D-aspartate modulates transcriptional activity in Harderian gland of frog, Rana esculenta: Morphological and molecular evidence

✍ Scribed by Franca Raucci; Alessandra Santillo; Antimo D'Aniello; Paolo Chieffi; Gabriella Chieffi Baccari

• Publisher: John Wiley and Sons
• Year: 2005
• Tongue: English
• Weight: 788 KB
• Volume: 204
• Category: Article
• ISSN: 0021-9541
• DOI: 10.1002/jcp.20316

✦ Synopsis

Abstract

In the green frog, Rana esculenta, a substantial amount of D‐aspartate (D‐Asp) is found endogenously within the Harderian gland (HG) following its synthesis from L‐aspartate (L‐Asp) by an aspartate racemase. The frog HG is an orbital seromucoid gland that displays seasonal changes in secretory activity. Our in vivo experiments, consisting of i.p. injection of 2.0 μmol/g b.w. D‐Asp in frogs collected during two periods of differing glandular activity (high or medium‐low secretory activity), revealed that HG can to take up and accumulate D‐Asp and that this amino acid may modulate the exocrine secretion through a kinase pathway. At a time when the gland shows relatively low secretory activity, i.p. administration of D‐Asp rapidly induced activation of ERK1 and an increase in cells active in RNA synthesis. This increase in transcriptional activity was followed by a significant increase in mucous secretion. By contrast, administration of exogenous D‐Asp when HG was showing high activity rapidly induced inhibition of both ERK1 and transcriptional activity. Since D‐Asp is known to be recognized by receptors for N‐methyl‐D‐aspartic acid (NMDA), it is possible that in the HG, D‐Asp mediated NMDA activation may enhance the kinase pathway. The above activation of opposing stimulatory and inhibitory processes could reflect different levels of NMDA‐receptor activity, which could vary as a function of the level of gland activity. This study provides the first evidence of a role for this excitatory amino acid in exocrine secretion. The effects of D‐Asp in HG appear to be specific since they were not seen in frogs treated with other D‐ or L‐amino acids with known excitatory effects on neurosecretion. © 2005 Wiley‐Liss, Inc.