Gaze-stabilizing deficits and latent nystagmus in monkeys with early-onsetvisual deprivation: Role of the pretectal NOT

We studied the role of the pretectal nucleus of the optic tract (NOT) in th e development of monocular optokinetic nystagmus (OKN) asymmetries and late nt nystagmus (LN) in two monkeys reared with binocular deprivation (BD) cau sed by binocular eyelid suture for either the first 25 or 55 days of life. Single-unit recordings were performed in the right and left NOT of both mon keys at 2-3 yr of age and compared with similar unit recordings in normally reared monkeys. We also examined ocular motor behavior during electrical s timulation of the NOT and during pharmacological inactivation and activatio n using GABA(A) agonists and antagonists. In BD animals a large proportion of NOT units was dominated by the contralateral eye, in striking contrast t o normal animals where 100% of NOT units were sensitive to stimuli delivere d to either eye. In the 55-day BD animal no binocularly sensitive neurons w ere found, while in the 25-day BD animal 60% of NOT units retained at least some binocular sensitivity. Differences in direction sensitivity were also observed in BD animals. We found that 56% of units in the 55-day BD monkey and 10% of units in the 25-day BD monkey responded preferentially to contr aversive visual motion. In contrast, only 5% of the NOT units encountered i n normally reared monkeys respond preferentially during contraversive visua l motion, the rest were most sensitive to ipsiversive visual motion. NOT ne urons of BD monkeys showed a wide range of speed sensitivities similar to t hat of normal monkeys. Unilateral electrical stimulation of the NOT in BD a nimals induced a conjugate nystagmus with slow phases directed toward the s ide of stimulation. When we blocked the activity of NOT units with muscimol , a potent GABA(A) agonist, LN was abolished. In contrast, LN was increased when spontaneous activity of the NOT was enhanced with bicuculline, a GABA (A) antagonist. Our results indicate that the NOT in BD monkeys plays an im portant role in the OKN deficits and LN generation during monocular viewing . We hypothesize that the large proportion of units dominated by the contra lateral eye contribute to the development of monocular OKN asymmetries and LN.