Responses Evoked in the Cerebellar Cortex by the Pontine Stimulation

Following large and small lesions of the orbital gyrus in adult cats the ensuing degeneration in the pontine nuclei was studied with the silver impregnation methods of Nauta and of Fink and Heimer. Lesions were produced by transdural thermocoagulation. The main results are as follows :All parts of the orbital gyrus give off fibers to the pontine nuclei. The density of projection is less than from the anterior ectosylvian gyrus (second somatosensory area).The orbital gyrus projects upon four longitudinal columns within the pontine nuclei. One is located medially, one ventromedially, one ventrolaterally and one dorsolaterally.The exact localization of these columns has been compared with the localization of the columns projected upon by the anterior ectosylvian gyrus. Three of the columns (the medial, ventrolateral and dorsolateral) appear to be projected upon by both gyri, while the fourth one receives afferents from the orbital gyms only.A topical localization exists within the projection from the orbital gyms insofar as the anterior part of the gyrus projects onto the medial, ventrolateral and dorsolateral columns, while the posterior part projects onto the ventromedial column mainly.Whether a somatotopical localization is present within the projection to some or all of the columns can not be decided from the material. 1. 2. 3. 4.This paper is the fourth in a series which deals with the pontine projection from different parts of the cerebral cortex in the cat. It has been possible to demonstrate a precise organization within this projection from the primary sensorimotor (P. Brodal, '68a) and second somatosensory cortex (P. Brodal, '68b). Each region projects i n a somatotopical fashion upon several longitudinally oriented, differently situated cell columns in the pontine nuclei. In view of these findings it was deemed of interest to study in the same detailed manner the pontine projection from other cortical regions. In a preceding paper (P. Brodal, '71) it was shown that the proreate gyrus projects onto the same pontine areas as does the motor cortex. The present study deals with the projection from the orbital gyrus.Of the three most important brain stem nuclei relaying impulses from the cerebral cortex to the cerebellum (the pontine nuclei, the lateral reticular nucleus and the J. COMP. NEUR., 142: 141-152.inferior olive), in the cat only the pontine nuclei have been shown to receive fibers from the orbital gyrus (Mizuno, Sauerland and Clemente, '68). However, information of the sites of termination is not given by Mizuno et al. Other authors studying projections from the orbital gyrus to subcortical regions in the cat (Hirata, '65; Valverde, '65) do not mention efferent fibers to the pontine nuclei.Jansen ('57) studying the evoked potentials in the cerebellar hemisphere following electrical stimulation of the cerebral cortex of the cat, found that stimulation of the anterior part of the orbital gyrus evoked long and short latency potentials in the dorsal paraflocculus, crus I and 11, and the anterio...

The corticopontine projection in the cat. II. The projection from the orbital gyrus

Brodal

1971

The number of Purkinje cells and inferior olivary neurones in the cat

Mlonyeni

1973

It is generally assumed that (i) all neurones of the inferior olive send their axons to the cerebellum; (ii) the fibers from the olive end as climbing fibers; (iii) one climbing fiber establishes extensive synaptic contact with one Purkinje cell. From this i t has been inferred that there is one inferior olivary neurone per Purkinje cell. The number of neurones in both inferior olives from four cats have been counted in histologic sections. The totals obtained are 145380, 127270, 126920 and 121360, respectively. In two of the cats the Purkinje cells were counted. The ratios of inferior olivary neurones to Purkinje cells were found to be 1 : 10 and 1 : 11, respectively.Experimental anatomical studies in the cat and rabbit (Brodal, '40) have shown that practically all neurones i n the inferior olive send their axons to the cerebellum, that almost all olivo-cerebellar fibers cross the midline and enter the contralateral half of the cerebellum, and that there is a distinct topographical localization within the olivo-cerebellar projection (see Brodal, '54, for a review).According to Szent5gothai and Rajkovits ('5Y), the olivo-cercbellar projection is the source of almost all climbing fibers within the cerebellum, while all other cerebellopetal fibers terminate as mossy fibers (SzentBgothai, '65 A description of the structure and subdivisions of the inferior olive of the cat can be found elsewhere (Brodal, '40; Walberg, '56). Suffice it here to mention that in addition to the three main parts which are the principal olive, the medial and dorsal accessory olives, several minor subdivisions can be distinguished (Brodal, '40). MATERIALS AND METHODSThe pertinent data on the cats used in this study are given i n table 1. The animals were anaesthetised with Nembutal and sacrificed by perfusion with 10% formalin introduced through the left cardiac ventricle. After perfusion, the animals were left For two to three hours before the brains were dissected out. The medulla oblongata and the cerebellum were isolated and placed in fresh fixative for about 24 hours. After about 12 hours in running water. the specimens were dehydrated, embedded in paraffin and cut serially at 20 p. The medulla oblongata was cut transversely while the cerebellum was sectioned sagittally. The sections were stained in one of 1

Projections from the parietal cortex to the brain stem nuclei in the cat, with special reference to the parietal cerebro‐cerebellar system

Mizuno

Mochizuki

Matsushima

et al. 1973

Direct projections from the anterior portions of the parietal cortex of the cat to the brain stem nuclei, especially those sending fibers to the cerebellum, were investigated by the Nauta-Gygax and Fink-Heimer methods.Following unilateral lesions of the anterior portions of the middle suprasylvian and/or lateral gyri, a significant amount of pencellular degeneration was found almost entirely ipsilaterally in the rostra1 levels of the red nucleus and its vicinities, and in the pontine nuclei. Projection fibers to the pontine nuclei appeared to extend over several longitudinal, columnar zones in the pontine gray. Fibers from the anterior portion of the lateral gyrus were observed mainly in the paramedian and lateral nuclei, and those from the middle suprasylvian gyrus in the ventral, paramedian and lateral nuclei. Degeneration in the nucleus reticularis tegmenti pontis of Bechterew was slight, and found bilaterally with ipsilateral predominance.The significance of the anterior portion of the parietal cortex of the cat as a link of cerebro-cerebellar loops was discussed.It is well known that the interpositus and lateral nuclei of the cerebellum project to the motor cortex of the cerebrum through the nucleus ventralis lateralis of the thalamus, and that the motor cortex in turn projects back to the cerebellum via several brain stem nuclei (Bell and Dow, '67). Recently, Sasaki and his associates ('71, '72a, b ) have shown that electrical stimulation of the interpositus or the lateral nucleus of the cerebellum in the cat elicits evoked potentials in the parietal cortex (anterior portions of the middle suprasylvian and lateral gyri) as well as in the sensorimotor cortex. Although fiber projections from the sensorimotor cortex to those brain stem nuclei that send fibers to the cerebellum have been studied in the cat with silver impregnation techniques (Rinvik and Walberg, '63; Mabuchi and Kusama, '66; Brodal, Margala and Brodal, '67; Brodal, '68a; '69; '70; Brodal and Brodal, '71), projection fibers from the parietal cortex so far have not been investigated systematically.In this context the present study was J. COMP. NEUR., 147: 511-522.carried out to investigate projection fibers from the parietal areas to the brain stem nuclei, in particular, to the nuclei projecting to the cerebellum, in the hope of shedding more light upon the organization of the cerebro-cerebellar loops. MATERIALS AND METHODSThe experiments were carried out on nine young adult cats, weighing between 2 and 3.5 kg. With aseptic precautions, unilateral cortical lesions were produced in the anterior portions of the middle suprasylvian and/or lateral gyri by thermocauterization under general anesthesia (sodium pentobarbital 40 mg/kg i.p.). The animals were allowed to survive five to eight days before being perfused intravitally through the ascending aorta with 1000 ml of 10% neutral formalin under deep anesthesia. The brains and spinal cords were subsequently removed in toto and immediately placed into a large volume of 10% neutral formali...