Light-Induced Responses of Slow Oscillatory Neurons of the Rat Olivary Pretectal Nucleus

Abstract

BackgroundThe olivary pretectal nucleus (OPN) is a small midbrain structure responsible for pupil constriction in response to eye illumination. Previous electrophysiological studies have shown that OPN neurons code light intensity levels and therefore are called luminance detectors. Recently, we described an additional population of OPN neurons, characterized by a slow rhythmic pattern of action potentials in light-on conditions. Rhythmic patterns generated by these cells last for a period of approximately 2 minutes.MethodologyTo answer whether oscillatory OPN cells are light responsive and whether oscillatory activity depends on retinal afferents, we performed in vivo electrophysiology experiments on urethane anaesthetized Wistar rats. Extracellular recordings were combined with changes in light conditions (light-dark-light transitions), brief light stimulations of the contralateral eye (diverse illuminances) or intraocular injections of tetrodotoxin (TTX).ConclusionsWe found that oscillatory neurons were able to fire rhythmically in darkness and were responsive to eye illumination in a manner resembling that of luminance detectors. Their firing rate increased together with the strength of the light stimulation. In addition, during the train of light pulses, we observed two profiles of responses: oscillation-preserving and oscillation-disrupting, which occurred during low- and high-illuminance stimuli presentation respectively. Moreover, we have shown that contralateral retina inactivation eliminated oscillation and significantly reduced the firing rate of oscillatory cells. These results suggest that contralateral retinal innervation is crucial for the generation of an oscillatory pattern in addition to its role in driving responses to visual stimuli.

Acute effects of light on the brain and behavior of diurnal Arvicanthis niloticus and nocturnal Mus musculus

“…The OPN receives substantial input from melanopsin-containing cells in the retina [32], contains neurons that are capable of coding illumination levels [128] and it projects to at least one region that appears to play a role in masking, the IGL [129]. Additionally, removal of the OPN interferes with masking of REM sleep by darkness in albino rats [27].…”

Differential firing pattern and response to lighting conditions of rat intergeniculate leaflet neurons projecting to suprachiasmatic nucleus or contralateral intergeniculate leaflet

“…into the OPN only, which is passed from the OPN to IGL via a presumed glutamatergic innervation (Szkudlarek et al, 2012). The opposite direction of ISO transfer (i.e.…”

Gamma and infra‐slow oscillations shape neuronal firing in the rat subcortical visual system

“…Furthermore, this characteristic pattern is found in other structures of the subcortical visual system, such as the olivary pretectal nucleus, which is responsible for pupil constriction (OPN) (Szkudlarek et al . , ), and the suprachiasmatic nucleus of the hypothalamus, which comprises the master biological clock (SCN) (Miller & Fuller, ). The ISO pattern was shown to be synchronized in neurons innervated by the same (contralateral) eye and is dependent on retinal activity (Lewandowski & Blasiak, ; Szkudlarek et al .…”