Potentiation of cold-water swim analgesia by acute, but not chronic desipramine administration.

Like other stress responses, cold-water swim (CWS) analgesia can be altered by changes in norepinephrine (NE) availability. While clonidine pretreatment potentiates CWS analgesia, lesions placed in the noradrenergic locus coeruleus reduce this response. Desipramine (DMI) can alter both the availability and receptor function of catecholamines, particularly NE: while both acute and chronic DMI treatments decrease NE reuptake, subsensitivity of beta-adrenergic receptors occurs only after chronic DMI treatment. The present study examined whether acute and chronic DMI treatments differentially alter CWS analgesia as measured by the jump test, CWS hypothermia and basal jump thresholds. The first experiment determined that pretreatment at either 24, 5 and 1 hr or only at 1 hr with DMI doses of 20 and 5 but not 1 mg/kg potentiated CWS analgesia. The second experiment found that chronic DMI pretreatment at a dose of 10 mg/kg administered twice daily over seven days failed to alter CWS analgesia at 1, 24, 48 or 72 hr thereafter. Neither CWS hypothermia nor basal jump thresholds were affected by the acute or chronic DMI injection regimens. The selective potentiation of CWS analgesia by acute DMI pretreatment is discussed in terms of the differential actions of acute and chronic injection regimens upon NE availability, receptor function, and adaptation processes.