STRESS HORMONE RELEASE AND PROOPIOMELANOCORTIN MRNA LEVELS IN NEONATAL RATS TREATED WITH MONOSODIUM GLUTAMATE TO INDUCE NEUROTOXIC LESIONS

Stress hormone release and proopiomelanocortin (POMC) mRNA levels in the anterior pituitary were measured in neonatal rats exposed to repeated glutamate treatment (4 mg/g ip on postnatal days 2, 4, 6, 8 and 10) used to induce neurotoxic lesions in the experimental ‘MSG syndrome’. Since the solution of glutamate in the dose required is hypertonic, the effects of a similar treatment with hypertonic saline (10 percent) were also evaluated. Plasma corticosterone rose in response to both hypertonic saline and glutamate treatment and the response was of a higher magnitude on postnatal day 2 compared to that on day 10. Repeated stress associated with hypertonic saline and glutamate injections resulted in an increase in plasma ACTH and POMC mRNA levels in the anterior pituitary as observed on postnatal day 10. The data provide evidence that the exposure to stress is able to induce a rise in POMC transcription also during the stress-hyporesponsive period. The treatment of neonatal rats with monosodium glutamate provoked a considerable stress response which was significantly higher than that induced by hypertonic saline. © 1998 John Wiley & Sons, Ltd.