Correlation between water relations and within-canopy distribution of epiphytic ferns in a Mexican cloud forest.

The physiological traits associated with water relations of eight common epiphytic ferns in a Mexican cloud forest were investigated in relation to the distribution of these species within the canopy. Fern distribution was significantly correlated with the relative water content at which stomata close, leaf thickness, stomatal density and size. Trichomanes bucinatum desiccated completely within hours in moderately dry air and was confined to the stem bases, and Asplenium cuspidatum, with no evident adaptations to cope with drought, grew in the second most shaded zone within the tree crowns. Despite growing in a humid cloud forest, all other species had xeric adaptations including coriaceous leaves (Pleopeltis mexicana, Elaphoglossum glaucum), succulent rhizomes (Polypodium puberulum, Phlebodium areolatum), low rates of uncontrolled water loss (all species except P. puberulum), leaf scales (Elaphoglossum petiolatum, Polypodium plebeium), and high cell wall elasticity (all species). P. plebeium and Pl. mexicanum, which grow in the most exposed locations, tolerated water loss beyond the turgor loss point before the stomata closed and appear to be poikilohydric or at least to tolerate high water deficits.

Competition intensity as a function of resource availability in a semiarid ecosystem.

Two field experiments were conducted using three dominant perennial species of the Chihuahuan Desert: Hilaria mutica (a tussock grass), Larrea tridentata (a microphyllous shrub) and Opuntia rastrera (a flat-stemmed succulent cactus). Two hypotheses concerning competition in arid plant communities were tested. (1) Marked resource partitioning with no interspecific competition could be expected since the three species belong to different life-forms, and that plant growth in deserts is basically limited by harsh environmental conditions. (2) Alternatively, resource scarcity (particularly water) will result in strong plant competition. In a 1-year removal experiment, water status and plant growth of the three species were monitored in twelve 10 m × 10 m plots randomized in three blocks and assigned to the following treatments: (a) removal of all species, except H. mutica; (b) removal of all species, except L. tridentata; (c) removal of all species, except O. rastrera, and (d) control without any manipulation. In a watering experiment, under two neighbourhood conditions (growing isolated or in associations of plants of the three species in plots of 20 m2), the water status of the three species and the growth of H.mutica and L.tridentata were studied for 32 days after an irrigation equivalent to 30 mm of rain, similar to a strong storm event at the site. In the removal experiment, where plants were free to capture water, no evidence of competition was observed. However, during the watering experiment, in which water was forced into the soil, competitive effects were observed. Associated individuals of L. tridentata had lower xylem water potentials and osmotic potentials (OPs) and produced shorter twigs and less leaves and nodes. Although less pronounced, neighbours also had a negative effect on the OP in O. rastrera. According to these results, the intensity of the interspecific competition for water seems to depend on the level of resource availability in the soil. Thus, the validity of the two hypotheses tested in this study also depends on the level of resources. Competition could be absent or very low in years of low precipitation, as in the year of this study (173 mm against a 25-year average of 264 mm). However, when soil water availability is high, e.g. following heavy rain, the negative interactions between species could be more intense.

A microscopic study of herpes simplex virus retinopathy in mice.

ICR white mice were inoculated with herpes simplex virus (HSV) type I in the anterior chamber of one eye. Animals were killed at intervals of 2, 4, 6, 8, and 10 days and both eyes were obtained for light and electron microscopic study of retinal changes. HSV retinopathy developed in 42 (91%) of 46 inoculated eyes. Fourteen (88%) of sixteen noninoculated eyes examined after the sixth postinoculation day developed HSV retinopathy. The earliest signs of retinopathy in the inoculated eye were peripheral retinal vasculitis and inflammatory cells throughout the nerve fiber layer on day 2. No virus was found in retinal tissue until day 4, at which time disruption of outer retinal layers (outer nuclear layer and layer of rods and cones) was observed in the peripheral retina. The earliest signs of retinopathy in the noninoculated eye were isolated foci of outer retinal disruption in the posterior retina on day 6. The inflammation accompanying early retinal changes of HSV retinopathy were more severe in the inoculated eye. Electron microscopy of both eyes revealed viral particles in the inner nuclear and ganglion cell layers at the time of outer retinal disruption, but viral particles were seen only rarely in the outer retinal layers at this stage. Early disruption of normal retinal architecture may be due to infection and destruction of Muller cells. The retinopathy progressed in both eyes to total destruction of the retina by day 10. Viral infection of the retinal pigment epithelium occurred, but viral particles were seen only rarely in the underlying choroid. This model may be useful for the study of HSV retinopathy in humans.

Peripheral adrenergic stimulation and indomethacin in experimental ocular shedding of HSV.

The application of 6-hydroxydopamine to the cornea by iontophoresis, followed by topical epinephrine, effectively induces herpes simplex virus (HSV) shedding from the external eye of latently infected rabbits. In this study the beta adrenergic blocker, Timolol, reduced virus shedding when applied immediately before the epinephrine, but continued administration resulted in increased viral shedding. While indomethacin, a prostaglandin synthesis inhibitor decreased HSV replication in cell culture, it failed to decrease virus shedding when applied topically to the eye in adrenergically stimulated animals. Timolol may act then by its effect on the peripheral cells of the eye rather than by stimulation of virus production in ganglionic neurons. These same animals were subsequently tested for latent infection of the trigeminal and superior cervical ganglia and corneas 14 months after primary infection. Only 2 of 14 animals had virus in the trigeminal ganglia, a finding which suggests that latent virus may be depleted by repeated reactivations. Virus was recovered from corneas of five rabbits by co-cultivation so it is possible that corneal latency occurs in this rabbit model as it does in humans.

Effect of autonomic mediators in recurrent shedding of herpes simplex in the rabbit eye.

After recovery from primary herpes simplex virus (HSV) infection of the eye in rabbits, recurrent shedding of virus in the external eye can be produced by the local application of 6-hydroxydopamine (6-HD) and epinephrine. Surgical sympathectomy did not prevent shedding of HSV with 6-HD/epinephrine so the source of the virus in the outer eye induced by adrenergic stimulation is not just the superior cervical ganglia (SCG). Chemical sympathectomy with 6-HD prior to HSV infection of the cornea led to decreased viral replication in the SCG during acute infection but did not interfere with uptake of the virus and latent or low grade infection of the ganglion. Shedding of virus in the outer eye induced by 6-HD/epinephrine was reduced by treatment with the beta-adrenergic blocker, timolol. These experiments strongly suggest that recurrent HSV shedding in the eye induced by catecholamines is due in part to effects on the peripheral (i.e. post synaptic) cells. While the peripheral neurons are the source of virus, it is possible that not all HSV detected in the external eye is due to release of preformed virus from nerve endings.

Vitamin A in experimental herpetic keratitis.

Systemic vitamin A palmitate at three dosage levels was evaluated for its effect on experimental herpes simplex virus (HSV) keratitis in corticosteroid-treated rabbits. High-dose vitamin A palmitate reduced the severity of herpetic keratitis, but the low or moderate doses did not, and none of the vitamin A treatments affected virus recovery. Vitamin A treatment, however, produced substantial weight loss in uninfected rabbits and in corticosteroid-treated, HSV-infected rabbits. Steroid treatment alone significantly increased the antibody response to HSV, but this effect was not enhanced by vitamin A. The slight beneficial effect on HSV keratitis could be attributed to the known effect of vitamin A on promoting epithelial healing rather than an enhancement of immunity. For this purpose, local application of vitamin A may be just as effective and much less toxic than administration for systemic effect.

Intermittent trachoma chemotherapy: a controlled trial of topical tetracycline or erythromycin.

In communities with endemic blinding trachoma, mass (or "blanket") treatment with a topically applied tetracycline derivative is a standard control measure. The widely used "intermittent" treatment schedule consists of the twice daily application of antibiotic ointment for five consecutive days once a month for six months. In this study, the efficacy of "intermittent" treatment was evaluated for the treatment of severe and moderate intensity trachoma in children in southern Tunisia. Tetracycline or erythromycin ointments (specific antichlamydial drugs) were compared with 5% boric acid ointment (a simple antiseptic) given by the intermittent schedule during the winter and spring. There was a statistically significant degree of improvement at only one examination, four weeks after the full course of treatment had been completed. When re-examined five months later there were no differences in intensity in the three groups. The limited effect of topical chemotherapy might be attributable to several causes, among which could be inadequate drug levels, inadequate treatment periods, reinfection from non-treated children in the community, and auto-infection from extraocular sites (e.g., respiratory tract) in the same child. The possible value of short-term (two weeks) systemic antimicrobial therapy as an additional strategy to prevent blindness of children with potentially blinding active trachoma is discussed.

Herpetic eye disease in rabbits after inoculation of autonomic ganglia.

Since herpes simplex virus (HSV) can cause persistent infection of autonomic ganglia of both humans and experimentally infected animals, we followed the pattern of eye disease and viral growth after HSV inoculation of one superior cervical ganglion in rabbits. Of 27 inoculated animals, eye disease or detectable virus developed in 18. Anterior uveitis was the most common clinical manifestation (94%), but conjunctivitis and dendritic keratitis were also frequent (60%). All 12 uveal-retinal specimens tested and five of seven ipsilateral superior cervical ganglia had detectable virus. If recurrent herpetic iritis in humans is associated with persistent infection of the superior cervical ganglion, autonomic mediators might trigger episodes of virus shedding. In patients with herpetic iritis, then, the use of epinephrine and other adrenergic agonists or antagonists should be avoided.