Dorsal Cap Of Inferior Olive Research Articles

Electrophysiological and morphological properties of neurons in the prepositus hypoglossi nucleus that express both ChAT and VGAT in a double-transgenic rat model.

Although it has been proposed that neurons that contain both acetylcholine (ACh) and γ-aminobutyric acid (GABA) are present in the prepositus hypoglossi nucleus (PHN), these neurons have not been characterized because of the difficulty in identifying them. In the present study, PHN neurons that express both choline acetyltransferase and the vesicular GABA transporter (VGAT) were identified using double-transgenic rats, in which the cholinergic and inhibitory neurons express the fluorescent proteins tdTomato and Venus, respectively. To characterize the neurons that express both tdTomato and Venus (D+ neurons), the afterhyperpolarization (AHP) profiles and firing patterns of these neurons were investigated via whole-cell recordings of brainstem slice preparations. Regarding the three AHP profiles and four firing patterns that the D+ neurons exhibited, an AHP with an afterdepolarization and a firing pattern that exhibited a delay in the generation of the first spike were the preferential properties of these neurons. In the three morphological types classified, the multipolar type that exhibited radiating dendrites was predominant among the D+ neurons. Immunocytochemical analysis revealed that the VGAT-immunopositive axonal boutons that expressed tdTomato were primarily located in the dorsal cap of inferior olive (IO) and the PHN. Although the PHN receives cholinergic inputs from the pedunculopontine tegmental nucleus and laterodorsal tegmental nucleus, D+ neurons were absent from these brain areas. Together, these results suggest that PHN neurons that co-express ACh and GABA exhibit specific electrophysiological and morphological properties, and innervate the dorsal cap of the IO and the PHN.

1309 Differential induction of Zif268 and c-Fos in rat beta nuclues and dorsal cap of inferior olive during vestibular compensation

The functional significance of newly formed granule neurons in the adult mammalian hippocampus remains a mystery. Recently, it was demonstrated that wheel running increases new neuron survival and c-Fos expression in new and pre-existing granule cells in an activity-dependent manner. It is currently unknown whether other immediate early genes (IEGs) become expressed in granule neurons from running. Further, it is unknown whether locomotor activity in home cages without wheels can influence neurogenesis and IEG expression similar to running. The purpose of this study was three-fold: (1) to determine if Arc and Zif268 expression are also induced from wheel running in both pre-existing and newly formed neurons (2) to determine if neurogenesis and IEG induction is related to horizontal distance traveled in home cages without wheels, and (3) to determine whether IEG induction is related to acute bouts of running or chronic effects. Adult C57BL/6J female mice were placed in cages with or without running wheels for 31 days. The first 10 days, mice received daily injections of 5-Bromo-2′-deoxyuridine (BrdU) to label dividing cells. On day 1, running and non-running animals were euthanized either 2 h after peak activity, or during a period of relative inactivity. Immunohistochemistry was performed on hippocampal sections with antibodies against BrdU, mature neuron marker NeuN, c-Fos, Arc, and Zif268. Results demonstrate that Arc, Zif268, and c-Fos are induced from wheel running but not movement in cages without wheels. All IEGs were expressed in new neurons from running. Further, IEGs were induced acutely by running, as increased expression did not continue into the light cycle, a period of relative inactivity. The results suggest that robust movements, like running, are necessary to stimulate IEG expression and neurogenesis. Moreover, results suggest new neurons from running may be processing information about running behavior itself.

Differential induction of Zif268 and c-Fos in rat beta nuclues and dorsal cap of inferior olive during vestibular compensation

Differential induction of Zif268 and c-Fos in rat beta nuclues and dorsal cap of inferior olive during vestibular compensation

Pretectofugal fibers from the nucleus of the optic tract in monkeys

The nucleus of the optic tract (NOT) is the visuo-motor relay between the retina and preoculomotor structures in the pathway mediating optokinetic nystagmus (OKN). NOT lesions in monkeys produce no OKN toward the lesioned side. Then, efferent fibers from the NOT course through the brainstem and may reach the vestibular nucleus, which is proposed to be the final nucleus to the motor nucleus. In the present study, the tracer was injected through a micropipette in the NOT in four monkeys. Labeled terminals were observed ipsilaterally in the parabigeminal nucleus, superficial layers of the superior colliculus, dorsal and lateral terminal nuclei of the accessory optic system and pretectal nuclei and contralaterally in the NOT and superficial layers of the superior colliculus. Descending fibers from the NOT consisted of two major pathways: (1) fibers descended medially from the injection site through the reticularis pontis oralis to reach the lateral part of the ipsilateral nucleus reticularis tegmenti pontis; (2) fibers projecting into the dorsal cap of inferior olive, by far the greatest number of labeled fibers, descended ventrally along the lateral border of the reticularis pontis oralis and reached the medial lemniscus where they descended further and branched into the dorsolateral pontine nucleus, the lateral part of the nucleus reticularis tegmenti pontis, the peduncular pontine nucleus, the lateral pontine nucleus, the nucleus prepositus hypoglossi, the medial vestibular nucleus and finally the dorsal cap of the inferior olive. Consistent with the physiological data, the direct terminals to the medial vestibular nucleus could serve to drive the storage mechanisms and to produce OKN in the monkey.

Cholinergic projection to the dorsal cap of the inferior olive of the rat, rabbit, and monkey.

The inferior olive is divided into several subnuclei that receive specific sensory information. The caudal dorsal cap of the medial accessory subdivision of the inferior olive receives horizontal optokinetic information from the nucleus of the optic tract. The immediately subjacent beta-nucleus receives vertical vestibular information mediated by a GABAergic pathway originating from the ipsilateral descending and medial vestibular nuclei. None of the transmitters to the dorsal cap have been identified. Using choline acetyltransferase (ChAT) immunohistochemistry, we have identified a cholinergic pathway that terminates exclusively in the dorsal cap of rats and monkeys. No other division of the inferior olive received a significant cholinergic innervation. In the rabbit, immunostaining for ChAT reveals a weaker and more diffuse cholinergic innervation of both the dorsal cap and the subjacent beta-nucleus. In rats and rabbits we injected iontophoretically the orthograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) into the medial and descending vestibular nuclei (MVN, DVN) as well as the nucleus prepositus hypoglossi (NPH) in order to trace the possible origin of the cholinergic projection. PHA-L injections into the NPH and medial aspect of the MVN labeled terminals within the contralateral dorsal cap. PHA-L injections in the central and lateral aspects of the MVN as well as the DVN labeled the ipsilateral beta-nucleus. Pressure injections of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) in the caudal dorsal cap of the rabbit inferior olive demonstrated a predominantly contralateral projection to the dorsal cap from the lateral aspect of the NPH. However, pressure injections of HRP into the caudal dorsal cap combined with ChAT immunohistochemistry in the rabbit demonstrated that most of the neurons of the NPH that projected to the dorsal cap were not cholinergic, and that most of the ChAT-positive neurons within the NPH occupied a more ventral location than the neurons within the NPH that were retrogradely labeled from the HRP injection into the contralateral dorsal cap. In the rat, we made lesions in the MVN, DVN and NPH by injection of ibotenic acid (0.3-0.5 microliter), in an attempt to deplete the dorsal cap of the inferior olive of its cholinergic input. Lesions confined to the NPH and medial aspect of the MVN of the rat caused a loss of ChAT staining in the contralateral dorsal cap. Lesions placed more laterally within the MVN or DVN failed to deplete ChAT-positive terminals in the contralateral or ipsilateral dorsal caps. The dorsal cap of the rat and monkey receives a discrete cholinergic projection.(ABSTRACT TRUNCATED AT 400 WORDS)

Bilateral visual inputs to the dorsal cap of inferior olive: differential localization and inhibitory interactions.

There are two pathways known to mediate optic signals to the rabbit flocculus through the dorsal cap of the inferior olive; one (I) projects from the contralateral and the other (II) from the ipsilateral eye, both to the contralateral flocculus. The present study on anesthetized rabbits revealed that the two pathways are relayed at different loci of the dorsal cap, I at its caudal and II its rostral half. The ventrolateral outgrowth of the inferior olive also projects to the flocculus, but a prominent field potential could not be produced by optic signals. The present study further demonstrated that transmission in pathway I accompanies an inhibitory action upon that in II. Since direct stimulation of these pathways at preolivary levels revealed similar inhibition, and since this was reflected in the depression of antidromic invasion of dorsal cap neurons, it is concluded that inhibition occurs postsynaptically in dorsal cap neurons. Inhibition is unidirectional, as activities in pathway II did not influence those in I.

Eye movements evoked by microstimulation of dorsal cap of inferior olive in the rabbit.

1. Microstimulation was used in an attempt to activate selectively neurons of the dorsal cap of the inferior olive in unanesthetized rabbits, and the eye movements evoked by this microstimulation were recorded. 2. Trains of microstimulation (20--50 microA, 0.1- to 0.2-ms pulses, 10--60 pulses/s, 2--8 s duration) evoked low-velocity conjugate eye movements directed toward the side of the stimulated olive. These evoked eye movements were interrupted by resetting eye movements in the opposite direction and could be evoked only if the rabbit was in darkness. 3. The velocity of the evoked eye movements increased during a stimulus train and gradually decreased after the stimulation was terminated. 4. The low-velocity eye movements appeared to combine with eye movements evoked by vestibular stimulation without any significant interaction. 5. After transection of the olivocerebellar pathway or destruction of the contralateral cerebellar flocculus, dorsal cap microstimulation no longer evoked ipsilaterally directed eye movements.

Multiple-unit activity evoked in dorsal cap of inferior olive of the rabbit by visual stimulation.

1. Microelectrode recordings of multiple-unit activity were made from the dorsal cap of the inferior olive of anesthetized and unanesthetized rabbits during vestibular and optokinetic stimulation. 2. A large field potential could be evoked in the dorsal cap by photic stimulation of the contralateral eye when the rabbit was anesthetized with sodium pentobarbital or chloralose-urethan. This field potential could not be evoked in rabbits that were anesthetized with halothane or in unanesthetized rabbits. 3. Dorsal cap neurons were maximally excited by large, contrast-rich stimuli presented to the contralateral eye, moving in the posterior-anterior direction at a velocity of 1--2 degrees/s. The discharge rate of dorsal cap neurons was decreased by stimuli moving in the opposite direction. 4. The activity of dorsal cap neurons was not modulated by vestibular stimulation when visual inputs were excluded. 5. Dorsal cap neurons were sensitive to retinal slip velocity and higher derivatives of optokinetic stimulation. Their activity was related to eye movements only when the eye movements affected movement of optokinetic images on the retina.

Origin of descending afferents to the rostral part of dorsal cap of inferior olive which transfers contralateral optic activities to the flocculus. a horseradish peroxidase study

Neurons in the ventromedial tegmental area that project to the rostral part of the dorsal cap of the ipsilateral inferior olive were labeled by the technique of retrograde transport of horseradish peroxidase (HRP). Following iontophoresis of HRP into the rostral part of the dorsal cap a cluster of labeled cells are found ipsilaterally in the area ventromedial to the red nucleus as well as in the area between the substantia nigra and the medial lemniscus. Following HRP injections into the medial accessory olive just beneath the dorsal cap, labeled cells are found exclusively contralaterally in the deep layers of the superior colliculus and in the adjacent reticular formation. These findings clearly show that neuronal groups in the ventromedial tegmental area are involved in the pathway which from the contralateral eye via the rostral half of the dorsal cap conveys impulses to the flocculus, recorded as climbing fiber activation.