The posterior pretectal nucleus: evidence for a direct projection to the inferior olive of the cat

In our horseradish peroxidase (HRP) study of the afferents to the medullary raphe nuclei in the cat, HRP uptake by damaged axons en route to the inferior olive (IO) was thought to be responsible for retrograde labelling of specific midbrain nuclei. To control for such indirect labelling, HRP was injected iontophoretically into the inferior olive. The location of retrogradely labelled neurons was related to the specific locus of HRP injection within the IO. Injection of HRP into the caudal dorsal accessory olive resulted in dense neuronal labelling in the ipsilateral caudal pole of the posterior pretectal nucleus (PPN). There was no labelling of the nucleus of Darkschevitch (Dk), interstitial nucleus of Cajal (ICA) or Edinger-Westphal nucleus (EW). In contrast, an injection focussed more rostrally, into the rostral, dorsal accessory, the medial accessory and the principal olive, produced dense labelling of Dk, ICA and EW; there was much less PPN labelling. It is concluded that labelling of Dk and PPN after HRP injections rostral to the IO, is due, at least in part, to uptake of HRP by damaged medial longitudinal fasciculus axons en route to the inferior olive. The direct PPN-inferior olivary projection provides a potential disynaptic retino-cerebellar connection, which may be involved in rapidly timed eye-body coordinate movements.     

Descending projections to the inferior olive from the mesencephalon and superior colliculus in the cat

Summary Descending projections from the mesencephalon and superior colliculus to the inferior olive were analyzed by an autoradiographic tracing method. Injections of tritium-labelled leucine were placed in regions which had previously been identified as sources of afferents to the olive. These were located adjacent to the central gray and extended from the rostral red nucleus to the posterior thalamus. Additional injections were made in the superior colliculus. Other injections were placed in the basal ganglia and thalamus. Injections restricted to one side of the central mesencephalon resulted in predominantly ipsilateral labelling of the olive. After injections in the caudo-medial parafascicular and subparafascicular nuclei and rostral nucleus of Darkschewitsch, deposits of grains were observed in the rostral pole of the medial accessory olive and adjacent ventral lamella of the principal olive. The medial accessory olive contained grains into its middle third. More caudal injections which involved the interstitial nucleus of Cajal as well as the nucleus of Darkschewitsch and rostral red nucleus resulted in the dense labelling of the entire principal olive (except the dorsal cap), the entire medial acessory olive (except subnucleus and the caudo-medial pole) and the caudo-dorsal accessory olive. Injections centered in the caudal magnocellular red nucleus and extending into the rostral parvocellular division labelled the dorsal lamella of the principal olive almost exclusively. When only the caudal part of the red nucleus was involved in the injection, the olive was entirely clear of grains. Minor contralateral distributions were observed in the dorsomedial cell column, the medial tip of the dorsal lamella and in the caudal medial accessory olive. The deep layers of the superior colliculus were found to project strongly to the contralateral medial accessory olive immediately beside subnucleus and weakly to the same area ipsilaterally.Four pathways were identified as contributing fibers to the olivary projections. These were the medial longitudinal fasciculus, the medial tegmental tract, the central tegmental tract and tectospinal or tectobulbar fibers. The rubrospinal tract did not contribute projections to the olive. Injections in the caudate nucleus, entopeduncular nucleus and ventral anterior and ventral lateral thalamic nuclei, did not result in any labeling in the olive.List of Abbreviations AC anterior commissure - Cd caudate nucleus - CG central gray - CP cerebral peduncle - CTT central tegmental tract - DAO dorsal accessory olive - dc dorsal cap of Kooy - dmcc dorsomedial cell column of the inferior olive - dlPO dorsal lamella of the principal olive - Entop entopeduncular nucleus - EW nucleus of Edinger-Westphal - FR fasciculus retroflexus - Fx fornix - GP globus pallidus - H H field of Forel - HRP horseradish peroxidase - IC inferior colliculus - INC interstitial nucleus of Cajal - Int Cap internal capsule - IPN interpeduncular nucleus - LRN lateral reticular nucleus - MAO medial accessory olive - MB mammillary body - MGB medial geniculate body - MLF medial longitudinal fasciculus - MRF mesencephalic reticular formation - MTT medial tegmental tract - ND nucleus of Darkschewitsch - NFF nucleus of the fields of Forel - NPC nucleus of posterior commissure - NPP posterior pretectal nucleus - NRTP nucleus reticularis tegmenti pontis - n III third cranial nerve fibers - OT optic tract - PC posterior commissure - PF parafascicular nucleus - PG pontine gray - PO principal olive - PTM medial pretectal nucleus - RNp parvocellular red nucleus - RN red nucleus - RST rubrospinal tract - subnucleus beta of the inferior olive - sPf subparafascicular nucleus - SC superior colliculus - TH thalamus - vlPO ventral lamella of the principal olive - vlo ventral lateral outgrowth of the principal olive - VTA ventral tegmental area of Tsai - ZI zona incerta - III nucleus of third cranial nerve - XII nucleus of twelfth cranial nerve Supported by a grant from the Canadian Medical Research Council to the Group in Neurological Sciences at the Université de MontréalSupported by a postdoctoral fellowship of the Centre de Recherche en Sciences Neurologiques of the Université de Montréal     

The parieto-rubro-olivary pathway in the cat

Summary Stimulation of the parietal association cortex as well as the frontal motor cortex elicited clearly extracellular unitary activities or field potentials in the ipsilateral inferior olive in the cat. The parietal-induced responses came out generally at a longer and more variable latency than the frontal-induced ones. This suggested the existence of an indirect pathway from the parietal association cortex to the inferior olive.The recording sites for the parietal-induced responses were located not only in the dorsal lamella but also in the ventral lamella of the principal olive and in the medial accessory olive. Such olivary sites were exclusively in the rostral half of the inferior olive, and these areas in the olive were considered to give projection fibres predominantly to the hemispherical parts of the cerebellar cortex (neocerebellum).Small neuronal cells were labelled with horseradish peroxidase (HRP) homolaterally in the midbrain tegmentum, after HRP was injected through recording glass microelectrodes into the inferior olive where only the parietal-induced responses were evidently recorded. These small cells were distributed in the rostral one-third of the red nucleus and/or around the adjacent midbrain reticular formation close to the lateral border of the red nucleus. In referring to recent anatomical and physiological data, such small neurones labelled with HRP could be identified as the parvocellular red nucleus neurones.The present results indicate the existence of the parieto-rubro-olivary pathway system in the cat and suggest, in association with our previous studies, that the parvocellular red nucleus neurones participate in control of highly co-ordinated posture and movement predominantly through the neocerebellum.     

Physiological and anatomical identification of the nucleus of the optic tract and dorsal terminal nucleus of the accessory optic tract in monkeys

Summary Physiological and anatomical criteria were used to clearly establish the existence of a pretectal relay of visual information to the ipsilateral inferior olive in the macaque monkey. After injection of horseradish peroxidase into the inferior olivary nucleus, retrogradely labelled neurons were found in the nucleus of the optic tract (NOT) and the dorsal terminal nucleus of the accessory optic tract (DTN). The labelled cells were distributed in a sparse band arching below the margin of the brachium of the superior colliculus between the dorsal and lateral borders of the brainstem at the caudal edge of the pulvinar. Various types of cells could be distinguished. More superficially the cells were extremely spindle shaped, cells deeper within the midbrain had more compact somata. NOT-DTN neurons in the same region were also found to respond with short latencies to electrical stimulation of both the inferior olive and the optic chiasm. All neurons in the NOTDTN which were antidromically activated from the inferior olive were also found to have direction specific binocular visual responses. Such neurons were excited by ipsiversive motion and suppressed by contraversive motion, regardless of whether large area random dot stimuli moved across the visual field or small single dots moved across the fovea. Direct retinal input to these neurons was via slowly conducting fibers (3–9 m/s) from the monkey's optic tract conduction velocity spectrum. As shown previously for non-primates, NOT-DTN cells may also in the monkey carry a signal representing the velocity error between stimulus and retina (retinal slip), and relay this signal into the circuitry mediating the optokinetic reflex.     

The afferent connections of the inferior olivary complex in rats. An anterograde study using autoradiographic and axonal degeneration techniques

Autoradiographic and axonal degeneration techniques were employed to determine the distribution patterns of inferior olivary afferents whose origins were determined using the horseradish peroxidase method.⁷⁰ The Fink-Heimer stain for degenerating axons was used following lesions of the cerebral cortex and spinal cord, while brainstem and cerebellar afferents were mapped by tritiated leucine autoradiography.After unilateral lesions of the mid-thoracic spinal cord, degenerating axons were observed within the subnuclei a and b of the caudolateral medial accessory olive and in the caudolateral dorsal accessory olive. Degeneration after upper cervical cord lesions extended more rostrally and medially within the same olivary subdivisions.Several nuclei within the caudal brainstem projected to the inferior olivary complex. The dorsal column nuclei distributed fibers primarily contralaterally to the lateral part of the dorsal accessory olive and to the caudolateral part of the medial accessory olive; the spinal trigeminal nucleus projected contralaterally to the rostromedial dorsal accessory olive; the medial and inferior vestibular nuclei projected to the ipsilateral subnuclei b, c, and β of the medial accessory olive and to the contralateral dorsomedial cell column; the nucleus prepositus hypoglossi sent fibers to the subnuclei c and β, the dorsal cap and the ventrolateral outgrowth; the lateral reticular nucleus projected to the subnucleus a of the caudolateral medial accessory olive bilaterally; and the reticular formation distributed fibers to the dorsal accessory olive contralaterally and to the β subnucleus ipsilaterally.Study of inferior olivary complex afferents from the deep cerebellar nuclei showed a projection from the fastigial nucleus to the β subnucleus and the ventrolateral outgrowth. The dentate and interpositus nuclei demonstrated topographic connections from these nuclei to the principal olive and accessory olives, respectively. All cerebellar connections were predominantly contralateral.Analysis of mesencephalic and diencephalic areas also demonstrated several inferior olivary complex afferent systems: the caudal pretectum and the superior colliculus projected to the subnucleus c contralaterally and the dorsal lamella of the principal olive ipsilaterally; the nucleus of the optic tract sent fibers to the dorsal cap; the lateral deep mesencephalic nucleus distributed fibers to the ipsilateral dorsal accessory olive and β subnucleus; the medial terminal nucleus of the accessory optic tract projected ipsilaterally to the ventrolateral outgrowth; and several areas including the medial deep mesencephalic nucleus, periaqueductal gray, the nucleus of Darkschewitsch, the subparafascicular nucleus, the rostral red nucleus and the prerubral field all projected ipsilaterally to the principal olive, rostral medial accessory olive, ventrolateral outgrowth and, to a lesser extent, the caudal medial accessory olive, dorsal cap and β subnucleus.Lesions of the frontal cortex produced axonal degeneration primarily ipsilaterally within many olivary subdivisions, especially the medial dorsal accessory olive and the caudomedial medial accessory olive.Although some notable differences in the distribution and laterality of fibers are described, our findings generally corroborate several earlier reports which used different techniques on a variety of species. Inferior olivary afferents from functionally related areas typically demonstrated similar distribution patterns within the subdivisions of the inferior olivary complex. These patterns suggest a functional localization within the inferior olivary complex which may facilitate an understanding of afferents from areas whose functions are not clearly known.     

Efferent projections of the pretectum in the cat

Summary Direct projections from the pretectum in the cat were investigated by means of the Nauta-Gygax and the Fink-Heimer method in an attempt to identify the morphological substrates subserving possible neural mechanisms involved in visual behaviour and reflexes.Degeneration in the diencephalon was found ipsilaterally in the nucleus limitans, lateral pulvinar nucleus, lateral posterior nucleus, lateral dorsal nucleus, dorsal and ventral lateral geniculate nuclei, centre medianparafascicular complex, central medial nucleus, paracentral nucleus, central lateral nucleus, ventroanterior and ventrolateral nuclear complex, zona incerta, H field of Forel and the reticular nucleus. The pretectal fibers projecting to the ventral lateral geniculate nucleus appeared to be topically organized.In the midbrain, the pretectal fibers were observed to terminate ipsilaterally within the superior colliculus, nucleus of Darkschewitsch, dorsolateral portion of the red nucleus, lateral terminal nucleus of the accessory optic tract and the reticular formation, and bilaterally within the central gray, interstitial nucleus of Cajal and the rostral portion of the nucleus of Edinger-Westphal. Degeneration in the superior colliculus was marked in laminae II, III and IV. The fibers arising from more anterior part of the pretectum appeared to be distributed more medially in laminae II and III.The pretectopontine fibers terminated ipsilaterally in the paramedial and the dorsolateral pontine nuclei as well as the reticular formation. In the inferior olivary complex, degeneration was found in caudal levels of the dorsal cap and -nucleus, and additionally in the rostral portion of the dorsal accessory olive.     

Olivary afferents from the raphe nuclei as studied with retrograde transport of horseradish peroxidase

Summary The afferent projection to the olive from the raphe nuclei in the cat has been studied in animals where microinjections of horseradish peroxidase have been made into the inferior olive from a ventral approach. Retrogradely labelled cells were present in the three caudalmost raphe nuclei: the nucleus raphe pallidus, obscurus and magnus. The retrogradely labelled cells are of all sizes, and there appears to be a higher concentration of cells on the side ipsilateral to the injection. The observations demonstrate that all three major subdivisions of the olive — the medial accessory, the dorsal accessory and the principal olive — all receive efferent raphe fibres. No retrogradely labelled cells were present in the other raphe nuclei.The findings are discussed and related to other tracer studies dealing with olivary afferents from the raphe complex.     

Projections from the reticular formation of the medulla, the spinal trigeminal and lateral reticular nuclei to the inferior olive

Injections of tritiated L-leucine were placed in the reticular formation of the medulla, the spinal trigeminal and lateral reticular nuclei of cats and silver grain accumulations in the inferior olivary nucleus were demonstrated by autoradiography. Cells of the reticular formation located at the junction of nuclei reticularis magnocellularis and reticularis parvocellularis in the rostral medulla and within nucleus reticularis ventralis in the caudal medulla contribute four distinct projections to the olive. Three projections are distributed ipsilaterally in the caudal part of the medial accessory olive, at mid-level of the dorsal accessory olive and in the ventrolateral bend of the principal olive, at rostral levels. There is also a small controlateral projection to the caudal part of the medial accessory olive. the spinal trigeminal nucleus sends crossed projections to the rostral part of the dorsal accessory olive and adjacent ventral lamella as well as to the caudal part of the medial accessory olive. The lateral reticular nucleus sends an extensive ipsilateral projection to the caudal part of the medial accessory olive and provides a small contribution to the same subdivision, contralaterally. All these projections converge with other known afferents to the olive.     

Cerebellar and olivary projections of the external and rostral internal cuneate nuclei in the cat

Summary The cerebellar projection of the external cuneate nucleus and the adjoining rostral part of the internal cuneate nucleus were investigated by means of anterograde transport of tritiated leucine. The cuneocerebellar tract terminates as mossy fiber rosettes in the granular layer. The termination area has a more or less spherical form with its centre at the ipsilateral side. It comprises the anterior and posterior vermes bilaterally and the ipsilateral hemispheral parts of the anterior and simple lobules, the medial aspect of the ansiform lobule and the paramedian lobule. Within this area the mossy fiber terminals are arranged in continuous sagittal strips, some of them clearly separated from one another. The strips were found in the cerebellar modules A-D. Concomitant bilateral projections to several subdivisions of the inferior olive were found. Some of these provide the anatomical substrate for the simultaneous activation of a number of mossy and climbing fiber zones observed in the anterior lobe following stimulation of different forelimb nerves. No evidence was found for a termination of mossy fiber collaterals in the central cerebellar nuclei.Abbreviations subnucleus - bp brachium pontis - CCT cuneocerebellar tract - CE nucleus cuneatus externus - cf climbing fiber - CI nucleus cuneatus internus - cr corpus restiforme - DAO dorsal accessory olive - DCN dorsal column nuclei - DF-SOCP dorsal funiculus spino-olivocerebellar pathway - dl dorsal lamina of the PO - dmcc dorso-medial cell column - DV nucleus vestibularis descendens - E-CCP exteroceptive cuneocerebellar pathway - F nucleus fastigii - FL flocculus - flm fasciculus longitudinalis medialis - G nucleus gracilis - HRP horseradish peroxidase - HVI hemisphere of lobule VI (Roman numerals) - IA nucleus interpositus anterior - IP nucleus interpositus posterior - L nucleus lateralis - MAO medial accessory olive - mf mossy filber - mft mossy fiber terminal - MV nucleus vestibularis medialis - PAR lobus paramedianus - PFLD dorsal paraflocculus - PFLV ventral paraflocculus - PH nucleus prepositus hypoglossi - PO principal olive - P-CCP proprioceptive cuneocerebellar pathway - rV ramus descendens of the nucleus trigeminus - TS nucleus solitarius - Vi pars interpolaris of the nucleus trigeminus - vl ventral lamina of the PO - I-X lobules I to X (Roman numerals) - XII nucleus hypoglossi (Roman numerals)     

Classical conditioning of the nictitating membrane response of the rabbit

Summary We report the connections of cerebellar cortical lobule HVI in the rabbit. We have studied the anterograde and retrograde transport of wheatgerm-agglutinated horseradish peroxidase (WGA-HRP) following its injection into HVI to reveal efferent and afferent connections. All of the cases showed strong anterograde transport to the anterior interpositus nucleus (AIP) — indicating that this is the major efferent target of HVI. Retrogradely labelled cells were found in the inferior olivary, spinal trigeminal, lateral reticular, inferior vestibular and pontine nuclei. Within the olive, the medial part of the rostral dorsal accessory olive (DAO) and the adjacent medial part of the principal olive (PO) were consistently labelled in all cases. This area is known to receive somatosensory information from the face and neck. There was no projection to the hemispheral part of lobule VI from visual parts of the olive within the dorsal cap and medial parts of the medial accessory olive. Likely sources of visual and auditory information to HVI are the dorsolateral basilar pontine nuclei and nucleus reticularis tegmenti pontis, which were densely labelled in all cases. These anatomical findings are consistent whith the suggestion that, during NMR conditioning, information related to the periorbital shock unconditional stimulus (US) may be provided by climbing fibres to HVI and light and white noise conditional stimulus (CS) information may be supplied by pontine mossy fibres.     

Descending projections of Forel's field H neurones to the brain stem and the upper cervical spinal cord in the cat

Summary 1. Descending projections from Forel's field H (FFH) to the brain stem and upper cervical spinal cord were studied in cats. 2. Following implantation of HRP pellets into the spinal gray matter (C1-C3) or in the ponto-medullary reticular formation, the nucleus reticularis pontis caudalis (NRPC) or in the nucleus reticularis gigantocellularis (NRG), numerous neurones were retrogradely labelled in FFH on the ipsilateral side. In the former cases, the sizes of labelled neurones were medium-large (2040 m in diametre) while both small and medium-large neurones were labelled in the latter cases. 3. The lowest levels of spinal projection of single FFH neurones (n=70) were assessed by antidromic spikes elicited by stimulating electrodes placed in C1, C3 and C7. The majority (59%) projected to C1 (but not to C3), about 27% to C3 (but not to C7), and only 14% to C7. 4. Axonal trajectories of single FFH neurones in C1-C3 segments were investigated by antidromic threshold mapping methods. The stem axons of spinal-projecting FFH neurones descended in the ventral or in the ventrolateral funicli and the collaterals were projected to neck motor nuclei (lamina IX, Rexed 1954) and laminae V–VIII. The conduction velocities were estimated as 8–37 m/s from the antidromic latencies. 5. Axonal trajectories of 7 FFH neurones were investigated in the ponto-medullary reticular formation. All were antidromically activated from C1. In six neurones, the stem axons were located in the ventral part of the central tegmental tract and collaterals were projected to the NRPC and/or the NRG. Some of them projected to the inferior olive and the nucleus prepositus hypoglossi as well. The stem axon, in the remaining cell, was in the most dorso-medial part of the medial longitudinal fasciculus and collaterals were projected mainly to the dorsal part of the NRPC and the NRG, and also to the medial vestibular nucleus. 6. Anterograde transport of WGA-HRP injected into FFH revealed that in the upper cervical spinal cord, stem axons were found in the ventral funiculus and ventral part of the lateral funiculus. Collateral projections and presumed bouton-like deposits were observed in the laminae VI–IX, especially in their medial part. In the brain stem, dense bundles of the descending fibres were found in the central and the medial tegmental tracts and in the medial longitudinal fasciculus. FFH neurones projected densely to the caudal half of the NRPC and to the rostral half of the NRG. Extremely dense projections to the inferior olive were noted.Abbreviations AM anteromedian nucleus of the Edinger-Westphal - BCC m. biventer cervicis and complexus - CCN central cervical nucleus - CP cerebral peduncle - CTT central tegmental tract - DAB diaminobenzidine - DAO dorsal accessory nucleus of the inferior olive - DW nucleus Darkschewitsch - FFH Forel's field H - FMN fasciculus mammillothalamics - FR fasciculus retroflexus - G genu of the facial nerve - HB habenula - HRP horseradish peroxidase - INC interstitial nucleus of Cajal - IO inferior olive - LGN lateral geniculate nucleus - LHT lateral hypothalamic nucleus - MAO medial accessory nucleus of the inferior olive - MB mammillary body - MLF medial longitudinal fasciculus - MTT medial tegmental tract - MVN medial vestibular nucleus - NRG nucleus reticularis gigantocellularis - NRPC nucleus reticularis pontis caudalis - NRTP nucleus reticularis tegmenti pontis - OT optic tract - PAG periaqueductal gray matter - PC posterior commissure - PCN posterior commissure nucleus - PF parafascicular nucleus - PH nucleus prepositus hypoglossi - PHT posterior hypothalamic nucleus - PN pontine nucleus - PO principal nucleus of the inferior olive - Py pyramid - RN red nucleus - RSNs reticulospinal neurones - SN substantia nigra - SNr substantia nigra pars reticulata - sPF subparafascicular nucleus - STH subthalamic nucleus - TB trapezoid body - TMB tetramethylbenzidine - V3 third ventricle - ZI zona incerta - VI abducens nucleus/nerve - XII nucleus hypoglossi     

Rearrangements in the retino-geniculate projections of rats following ablation of the superior colliculus in infancy

Summary The superior colliculus was bilaterally or unilaterally ablated at different early postnatal ages in rats. When adult, each rat received a unilateral eye injection of Horesradish peroxidase to reveal the crossed and uncrossed retinal terminal fields within the dorsal lateral geniculate nucleus. Collicular ablation in the first seven days after birth, but not thereafter, produced a small hole or vacancy within the contralateral retinal terminal field which was occupied by an aberrant ipsilateral retinal terminal field. These rearrangements in the retino-geniculate projections occurred in the caudal quarter of the nucleus dorso-laterally just beneath the optic tract, solely ipsilateral to the ablated colliculus. Possible causes of the formation of these rearrangements are discussed, and similarities with other aberrant retinal projections following early damage to the visual system are considered.Abbreviations dLGN Dorsal geniculate nucleus - DTN Dorsal terminal nucleus of the accessory optic tract - HRP Horseradish peroxidase - LP Latero-posterior nucleus - NOT Nucleus of the optic tract - OT Optic tract - PO Olivary pretectal nucleus - PP Posterior pretectal nucleus - SC Superior colliculus - TMB Tetramethyl benzidine     

The rat inferior olive as seen with immunostaining for glutamate decarboxylase

Summary Boutons presumed to use -aminobutyric acid as neurotransmitter (GABAergic boutons) were detected by glutamate decarboxylase (GAD) immunocytochemistry in all regions of the rat inferior olive. The remarkably high concentration of these boutons allowed a clear visualization of olivary subnuclei boundaries. Regional variations in GAD immunostaining intensity were observed within the nuclear complex and were graded both visually and photometrically. The regional staining variations, for the most part, followed subnuclei boundaries and olivary zonal compartments that have been delineated by the topography of climbing fiber projections. Some subnuclei were grouped by similar staining intensities. The beta nucleus and a medial region in the ventral fold of the dorsal accessory olive were most intensely immunostained, followed by the subnucleus c of the medial accessory olive. Lower staining intensities were observed in the dorsomedial cell column, the dorsal fold of the dorsal accessory olive and the dorsal cap. The lowest intensities were observed in the subnuclei a and b of the medial accessory olive, the ventrolateral outgrowth, the rostral lamella of the medial accessory olive, the principal olive, and the lateral part of the ventral fold of the dorsal accessory olive. The factors contributing to the variations in immunostaining intensity (bouton size and frequency of occurrence) were investigated. The largest boutons were observed in the beta nucleus. Intermediate sized boutons were observed in the dorsomedial cell column, dorsal cap and the dorsal fold of the dorsal accessory olive. The smallest boutons were present in the remaining regions of the inferior olive, including the principal olive, the rostral lamella of the medial accessory olive, and the ventral fold of the dorsal accessory olive. The medial region of the dorsal accessory olive ventral fold contained a higher density of GABAergic boutons than other regions. GABAergic bouton size and innervation density therefore largely accounted for the variations in GAD immunostaining intensity. This study provides a map of the rat inferior olive based on the distribution of GABAergic nerve terminals, and may serve as a basis for characterizing different GABAergic afferent systems in the inferior olive.Abbreviations aMAO subnucleus a of MAO - bMAO subnucleus b of MAO - beta subnucleus beta - cMAO subnucleus c of MAO - DAO dorsal accessory olive - dc dorsal cap - dfDAO dorsal fold of DAO - dl dorsal lamella of PO - dIPO dorsal lamella of PO - dmcc dorsomedial cell column - lat vfDAO lateral portion of ventral fold of DAO - MAO medial accessory olive - med vfDAO medial portion of ventral fold of DAO - PO principal olive - MAO rostral lamella of MAO - vfDAO ventral fold of DAO - vl ventral lamella of PO - vlPO ventral lamella of PO - vlo ventrolateral outgrowth - GABA gamma-aminobutyric acid - GAD glutamate decarboxylase     

Functional linkage between the electrical activity in the vermal cerebellar cortex and saccadic eye movements

Summary In order to identify cells of origin in the spinal cord of non-primary afferents to the dorsal column nuclei (DCN), the retrograde transport of horseradish peroxidase (HRP) has been utilized in adult cats. 10 to 30% HRP was injected bilaterally (0.6 l per side) in the dorsal medulla of nine cats. In most instances the spread of the injected enzyme extended a few millimeters rostrocaudally and infiltrated the DCN as well as other nuclei and fiber tracts. Labelled cells in these cases are numerous in the upper cervical, brachial and lumbosacral cord but are sparse in thoracic segments below T₁. At upper cervical levels (C₁-C₄) HRP-positive neurons are distributed throughout the grey matter but are especially concentrated in the medial part of lamina VI. Cells projecting to the dorsal medulla are mainly localized in lamina IV and, more ventrally, along the medial border of the dorsal horn in the brachial and lumbosacral cord. Labelled cells at these levels are also scattered within lamina I and laminae VI through VIII in cases in which the focus of the injection involved extensive portions of the medulla. From cases in which bilateral HRP injections were preceded by spinal tractotomy, it appears that the axons of at least the majority of labelled cells in lamina IV ascend in the ipsilateral dorsal quadrant of the spinal cord.In another group of adult cats, 0.1 to 0.25 l of 30 to 50% HRP was injected unilaterally in the dorsal medulla at the level of, or rostral to, the obex. With these volumes of exogenous enzyme, an intense reaction product is largely confined within the limits of the DCN. Labelled cells in these cases are found almost exclusively in the medial part of lamina VI at upper cervical levels and, at brachial and lumbosacral levels, throughout lamina IV and medially in lamina V on the side of the cord ipsilateral to the injection.The results are discussed in relation to the organization of the dorsal horn and ascending pathways with special reference to cells of origin of the spinocervical tract.List of Abbreviations CUN cuneate nucleus - D descending nucleus of the vestibular complex - DV dorsal motor nucleus of the vagus - EC external cuneate nucleus - GR gracile nucleus - HYP hypoglossal nucleus - IO inferior olivary complex - LRN lateral reticular nucleus - PM paramedian nucleus - PYR pyramids - SOL solitary tract and nucleus spin - V spinal trigeminal nucleus     

Axonal collateral branching of neurones in the inferior olive projecting to the cerebellar paramedian lobule in the rabbit

The double fluorescent retrograde technique was employed to examine the distribution of the inferior olive (IO) neurones projecting to the cortex of the rostral and caudal parts of the paramedian lobule (PML) in the rabbit cerebellum, known to be the face-forelimb and hindlimb receiving areas, respectively. Moreover, this technique was also used to investigate the possibility that IO projections reaching these two somatotopically non-homologous PML regions are collaterals of the same axones. No other reports have addressed this question. After non-overlapping unilateral injections of the cytoplasmic tracer fast blue (FB) and the nuclear dye diamidino yellow (DY) into the rostral and caudal PML, respectively, numerous single FB- or DY-labelled cells were found in the defined regions of the contralateral IO. These regions showed considerable overlap, apart from the dorsal accessory olive where a clear spatial separation of labelled cell groups was observed. Furthermore, double FB + DY-labelled neurones (n = 310) were seen in the medial accessory olive, the dorsal and ventral laminas of the principal olive, in the dorsomedial cell column and the beta nucleus. It suggests that IO neurones may branch to supply the two functionally different PML regions and in this way participate in the mechanisms of forelimb-hindlimb coordination.     

A re-examination of the rubro-olivary tract in the cat,using horseradish peroxidase as a retrograde and an anterograde neuronal tracer

Most authors using free horseradish peroxidase as a retrograde tracer have had difficulties in demonstrating a rubro-olivary tract. Injections of this tracer into the inferior olive in animals of different species resulted in only a few retrogradely labelled rubral cells within the rostral part of the ipsilateral nucleus. The present study, which is based on the highly sensitive technique of Mesulam (1978), confirms this observation. Injections of free horseradish peroxidase (Serva or Sigma VI type) into the dorsal lamella of the principal olive in eleven cats gave a positive retrograde labelling of rostral rubral cells in only three animals, with a very few cells in each case. In contrast to this, olivary injections of horseradish peroxidase labelled lectin (wheat germ agglutinin) result in an abundance of retrogradely labelled cells within the rostral part of the ipsilateral red nucleus, the great majority of these cells being of the small and medium-sized type. Many of the retrogradely labelled rubral cells are only faintly stained. However, free horseradish peroxidase appears to be well suited as an anterograde tracer for a demonstration of the rubro-olivary tract.The findings are discussed in relation to the observation that in the cat only peroxidase conjugated to lectin can be used successfully as a retrograde tracer for a visualization of the rubro-olivary connection.     

Organization of afferent connections to the lateral and interpositus cerebellar nuclei from the brainstem relay nuclei: a horseradish peroxidase study in the cat

Afferent projections to the lateral (dentate) and interpositus cerebellar nuclei from the brainstem relay nuclei were studied in cats using the horseradish peroxidase (HRP) method. In the first series of experiments, HRP was injected into the brachium pontis. Mossy fiber terminals were anterogradely labeled, predominantly in the lateral (hemispherical) part, moderately in the intermediate part, and slightly in the vermal part of the cerebellum. Besides these terminals in the cerebellar cortex, axon terminals labeled anterogradely were also found in the cerebellar nuclei. The labeled terminals appeared almost exclusively in the lateral nucleus and rarely in the interpositus nucleus. Cells labeled retrogradely were found both in the pontine nuclei and the tegmental reticular nucleus, but not in other brainstem nuclei. In the second series of experiments, HRP was injected into the lateral and interpositus nuclei, and retrograde labeling was examined in the brainstem relay nuclei. After HRP injection into the lateral nucleus, the number of labeled cells was significantly large in the pontine nuclei, but fairly small in the reticular or vestibular nuclei. The number of labeled cells was generally large in the inferior olive, mainly in the principal olive. After HRP injection into the interpositus nucleus, the number of labeled cells was moderate in the reticular or vestibular nuclei, but small in the pontine nuclei. The number of labeled cells in the inferior olive was also large, being distributed mainly in the accessory olives. These results indicate that the pontine nuclei and the principal olive provide major afferent inputs to the lateral nucleus, whereas the reticular nuclei, the vestibular nuclei and the accessory olives are the major afferent sources to the interpositus nucleus.     

The cerebellar nucleo-olivary and olivo-cerebellar nuclear projections in the cat as studied with anterograde and retrograde transport in the same animal after implantation of crystalline WGA-HRP

Summary The bidirectional connections between the inferior olive and the fastigial nucleus were studied by means of anterograde and retrograde transport after implantation of crystalline wheat germ agglutinin-horseradish peroxidase (WGA-HRP) complex into the fastigial nucleus. The fastigio-olivary fibres terminate in the caudal half of the medial accessory olive, nucleus and the dorsal cap, and the olivofastigal projection has its origin within the same olivary regions. A topical arrangement is indicated for both pathways. The lateral part of the medial accessory olive appears to be connected with the lateral part of the fastigial nucleus, while the medial part of the medial accessory olive appears to be connected with more medial fastigial regions. Retrogradely labelled olivo-fastigial neurons were often located within the terminal field of anterogradely labelled fastigioolivary fibres, indicating that the olivo-fastigial and fastigio-olivary projections are at least in part reciprocally organized.The findings are discussed and related to previous studies on the olivo-cerebellar nuclear and cerebellar nucleo-olivary pathways. Some methodological considerations are made, and comments are made concerning the active area for uptake and transport from the stained area at the WGA-HRP injection site.     

Up-regulation of 5-hydroxytryptamine2 and neurokinin-1 receptors associated with serotonin/substance P hyperinnervation in the rat inferior olive.

The fate of serotonin and substance P receptors following serotonin/substance P hyperinnervation of CNS tissue was investigated in the inferior olivary complex of adult rats subjected to earlier intraventricular administration of 5,6-dihydroxytryptamine. [3H]8-hydroxy-2-(Dl-n-propylamino)tetralin, [3H]5-hydroxytryptamine, [3H]ketanserin and [125I]Bolton-Hunter-substance P were respectively used to label 5-hydroxytryptamine1A, 5-hydroxytryptamine1B, 5-hydroxytryptamine2 and neurokinin-1 receptor sites for quantitative ligand binding autoradiography. Only 5-hydroxytryptamine2 and neurokinin-1 sites were detected in the normal or serotonin/substance P-hyperinnervated inferior olivary complex. In the normal inferior olivary complex, the density of [3H]ketanserin binding (5-hydroxytryptamine2 receptors) was relatively low, being the highest in pars a of the caudal medial accessory olive and the principal olive; moderate in pars c of the caudal medial accessory olive; truly low in the medial and the lateral dorsal accessory olive, nucleus b and pars b of the caudal medial accessory olive; and negligible in the middle medial accessory olive, rostral medial accessory olive and the smaller subnuclei. [125I]Bolton-Hunter-substance P binding (neurokinin-1 receptors) appeared denser, being highest in nucleus beta and the middle medial dorsal accessory olive; moderate in the three portions of the caudal medial accessory olive, the lateral dorsal accessory olive and the dorsal cap of Kooy; low in the rostral medial accessory olive, the ventrolateral outgrowth and the dorsomedial cell column; and very low or null in the principal olive and the medial dorsal accessory olive. After serotonin/substance P hyperinnervation, there were striking increases in the apparent density of both populations of receptor. [3H]Ketanserin binding was now stronger in the most olivary subnuclei, including some in which it had not been found in the normal, such as the middle and the rostral medial accessory olive. [125I]Bolton-Hunter-substance P binding showed even greater elevations in a few subnuclei, such as the principal olive and the dorsomedial cell column; it was now detectable in the medial dorsal accessory olive, unchanged in the dorsal cap of Kooy and the ventrolateral outgrowth, and slightly decreased in the lateral dorsal accessory olive. The normal and altered distributions of both ligands did not match the respective patterns of serotonin and substance P innervation and hyperinnervation previously demonstrated with immunocytochemistry. In some sectors of the inferior olivary complex where both transmitters are presumably co-localized, there was no overlap in the distribution of the respective binding sites either in the normal or in the hyperinnervated state.(ABSTRACT TRUNCATED AT 400 WORDS)     

Olivary afferents from the brain stem reticular formation

Summary The projections from the brain stem reticular formation to the inferior olive have been studied in cats in which microinjections of horseradish peroxidase have been made into the inferior olive from a ventral approach. Retrogradely labelled cells were observed within the reticular formation proper of the medulla, pons and mesencephalon (within the nucleus reticularis parvicellularis, reticularis ventralis, reticularis gigantocellularis, reticularis lateralis, reticularis pontis caudalis, reticularis pontis oralis, cuneiformis and subcuneiformis). Labelled cells were also found within the lateral reticular nucleus (the nucleus of the lateral funiculus), the paramedian reticular and the perihypoglossal nuclei. The connections are bilateral (the projection from the lateral reticular nucleus is only contralateral). The observations demonstrate a more widespread origin for the reticulo-olivary fibres than has previously been shown and indicate that the medullary reticular formation is the area with the highest number of cells projecting to the olivary complex.Abbreviations ß nucleus ß - Br.c. superior cerebellar peduncle (brachium conjunctivum) - Br.p. middle cerebellar peduncle (brachium pontis) - C.i. inferior colliculus - C.r. inferior cerebellar peduncle (restiform body) - Cu nucleus cuneiformis - D dorsal accessory olive - dl dorsal lamella - dors.c. dorsal cap - dorsomed.c.col. dorsomedial cell column - F.l.m. medial longitudinal fasciculus - Ic or ic nucleus intercalatus - l lateral - M medial accessory olive - m medial - N.III,V,VI,VII,X,XII root fibres of cranial nerves - N.c. nucleus cuneatus - N.c.e. external (accessory) cuneate nucleus - N.c.t. nucleus of corpus trapezoideum - N.l.l. nucleus of lateral lemniscus - N.m.X dorsal motor (parasympathetic) nucleus of vagus - N.mes. mesencephalic trigeminal nucleus - Nr nucleus ruber - Nrl or N.r.l lateral reticular nucleus (nucleus of lateral funiculus) - Nrp or N.r.p. nucleus reticularis paramedianus - N.r.t. nucleus reticularis tegmenti pontis - nucl. nucleus ß - Ol.s. superior olive - P principal olive - ph or P.h. nucleus praepositus hypoglossi - PN perihypoglossal nuclei - Pp nucleus peripeduncularis - Py pyramid - Rg or R.gc. nucleus reticularis gigantocellularis - Rl or R.l. nucleus reticularis lateralis (of Olszewski) - Rp or R.pc. nucleus reticularis parvicellularis - Rpc or R.p.c. nucleus reticularis pontis caudalis - Rpo or R.p.o. nucleus reticularis pontis oralis - Rv or R.v. nucleus reticularis ventralis - Scu nucleus subcuneiformis - S.n. substantia nigra - Tr.sp.V. spinal tract of trigeminal nerve - T.s. tractus solitarius surrounded by nucleus of solitary tract - vl ventral lamella - vlo or ventrolat outgr. ventrolateral outgrowth - V.m. medial vestibular nucleus - I-XV transverse sections through the olive from caudal (I) to rostral (XV) - III,IV,V,VI,VII,X and XII motor nuclei of cranial nerves (X: nucleus ambiguus)