Intracranial self-stimulation in female and male rats: no sex differences using a rate-independent procedure.
Given gender differences in human drug use and dependence, this study examined sex differences in reinforcement processes that may underlie such behavior. A psychophysical determination of reinforcement threshold was made using an intracranial self-stimulation (ICSS) paradigm, electrically activating the medial forebrain bundle (MFB) as it passes through the lateral hypothalamus (LH). Using this response rate-independent procedure, basal reinforcement thresholds were not significantly different in male vs. female rats (119.4 +/- 3.3 microA vs. 110.8 +/- 4.0 microA, respectively; N = 8/sex). Further, baseline reinforcement threshold did not fluctuate systematically across stages of the estrous cycle in female rats. The psychostimulants D-amphetamine (0.056-0.56 mg/kg s.c.) and cocaine (1.8-18.0 mg/kg i.p.) dose-dependently lowered reinforcement threshold, with no significant sex difference. The opioid morphine (0.56-5.6 mg/kg s.c.) did not significantly lower reinforcement threshold in either sex. These results contrast those of some previous studies that have used response rate-dependent measures of reinforcement threshold; procedures which are less rate-dependent may be more appropriate when examining subject variables such as sex and stage of estrous.
Stratmann
J A
JA
Department of Psychology, Washington State University, Pullman 99164-4820, USA.
Craft
R M
RM
D000818:Animals; D001931:Brain Mapping; D000697:Central Nervous System Stimulants / Q000494:pharmacology; D003042:Cocaine / Q000494:pharmacology; D003913:Dextroamphetamine / Q000494:pharmacology; D004558:Electric Stimulation; D004971:Estrus / Q000187:drug effects / Q000502:physiology; D005260:Female; D006801:Humans; D007026:Hypothalamic Area, Lateral / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008474:Medial Forebrain Bundle / Q000187:drug effects / Q000502:physiology*; D009020:Morphine / Q000494:pharmacology; D009042:Motivation; D009434:Neural Pathways / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012653:Self Stimulation / Q000187:drug effects / Q000502:physiology*; D012727:Sex Characteristics
D000697:Central Nervous System Stimulants; D009020:Morphine; D003042:Cocaine; D003913:Dextroamphetamine