Localization of the NBMPR-sensitive equilibrative nucleoside transporter, ENT1, in the rat dorsal root ganglion and lumbar spinal cord

ENT1 is an equilibrative nucleoside transporter that enables trans-membrane bi-directional diffusion of biologically active purines such as adenosine. In spinal cord dorsal horn and in sensory afferent neurons, adenosine acts as a neuromodulator with complex pro- and anti-nociceptive actions. Although uptake and release mechanisms for adenosine are believed to exist in both the dorsal horn and sensory afferent neurons, the expression profile of specific nucleoside transporter subtypes such as ENT1 is not established. In this study, immunoblot analysis with specific ENT1 antibodies (anti-rENT1(227-290) or anti-hENT1(227-290)) was used to reveal the expression of ENT1 protein in tissue homogenates of either adult rat dorsal horn or dorsal root ganglia (DRG). Immunoperoxidase labeling with ENT1 antibodies produced specific staining in dorsal horn which was concentrated over superficial laminae, especially the substantia gelatinosa (lamina II). Immunofluorescence double-labeling revealed a punctate pattern for ENT1 closely associated, in some instances, with cell bodies of either neurons (confirmed with NeuN) or glia (confirmed with CNPase). Electron microscopy analysis of ENT1 expression in lamina II indicated its presence within pre- and post-synaptic elements, although a number of other structures, including myelinated and unmyelinated, axons were also labeled. In sensory ganglia, ENT1 was localized to a high proportion of cell bodies of all sizes that co-expressed substance P, IB4 or NF, although ENT1 was most highly expressed in the peptidergic population. These data provide the first detailed account of the expression and cellular distribution of ENT1 in rat dorsal horn and sensory ganglia. The functional significance of ENT1 expression with regard to the homeostatic regulation of adenosine at synapses remains to be established.     

Septal innervation regulates the function of alpha7 nicotinic receptors in CA1 hippocampal interneurons

The hippocampus receives substantial input from the medial septum/diagonal band of broca (MS/DB) via the fibria-fornix (FF). Projections from the MS/DB innervate hippocampal interneurons that express alpha7 nicotinic receptors and regulate excitation in principal cell populations. In the present report we used stereotaxic surgery, whole-cell patch clamping, and immunohistochemical techniques to evaluate the effects of FF and MS/DB lesions on alpha7 nicotinic receptors in stratum radiatum interneurons. Focal somatic application of ACh (1 mM) evoked methyllycaconitine (MLA)-sensitive currents that were markedly reduced following aspirative lesions of the FF. Reductions in current amplitudes were prevented or restored to levels not significantly different from controls following in vivo treatment with the alpha7-selective agonist GTS-21, and GTS-21 treatment did not change current amplitudes measured in tissue from unlesioned animals. MS/DB injections of the selective cholinergic neurotoxin 192 IgG-saporin did not affect alpha7 receptor currents, although MS/DB ChAT and hippocampal AChE immunolabeling were significantly reduced. In contrast, kainic acid lesions of the MS/DB, potentially more selective for GABAergic projection neurons, produced significant reductions in current amplitudes. These findings are the first to show functional changes in alpha7 receptors following hippocampal denervation and suggest that MS/DB hippocampal innervation regulates functional aspects of hippocampal alpha7 receptors. The results confirm hippocampal alpha7 nicotinic receptors as viable therapeutic targets in diseases that involve degradation of the septohippocampal pathway and may indicate that GABAergic MS/DB hippocampal input plays a more substantial role in the regulation of alpha7 nicotinic receptor function than MS/DB hippocampal cholinergic input.     

Glutamate induces rapid loss of axonal neurofilament proteins from cortical neurons in vitro

One of the primary hallmarks of glutamate excitotoxicity is degradation of the neuronal cytoskeleton. Using a tissue culture approach, we have investigated the relationship between excitotoxicity and cytoskeletal degradation within axons, with particular reference to the axon specific neurofilament proteins. Neurofilaments were rapidly lost from axons over a 24-h period in response to excitotoxic insult (as observed by immunocytochemistry and western blotting), while other axonal cytoskeletal markers (such as betaIII-tubulin) remained intact. Treatment with kainic acid and NMDA, or complementary experiments using the pharmacological glutamate receptors blockers CNQX (kainate/AMPA receptor antagonist) and MK-801 (NMDA receptor antagonist), demonstrated that neurofilament degeneration was mediated primarily by NMDA receptor activity. This work suggests that excitotoxicity triggers a progressive pathway of cytoskeletal degeneration within axons, initially characterised by the loss of neurofilament proteins.     

Procedure for minimizing stress for fMRI studies in conscious rats

Functional magnetic resonance imaging (fMRI) in conscious animals is evolving as a critical tool for neuroscientists. The present study explored the effectiveness of an acclimation procedure in minimizing the stress experienced by the animal as assessed by alterations in physiological parameters including heart rate, respiratory rate, and serum corticosterone levels. Results confirm that as the stress of the protocol is minimized, there is a significant decrease in head movements and enhancement in data quality. The feasibility of improving the quality of fMRI data acquired in alert rats by utilizing a relatively simple technique is presented.     

IL-2 deficiency results in altered septal and hippocampal cytoarchitecture: relation to development and neurotrophins

We have found previously that brain IL-2 receptors are enriched in the hippocampal formation, and that loss of this cytokine results in cytoarchitectural alterations in the hippocampus and septum and related behavioral changes in IL-2 knockout (IL-2 KO) mice. These alterations included decreased cholinergic somata in the medial septum/vertical limb of the diagonal band of Broca (MS/vDB) and decreased distance across the infrapyramidal (IP) granule cell layer (GCL) of the dentate gyrus (DG). To extend our previous findings, several experiments were conducted comparing IL-2 KO mice and wild-type littermates to determine (1) whether the GABAergic projection neurons of IL-2 KO mice in this region were also affected; (2) if the reduction in septal cholinergic projection neurons found in adult IL-2 KO mice is present at weaning (and prior to the development of peripheral autoimmune disease); and (3) if loss of IL-2 may result in changes in the neurotrophins, brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF), involved in maintenance of hippocampal neurons. No differences in GABAergic neurons in the MS/vDB were found in adult mice, and the reduction in cholinergic neurons seen in adult IL-2 KO mice was not found in animals at postnatal day 21. The number of neurons in the IP-GCL was also significantly reduced. Compared to wild-type mice, IL-2 KO mice had significantly reduced concentration of BDNF protein and increased concentrations of NGF. These data suggest that the septohippocampal neuronal loss in IL-2 KO mice is selective for the cholinergic neurons and appears to be due to a failure in neuronal maintenance/survival that may be, in part, associated with changes in neurotrophins.     

Hormonal responses to the 6-minute walk test in women and men with coronary heart disease: a pilot study

BACKGROUND: Women with coronary heart disease (CHD) are more likely than men to develop congestive heart failure (CHF). Dysregulation of sympathetic and volume-regulatory hormones may contribute to the onset of symptomatic CHF. We hypothesized that this hormonal dysregulation develops at an earlier stage of CHD in women than in men. OBJECTIVES: The study goals were (1) to determine the effect of gender on basal and exercise-induced plasma concentrations of catecholamines and volume-regulatory hormones in patients diagnosed with CHD, New York Heart Association class I and (2) to determine efficacy of the 6-minute walk test as a stimulus for release of these hormones. METHODS: Study participants were 9 women and 9 men with normal left ventricular ejection fraction (>50%) and CHD confirmed by arteriography. Data were collected under resting conditions, and after the 6-minute walk test, in the general clinical research center of a northeastern university medical center. RESULTS: Basal plasma vasopressin (VP) concentration was significantly higher in men than in women (P = .018). Exercise, for women and men combined, significantly increased atrial natriuretic peptide (P < .0005), VP (P = .04), norepinephrine (P < .0005), and epinephrine (P = .038) but not plasma renin activity (P = .09). No further gender differences were detected for basal levels, or for the magnitude of exercise-induced increases, for any of the hormones measured. CONCLUSIONS: The 6-minute walk test is an exercise of sufficient intensity and duration to initiate the release of hormones associated with sympathetic activation and fluid-electrolyte regulation in both women and men with CHD. It appears that a gender difference was detected only for basal VP levels.