HEMILABYRINTHECTOMY CAUSES BOTH AN INCREASE AND A DECREASE IN CORTICOTROPIN-RELEASING FACTOR MESSENGER-RNA IN RAT INFERIOR OLIVE

It was previously shown [NeuroReport, 3 (1992) 829-832] that unilatera l labyrinthectomy (UL) induces Fos expression in several brainstem reg ions, including the beta subnucleus of the inferior olive. Using isoto pic P-33 in situ hybridization, the present results demonstrate signif icant changes in oligonucleotide-probed mRNA levels for corticotropin- releasing factor (CRF) in the rat inferior olivary nucleus 4 days foll owing unilateral labyrinthectomy (UL). In the medulla of normal animal s there was strong CRF mRNA labeling in the inferior olivary nucleus, and weaker labeling in the vestibular nuclei and prepositus hypoglossi . Following unilateral labyrinthectomy, the contralateral olivary beta subnucleus showed a significant increase in CRF message, similar to t he contralateral Fos labeling observed after hemilabyrinthectomy [Neur oReport, 3 (1992) 829-832]. In addition, the contralateral A and B sub nuclei (IOA/B) of the inferior olive showed a strong increase in CRF l abeling, while the ipsilateral dorsal cap of Kooy (IOK) showed a decre ase. This novel bidirectional alteration in CRF message in different s ubdivisions of the same nuclear group indicates the existence of both up and down regulatory mechanisms controlling CRF peptide expression, and reflects the dynamic neurochemical alterations occurring during ve stibular compensation.