Consequently, there has been an intense effort to elucidate the molecular mechanism of integrin activation. This has resulted in the recent identification of novel cytoplasmic partners for integrins and the emerging characterization of the signal-transduction pathways that regulate integrin 'inside-out' signalling. Here, the authors review the recent developments that have provided us with an increased understanding of the basis of integrin activation.

Metabolic compromise with systemic 3-nitropropionic acid produces striatal apoptosis in Sprague-Dawley rats but not in BALB/c ByJ mice

Metabolic compromise with systemic 3-nitropropionic acid (3-NP) results in the degeneration of striatal cells, mimicking the pathology of Huntington's disease (HD). Here we show that 10-week- and 8-month-old BALB/c ByJ mice show an unexpected striatal resilience to single and multiple systemic injections of 3-NP, while Sprague-Dawley rats are vulnerable, albeit in a variable manner. Identification of lesions was made by staining of DNA fragmentation with terminal deoxytransferase-mediated dUTP-biotin nick-end labeling (TUNEL) and hematoxylin/eosin, 1-10 days after injection. Quantitative imaging of histochemistry for succinate dehydrogenase (SDH) activity, the target of 3-NP inhibition, revealed that vulnerable rats reached maximal inhibition in brain at 1 day after 3-NP, whereas mice and resilient rats took 7 days to reach maximal inhibition. All groups of animals reached similar maximal decreases in SDH activity in striatum and cortex. Remarkably, only the fast decline in SDH activity seen in vulnerable rats was associated with TUNEL labeling. In addition, vulnerable rats developed a region within striatum where SDH activity was fully depleted and a similarly depleted region in CA1 hippocampus. While mice did not develop this region in striatum, some developed one in CA1. These regions of SDH depletion in both structures were associated with widespread TUNEL staining, with maximal labeling at 3 days after 3-NP. The existence of an animal strain resilient to 3-NP suggests that there are mediating factors involved in the preferential vulnerability of striatum to metabolic lesioning. The identification of these factors could provide strategies for therapeutic intervention in HD.

3-Nitropropionic acid's lethal triplet: cooperative pathways of neurodegeneration

3-Nitropropionic acid (3-NP) is a mitochondrial toxin which interferes with ATP synthesis. Accidental ingestion of 3-NP by humans as well as other mammals results in neuronal degeneration within the basal ganglia and movement dysfunction characterized by dystonia, chorea, and hypokinesia. The selective degeneration of structures of the basal ganglia occurs despite the non-selective impairment of energy metabolism throughout the brain and body. These effects of 3-NP are shared with the genetic disorder Huntington's disease (HD), which is characterized by progressive neurodegeneration of the basal ganglia and choreic motor dysfunction. These similarities have prompted further investigation of 3-NP as an animal model of HD. Metabolic compromise with 3-NP causes neurodegeneration that involves three interacting processes: energy impairment, excitotoxicity, and oxidative stress. This triplet of cooperative pathways of neurodegeneration helps to explain 3-NP's regional selectivity of neurotoxicity to the basal ganglia. This mini-review will focus on the actions of 3-NP and the related compound, malonic acid (MA), in the central nervous system, with an emphasis on the more current findings regarding their mechanisms of action.

The effects of post-weaning progestagen treatment (Regumate) of early-weaned primiparous sows on subsequent reproductive performance

This study investigated the effects of feeding the orally active progestagen, altrenogest (Regumate) post-weaning on the subsequent reproductive performance of early weaned sows. Ninety (90) Large White/Landrace first parity sows were randomly assigned to three treatments. Treatment 1 (EW) and treatment 3 (CW) sows were weaned on day 12 and day 24 post-partum, respectively while treatment 2 sows (EW-R) were weaned on day 12 post-partum and received an individual daily dose of 20 mg of Regumate on days 13 to 24 post-partum inclusive. Each sow was mated naturally at least twice at the first post-weaning or post-treatment oestrus and slaughtered on days 25-28 of pregnancy to determine the number of corpora lutea and embryos. Regumate-to-oestrus and weaning-to-oestrus intervals were similar for EW-R and CW sows (6.2 vs. 5.6 days). However, both intervals were significantly shorter (P < 0.01) than the weaning-to-oestrus interval of EW sows (7.3 days). An excellent synchronization of oestrus was achieved with Regumate treatment with 97% of treated sows in oestrus within 7 days of Regumate withdrawal compared with 64% for EW sows (P < 0.01) and 87% for CW sows (P > 0.05). Treatment with Regumate resulted in a significant increase in ovulation rate (16.9 vs. 15.4 and 14.9 for treatments EW-R, EW and CW, respectively; P < 0.05) and a non-significant increase in early embryonic survival (77% vs. 68% vs. 68% for treatments EW-R, EW and CW, respectively; P > 0.05). These results indicate that Regumate feeding is a potential management tool to alleviate the diminished reproductive performance associated with early weaning regimes since it leads to successful control of oestrus, higher ovulation and embryo survival rates and thus a greater potential litter size.

Repeated acute activation of the hypothalamo-pituitary adrenal axis prior to and during estrus did not affect reproductive performance in gilts

We investigated the effects of repeated acute activation of the hypothalamo-pituitary adrenal axis, prior to and during estrus, on reproduction in gilts. Individual gilts (n = 24 per treatment) either served as controls or were subjected to daily acute stress ("negative handling," brief electric shock with a battery-operated prodder during confinement with the experimenter) commencing, on average, 8 days prior to estrus. Gilts subjected to negative handling had a significant elevation in plasma concentrations of cortisol that lasted at least 3-4 h, and these gilts were slower than control gilts to approach and interact with the experimenter in a standard test. Nevertheless, reproductive performance--as measured by sexual receptivity and proceptivity, ovulation, the percentage of gilts that became pregnant, the number of embryos 20-21 days after insemination, and the weight of embryos--was not affected by repeated acute activation of the hypothalamo-pituitary adrenal axis. Our results suggest that repeated acute activation of the hypothalamo-pituitary adrenal axis prior to and during estrus does not affect the factors that control estrus and ovulation in gilts.

The effect of repeated boar exposure on cortisol secretion and reproduction in gilts

It has been proposed that short-term activation of the hypothalamo-pituitary adrenal axis, with a consequent increase in the secretion of cortisol, amy disrupt the endocrine events prior to ovulation and thereby impair reproduction in females. We investigated this concept in gilts in which oestrus was detected by introduction to boars, where intense physical contact is possible, or by applying pressure to the back of gilts (back-pressure test) during fence-line exposure to boars, where intense physical contact is prohibited. We expected that there would be a greater release of cortisol and that reproduction would be inhibited in gilts introduced to boars compared to gilts in which the back-pressure test was used. As expected, introduction of gilts to boars resulted in a significant transient increase in plasma concentrations of cortisol while there was no significant effect of using the back-pressure test on plasma cortisol. Nevertheless, introduction of gilts to boars did not impair reproduction and there was no effect of method of detecting oestrus on duration of oestrus, sexual receptivity, fertility or fecundity. The length of the oestrous cycle was decreased and ovulation rate increased in gilts that were introduced to boars compared to gilts that underwent the back-pressure test, indicating that introduction of gilts to boars may have stimulated these aspects of reproduction. These stimulatory effects may have been due to an increased exposure of gilts to sexual behaviour and stimuli from boars when introduced to boars and/or to stimulatory effects of the hypothalamo-pituitary adrenal axis on some aspects of reproduction.

Differential regulation by MK801 of immediate-early genes, brain-derived neurotrophic factor and trk receptor mRNA induced by a kindling after-discharge

Transient changes in immediate-early genes and neurotrophin expression produced by kindling stimulation may mediate secondary downstream events involved in kindling development. Recent experiments have demonstrated conclusively that both kindling progression and mossy fibre sprouting are significantly impaired by administration of the N-methyl-D-aspartate (NMDA) receptor antagonist MK801. To further examine the link between kindling, changes in gene expression and the NMDA receptor, we examined the effects of MK801 on neuronal induction of immediate-early genes, brain-derived neurotrophic factor (BDNF) and trk receptor mRNA expression produced by a single electrically induced hippocampal after-discharge in rats. The after-discharge produced a rapid (after 1 h) increase in Fos, Jun-B, c-Jun, Krox-24 mRNA and protein and Krox-20 protein in dentate granule neurons and a delayed, selective expression of Fos, Jun-D and Krox-24 in hilar interneurons. MK801 pretreatment produced a very strong inhibition of Fos, Jun-D and Krox-20 increases in dentate neurons but had a much smaller effect on Jun-B and c-Jun expression. MK801 did not inhibit Krox-24 expression in granule neurons or the delayed expression of Fos, Jun-D and Krox-24 in hilar interneurons. BDNF protein and trk B and trk C mRNA expression were also strongly induced in dentate granule cells 4 h following an after-discharge. MK801 abolished the increase in BDNF protein and trk B, but not trk C mRNA in granule cells at 4 h. These results demonstrate that MK801 differentially regulates the AD-increased expression of a group of genes previously identified as being likely candidates for an involvement in kindling. Because MK801 significantly retards the development of kindling and mossy fibre sprouting, it can be argued that those genes whose induction is not significantly attenuated by MK801 are unlikely to play an important role in the MK801-sensitive component of kindling and the changes in neural connectivity (mossy fibre sprouting) associated with kindling. Conversely, the role in kindling of those genes whose expression was significantly attenuated by MK801 (Fos, Jun-D, Krox-20, trkB and BDNF) requires further examination.

Complementation of dominant suppression implicates CD98 in integrin activation

The integrin family of adhesion receptors are involved in cell growth, migration and tumour metastasis. Integrins are heterodimeric proteins composed of an alpha and a beta subunit, each with a large extracellular, a single transmembrane, and a short cytoplasmic domain. The dynamic regulation of integrin affinity for ligands in response to cellular signals is central to integrin function. This process is energy dependent and is mediated through integrin cytoplasmic domains. However, the cellular machinery regulating integrin affinity remains poorly understood. Here we describe a genetic strategy to disentangle integrin signalling pathways. Dominant suppression occurs when overexpression of isolated integrin beta1 cytoplasmic domains blocks integrin activation. Proteins involved in integrin signalling were identified by their capacity to complement dominant suppression in an expression cloning scheme. CD98, an early T-cell activation antigen that associates with functional integrins, was found to regulate integrin activation. Furthermore, antibody-mediated crosslinking of CD98 stimulated beta1 integrin-dependent cell adhesion. These data indicate that CD98 is involved in regulating integrin affinity, and validate an unbiased genetic approach to analysing integrin signalling pathways.

Cycloheximide phase-shifts, but does not prevent, de novo Krox-24 protein expression

Previous studies show that focal hippocampal injury transiently increases NMDA receptor-dependent expression of inducible transcription factors (ITFs including Krox-24) in rat dentate gyrus neurons. Furthermore, pretreatment with the protein synthesis inhibitor, cycloheximide (CHX), prevents de novo ITF protein expression 1 h post-injury. Here, we further characterize the effects of a single pretreatment dose of CHX on injury-induced expression of Krox-24 and show that CHX pretreatment phase-shifts (delays), but does not prevent, de novo expression of Krox-24 in hippocampal dentate gyrus neurons following injury. This may have implications for studies which use CHX pretreatment to examine the role of gene expression and de novo protein synthesis in long-term memory formation, the stabilization of long-term potentiation, kindling and neuronal injury.