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Multiple-unit activity from rabbit cerebellar cortex and interpositus nucleus during classical discrimination/reversal eyelid conditioning.

Multiple-unit activity was monitored in the hemispheric lobule VI (HVI) and the interpositus nucleus of the cerebellum during classical discrimination and reversal eyelid conditioning in rabbits. During both phases of conditioning similar patterns of activity were observed in lobule HVI: conditioned response (CR)-related activity was present on conditioned stimulus (CS)+trials but not on CS-trials. Activity in the interpositus nucleus differed during the two phases of conditioning. After discrimination training, CR-related activity was present on CS+but not CS-trials. After reversal training, however, only a weak activation of the interpositus nucleus was seen on CS+trials with no activation present on CS-trials. These data suggest that lobule HVI and the interpositus nucleus may play different roles in classical eyelid conditioning.

Action Potentials↗

Cerebellar cortex and eyeblink conditioning: a reexamination.

We examined the effects of cerebellar cortical lesions upon conditioned nictitating membrane responses in rabbits. Using extended postoperative conditioning and unpaired presentations of the conditioned stimuli (CSs), we confirmed that combined lesions of lobules HVI and ansiform lobe abolished conditioned responses (CRs) established to light and white noise CSs. Extended retraining enabled some slight recovery of CR frequencies. Less extensive cortical lesions produced initial abolition of CRs but allowed more complete recoveries. Although CR frequencies and amplitudes were profoundly depressed by cortical lesions, unconditioned response (UR) amplitudes to periorbital electrical stimulation were enhanced. The dissociation of lesion effects upon conditioned and unconditioned responses is consistent with the suggestion that cerebellar cortical mechanisms are important for the learning and execution of eyeblink conditioning.

Acoustic Stimulation↗

Projections from the lateral reticular nucleus to the cerebellar cortex and nuclei in the cat.

The fiber projection from the lateral reticular nucleus (LRN) to the cerebellum was examined in the cat. Electrolytic lesions were placed in a confined area of the LRN using a parapharyngeal approach, and the ensuing degeneration was studied in sections stained by the Nauta and the Fink-Heimer methods. Fibers from the LRN ascend the ipsilateral restiform body, terminating bilaterally but chiefly in the ipsilateral cerebellum. In the ipsilateral cortex projections were found to lobules I to V, with denser terminations in sublobules IVb to Ve. The projections are stronger in the intermediate-lateral zones than in the vermis proper. There is also a dense projection to sublobules VId and VIf and to the medialmost part of the simple lobule (HVI). Scanty termination was seen in the medialmost part of crus I. There is a moderate projection to the caudalmost folium of sublobule VIIb and to the rostral folia of sublobule VIIIa and the paramedian lobule. The contralateral projection by fibers crossed within the cerebellum is far less dense but clearcut in the anterior lobe, the rostral folia of lobule VI and the medial part of the simple lobule. In the ipsilateral nuclei strong projections were found to rostral portions of the medial nucleus (M) and the caudal two thirds of the anterior interpositus nucleus (IA) with predominance in the lateral part of the latter. A focal projection was found to rostrodorsal portions of the posterior interpositus nucleus (IP). No projection was found to the lateral nucleus (L). Contralaterally there is a weak projection to the rostral part of M and the medial parts of IA and IP.

Afferent Pathways↗

An HRP and autoradiographic study of the projection from the cerebellar cortex to the nucleus interpositus anterior and nucleus interpositus posterior of the cat.

The recently developed anatomical techniques of retrograde transport of the enzyme horseradish peroxidase (HRP), anterograde transport of tritiated amino acid, and intracellular injections of HRP were used to study the organization of the corticonuclear projection to the nucleus interpositus anterior (NIA) and the nucleus interpositus posterior (NIP) of the cat. Injections of HRP into the NIA and the NIP revealed that the major areas of the cortex which provided afferents to these two nuclei were the intermediate cortex of the anterior lobe (IAL) and the paramedian lobule (PML). There were, however, significant differences in the distribution of Purkinje (Pk) cells which projected to each nucleus. The NIA received afferents from all areas of the IAL while the NIP projection area was restricted to a band located at the medi-almost aspect of the lobe. All areas of the PML, in particular the intermediate folia, projected to the NIP, while the Pk cells which sent axons to the NIA were restricted to the rostral and caudal folia of this lobule. The projection from each area was somatotopically organized. The axons of intracellularly stained Pk cells were followed to their termination in the NIA and NIP confirming the results obtained with the two extracellular techniques. An attempt was made to examine the organization of the corticonuclear projection at the single cell level in the PML. Pk cells located in the same sagittal plane appeared to terminate in the same area of the same nucleus while Pk cells located not more than 500 micrometers medial or lateral to each other terminated in different nuclei. Basically, the organization of the corticonuclear projection from the IAL is longitudinally organized while the PML has a much more complex arrangement in which the Pk cells projecting to the NIA and NIP are interspersed.

Amino Acids↗