Search

The topical and laminar distribution of corticotectal cells, as well as their size and morphology, were studied in the macaque monkey with the horseradish peroxidase (HRP) technique. After HRP injections restricted primarily to the superficial layers of the colliculus, labelled cells were found in visual cortex (areas 17, 18, and 19) and both in the frontal eye field (area 8) and the adjacent part of premotor cortex (area 6). The clustering of labelled cells in visual cortex indicated that each of the anatomically and functionally distinct visual areas has its own set of collicular projections. When intermediate and deeper layers of the colliculus were injected, labelled cells were found also in posterior parietal cortex (area 7) where they were concentrated mainly on the posterior bank of the intraparietal fissure, in inferotemporal cortex (areas 20 and 21), in auditory cortex (area 22), in the somatosensory representation SII (anterior bank of sylvian fissure, area 2), in upper insular cortex (area 14), in motor cortex (area 4), in premotor cortex (area 6), and in prefrontal cortex (area 9). In the motor and premotor cortex, labelled cells formed a continuous band which appeared to stretch across finger-hand-arm-shoulder-neck representation. Similarly, the cluster of labelled cells in area 2 may correspond to the finger-hand representation of SII. The cortical regions not containing labelled cells were the somatosensory representation SI (areas 3, 1 and 2) and the infraorbital cortex. Labelled cells were restricted to layer V of all cortical areas except in the primary visual cortex, where labelled cells were found in both layer V and layer VI. The size spectrum of corticotectal cells ranged from 14.8 micron (average diameter) in area 17 to 27.8 micron in area 6, comprising cells as small as 8 micron and as large as 45 micron. Labelled cells in posterior parietal (area 7), in auditory (area 22), and in motor cortex (area 4) were small and distributed over only a narrow range of sizes. Those in premotor cortex (area 6) were often large and had a wide range in size distribution. The differences in size and morphology of corticotectal neurons suggest that they do not form a uniform class of neurons.

Recordings were made from 180 single cells, or cell clusters, in the Clare-Bishop area of two Siamese cats. In one cat, the corpus callosum had been sectioned prior to recording and all cells were driven by the contralateral eye exclusively. In the other recordings were made before and after callosal section. Before callosal section, most cells were binocularly driven but dominated by the contralateral eye. There were striking examples of binocular interaction and some cells could only be activated by simultaneous binocular stimulation. After callosal section, cells were driven by the contralateral eye only. The same experiment performed in a normal cat revealed no change in binocularity following section of the corpus callosum. We conclude that one of the functions of the corpus callosum in the Siamese cat is to generate binocular neurons.

Omnipause neurons take part in the generation of saccadic eye movements. They lie around the midline in the caudal pontine reticular formation, in an area usually ascribed to the nucleus raphe pontis (rp). In this study of the monkey (Macaca fascicularis and M. mulatta), we describe four series of experiments aimed at establishing that omnipause neurons lie within a distinctive cytoarchitectonic entity, which we call the nucleus raphe interpositus (rip): (1) cytoarchitectural study, (2) recording-lesion experiments to establish in which cell group omnipause neurons lie, (3) cytochrome oxidase distribution in the omnipause region and neighboring structures, and (4) neuroanatomical tracing experiments to demonstrate afferents to the omnipause region. In the detailed cytoarchitectural study of the midline structures in the caudal pons and rostral medulla, a distinctive group of neurons (rip) adjoining the ventrocaudal border of rp and dorsal to the nucleus raphe magnus (rm) is described. The striking features of rip are the uniformly arranged, narrow row of the cells either side of the midline, and the extensive horizontally oriented dendritic trees of its neurons. The abducens rootlets (NVI) pass through the reticular formation at the same rostrocaudal level as rip and form a reliable landmark for its location. Cytochrome-oxidase-stained sections demonstrated additional differences between rip and adjacent cell groups: in rip the neurons and their extensive dendrites stained strongly, but not the surrounding neuropile, whereas in rp both the neurons and the neuropile stained darkly, so that individual neurons were difficult to see. Unlike rp, rip coincides with the location of omnipause neurons, and lesions marking the sites of individual omnipause units lay within its boundaries. Tritiated leucine was injected into superior colliculus (sc), which is known to have monosynaptic connections with omnipause neurons. Labelled axons and patterns of silver grains taken to indicate the presence of terminal branching were found in and around rip, but no significant labelling was seen in rp or rm. It is concluded that the omnipause neurons lie within the rip in the monkey. These functional and morphological differences between rip and the adjacent raphe nuclei are used to justify its characterization as an independent cell group in the monkey. In order to relate these findings to man, cytochrome oxidase experiments were carried out on the human brainstem, and the pattern of staining at the level of the abducens rootlets was correlated with the cytoarchitecture.(ABSTRACT TRUNCATED AT 400 WORDS)

We report here that diazepam (Valium, Roche) has an inhibitory effect on proliferation of synchronously dividing cultures of Dunaliella, whenever the drug is added during the cell cycle. The drug induced an accumulation of abnormal mitotic figures after 17 to 24 hr of treatment with the chromosomes distributed around the nuclei and a monopolar spindle, although the pole-to-chromosome microtubules were well-formed. Diazepam seemed to affect mitosis by inhibiting the separation of the basal bodies, whose duplication was perturbed in a dose-related manner. After 48 hr of treatment, the nucleus returned to interphase without having undergone mitosis, but cytokinesis might have taken place. The mechanism of this action of diazepam on mitosis remains to be elucidated. However, it does not appear to act in the same way here as it does on the central nervous system.

An otolith disorder is described in a patient with a subluxed stapes footplate. Otoneurological examination, including tympanoscopy, showed that nonphysiological mechanical stimulation of the otoliths by a (pathologically) hypermobile stapes footplate typically manifests with a pattern of sound-induced paroxysms of ocular tilt reaction (OTR), oscillopsia and postural imbalance (otolith Tullio phenomenon). The rare condition of sound-induced otolithic stimulation in an otherwise healthy young man offered a unique opportunity to investigate otolith reflex control of the eye, head and posture in man. Electro-oculographic recordings and special video analysis (time resolution: 1000 images/s) revealed an initial rapid and phasic counterclockwise rotatory upward deviation with a latency of 22 ms, followed by a smaller tonic effect which lasted as long as sound stimulation (480 +/- 20 Hz, 95 dB A). Latencies of the otolithic vestibulospinal reflex, recorded using surface EMG during upright stance with the eyes closed, were surprisingly short with activation of the ipsilateral tibialis anterior muscle 47 ms after the stimulus, and of the ipsilateral gastrocnemius muscle after 52 ms. A considerable postural pertubation was measured by means of a Kistler platform, with the shortest latency for displacement of the centre of pressure of 80 ms and a preferred body sway direction from right-backward to left-forward. When the Valsalva manoeuvre was performed, tonic eye movements and oscillopsia were induced opposite in direction to those produced by the sound reflecting a push-and-pull deviation of the otoliths.