Isolation of N-acetylaspartic acid from hypothalamic tissue and significance of its ACTH-releasing activity

Peptide chemistry: development of high performance liquid chromatography and capillary zone electrophoresis

The development of relatively non-compressible supporting media of small particle size as well as pumps that deliver constant flow rates at high pressures has enabled investigators to perform rapid, high resolution liquid chromatography for more than two decades. Studies initiated in this laboratory in 1975, evaluating the compatibility of unprotected peptides with commercially available chromatographic supports and development of solvent systems ultimately led to separations not previously observed with both synthetic peptides and native peptides from tissue extracts. It was rapidly realized however, that recovery of certain molecules could be problematic. To meet the challenges presented by the isolation of natural hormones (such as corticotropin releasing factor and growth hormone releasing hormone) and proteins (such as inhibin and activin) and the need for large quantities of highly purified peptides for clinical investigations, our group invested heavily in identifying new supports (high carbon loading and 300 A pore sizes) and solvent systems (triethylammonium phosphate and trifluoroacetic acid) compatible with reverse phase, size exclusion and ion exchange chromatographies from a practical and economical perspective. More recently, we have contributed to the identification of unusual buffer systems (inclusive of organic modifiers) compatible with capillary zone electrophoresis that will both modulate the capillaries' selectivity, increase resolution and serve as an orthogonal approach to determining peptide purity. From a pragmatic point of view, in this paper we highlight the original and timely contributions (technical and strategical) of this laboratory in the field of analytical and preparative high performance liquid chromatography and capillary zone electrophoresis of synthetic and native biologically active peptides and proteins over the past twenty years.

Inhibition by N-acetyl-aspartate of aspartate binding to a proteolipid fraction from rat cerebral cortex

Many roles have been suggested for N-acetyl-aspartate in brain function because of it being located almost exclusively in that organ. However, its true role remains to be demonstrated. We show here that N-acetyl-aspartate: 1) binds to a hydrophobic protein fraction from the cerebral cortex of the rat, which specifically binds L-aspartate, L-glutamate, and gamma-amino-butyric acid; and 2) has a marked inhibitory effect on the aspartate binding sites of this proteolipid fraction. Structural analogs of N-acetyl-aspartate, i.e. N-carbamyl-aspartate and N-methyl-aspartate also inhibit the L-aspartate binding by the brain protein fraction used.

Immunocytochemical localization of corticotropin-releasing factor (CRF) in the rat brain

The immunocytochemical localization of neurons containing the 41 amino acid peptide corticotropin-releasing factor (CRF) in the rat brain is described. The detection of CRF-like immunoreactivity in neurons was facilitated by colchicine pretreatment of the rats and by silver intensification of the diaminobenzidine end-product. The presence of immunoreactive CRF in perikarya, neuronal processes, and terminals in all major subdivisions of the rat brain is demonstrated. Aggregates of CRF-immunoreactive perikarya are found in the paraventricular, supraoptic, medial and periventricular preoptic, and premammillary nuclei of the hypothalamus, the bed nuclei of the stria terminalis and of the anterior commissure, the medial septal nucleus, the nucleus accumbens, the central amygdaloid nucleus, the olfactory bulb, the locus ceruleus, the parabrachial nucleus, the superior and inferior colliculus, and the medial vestibular nucleus. A few scattered perikarya with CRF-like immunoreactivity are present along the paraventriculo-infundibular pathway, in the anterior hypothalamus, the cerebral cortex, the hippocampus, and the periaqueductal gray of the mesencephalon and pons. Processes with CRF-like immunoreactivity are present in all of the above areas as well as in the cerebellum. The densest accumulation of CRF-immunoreactive terminals is seen in the external zone of the median eminence, with some immunoreactive CRF also present in the internal zone. The widespread but selective distribution of neurons containing CRF-like immunoreactivity supports the neuroendocrine role of this peptide and suggests that CRF, similarly to other neuropeptides, may also function as a neuromodulator throughout the brain.

Extrahypothalamic distribution of CRF-like immunoreactivity in the rat brain

CRF-like immunoreactivity was measured by radioimmunoassay in the brains of normal adult rats and found to be widely distributed in extrahypothalamic areas (e.g., thalamus, amygdala, hippocampus, frontal cerebral cortex, striatum, midbrain, pons-medulla and cerebellum) at levels approximately 10% of the hypothalamus. Sephadex G-50 gel filtration reveals that CRF-like immunoreactivity in the hypothalamus coelutes with synthetic ovine CRF and is also present in the void volume. However, in the extrahypothalamic areas of the rat brain, only CRF-like immunoreactivity that coelutes with synthetic ovine CRF was detected. High performance liquid chromatography revealed equal amounts of immunoreactivity coeluting with CRF and methionine sulfoxide CRF in hypothalamic extracts.