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This study summarizes the nervous circuitry of the lateral nucleus from evidence presented in the previous papers in this investigation. The large and small neurons receive three types of extracerebellar afferent fibers-collaterals of climbing fibers and mossy fibers on their way to the cerebellar cortex, and fluorescent CAT fibers of two varieties. The large projection neurons receive a large inhibitory corticonuclear input via synapses of Purkinje cell axons upon their somatic and dendritic surfaces, as well as upon initial axonal segments. On their way into the superior cerebellar peduncle, the axons of these neurons send recurrent collateral branches, which provide a positive feedback circuit within the nucleus. The small inhibitory interneurons depend to a large extent on the activating input upon their dendrites; their corticonuclear input from Purkinje cells is less numerous than that of large neurons. Their myelinated axons provide a rapid system of internal inhibitory control. In cases in which the axons are long and leave the nucleus, like those emitted by the small neurons in the medial hilus zone, they may provide a route of internuclear communication. The arrangements of neurons in the columnar zone are reviewed. The large neurons are oriented at an angle to incoming extracerebellar fibers and present a profile to the Purkinje cell axon. The interneuronsare tilted at ninety degrees to the dendritic trees of the large neurons, and they receive a larger extracerebellar afferent input. Whereas the corticonuclear input to the large columnar neurons probably expresses a ratio of one Purkinje cell to one large neuron, the tilt assumed by the small neurons may increase this ratio. Electron microscopy has shown that small neurons receive a smaller corticonuclear input than large neurons. Elsewhere in the swirled zones of the nucleus, these influences are less precisely oriented, and therefore less restrictive interplay exists between corticonuclear influences and the large multipolar neurons. [ABSTRACT FROM AUTHOR]

The embryonic cerebral cortex was examined for signs of a columnar organization. In vertical montages extending from the intermediate lamina to the pia, nerve cells arranged in columns are separated by bundles of radial processes. However, sections tangential to the pial surface revealed little evidence for repeating modular units; bundles of radial processes are not regular in outline, and surrounding groups of cells display little symmetry in their distribution. Tangential processes representing the development of a rudimentary neuropile are present in the marginal lamina and at lower levels of the cortical plate. However, well defined synapses were not seen at this stage of development when proliferation and migration of neuroblasts continues to provide cells to the upper part of the cortical plate. The association of neuroblasts with bundles of radial fibers suggests that these vertical elements serve as preferential pathways for cells migrating to the cortex. [ABSTRACT FROM AUTHOR]

Blinded rats with either no preoperative training, preoperative training to criterion, or 100% overtraining were tested for the ability to make tactile discriminations after somatosensory cortical lesions or control operations. Postoperative deficits on the first tactile discrimination (retest) varied with the amount of preoperative training. Animals having no preoperative training showed the most severe deficits, and although trained and overtrained lesion groups did not differ from each other, only the overtrained rats with lesions did not differ from controls. All three lesion groups performed poorly in postoperative acquisition of a new and more difficult tactile discrimination. These data suggest that postoperative performance on a given task may vary as a function of the amount of preoperative training on that task, but that increased practice on one discrimination may not minimize lesion effects on a new, more difficult problem in the same modality. [ABSTRACT FROM AUTHOR]

Rats with histologically confirmed bilateral lesions of one or both somatosensory cortical areas, occipital cortex, or sham operations were tested in a T-maze for the ability to relearn five tactile discriminations acquired before surgery. Although some lesioned rats were slow in relearning the discriminations, almost all animals mastered each of the problems in the allotted time, and analyses of variance failed to reveal group differences in errors to criterion on any of the tasks. Results contrast with severe deficits obtained in acquisition experiments under otherwise similar conditions. [ABSTRACT FROM AUTHOR]

Rats with histologically confirmed bilateral lesions of one or both somatosensory cortical areas, occipital cortex, or sham operations were tested in a T-maze for retention of 29° vs. 39° C and 29° vs. 34° C temperature discriminations, and for acquisition of a 29° vs. 31° C habit. Statistical analyses failed to reveal group differences on the three postoperative discriminations. The suggestion that thermal habits are mediated by a diffuse and redundant forebrain afferent system is discussed. [ABSTRACT FROM AUTHOR]

In cats under pentobarbitone anaesthesia, GABA was tested on cortical, pericruciate neurones and its action compared with IPSPs evoked by surface stimulation. GABA was applied to individual cells by microiontophoresis, while recording the membrane potential and resistance. When K citrate-recording electrodes were used, GABA always hyperpolarized the cell and lowered its resistance, like the synaptic inhibitory effect. By adequate polarization both the action of GABA and the IPSP could be reversed, at a similar level of membrane potential. Both could also be reversed by injecting Cl into a cell from a KCl recording electrode and the new reversal potentials also did not differ significantly from each other: after this treatment, some cells could be excited with GABA. All these effects of GABA were only seen when it was applied outside the neurones; intracellular injections were ineffective. Since the reversal potentials for the action of GABA and the IPSP are approximately similar, it is concluded that GABA could be the main cortical inhibitory transmitter. [ABSTRACT FROM AUTHOR]

D-C potential changes were evoked in the sensorimotor cortex and the hypothalamus of unanesthetized cats with chronically implanted electrodes by repetitive stimulation of the mesencephalic reticular formation. Stimulation at 30 to 300 p/sec. frequencies induced negative d-c shifts which were quite abrupt in onset, starting after the second or third shock with a peak of negativity reached within the first 50 to 100 msec of the 1 second duration of stimulation. Typically these negative shifts were sustained for the duration of stimulation with a prolonged 1 to 1.5 second return to baseline after termination of stimulation. Such d-c shifts were relatively independent of the site of the reference electrode but highly dependent on the location of the 'active' recording electrodes and the stimulating electrodes. Reasons have been advanced to suggest that these negative d-c shifts reflect summated neuronal discharge in the immediate environs of 'active' recording electrodes in the cerebral cortex and hypothalamus. In contrast to the consistent, stimulus-locked negative d-c shifts, less consistent changes, usually positive in polarity, were observed to begin 2 to 3 seconds after termination of RF stimulation. These slower d-c changes were highly dependent on the site of the reference electrode and the physical state of tissue at the electrode tip and therefore far less directly related to neuronal events in cortical and hypothalamic tissue. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented in response to an article about scanning electron microscopy of wool fibers damaged by insects.

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It is shown by scanning electron microscopy that cuticle cells can be removed virtually completely from wool fibers with minimal removal of cortical cells by refluxing in formic acid for 20 min, followed by shaking for 16 hr in formic acid at room temperature. Control fibers with cuticle retained are produced by a similar treatment, but without agitation. The descaled fibers show a large increase in the amount of water sorbed at saturation as compared with the control.Descaled fibers of this type may serve as useful models in attemps to elucidate the relative contributions of cuticle and cortex to the overall properties of wool fibers. [ABSTRACT FROM PUBLISHER]

A response by J. D. Collins and M. Chaikin to a letter to the editor about their article "The Mechanical Properties of Wool Fibres and the Influence of Fibre Structural and Dimensional Variation: The Stress-Strain Behaviour at Varying Humidities" in the 1971 issue is presented.

The molar ratios of N-acetyl neuraminic acid, hexose, hexosamine, and sphingosine have been determined for the abnormal ganglioside in Tay-Sachs disease that was previously detected as a fast-moving band in thin-layer chromatography, and in two abnormal fast-moving bands of gangliosides from the cortex and white matter of the brain in cases of gargoylism and Niemann-Pick's disease. The fastest-moving ganglioside band in these two conditions contains neither hexosamine nor glucose.