Increase in Locomotor Activity Following Shielding of the Parietal Eye in Night Lizards

Further observations on the fine structure of the parietal eye of lizards

An electron microscopical study of the third eye of the Western Fence Lizard, Sceloporus occidentalis, fixed with 1 per cent osmium tetroxide, pH 7.4–7.6, for 16 to 20 hours at 0°C., revealed the following new facts. The fibrillar system of the retinal photoreceptor consists of nine double fibrils enclosed in a sheath. Pigment cells and lens cells possess similar systems. Two short cylindrical centrioles are associated with the fibrillar apparatus: one, from which striated rootlets extend inward, lies at the base of the fibrils, with the other at an oblique angle to the axis of the system. A Golgi complex, whorls of endoplasmic reticulum, lipid (?) droplets, and other organelles and inclusions in the photoreceptors are described. An axon leads from the base of the photoreceptor into the nervous layer of the retina which consists of many nerve fibers and large ganglion cells. Although the pattern of neural connections has not yet been determined, some synapses were found. The parietal nerve consists of about 250 non-medullated fibers. The capsule of the eye usually has a layer of iridocytes, which contain rows of guanine (?) rods. A few parietal eyes of the Granite Night Lizard, Xantusia henshawi, were also examined. Large lipid (?) droplets occur in the bases of their receptoral processes.

Neural elements in the pineal complex of the frog, Rana esculenta, I: Centrally projecting neurons

The pineal complex of anuran amphibians is a directly photosensory organ, encompassing both an extracranial portion, the frontal organ, and an intracranial portion, the pineal organ proper. The projection neurons of the frontal organ respond differentially according to the wavelengths of the light stimuli. The pineal organ, on the other hand, functions mainly as a luminosity meter. Most of its centrally projecting neurons respond to all increases in ambient illumination with decreases in spontaneous firing of action potentials, although some neural units in the pineal organ may respond according to wavelength. This difference in responses to light stimulation may be reflected in the neural organization of the two parts of the pineal complex. In the present study, we have analyzed the morphology of the projection neurons of the frontal and pineal organs of the frog, Rana esculenta, by backfilling of the neurons with horseradish peroxidase through their cut axons. In the pineal organ, several types of centrally projecting neurons were observed: peripherally situated unipolar and multipolar neurons, the dendrites of which extend into a superficial axon plexus that surrounds the pineal epithelium; smaller unipolar, bipolar, or multipolar neurons situated close to the central pineal tract; and radially oriented bipolar neurons, with short dendritic processes oriented towards the lumen of the pineal organ.(ABSTRACT TRUNCATED AT 250 WORDS)

Habenular asymmetry and the central connections of the parietal eye of the lizard

Histochemical and autoradiographic analyses of the axonal transport of horseradish peroxidase and tritiated amino acids were employed to study the central connectivity of the lizard parietal eye. Somata and processes of centrifugal fibers to the parietal eye were localized in tissue of the dorsal sac and in the leptomeningeal sheath of the pineal gland. Analyses of series of transverse sections of the brain showed the left medial habenular nucleus to be subdivided into pars dorsolateralis and pars ventromedialis, and the right medial habenular nucleus not to be so subdivided. Centripetal fibers of parietal eye ganglion cells project to only the pars dorsolateralis of the left medial habenular nucleus and terminate there in two distinct fields. The asymmetry of the lizard habenula may be a specialization associated with the unilateral projection from the parietal eye.

Parietalectomy and thermal selection in the lizard Sceloporus magister

Lizards were acclimatized to various regimes of temperature (15 degrees, 35 degrees C) and photoperiod (LD 08:16, 16:8). Parietalectomized, sham operated, and control animals were placed in thermal gradients and their body temperatures monitored for periods of up to 15 days. Daily rhythms of thermal selection were evident with higher temperatures selected in late photophase and lower temperatures selected in scotophase. Thermal selection was more variable in scotophase than in photophase. Parietalectomized lizards chose significantly higher body temperatures than did shams or controls. Acclimatization to temperature and photoperiod had little or no effect on the thermal preferendum. The preferred body temperature of controls was 33.2 degrees C +/- 3.59. Length of time in the gradient tended to change thermal preference, especially in lizards acclimated to 15 degrees C. Through interactions with the pineal gland the parietal eye is probably important in synchronizing many bodily functions with photoperiod.

Body temperature of the lizard (Anolis carolinensis): effect of parietalectomy

Thermal behavior of parietalectomized, sham-parietalectomized or intact lizards (Anolis carolinensis) was recorded in a test chamber containing moving photothermal gradients. Following parietalectomy, animals chose significantly higher temperatures than sham-parietalectomized or intact control animals, which chose lower and statistically identical temperatures. When pre-surgical and post-surgical means are compared within groups, the eccritic temperature was 2.10 degrees C higher following parietalectomy, 0.72 degrees C higher following sham-parietalectomy, and 0.31 degrees C higher in intact controls during the post-operative measurements. The effects of parietalectomy indicate that the parietalpineal complex may be involved in behavioral thermoregulation by precisely regulating exposure to heat sources (e.g. sunlight).

Thermoregulatory function of the parietal eye in the lizard Anolis carolinensis

Animals were acclimitized to a daily cycle of 15-25°C and a photoperiod of LD 12:12. Parietalectomized animals in an experimental thermal gradient (15°C-40°C, LD 12:12) selected significantly higher temperatures than controls at all hours of the day except from 0800-1200. These results suggest that the lizard parapineal plays a direct role in thermoregulation in addition to the indirect function as an illuminometer.