Monosodium glutamate does not alter ACTH- or apomorphine-induced penile erection and yawning

The effect of the intracerebroventricular (ICV) injection of ACTH 1-24 (1, 5 and 10 micrograms) or the subcutaneous administration of apomorphine (20 and 80 micrograms/kg SC) on spontaneous penile erection and yawning was studied in rats treated with monosodium glutamate (MSG), a treatment that depletes hypothalamic ACTH, alpha-MSH and endorphin-like peptides. Neonatal MSG treatment failed to antagonize either apomorphine- or ACTH-induced yawning in male and female rats, or to alter the number of penile erection episodes induced by the two substances in male rats. In contrast, hypophysectomy, that does not alter the concentration of hypothalamic ACTH and alpha-MSH, caused a marked prevention of apomorphine- and ACTH-induced responses, in agreement with previous studies. The results suggest that the integrity of opiomelanotropinergic neurons in the hypothalamus is not necessary for the induction of yawning and penile erection by ACTH-derived peptides, and that apomorphine and other dopamine agonists apparently do not induce penile erection and yawning by releasing an ACTH-derived peptide in brain.