Thomas E. Ogden

The oscillatory waves of the primate electroretinogram

Abstract A study of light evoked oscillatory intraretinal and optic tract (OT) potentials was carried out in monkeys. Intraretinal depth and electrode marking studies suggest that the oscillatory waves of the ERG are generated in the inner ptexiform layer. The amplitude of the intraretinal ERG oscillatory waves varied linearly with log stimulus intensity and inversely with log intensity of an adapting light. The wavelets of the OT could be dissociated from those of the intraretinal ERG by intracarotid injections of barbiturate and differential effects of adapting lights. Tetrodotoxin blocked ganglion cell discharge without altering the intraretinal ERG wavelets. Deep Metofane anesthesia blocked the retinal wavelets without altering antidromic ganglion cell activity (P-wave). Spontaneous oscillations, prominent in the OT, were never observed in the retina. Evidence is presented to suggest that the OT oscillations result from massed activity of the larger fibers of the OT whose cells of origin are widely dispersed in the retinal periphery. The retinal wavelets were reduced in amplitude by repetitive stimulation of OT and chronic dennervation of the retina. These findings are discussed in terms of the membranes most likely involved in wavelet generation.

Studies of the optic nerve of the rhesus monkey: nerve fiber spectrum and physiological properties.

Abstract This report describes a combined study of the anatomy and physiology of the optic nerve of the rhesus monkey. An optic nerve was fixed in osmium tetroxide and embedded in epon for the histological study: 60,898 fibers were measured and tabulated according to outside diameter. The fiber spectrum was unimodal with a peak frequency at 1.2 μ and a range of 0.4–6 μ. The total number of fibers was 1,410,000. The compound action potentials of the entire optic nerve and of small fascicles of the optic nerve were recorded at the optic disk: conduction velocities, recovery cycles and afterpotentials were studied. These properties of the nerve fibers showed a continuous range of values which were associated with differences in fiber diameter. It is concluded that the fibers of the optic nerve form a homogeneous population; thus the anatomical and physiological findings are not in conflict. Differences between the properties of fibers in the optic nerve and in the retina are described and discussed in terms of the known ultrastructure of the retinal nerve fiber layer.

Cortical control of thalamic somato-sensory relay nuclei ☆

Abstract 1. 1. In cats deeply anaesthetised with Nembutal, depression of evoked responses in the thalamic somato-sensory relay nuclei by a preceding penicillin evoked discharge from somato-sensory cortex I has been described. 2. 2. The site of this depression has been located within the thalamic relay nuclei. 3. 3. A subconvulsive dose of strychnine given intravenously has been shown to abolish the depression, and cause enhancement by a preceding penicillin-evoked cortical discharge of the thalamic evoked responses. 4. 4. It is postulated that the penicillin evoked cortical discharge causes intense firing in cortico-thalamic neurones which have both inhibitory and excitatory synaptic endings in the somato-sensory relay nuclei, the inhibitory synapses predominant. The action of strychnine is inferred to be the selective blockade of the inhibitory synapses which in turn unmasks the excitatory activity, and changes inhibition of thalamic activity to facilitation. 5. 5. It is stressed that the functions of such a specific system of afferent control is probably quite different from that of the more general regulation exerted by the brainstem reticular formation.

The proximal negative response of the primate retina

Abstract The proximal negative response (PNR) of the mangabey and owl monkey has been studied by intraretinal recording. The primate PNR is best recorded from the inner plexiform layer, has a limited dynamic range (2 log 10 units), is spatially restricted and inverts in polarity with stimuli eccentrically placed or larger than 75 μ. The level of maximal amplitude of the PNR was slightly more proximal within the retina than the level of maximal amplitude of the P-wave , a slow potential evoked within the inner plexiform layer by electrical stimulation of the optic tract. Thus the distribution of these two responses in depth was different.

A technique for beveling fine micropipettes.

Abstract A technique is described for the production of extremely fine micropipetes for intracellular recording.