On and off activity in the retinal and tectal responses to focal stimulation with uniform or patterned stimuli

V. Porciatti, P. Bagnoli, R. Alesci

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Abstract

Electrical potentials were recorded in pigeons form the cornea and the tectal surface in response to focal stimulation of the fovea centralis. Stimuli consisted of: (i) On-Off luminance modulation of a uniform field surrounded by a larger steady field of the same mean luminance and (ii) onset-offset presentation of vertical sinusoidal gratings of various spatial frequencies. Patterned stimuli had the same field size and mean luminance as the uniform field. Retinal (ERG) and tectal (TEP) potentials were recorded before and after intravitreal injections of two glutamate analogues: 2-amino, 4-phosphonobutyric acid (ABP) and cis 2,3-piperidinedicarboxylic acid (PDA). ABP has been reported to selectively block the activity of depolarizing bipolar cells and responses in On channels of different species. PDA has been reported in the Necturus to selectively block cone input to hyperpolarizing bipolar cells and horizontal cells. Uniform field ERG's consisted typically of a-, b- and d-waves. Pattern ERG's (P-ERG's) consisted of a positive wave at both onset and offset of the pattern. Onset and offset potentials had remarkably similar amplitude. Uniform field TEP's showed a predominant negative wave at both light onset and light offset. The offset potential was of much larger amplitude than the onset potential. Pattern TEP's consisted of a main negative wave at both onset and offset of the pattern. Like the P-ERG's, onset and offset pattern TEP's (P-TEP's) were similar in amplitude. One hour after intravitreal ABP injection (400 μM at the retina) the ERG b-wave was lost whereas either the PIII or the d-wave were enhanced. The P-ERG was relatively unchanged. The P-TEP's were also relatively unchanged whereas the uniform field TEP's showed a marked enhancement of the offset potential. Full recovery of ERG's and TEP's occurred 6 h post-injection. One hour after intravitreal PDA injection (6 mM at the retina) the ERG b-wave was markedly enhanced, whereas both the d-wave and the P-ERG were reduced in amplitude. P-TEP's were also reduced in amplitude. Uniform field TEP's showed a striking enhancement of their onset potentials whereas offset potentials were reduced and delayed. Recovery of ERG's and TEP's to pre-injection values occurred after 18 h. The results suggest: (i) the b-wave of the focal ERG and the P-ERG are related to different retinal events, (ii) On activity is not necessary for the generation of P-ERG's and P-TEP's and (iii) P-ERG's and P-TEP's appear related mainly to Off activity.

Original languageEnglish (US)
Pages (from-to)93-102
Number of pages10
JournalClinical Vision Sciences
Volume2
Issue number2
StatePublished - Jan 1 1987

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ASJC Scopus subject areas

  • Ophthalmology

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