Abstract
To study the involvement of endogenous opioid peptides in the development of shock-induced fighting, naloxone (2 mg/kg) or β-endorphin (10 μg/kg) was administered subcutaneously immediately after the session and during nine consecutive daily sessions to rats repeatedly exposed to electric shocks. β-Endorphin blocked the development of shock-induced fighting while naloxone facilitated it but only when shock-induced fighting occurred at a low rate. The effects of β-endorphin were time dependent since when β-endorphin was injected 90 min after the shock session instead of immediately after, its impairing effect disappeared. In addition, naloxone blocked the impairment produced by β-endorphin. Differential postsession treatment of each member of pairs of rats with naloxone and β-endorphin resulted in a higher probability of rats treated with naloxone to be dominant over rats treated with β-endorphin in the test situation. These results are discussed in relation with the possible involvement of endogenous opioids in the modulation of the physiological consequences of defensive behavioral response to shock.
Original language | English (US) |
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Pages (from-to) | 192-202 |
Number of pages | 11 |
Journal | Behavioral and Neural Biology |
Volume | 39 |
Issue number | 2 |
DOIs | |
State | Published - Nov 1983 |
Externally published | Yes |
ASJC Scopus subject areas
- Physiology