Heterogeneity in cytosolic calcium regulation among different microvascular smooth muscle cells of the rat retina

Rat retinae were dissociated to yield intact microvessels 7 to 42 microm in diameter. These were loaded with fura-2 AM and single fragments anchored down in a recording bath. Intracellular Ca(2+) levels from 20- to 30-microm sections of vessel were estimated by microfluorimetry. The vessels studied were identified as metarterioles and arterioles. Only the microvascular smooth muscle cells loaded with fura-2 AM and changes in the fluorescence signal were confined to these cells: Endothelial cells did not make any contribution to the fluorescence signal nor did they contribute to the actions of the drugs. Caffeine (10 mM) or elevated K(+) (100 mM) produced a transient rise in cell Ca(2+) in the larger vessels (diameters >18 microm) but had no effect on smaller vessels (diameters 30 min) on washing out the endothelin and the vessel failed to relax. These results demonstrate heterogeneity between smaller and larger retinal vessels with regard to Ca(2+) mobilisation and homogeneity with respect to the actions of vasoactive peptides.

The combined effect of diabetes and ionising radiation on the retinal vasculature of the rat

The clinical impression that pre-existing diabetes exacerbates radiation injury to the retinal vasculature was studied in STZ diabetic rats. Half of 2 groups of streptozotocin (STZ)-induced diabetic rats and 1 group of normal animals had their right eyes irradiated with 1000 cGy of 90 KVP x-rays. The prevalence of acellular capillaries in trypsin digests of the retinal vasculature was quantified for each of the 6 groups of animals at 6.5 months post-irradiation. The prevalence of acellular capillaries in both non-irradiated diabetic groups was significantly higher than in controls while the irradiated animals in each of the three main categories showed a statistically significant increase compared to their non-irradiated equivalents. However, the net increase in acellular capillaries following irradiation was much greater in rats with an 8 month term of pre-existing diabetes (180%) than in those which had only been diabetic for 3 months (36%). The results of this study suggest a synergistic relationship between pre-existing diabetes and ionising radiation in the development of retinal vasculopathy, and that the potentiation of the vascular damage is dependent on the duration of diabetes prior to radiation exposure.

Late ultrastructural changes in the retina of the rat following low-dose X-irradiation

This study describes ultrastructural changes in the pigmented hooded Lister rat retina, 3-12 months following X-irradiation with single doses of between 200 and 2000 cGy. The extreme radiosensitivity of the photoreceptor cells was underlined by the continued manifestation of fine structural changes and cell death up to 6 months post-radiation in animals receiving doses above 500 cGy. The retinal pigment epithelial (RPE) cells were more radioresistant than photoreceptors and RPE cell loss was only observed at doses of more than 1500 cGy. One year after irradiation with 1500 cGy the retinal vasculature showed capillary occlusion with some evidence of recanalisation. Telangiectasia was observed in the large retinal veins. Although the inner retinal neurones and glial cells showed no evidence of direct radiation damage, the nerve fibre layer adjacent to occluded retinal vessels demonstrated ultrastructural evidence of ischaemic neuropathy and retinal oedema. At doses above 1500 cGy the choriocapillaris showed platelet aggregation and capillary loss.

Early ultrastructural changes after low-dose X-irradiation in the retina of the rat

In this study Lister rats were given doses of X-rays ranging from 200-2,000 Rads to the retina of one eye, sacrificed at various time intervals between one hour and one month later and the irradiated eye processed for electron microscopy. The rod photoreceptor cells were by far the most radiosensitive cells in the retina, their outer segments showing distinctive membrane damage at one hour after 200 Rads of X-rays. Photoreceptor cell death was not seen at doses less than 1,000 Rads in the time period of the experiment. The retinal pigment epithelial (RPE) cells showed damage in the form of mitochondrial swelling but only in doses over 500 Rads. Retinal pigment epithelial cell loss did not occur under 2,000 Rads. The inner retinal neurones, glial elements and the retinal vasculature did not show any ill effects in the time period of this study.

Map of part of the “Smith & Kerby” tract in the City of Brantford, County of Brant, Ontario, no date.

An abstract map of a part of the “Smith & Kerby tract” lying within the City of Brantford, County of Brant, Ontario. There is no date on the map. The map shows parts from McMurray’s Survey, Mrs. G.S. Wilkes Survey, and the Howell Survey.

Regenerative capabilities of the rat seventh nerve using suture and collagen splint techniques: a comparative study

This paper discusses the effectiveness of repair procedures on the rat facial nerve using the current clinical surgical procedure of suturing nerve ends and a proposed technique utilizing splints made of collagen.

Microbiology of the human intestinal tract and approaches for its dietary modulation

Gut bacteria can be categorised as being either beneficial or potentially pathogenic due to their metabolic activities and fermentation end-products. Health-promoting effects of the microflora may include immunostimulation, improved digestion and absorption, vitamin synthesis, inhibition of the growth of potential pathogens and lowering of gas distension. Detrimental effects are carcinogen production, intestinal putrefaction, toxin production, diarrhoea/constipation and intestinal infections. Certain indigenous bacteria such as bifidobacteria and lactobacilli are considered to be examples of health-promoting constituents of the microflora. They may aid digestion of lactose in lactose-intolerant individuals, reduce diarrhoea, help resist infections and assist in inflammatory conditions. Probiotics, prebiotics and synbiotics are functional foods that fortify the lactate producing microflora of the human or animal gut.

Regulation of expression of the rat orthologue of mouse double minute 2 (MDM2) by H2O2-induced oxidative stress in neonatal rat cardiac myocytes.

The Mdm2 ubiquitin ligase is an important regulator of p53 abundance and p53-dependent apoptosis. Mdm2 expression is frequently regulated by a p53 Mdm2 autoregulatory loop whereby p53 stimulates Mdm2 expression and hence its own degradation. Although extensively studied in cell lines, relatively little is known about Mdm2 expression in heart where oxidative stress (exacerbated during ischemia-reperfusion) is an important pro-apoptotic stimulus. We demonstrate that Mdm2 transcript and protein expression are induced by oxidative stress (0.2 mm H(2)O(2)) in neonatal rat cardiac myocytes. In other cells, constitutive Mdm2 expression is regulated by the P1 promoter (5' to exon 1), with inducible expression regulated by the P2 promoter (in intron 1). In myocytes, H(2)O(2) increased Mdm2 expression from the P2 promoter, which contains two p53-response elements (REs), one AP-1 RE, and two Ets REs. H(2)O(2) did not detectably increase expression of p53 mRNA or protein but did increase expression of several AP-1 transcription factors. H(2)O(2) increased binding of AP-1 proteins (c-Jun, JunB, JunD, c-Fos, FosB, and Fra-1) to an Mdm2 AP-1 oligodeoxynucleotide probe, and chromatin immunoprecipitation assays showed it increased binding of c-Jun or JunB to the P2 AP-1 RE. Finally, antisense oligonucleotide-mediated reduction of H(2)O(2)-induced Mdm2 expression increased caspase 3 activation. Thus, increased Mdm2 expression is associated with transactivation at the P2 AP-1 RE (rather than the p53 or Ets REs), and Mdm2 induction potentially represents a cardioprotective response to oxidative stress.

Evidence for involvement of both IKCa and SKCa channels in hyperpolarizing responses of the rat middle cerebral artery

Endothelium-derived hyperpolarizing factor responses in the rat middle cerebral artery are blocked by inhibiting IKCa channels alone, contrasting with peripheral vessels where block of both IKCa and SKCa is required. As the contribution of IKCa and SKCa to endothelium-dependent hyperpolarization differs in peripheral arteries, depending on the level of arterial constriction, we investigated the possibility that SKCa might contribute to equivalent hyperpolarization in cerebral arteries under certain conditions. METHODS: Rat middle cerebral arteries (approximately 175 microm) were mounted in a wire myograph. The effect of KCa channel blockers on endothelium-dependent responses to the protease-activated receptor 2 agonist, SLIGRL (20 micromol/L), were then assessed as simultaneous changes in tension and membrane potential. These data were correlated with the distribution of arterial KCa channels revealed with immunohistochemistry. RESULTS: SLIGRL hyperpolarized and relaxed cerebral arteries undergoing variable levels of stretch-induced tone. The relaxation was unaffected by specific inhibitors of IKCa (TRAM-34, 1 micromol/L) or SKCa (apamin, 50 nmol/L) alone or in combination. In contrast, the associated smooth-muscle hyperpolarization was inhibited, but only with these blockers in combination. Blocking nitric oxide synthase (NOS) or guanylyl cyclase evoked smooth-muscle depolarization and constriction, with both hyperpolarization and relaxation to SLIGRL being abolished by TRAM-34 alone, whereas apamin had no effect. Immunolabeling showed SKCa and IKCa within the endothelium. CONCLUSIONS: In the absence of NO, IKCa underpins endothelium-dependent hyperpolarization and relaxation in cerebral arteries. However, when NOS is active SKCa contributes to hyperpolarization, whatever the extent of background contraction. These changes may have relevance in vascular disease states where NO release is compromised and when the levels of SKCa expression may be altered.