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K Iwama

Publications and source records attributed to K Iwama.

At least 37 records · Page 2Linked to original sources
PubMed1978

Characteristics of optic nerve innervation in the rat superior colliculus as revealed by field potential analysis.

With lightly anesthetized rats, field responses to single optic nerve (ON) and optic chiasm shocks were studied in superficial layers of the superior colliculus, i.e., St. zonale (SZ), St. griseum superficiale (SGS) and St. opticum (SO). Based upon characteristics in the depth profile of the field response within the superficial layers, we identified three zones of N3, N2, and N1 from the SZ in this order. The narrow N2-zone was localized around the middle part of the SGS and less distinct than the other two zones. The N3-zone was characterized by a N3-wave and the N1-zone with N1- and P3-waves. N3- and P3-waves were activated by slowly conducting ON fibers (5.0 +/- 1.4 and 4.2 +/- 0.6 m/sec, respectively) while the N1-wave was by fastest conducting fibers (16.3 +/- 4.1 m/sec). According to recent Golgi studies, hypothetical mechanisms underlying the three waves were proposed: the N3-wave was ascribed to the activities of small vertical fusiform cells in the SZ or the upper half of SGS, the N1-wave to those of narrow field vertical cells which predominate in the lower half of SGS, and the P3-wave to those of wide field vertical cells whose somata are in the lower half of SGS or in the SO. The N3-, N1-, and P3-waves were found to differ from each other in recovery function tested with double ON shocks as well as in the topographical analysis of amplitudes through a whole extent of the colliculus. The three systems represented by the three waves were suggested to play different roles in visual information processing within the superficial strata.

Animals↗
PubMed1978

A four group classification of the rat superior collicular cells responding to optic nerve stimulation.

With lightly anesthetized rats, activities of single cells responding to single optic nerve (ON) shocks were recorded from the superficial layers of the superior colliculus, i.e., St. zonale(SZ), St. griseum superficiale (SGS) and St. opticum (SO). According to response latencies and recording depths, four classes of cells were identified: I-, II-, III-, and IV-cells. Class I cells, recorded in the SZ or the upper half of SGS, were innervated by slowly conducting ON fibers of velocities slower than 4 m/sec. Class II cells, recorded from the middle part of the SGS, were innervated by ON fibers of intermediate velocity (4--8 m/sec). Class III cells, recorded from the lower half of SGS or the upper part of SO, were innervated by fast conducting ON fibers (faster than 8 m/sec). Class IV cells were recorded from the depth similar to the class III but they were innervated by slowly conducting fibers (4-1.7 m/sec). Class I cells revealed a long-lasting inhibition after initial excitation, being a sharp contrast with cells of classes II and III which were almost free from inhibition. Inhibition exerted upon class IV cells were of intermediate strength. Possible anatomical correlates of the four classes of cells and hypothetical modes of their ON innervation were discussed.

Action Potentials↗
PubMed1978

Visual receptive-field properties of single cells in the rat superior colliculus.

Receptive-field properties were studied in single cells in the visual layer of the albino rat's superior colliculus. All the samples (N = 195) were identified as one of the four classes (I-, II-, III- and IV-cells) which were established previously on the bases of the response properties to single shocks to the optic pathway and of the recording sites. The four classes were located more deeply in the superior colliculus roughly in the order of from I to IV. Response latencies to single shocks to the optic chiasm were shortest in the III-cells, intermediate in the II-cells and longest in the I- and IV-cells. These cell classes turned out to be different from each other in a number of visual properties. 1) Receptive-field centers in the I- and II-cells (N = 26 and 27, respectively) were of either the ON-OFF or the ON type. Of class III (N = 47), one subgroup (IIIa) consisted mostly of the OFF type whereas the other (IIb) was made up mostly of the ON-OFF type. About two-thirds of the IV-cells (71/95) were of either the ON, the OFF or the ON-OFF type; except for two cells, the rest were all of the moving-sensitive type. 2) The average size of the receptive-field center was small (5.4 degrees +/- 2.3 degrees) in the class I, intermediate in the classes II and III (8.1 degrees +/- 2.1 degrees and 7.1 degrees +/- 2.7 degrees, respectively) and large in the class IV (18.1 degrees +/- 15.9). 3) Responsiveness to moving light stimuli (speeds, 40 degrees--90 degrees/sec) decreased in the order of IIIa, II and IIIb, and I and IV. 4) Maintained activity was lower in the superficially located cells (I, II and IIIa) than in the deeply located ones (IIIb and IV).

Afferent Pathways↗
PubMed1977

Disinhibition of perigeniculate reticular neurons following chronic ablation of the visual cortex in rats.

Effects of chronic ablation of the visual cortex (VC) were studied in the perigeniculate reticular neurons (PGR neurones) which were located in the thalamic reticular nucleus immediately adjacent to the dorsal nucleus of the lateral geniculate body and identified as the I-cells of Burke and Sefton. In rats with the intact VC the PGR neurons responded to single shock stimulation of the optic tract (OT) with bursts of spike spaced regularly. During the inter-burst period the neurons were inhibited, indicating that except for the primary spike burst, others were postinhibitory rebound excitation. In the VC-ablated PGR neurons there were no changes in the primary spike burst, but the remaining ones were very weak or sometimes missing, suggesting that the inhibition was poorly developed. With double shock stimulation of OT it was established that after showing the primary spike burst, the VC-ablated PGR neurons suffered a less intense inhibition than control. To a diffuse, sustained illumination, the normal PGR neurons showed on- and off- responses, whereas the VC-ablated ones were tonically activated during the presence of illumination. These findings were taken as indicating that the inhibitory mechanism for the PGR neurons were made less active after the VC had been ablated chronically.

Animals↗
PubMed1976

Optic nerve innervation of so-called interneurons of the rat lateral geniculate body.

In urethane-anesthetized rats, neurons responding to electrical stimulation of the optic nerve (ON) with bursts of spikes were searched for in the region of the thalamic reticular nucleus close to the dorsal nucleus of the lateral geniculate body (LGBd). These neurons were identical with those which had been presumed to be inhibitory internerons (I-cells) of LGBd. Conduction velocityes of ON fibers innervating I-cells were determined by measuring differences in response latency between stimulations of two separate sites along the contralateral ON. The velocity ranged from 1.9 to 7.3 m/sec with an average of 4.6 m/sec, indicating that among the three groups of ON fibers with different velocities, only the slowest group is involved in activation of I-Cells. Calculation of synaptic delays revealed that one group of I-cells was excited monosynaptically and another, disynaptically. Experiments on rats with the visual cortex chronically ablated provided evidence that the disynaptically excited I-cells received ON impulses via axon collaterals of principal cells of LGBd. The region of the thalamic reticular nucleus containing I-cells was found to receive inputs not only from the contralateral but also from ipsilateral ON.

Animals↗
PubMed1975

Pyramidal tract control over cutaneous and kinesthetic sensory transmission in the cat thalamus.

In the thalamic ventrobasal complex (VB) of the cat, effects of electrical stimulation of the pyramidal tract (PT) upon activities of 112 relay cells and 18 internuncial cells were examined. Single PT shocks to the cerebral peduncle elicited short-latency discharges in 31 relay cells (mean latency, 1.4 +/- 0.5 msec). When weak PT stimuli were employed as conditioning shocks, facilitatory effects upon responses to medial lemniscal (ML) stimulation were observed. It was revealed that VB relay cells were excited monosynaptically via collaterals of the fast PT fibers. Among 31 PT-excited cells 22 were fired by movements of joints (joint-movement units) and they made up 88% of all the joint-movement units. A majority of the relay cells responding to stimulation of hairs (hair units) did not receive excitatory effects from PT, except some special ones which represented long hairs at the distal or proximal end of the forearm-forepaw. In 44 relay cells repetitive PT shocks suppressed both evoked responses to ML stimulation and spontaneous discharges for 70--100 msec. Of these, 34 were hair units. The PT-induced inhibition in the hair units increased as their receptive fields shifted from the trunk towards the digits. Some intracellular recordings showed that the PT-induced inhibition was due to IPSPs generated disynaptically. Among 18 interneurons presumed to be inhibitory 10 responded with short latencies to PT stimulation. These were mostly the interneurons which presumably subserve the recurrent collateral inhibition in VB.

Animals↗