Differential regulation of forebrain glutamic acid decarboxylase mRNA expression by aging and stress.

In aging brain, degeneration or functional impairment of the hippocampus has been connected with stress dysregulation, serving to disinhibit stress responses and allow for glucocorticoid hypersecretion and its attendant pathophysiology. Hippocampal dysfunction appears to be communicated to paraventricular hypothalamic corticotropin-releasing hormone neurons by way of subcortical GABAergic neurons. As such, hippocampal-hypothalamic relays are likely to play an important role in age-related stress dysfunction. To test this hypothesis, regulation of glutamic acid decarboxylase isoform mRNA was studied in young (3 months), middle aged (15 months) and aged (30 months) Fischer 344/Brown Norway F1 hybrid rats. Basal expression of glutamic acid decarboxylase (GAD) 65 mRNA was increased in the medial preoptic area and posteromedial bed nucleus of the stria terminalis (BST) in aged rats relative to both middle-aged and young groups. Unlike young or middle-aged animals, exposure to chronic intermittent stress decreased GAD65 mRNA levels in the medial preoptic area and posteromedial BST of aged rats. Thus, while aged rats show evidence of elevated basal GABA synthesis, chronic stress causes differential loss of GAD in hippocampal-PVN relays, consistent with reduced PVN inhibition.

Hypothalamo-pituitary-adrenocortical dysregulation in aging F344/Brown-Norway F1 hybrid rats.

Hypothalamo-pituitary-adrenocortical (HPA) axis aging was studied in young (3 mo), middle aged (15 mo) and aged (30 mo) F344/Brown Norway hybrid rats. This strain was selected to obviate HPA-relevant pathologies found in other aging models. Aged, unstressed rats showed enhanced central HPA drive, marked by elevated ACTH release and decreased pituitary proopiomelanocortin and corticotropin-releasing factor receptor 1 (CRH-R1) mRNAs. Acute corticosterone responses to spatial novelty were exacerbated in aged rats; however, responses to restraint or hypoxia were not affected. Chronic stress exposure also differentially increased HPA drive in aged animals, marked by elevated paraventricular nucleus CRH peptide levels and pituitary proopiomelanocortin mRNA. Plasma ACTH and pituitary POMC and CRH-R1 mRNA expression in middle-aged rats were intermediate those of young and aged animals. Middle-aged animals responded to chronic stress with disproportionate increases in CRH mRNA levels, and increased corticosterone secretion following hypoxia but not novelty. The results suggest a gradual increase in HPA tone across the aging process, culminating in marked hyperresponsivity to both acute and chronic stress in senescence.

Purification and partial characterization of a bovine epidermal growth factor-like polypeptide.

A heterologous radioreceptor assay was developed to follow the purification of an EGF-like polypeptide from bovine kidney. Purification of the growth factor was facilitated by the use of a novel affinity column using fixed A431 cells attached to sephadex beads. The mol. wt. of the purified EGF-LP was estimated to be 5480 from the amino acid composition. The purified EGF-like polypeptide stimulated the proliferation of bovine mammary epithelial cells and appeared to be equipotent to mouse EGF. Available evidence suggests that the purified molecule is distinct from bovine TGF-alpha.

A model system for mass spectrometric sequencing of orthophthalaldehyde peptide derivatives.

Presented is a pilot project describing a new strategy for mass spectrometric peptide sequencing. Using orthophthalaldehyde (OPA), two peptides were derivatized and their fluorescent adducts isolated using reversed phase high performance liquid chromatography. The OPA-peptides were permethylated and the derivatized molecules subjected to direct probe mass spectral analysis. The spectra obtained from OPA-peptides was analogous to those observed for standard N-acyl permethyl derivatives enabling the complete sequence of the peptides to be determined.