David Y. Lo

Date of Award

7-15-2010

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Anatomy and Cell Biology

First Advisor

John Watt

Abstract

Ciliary neurotrophic factor, a member of the interleukin-6 family of cytokines, promotes neuronal survival and axonal sprouting in various populations of neurons including sensory neurons, motor neurons, and magnocellular neurons (MCN's) of the supraoptic nucleus (SON). Unilateral lesion of the hypothalamo-neurohypophysial tract (HNT) results in an initial period of axonal degeneration followed by a restoration of axonal density in the neurohypophysis by 30 days post-lesion. The restoration of axonal density is attributed to collateral sprouting from MCN's of the intact contralateral SON. A statistically significant increase in CNTF levels was demonstrated previously in the intact contralateral SON following unilateral lesion of the HNT. A statistically significant increase in the number of CNTF-immunoreactive cells was also observed in the neurohypophysis following unilateral lesion of the HNT. These findings suggest that CNTF may play an important role in modulating neuronal plasticity in the injured hypothalamo-neurohypophysial system (HNS). However, the cellular phenotype that expresses CNTF in the neurohypophysis and the functionality of CNTF receptors in the HNS has not been addressed. Therefore, the purpose of the current study was three fold; to identify the CNTF expressing cell type in the neurohypophysis and elucidate the mechanism by which it up-regulates CNTF, and to identify and assay the functionality of CNTF-related signaling components in the HNS. CNTF rmmunoreactivity was localized to p75 low affinity neurotrophin receptor (p75)-positive perivascular cells in the neurohypophysis using dual-label immunocytochemistry. Phagocytosis-dependent labeling of p75-positive perivascular cells established a link between CNTF up-regulation and neuronophagia. These findings indicate that CNTF expressing perivascular cells of the neurohypophysis participate in degenerative and regenerative events following MCN axotomy. The CNTF specific receptor, CNTF receptor α, was immunocytochemically localized to neurons and astrocytes of SON and to pituicytes of neurohypophysis. CNTF-mediated signal transduction was investigated through acute injections of rat recombinant CNTF. Bio-Plex analysis of the SON 1 hr and 3 hrs post-CNTF injection demonstrated an upregulation of the JAK/STAT, PI3/Akt, and the MEK/ERK pathways and a down-regulation of the JNK pathway. These results indicate that cells of the SON possess functional CNTF receptors that mediate the biological effects of CNTF.

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