50-kHz vocalization subtypes emitted by male rats anticipating a sexual partner: Lack of effect of amphetamine withdrawal.

Abstract

The sucrose preference test is the primary measure of anhedonia in rat models of depression, but it does not specifically assess anticipatory anhedonia, a deficit commonly observed in patients. Anticipatory 50-kHz ultrasonic vocalizations (USVs) may offer a more translationally relevant affective measure, yet the subtypes linked to reward anticipation and their alteration in depression models remain poorly characterized. The present study investigated whether certain USV measures (i.e., 50-kHz call rate, call subtype prevalence) were modified in male rats while they anticipated access to a sexually-receptive female partner vs. no partner. The study also examined whether withdrawal from a chronic amphetamine regimen (2 mg/kg IP, once daily for 14 days), intended to induce a depressive-like state, would inhibit the anticipation-associated changes in USV measures, and modify performance in conventional measures of depressive-like state (sucrose preference test, forced swim test). However, in contrast to previous reports, no behavioural signs of withdrawal were observed. Independent of amphetamine history, male rats anticipating a sexual partner emitted more 50-kHz calls, with a preferential increase in two rare 50-kHz call subtypes: split and composite calls. Our findings support the notion that subtypes other than the predominantly studied "flat" and "trill" can potentially serve as markers of affect. In particular, split and composite calls may provide novel translationally relevant measures of anticipatory anhedonia, but they need to be evaluated in other rat models of depression.