Electrophysiology of nitrous oxide on cerebellar granule cells: a single-cell study

We recorded 18 single cells in the granule cell layer of the cat. Each single cell was screened and identified as a granule cell based on a set of criteria derived from known electrophysiological properties of granule cells. We then monitored the effects of nitrous oxide on the spontaneous activities and the auditory responses of these cells. Nitrous oxide consistently caused a severe inhibition of spontaneous activities as well as responses to sound in these cells. Furthermore, the amplitudes of their action potentials decreased during the inhibition. Three of the 18 cells were subsequently injected intracellularly with HRP. All three were verified to be granule cells. In those granule cells we recorded intracellularly, nitrous oxide did not change the resting membrane potentials. The gradual decrease in the amplitudes of action potentials suggested that some of the mechanisms leading to the genesis of action potentials were being altered by nitrous oxide. It is also possible that nitrous oxide may act on synaptic transmission at a site located postsynaptically on the granule cells.

Nitrous oxide inhibits auditory and visual responses of granule cells in the cerebellum

Much of the laboratory investigation on the auditory and visual areas of the posterior vermis has been carried out under barbiturate anesthesia. It is now known that barbiturates potentiate GABA inhibition by binding directly to the GABA receptor protein. Since GABAergic receptors are present in many cell types of the cerebellar cortex, barbiturate anesthesia is likely to interfere severely with cerebellar physiology. We have examined auditory and visual responses in granule cells in the cerebellum of the cat under nitrous oxide anesthesia. To our surprise, nitrous oxide abolished auditory as well as visual responses in the granule cell layer in the posterior vermis. However, both auditory and visual responses recovered after the cessation of nitrous oxide.

Auditory receptive area in the cerebellar hemisphere is surrounded by somatosensory areas

We mapped the neuronal discharges in response to sound in the granule cell layer of the cerebellar hemisphere of the rat. An auditory receptive area was located in the lateral part of Crus IIb. The size of the auditory area was approx. 1 mm2. It was surrounded by somatosensory receptive areas representing the regions in and around the mouth, particularly the lips, the incisors, and areas inside the mouth. Frequency selectivity of neurons in the auditory area was so broad that it resembled the audiogram of the ear of the animal. The auditory responses were not particularly sensitive to binaural intensity differences. On the basis of the response properties of these neurons to sound and the receptive field properties of the adjacent somatosensory areas, we suggest that the function of the auditory area in the cerebellar hemisphere may be in the control of movements involved in vocalization.

Two types of thalamic reticular cells in relation to the two visual thalamocortical systems in the rat

We found in urethane-anesthetized rats that thalamic reticular (TR) cells responding to an electrical stimulus of the optic tract (OT) can be further subdivided into two types, viz. S- and L-type cells. S-type cells, which were selectively excited from area 17 of the visual cortex, were characterized by short latency responses (2.3-6.1 ms) to OT stimulation. TR cells activated antidromically from the dorsal lateral geniculate nucleus were all classified as S-type. Long OT latencies (5.2-15.3 ms) and selective excitation from area 18a were peculiar to L-type cells, which showed antidromic responses to the lateral posterior nucleus stimulation. Mapping studies documented that cells belonging to each type were segregated in the thalamic reticular nucleus; L-type cells were located in the most posterior part. It is suggested that S- and L-type cells are inhibitory interneurons modulating activity of geniculocortical and extrageniculocortical projection cells, respectively.

Alpha and beta cells projecting from retina to lamina A of the lateral geniculate nucleus in normal cats, monocularly deprived cats, and young kittens

We strictly limited small injection of horseradish peroxidase (HRP) to lamina A of the lateral geniculate nucleus of cats. This was done to label retrogradely only the alpha (Y) and beta (X) classes of retinal ganglion cell. Eighty-six such injections at a range of matched eccentricities were made bilaterally in 9 normal adult cats, 7 cats reared from birth to adulthood with monocular lid suture, and 9 normal kittens at 4 weeks of age; 5348 alpha and beta cells were retrogradely labeled from these injections. Quantitative measurements were made from these labeled cells and compared among 4 experimental conditions, these being normal adult retinas, the nondeprived and deprived retinas of lid sutured cats, and the retinas of kittens. Each injection led to a similar relative ratio of labeled alpha and beta cells (typically 5-15% alpha cells) that did not differ significantly among the experimental conditions, but further analysis suggested a slight diminution of labeled alpha cells in deprived retinas. Because the larger arbors of retinogeniculate Y axons are more likely to penetrate small geniculate HRP injection sites from eccentric locations than would be the case for the more restricted arbors of X axons, a normal tendency resulted for the peripheral halo of zones of retrograde labeling to be dominated by alpha cells. Thus a more accurate reflection of the relative numbers of labeled alpha and beta cells would result from considering only the core of zones of retrograde labeling. When this is done, deprived retinas exhibited relatively fewer labeled alpha cells than did normal, nondeprived, or kitten retinas. This may relate to prior observations (Sur et al. 1982) that abnormally few Y axons from the deprived retina innervate lamina A. No statistically significant differences in alpha or beta cell size were seen among normal, nondeprived, and deprived retinas, although both of these cell types in the kittens were equally smaller than their normal adult counterparts. This is particularly interesting in view of the postnatal growth of retinogeniculate axon arbors (Sur et al. 1984). The results are not surprising for alpha cells, since retinogeniculate Y axon arbors grow considerably after 4 weeks of age, but they are surprising for beta cells, since retinogeniculate arbors of X axons decrease after 4 weeks of age. This suggests no clear, general relationship between soma size and the extent of a cell's axonal arbor.(ABSTRACT TRUNCATED AT 400 WORDS)

Electron microscopic analysis of amacrine and bipolar cell inputs on Y-, X-, and W-cells in the cat retina

In the cat retina, bipolar and amacrine cell inputs were analyzed electron microscopically in 5 ganglion cells (two Y-cells, two X-cells and one W-cell) that were well-isolated and had clear morphological features. For Y- and X-cells, subtypes of a and b were further identified according to the sublamina of the inner plexiform layer in which their dendrites extended. Y-a and Y-b ganglion cells had large somas, thick axons, and several thick dendrites that branched extensively with a large dendritic field. X-a and X-b cells had medium-sized somas, medium-sized axons and extremely narrow dendritic fields. The W-cell studied had a medium-sized soma, a medium-sized axon, and extremely thin dendrites that extended widely. For each of the 5 ganglion cells, ultrathin serial sections were made to study relative occurrence of amacrine and bipolar synapses in whole length of dendrites. About 50% of the terminals were bipolar in the Y-a and Y-b cell dendrites, 36-38% in the X-a and X-b cell dendrites, whereas only 19.7% were bipolar in the W cell dendrites. Bipolar terminals tended to make synaptic contacts with the distal dendrites of Y- and W-cells.

Temporary double representation in expanded ipsilateral retinocollicular projection of neonatally one-eye-removed rats

Retinotopic representations of the expanded projection to the ipsilateral colliculus were studied in albino rats of various ages after neonatal unilateral eye removal. Besides the projection from the lower temporal retina the projection from the central retina was observed in 3-6 month-old one-eyed rats. Such double retinotopic representation was not observed in 1-month- or 1-year-old one-eyed rats. A postnatally growing temporary process was suggested for the expanded ipsilateral retinocollicular projection in rats.

Morphological correlates of Y, X and W type ganglion cells in the cat's retina

After physiological recordings with microelectrodes containing horseradish peroxidase (HRP), morphological properties of Y, X and W type ganglion cells were studied on flat-mounted cat's retinas. While all the Y cells (N = 9) and the X cells (N = 8) revealed alpha and beta cell morphologies of Boycott and Wässle [J. Physiol. 240, 397-419 (1974)], respectively, W cells (N = 4) revealed various morphological types including their gamma and delta cells. The Y cells were larger than X cells in soma diameter, but the W cells were of the same range as X cells. Electron microscopic observations of the cross-sectioned nerve fiber bundles provided evidence for the segregation of axon diameters into the three groups corresponding to Y, X and W axons. It was discussed that functional trichotomy of retinal ganglion cells is related to the differentiation more in axon diameter rather than in soma size.

Morphological correlates of physiologically identified Y-, X-, and W-cells in cat retina

The action spike activities of single ganglion cells were recorded from the nasal retina of the intact eye of anesthetized and immobilized cats. Each ganglion cell was identified as a Y-, X-, or W-cell on the basis of its axonal conduction velocity, its receptive-field properties, and the level of maintained activity. Of about 100 ganglion cells physiologically identified and penetrated with horseradish peroxidase (HRP)-containing glass microelectrodes, 21 cells were subsequently identified in flat-mount preparations of the retinas and processed for detection of HRP. Of a total of nine Y-cells recovered, four had been penetrated at the soma and five at the axon. All had the morphology of the alpha-cell of Boycott and Wässle. Eight X-cells recovered. All had been penetrated at the soma and showed beta-cell morphology. Four W-cells were penetrated at the soma and recovered. Two off-tonic W-cells had small somas (15-16 micron in diam) and sparse dendritic fields, resembling gamma-cells of Boycott and Wässle. They are also similar to "G4" and "G18" of Kolb et al.'s classification. One on-tonic W-cell had somewhat larger soma (18 micron) with a relatively densely branched dendritic field. This corresponds to delta-cell of Boycott and Wässle or to "G15" of Kolb et al. One on-off phasic W-cell had a medium-sized soma (25.3 micron) with a fanlike dendritic expansion characteristic of the "unilateral horizontal broad range cell" of Shkolnik-Yarros or of "G22" of Kolb et al. Alternatively, all these W-cells can be called medium-sized gamma-cells. Among all three classes of ganglion cells, a positive correlation was found between the diameter of the receptive-field center and the dendritic field. Assuming that in the cat retina 1 degree of visual angle = 230 micron, dendritic fields of Y-cells seemed larger than their physiologically determined receptive-field centers. By contrast, the reverse relation was found between these two dimensions in X-cells. Axon diameters ranged from 4.0 to 5.6 micron (mean, 4.5 micron) in Y-cells and from 1.9 to 2.7 micron (mean, 2.2 micron) in X-cells. Three W-cells showed axon diameters of 0.6, 1.1, and 1.8 micron. The axon diameter distributions made from axons labeled by massive injections of HRP into the optic nerve fiber layer showed a pattern of distribution similar to that obtained from physiologically identified Y-, X-, and W-cell axons.

Retinotopic organizations of the expanded ipsilateral projection to the rat's superior colliculus; variations along its rostrocaudal axis

The retinotopic organization of the expanded projection to the ipsilateral colliculus was studied electrophysiologically in 12 adult albino rats with one eye removed at birth. For comparison, the contralateral projection was rather variable in the representation of the nasotemporal axis of the retina along the rostrocaudal dimension of the colliculus; on the other hand, the representation of dorsal-to-ventral retinal axis onto the mediolateral dimension of the colliculus was relatively stable.

The relation between axon diameter and axonal conduction velocity of Y, X and W cells in the cat retina

Axon diameters of ganglion cells were measured electronmicroscopically from the cross-sections of the optic nerve fiber layer in the cat retina. The diameter distribution revealed 3 well-separated groups which correspond to axons of Y, X and W cells. Mean intraretinal axonal conduction velocities were estimated physiologically for the 3 classes. Between the means of axon diameter (D, micron) and conduction velocity (V, m/s) the following positive correlations were obtained: V = 3.85 square root D-2.3 when short axes of cross-sections were measured, and V = 3.33 square root D-2.3 when long axes were measured.

Plastic changes in the distribution and soma size of retinal ganglion cells after neonatal monocular enucleation in rats

Using the method of retrograde labeling of ganglion cells with HRP, we studied in adult rats the plastic changes in the retinogeniculate projections due to monocular enucleations shortly after birth. Four normal and 6 neonatally enucleated rats were used. In two of the normal and 4 of the enucleated rats a small amount of HRP was injected into the dorsal lateral geniculate nucleus (LGd) and in 4 other rats massive injections were made into the optic tract near the LGd. Neonatally unilaterally eye-enucleated rats were characterized by an expanded distribution of ipsilaterally projecting ganglion cells all over the retina of the remaining eye and by a densely packed distribution of these cells in the lower temporal retina in which area these cells have only a moderate density in normal rats. On the contrary, in the lower temporal retina of monocularly enucleated rats the incidence of contralaterally projecting ganglion cells was decreased. Soma areas of ipsi- and contralaterally projecting ganglion cells were measured for the peripheral crescent in lower temporal and lower nasal retinas. As compared with normal rats, neonatally enucleated rats had a larger mean soma area of ipsilaterally projecting cells and a smaller mean soma area of contralaterally projecting cells. This result was interpreted as suggesting that after neonatal monocular enucleation medium to large cells had changed their side of axonal projection from the contralateral to ipsilateral LGd.

Bilateral changes in soma size of geniculate relay cells and corticogeniculate cells after neonatal monocular enucleation in rats

Soma areas of relay cells of the lateral geniculate nucleus and of corticogeniculate cells of normal rats (n = 4) were compared with those of neonatally unilaterally eye-enucleated adult rats (n = 13). These cells were labeled by retrogradely transported HRP. Monocular enucleation was performed on postnatal days 1 (PND 1) (n = 4), 3 (PND 3) (n = 5) and 6 (PND 6) (n = 4). The results are summarized as follows. In PND 1 rats soma areas of relay cells were 12-16% smaller than those of normal rats, but only for the geniculate nucleus ipsilateral to the remaining eye. In PND 3 and 6 rats the areal shrinkage of relay cells was 27-39% of the normal control for both hemispheres, though it was less marked in the hemisphere contralateral to the remaining eye. The corticogeniculate cells were distributed in layers V and VI in eye-enucleated rats as well as in normal rats. Soma areas of both layer V and VI cells increased in PND 1 rats for both hemispheres by about 15-47% of the normal control. In PND 3 rats increase in soma size tended to occur for layer VI cells, although the data varied from animal to animal. In summary, it was established that unilateral eye-enucleation in rats at birth induced soma size changes of the geniculate relay cells and of the corticogeniculate cells in the non-deafferented as well as in the deafferented hemisphere. Possible mechanisms for the bilateral changes in soma area of central visual cells after neonatal monocular enucleation are discussed.

Sensitivity to GABA of neurons of the dorsal and ventral lateral geniculate nuclei in the rat

GABA was applied iontophoretically to dorsal and ventral lateral geniculate (LGd and LGv) neurons in rats. Spontaneous discharges were readily suppressed in both species of neurons. While in LGd neurons, evoked discharges by optic nerve stimulation were suppressed as readily as were spontaneous discharges, LGv neurons were characterized in that evoked discharges were much more resistant than spontaneous discharges.

Properties of ipsilateral retinogeniculate afferents in albino and hooded rats

By recording single unit activities from the dorsal lateral geniculate nucleus in albino and hooded rats, physiological properties of the ipsilateral retinogeniculate afferents were compared with those of the contralateral ones. The results show that the ipsilateral retinogeniculate pathway was characterized by intermediate conduction velocities, relatively high incidence of the tonic response and the visual field representation of central 30 degrees from the vertical midline on both sides.