Corticotropin-releasing factor in cerebellar afferent systems: a combined immunohistochemistry and retrograde transport study

Abstract

The flocculus and paraflocculus of cat and sheep cerebellum were studied with immunohistochemical methods, using antisera to corticotropin-releasing factor (CRF). CRF immunoreactivity was present within 3 populations of varicose nerve fibers. One population of CRF- immunoreactive (CRF-IR) fibers appeared to appose Purkinje cell somata and to follow their dendrites into the molecular layer. This arrangement suggested they were climbing fibers. A second group of CRF- IR profiles reminiscent of mossy fibers was widely distributed throughout the granule cell layer. A third population of CRF-IR fibers was present as a beaded plexus lying parallel to the pial surface, above and subadjacent to the Purkinje cell layer. The fibers of this plexus extended into the Purkinje cell layer and surrounded these somata. The source of some of the CRF-IR fibers within the flocculus and paraflocculus was determined by a retrograde axonal transport study utilizing the fluorescent tracer Fast blue (FB) in combination with the immunohistochemical localization of CRF. It was determined that CRF-IR perikarya within the inferior olivary nucleus gave rise to a population of climbing fibers within those lobules. Furthermore, all divisions of the inferior olive were found to contain CRF-IR somata. This latter finding suggests the potential for CRF-IR climbing fiber projections from the inferior olive to other regions of the cerebellar cortex. The existence of CRF-IR mossy fibers and fibers within the ganglionic plexus suggests the possibility of CRF-IR afferent projections from other regions of the brain stem to the flocculus and paraflocculus.

Corticotropin-releasing factor in olivocerebellar climbing-fiber system of monkey (Saimiri sciureus and Macaca fascicularis): parasagittal and regional organization visualized by immunohistochemistry

“…In agreement with the observations of Cummings et al (1988) in cat and sheep, 2 other populations of labeled axons were also evident. First, some of the labeled elements in the granular layer of monkey exhibit the morphological characteristics of mossy fiber axons, i.e., enlargements and rosette configurations.…”

“…Labeled fibers were much less dense and were not clustered in the lateral hemispheres. The present observation of CRF-like immunoreactivity in the monkey olivocerebellar pathway is compatible with the previous observation of CRF mRNA within olivary neurons of rat, baboon, and human (Young et al, 1988) and with recent immunohistochemical findings in rat (Sakanaka et al, 1987;Palkovits et al, 1987), cat (Cummings et al, 1988;Kitahama et al, 1988), sheep (Cummings et al, 1988), and human (Powers et al, 1987). The present report thus reinforces the suggestion that CRF is contained within the primate olivocerebellar pathway.…”

“…Second, fine, varicose fibers were often evident running within and adjacent to the Purkinje cell layer. As indicated by Cummings et al (1988), these observations suggest that there are also extraolivary, CRF-containing afferents to cerebellar cortex. In any case, the present morphological observations strongly indicate that CRFLI is contained (although not exclusively) within the olivocerebellar pathway since processes exhibiting all known morphological features of climbing fibers and their collaterals are observed to contain CRPLI in these 2 species.…”

“…Both immunohistochemical and in situ hybridization techniques have yielded data compatible with this hypothesis. For example, CRFLI has been observed in inferior olive perikarya of rat (Palkovits et al, 1987;Sakanaka et al, 1987), cat (Cummings et al, 1988;Kitahama et al, 1988), and sheep (Cummings et al, 1988). In rodent studies, it has generally been observed that unambiguous staining of neuronal perikarya for CRF, except in the paraventricular nucleus, is obtained only when colchicine has been administered prior to sacrifice.…”

“…In most early immunohistochemical studies, CRFLI was either not observed in the olivocerebellar system or only weak immunoreactivity was evident (Merchenthaler et al, 1982Cummings et al, 1983;Schipper et al, 1983). However, recent light-microscopic observations in rat (Palkovits et al, 1987;Sakanaka et al, 1987) cat (Cummings et al, 1988;Kitahama et al, 1988), and sheep (Cummings et al, 1988) have demonstrated substantial CRFLI in inferior olive perikarya and in axons in cerebellum. This is compatible with reports of high levels of CRF in inferior olive as measured by radioimmunoassay (Palkovits et al, 1983(Palkovits et al, , 1985 and with demonstrations of CRF mRNA in these neurons by in situ hybridization in rat (Young et al, 1986;Palkovits et al, 1987) baboon, and human (Young et al, 1986).…”