Effects of kappa-opioid receptor ligands
on intracranial self-stimulation in rats
by
Todtenkopf MS, Marcus JF,
Portoghese PS, Carlezon WA Jr.
Behavioral Genetics Laboratory,
Department of Psychiatry,
Harvard Medical School,
McLean Hospital, 115 Mill Street,
MRC 217, MA 02478, Belmont, USA.
Psychopharmacology (Berl). 2004 Jan 16

ABSTRACT

RATIONALE. Elevations in cAMP response element binding protein (CREB) function within the mesolimbic system of rats reduce cocaine reward in place conditioning studies and increase immobility in the forced swim test. Each of these behavioral adaptations can be interpreted as a depressive-like effect (i.e., anhedonia, despair) that may reflect reduced activity of brain reward systems. Furthermore, each effect appears due to increases in CREB-mediated expression of dynorphin, since each is attenuated by intracranial injections of the kappa-opioid receptor antagonist norBNI. OBJECTIVES. Intracranial self-stimulation (ICSS) studies were conducted in rats to determine whether administration of a kappa-agonist would have depressive-like effects on brain stimulation reward, and whether pretreatment with a kappa-antagonist would attenuate any such effects. Conditions that have depressive effects in people (e.g., drug withdrawal) increase the threshold amounts of stimulation required to sustain ICSS in rats. METHODS. Sprague-Dawley rats with lateral hypothalamic stimulating electrodes were tested in a "curve-shift" variant of the ICSS procedure after systemic administration of the kappa-agonist U-69593 alone, the novel kappa-antagonist 5'-acetamidinoethylnaltrindole (ANTI) alone, or co-administration of both drugs. RESULTS. U-69593 dose dependently increased ICSS thresholds, suggesting that activation of kappa-receptors reduced the rewarding impact of the brain stimulation. ANTI had no effects on its own, but it attenuated increases in ICSS thresholds caused by the agonist. CONCLUSIONS. These data provide further evidence that stimulation of brain kappa-receptors may trigger certain depressive-like signs, and that kappa antagonists may have efficacy as antidepressants without having reward-related actions of their own.

Mu
Pain
JDTIc
Enadoline
Tramadol
Tolerance
Endomorphins
Buprenorphine
Antidepressants
Kappa confusion
Receptor subtypes
Nor-binaltorphimine
Kappa upregulation and addiction
The kappa A agonist salvinorin A induces depression
Kappa opioids selectively control dopaminergic neurons
Depressive effects of the kappa-opioid receptor agonists
Kappa opioid antagonists as antidepressants: norbinaltorphimine
The kappa receptor antagonist norbinaltorphimine as an antidepressant
Central kappa opioid antagonist norbinaltorphimine: antidepressant mechanism

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