Axon collaterals of mossy fibers from the pontine nucleus in the cerebellar dentate nucleus

Abstract

1. Single axons of pontine nucleus neurons (PN axons) receiving cerebral input were stained intra-axonally with horseradish peroxidase (HRP) in the cerebellum of cats. The axonal trajectory of single PN axons was reconstructed from serial sections of the cerebellum and the brain stem. 2. Axons were penetrated in the white matter near the dentate nucleus, and, after electrophysiological identification, PN axons were injected iontophoretically with HRP. The identification criteria for the PN axons were 1) their direct responses to stimulation of the contralateral pontine nucleus (PN), 2) their synaptic activation from the contralateral cerebral cortex, and 3) the decrease in threshold for evoking direct spikes in stimulation of the PN by conditioning stimuli applied in the cerebral cortex. 3. Two hundred thirty-three axons were electrophysiologically identified as PN axons receiving the input from the cerebral cortex. Ninety-six of them were stained successfully with HRP, and reconstructions were made from 40 well-stained PN axons. All of them gave rise to mossy fibers and terminated in the granular layer of the cerebellar cortex as typical mossy fiber rosettes. Out of these, 22 gave axon collaterals to the dentate nucleus. Virtually all of the axon branches observed in the dentate nucleus were axon collaterals of mossy fibers from the PN to the cerebellar cortex. In 7 of these 22 PN axons, cell bodies were retrogradely labeled with HRP, and all of them were found in the contralateral PN. 4. The stained-stem axons arising from the PN ran medially in the pons, crossed the midline, and then ascended dorsocaudally in the branchium pontis. After passing in the white matter anterior to or lateral to the dentate nucleus, they entered into the cerebellar cortex. On their way, one to three axon collaterals were given off from parent axons to the dentate nucleus. The diameter of these collaterals was very thin (mean, 0.6 microns), compared with the large diameter of the parent axons (mean, 2.1 microns). 5. Some axon collaterals were very simple and had only one terminal branch with or without short branchlets, whereas others were more complex, and single axon collaterals ramified before forming a terminal arborization. Axon collaterals of single PN axons mainly spread mediolaterally or dorsoventrally in the frontal plane but had a very narrow rostrocaudal extension. 6. Terminal branches usually bore swellings en passant along their length and one terminal swelling at their end. The number of swellings per axon collateral ranged 23-180 (116 +/- 52, mean +/- SD).(ABSTRACT TRUNCATED AT 400 WORDS)

Neural Substrates of Eyeblink Conditioning: Acquisition and Retention

“…Thompson et al 1991;Shinoda et al 1992;Steinmetz and Sengelaub 1992;Mihailoff 1993). The pontine nuclei in turn receive projections from auditory, visual, somatosensory, and association systems, both cortical and subcortical (Glickstein et al 1980;Brodal 1981;Schmahmann and Pandya 1989.…”

Pontine Maps Linking Somatosensory and Cerebellar Cortices Are in Register with Climbing Fiber Somatotopy

“…However, other studies have shown that neighboring relationships may be preserved in the SI-pontine projection, suggesting instead that the fractured cerebellar map arises in the second link, the pontocerebellar projection (Leergaard et al, 2000a,b). Several studies have shown that pontocerebellar mossy fibers are highly collateralized (Mihailoff, 1983;Shinoda et al, 1992;Bjaalie and Brodal, 1997;Voogd et al, 2003), and physiological data indicate that mossy fiber collateralization underlies the fractured organization of the trigeminocerebellar projection (Woolston et al, 1981). Other data in rats that support the notion of fractured cerebellar maps created by such branching are that (1) pontine cells seem to have small peripheral receptive fields (Eycken et al, 2000;Rajan et al, 2000), and (2) pontine cells projecting to single body representations in the posterior cerebellum are distributed across the entire region of the pontine nuclei receiving inputs from SI cortex (present study).…”

Signalling properties of identified deep cerebellar nuclear neurons related to eye and head movements in the alert cat.

“…Cerebellar vermis and hemispheres seem also to be involved in saccadic eye movements and fixation (Kase et al 1980;Mano et al 1991). These cerebellar cortical areas have also been reported as receiving proprioceptive inputs from extraocular muscles (Baker, Precht & Llina's, 1972 (Bloedel & Courville, 1981;Shinoda et al 1992). Recent reviews of the brainstem afferents to the fastigial nucleus (Yamada & Noda, 1987;Blanks, 1988;Gonzalo-Ruiz et al 1988) have shown that fastigial neurons receive afferents from the medial and descending vestibular nuclei, the perihypoglossal nuclei, the paramedian pontine reticular formation, and from the perioculomotor region (see Roste & Dietrichs, 1988).…”

“…Cerebellar nuclear neurons are monosynaptically inhibited by overlying Purkinje cells (Ito, Yoshida, Obata, Kawai & Udo, 1970) and excited from axon collaterals of mossy and climbing afferent fibres projecting to the corresponding cerebellar cortex (Bloedel & Courville, 1981;Shinoda, Sugiuchi, Futami & Izawa, 1992). These ascending inputs originate in many brainstem structures related to eye and head movements, such as the superior colliculus, the paraoculomotor region, the nucleus reticularis tegmenti pontis, the paramedian pontine reticular formation, the vestibular nucleus, the nucleus prepositus hypoglossi and the inferior olive (Noda, Sugita & Ikeda, 1990; for a review see Blanks, 1988).…”