Effects of early visual experience and diurnal rhythms on BDNF mRNA and protein levels in the visual system, hippocampus, and cerebellum.

The expression of brain-derived neurotrophic factor (BDNF) mRNA and the secretion of BDNF protein are tightly regulated by neuronal activity. Thus, BDNF has been proposed as a mediator of activity-dependent neural plasticity. Previous studies showed that dark rearing (DR) reduces BDNF mRNA levels in the primary visual cortex (V1), but the effects of visual experience on BDNF protein levels are unknown. We report that rearing in constant light or DR alters BDNF mRNA and protein levels in the retina, superior colliculus (SC), V1, hippocampus (HIPP), and cerebellum (CBL), although the changes in mRNA and protein are not always correlated. Most notably, DR increases BDNF protein levels in V1 although BDNF mRNA is decreased. BDNF protein levels also undergo diurnal changes. In the retina, V1, and SC, BDNF protein levels are higher during the light phase of the circadian cycle than during the dark phase. By contrast, in HIPP and CBL, the tissue concentration of BDNF protein is higher during the dark phase. The discrepancies between the experience-dependent changes in BDNF mRNA and protein suggest that via its effects on neuronal activity, early sensory experience alters the trafficking, as well as the synthesis, of BDNF protein. The circadian changes in BDNF protein suggest that BDNF could cause the diurnal modulation of synaptic efficacy in some neural circuits. The fluctuations in BDNF levels in nonvisual structures suggest a potential role of BDNF in mediating plasticity induced by hormones or motor activity.

Neuregulin is a mitogen and survival factor for olfactory bulb ensheathing cells and an isoform is produced by astrocytes.

The rat olfactory bulb is an exceptional CNS tissue. Unlike other areas of the brain, growing axons are able to enter the olfactory bulb and extend within this CNS environment throughout adult life. It appears that the glial cells of the olfactory system, known as olfactory bulb ensheathing cells (OBECs), may have an important role in this remarkable process of CNS neural regeneration. OBECs are unusual glial cells, possessing properties of both astrocytes and Schwann cells. In this study we show that astrocytes (in the form of astrocyte-conditioned medium; ACM) produce two critical regulatory functions for OBECs: mitogenic activity and a survival factor. Interestingly, the ACM-derived activity for OBECs appears to reside in a signalling protein(s) belonging to the neuregulin (NRG) family of growth factors, and specifically appears to coincide with one or more products of the nrg-1 gene. Our observations provide evidence for the following: recombinant human neu differentiation factors (NDFbeta1, -2 and -3) are mitogenic to OBECs; the activity in ACM can be neutralized by NDF antibodies; these same antibodies detect a 50-kDa, non-heparin binding protein in concentrated ACM; astrocytes express detectable nrg-1 transcripts; and OBECs express functional NRG receptors erbB2 and erbB4.

A single purification procedure for the major resident proteins of the ER lumen: endoplasmin, BiP, calreticulin and protein disulfide isomerase.

We have developed a single purification procedure for the four major resident endoplasmic reticulum (ER) proteins: protein disulfide isomerase (PDI), BiP, endoplasmin, and calreticulin. Three of these proteins are thought to play a role in protein folding in vivo, whereas calreticulin is thought to be the major calcium binding protein in the ER. The proteins were purified from fresh bovine liver by taking advantage of individual characteristics of the proteins. Liver microsomes were prepared and then premeabilized to release the lumenal contents. After ammonium sulfate precipitation, the proteins were purified by chromatography; BiP was purified by affinity chromatography on ATP-agarose, and both endoplasmin and calreticulin were purified by affinity chromatography on Con A-Sepharose. PDI was purified by anionic ion exchange chromatography.