The distribution of corticotropin-releasing factor (CRF), CRF binding sites and CRF1 receptor mRNA in the mouse cerebellum

The purpose of the present study is to determine the distribution of CRF containing afferents, and correlate these findings with the distribution of CRF binding sites and the neuronal localization of mRNA for the CRF1 receptor in the cerebellum of a single species, the mouse. Corticotropin releasing factor (CRF) has been localized within climbing fibers and mossy fibers throughout the cerebellar cortex of the mouse using immunohistochemistry. CRF immunoreactive, axonal varicosities also are present within all four of the cerebellar nuclei. 125I-labeled CRF binding sites are evident throughout all three layers of the cerebellar cortex (molecular, Purkinje and granule cell layers), but are not seen within the cerebellar nuclei. In situ hybridization histochemistry was employed using an antisense riboprobe corresponding to the full length sequence of the rat mRNA for the CRF1 receptor. Positive signal is present throughout the cerebellum in Purkinje cells and the granule cell layer. CRF1 receptor mRNA also is expressed within all four of the cerebellar nuclei. Further experiments are required to reconcile the lack of CRF binding sites in the cerebellar nuclei with the positive mRNA receptor expression and the presence of immunoreactive axonal varicosities. In previous physiological experiments, iontophoretic application of CRF enhances spontaneous as well as quisqualate-induced activity of Purkinje cells in slice preparations of the mouse cerebellum. When the results of the anatomical techniques are compared to the physiological data, there is convergent evidence to suggest that CRF influences the firing rate or responsiveness of Purkinje cells directly via release of the peptide from the climbing fiber system and indirectly via the mossy fiber-granule cell-parallel fiber circuit. Taken together, these anatomical and physiological data provide strong evidence to suggest that, in the adult cerebellum, CRF functions as a neuromodulator.

Developmental expression of corticotropin-releasing factor in the postnatal murine cerebellum

Corticotropin-releasing factor (CRF) is present in climbing and mossy fibers and both have a distinct pattern of distribution in the adult cerebellar cortex. The intent of this developmental study is to determine when the lobular pattern of CRF distribution emerges, and to analyze the morphogenesis of CRF immunoreactive climbing and mossy fibers in individual cerebellar lobules. Between postnatal day (P)0 and P3, CRF-immunoreactive (IR) punctate elements are present throughout the cerebellum. By P3, there is a decrease in the density of staining in the white matter and punctate elements become concentrated within the developing cortex. Between P3 and P7 CRF-IR, varicosities circumscribe Purkinje cell bodies, and are present in the internal and external granule cell layers. Between P10 and P12, there is a major reduction in the density of CRF-IR puncta, especially in the internal and external granule cell layers. Varicosities remain around Purkinje cell bodies and some extend into the molecular layer. During this interval, CRF-IR profiles are first evident in axonal configurations characteristic of developing climbing fibers, although there are lobular differences in the degree of maturation of this afferent system. Axonal enlargements characteristic of immature mossy fibers can first be seen at P10 in lobules IX and X; they cannot be differentiated until P12-14 in more rostral or lateral lobules. CRF-IR fibers in lobules IX and X, the vestibulocerebellum, develop into mature climbing and mossy fibers before any other area of the cerebellum. In other lobules of the cerebellum the gradient of maturation for these axonal phenotypes is from medial to lateral and posterior to anterior. Between P10 and P12, CRF-IR climbing fibers are present in all lobules of the cerebellum. After P12, few climbing fibers are observed in the anterior lobe of the cerebellum at midvermal levels; those present are only faintly immunolabeled. Based on its early expression and uniform distribution between P0 and P10, CRF could have a role in cerebellar development. After this age, as climbing and mossy fiber terminal phenotypes mature, and the differential adult patterns of distribution emerge, CRF likely begins to function as a neuromodulator as has been shown in the adult cerebellum.

A comparison of the genotoxic effects of carboplatin and cisplatin in Escherichia coli

cis-Diammine(1,1,-cyclobutanedicarboxylato)platinum(II) (carboplatin) is a second generation platinum anticancer agent with antineoplastic properties like that of its parent compound, cis-diamminedichloroplatinum(II) (cisplatin) but with substantially less deleterious side effects in treated patients with cisplatin. We compared their genotoxic effects in Escherichia coli and found carboplatin to be less cytotoxic (measured as loss of colony forming ability) that cisplatin in that equitoxic doses required greater than 60 time more carboplatin. However, solutions of carboplatin containing chloride ion became more cytotoxic to E. coli after a 24 h incubation period than similar freshly made solutions. Two platinum conversion products which were neither present in freshly made solutions nor in solutions lacking chloride were resolved by thin-layer chromatography (TLC). One of the conversion products migrated like cisplatin and its occurrence in carboplatin solutions was associated with cisplatin-like properties, enhanced cytotoxicity and ability to induce the SOS responses in E. coli. The SOS-inducing abilities were determined by induction of a sulA::lacZ fusion. Likewise, adducts formed in end-labeled oligonucleotides treated with carboplatin appeared identical to those caused by cisplatin when carboplatin was preincubated in chloride-containing solutions but not by carboplatin in freshly made solutions. It is likely that responses evoked by carboplatin in biological systems are partly due to activation of carboplatin by its conversion of cisplatin.

Ontogeny and effect of activity on proenkephalin mRNA expression during development of the chick spinal cord

Numerous studies have shown in the adult nervous system that mRNA expression can be regulated by neuronal activity. To examine the effect of activity during embryogenesis, the ontogeny of proenkephalin mRNA expression and expression following activity blockade was investigated during development of chick spinal cord. A cDNA fragment (ca. 0.5 kb) coding for chick proenkephalin was cloned and sequenced. With this cDNA, a cRNA probe was made to examine proenkephalin mRNA expression in the spinal cord during embryogenesis. Proenkephalin mRNA was expressed in spinal cord in clusters of cells located in the developing dorsal horn and intermediate lamina at the earliest stages examined (stage 22; E4). Proenkephalin-positive cells in the intermediate lamina were located immediately adjacent to the ventricular zone. At stage 28 (E6) an additional cluster of proenkephalin mRNA-positive cells was seen at the lateral border of the developing intermediate lamina. At stage 33 (E7.5-5-8) the pattern of hybridization positive cells was similar to earlier stages, but individual cells could be identified. At stage 39 (E13) densely labeled cells were seen throughout the dorsal horn and intermediate laminae including the column of Terni. To determine whether neural activity affects proenkephalin mRNA expression, d-tubocurarine (an inhibitor of neural activity) was injected into developing embryos. Following administration of d-tubocurarine a dramatic decrease was seen in proenkephalin mRNA hybridization in the dorsal horn and intermediate lamina of the spinal cord. This study demonstrates in vivo that changes in the level of neural activity can alter gene expression during embryogenesis and suggests that activity is required for expression of nervous system-specific genes.