Pupil constriction evoked in vitro by stimulation of the oculomotor nerve in the turtle (Trachemys scripta elegans).

The pond turtle (Trachemys scripta elegans) exhibits a notably sluggish pupillary light reflex (PLR), with pupil constriction developing over several minutes following light onset. In the present study, we examined the dynamics of the efferent branch of the reflex in vitro using preparations consisting of either the isolated head or the enucleated eye. Stimulation of the oculomotor nerve (nIII) using 100-Hz current trains resulted in a maximal pupil constriction of 17.4% compared to 27.1% observed in the intact animal in response to light. When current amplitude was systematically increased from 1 to 400 microA, mean response latency decreased from 64 to 45 ms, but this change was not statistically significant. Hill equations fitted to these responses indicated a current threshold of 3.8 microA. Stimulation using single pulses evoked a smaller constriction (3.8%) with response latencies and threshold similar to that obtained using train stimulation. The response evoked by postganglionic stimulation of the ciliary nerve using 100-Hz trains was largely indistinguishable from that of train stimulation of nIII. However, application of single-pulse stimulation postganglionically resulted in smaller pupil constriction at all current levels relative to that of nIII stimulation, suggesting that there is amplification of efferent drive at the ganglion. Time constants for constrictions ranged from 88 to 154 ms with relaxations occurring more slowly at 174-361 ms. These values for timing from in vitro are much faster than the time constant 1.66 min obtained for the light response in the intact animal. The rapid dynamics of pupil constriction observed here suggest that the slow PLR of the turtle observed in vivo is not due to limitations of the efferent pathway. Rather, the sluggish response probably results from photoreceptive mechanisms or central processing.

International trade agreements: a threat to tobacco control policy.

International covenants establish a role for governments in ensuring the conditions for human health and wellbeing, which has been recognised as a central human right. International trade agreements, conversely, prioritize the rights of corporations over health and human rights. International trade agreements are threatening existing tobacco control policies and restrict the possibility of implementing new controls. This situation is unrecognised by many tobacco control advocates in signatory nations, especially those in developing countries. Recent agreements on eliminating various trade restrictions, including those on tobacco, have expanded far beyond simply international movement of goods to include internal tobacco distribution regulations and intellectual property rules regulating advertising and labelling. Our analysis shows that to the extent trade agreements protect the tobacco industry, in itself a deadly enterprise, they erode human rights principles and contribute to ill health. The tobacco industry has used trade policy to undermine effective barriers to tobacco importation. Trade negotiations provide an unwarranted opportunity for the tobacco industry to assert its interests without public scrutiny. Trade agreements provide the industry with additional tools to obstruct control policies in both developed and developing countries and at every level. The health community should become involved in reversing these trends, and help promote additional measures to protect public health.