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

Abstract

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.

Asymmetric Wavefront Aberrations and Pupillary Shapes Induced by Electrical Stimulation of Ciliary Nerve in Cats Measured with Compact Wavefront Aberrometer

“…This suggests that an asymmetrical constriction of ciliary muscle is induced by unilateral ciliary nerve stimulation, which may induce the deformation of crystalline lens. In patients with Adie’s syndrome, astigmatism is reportedly induced after accommodation [23]. Our findings in cats support the hypothesis that a segmental constriction of ciliary muscle occurs when patients with Adie’s syndrome accommodates which eventually causes the increase of asymmetrical astigmatism.…”

“…In addition, the dynamic pupillary dilations and eye movements in response to microstimulation of the superior colliculus or the optic tectum have been studied in monkeys and birds [21], [22]. Dearworth et al studied the pupillary constriction evoked in vitro by stimulating the ciliary nerve in turtles [23].…”

The Edinger‐Westphal nucleus: A historical, structural, and functional perspective on a dichotomous terminology

“…The involvement of CRF in stress‐related psychopathologies is beyond dispute (for reviews see Joels et al,2008; de Kloet,2008). However, increasing evidence suggests a role for EW Ucn1 neurons in the development of stress‐related mood disorders (Kozicz et al,2008b).…”

Role of the trochlear nerve in eye abduction and frontal vision of the red‐eared slider turtle (Trachemys scripta elegans)

“…, Table ). Responses by nIII are potentially the most complex, as innervations include the superior rectus, inferior rectus, inferior oblique, and internal rectus muscles and even the iris via the ciliary ganglion (Iske, 1942; Dearworth et al, ). The consequence of this is that the frequency that evokes peak pupil constrictions (126 Hz) (Romano et al, ) differs from that for evoking peak extorsion and adduction (59 Hz, cf.…”

“…Thresholds currents that produced half the maximal eye rotations were calculated by using the Hill equation, y = a · x b /( c b + x b ) (Dearworth et al, ). Equations were fit to plots of the rotations, y , versus current amplitude, x , on a log scale, where a is the maximum rotation, b is a slope constant, and c is the threshold current.…”