Psychopharmacology

, Volume 211, Issue 1, pp 1–13

Identification of multiple call categories within the rich repertoire of adult rat 50-kHz ultrasonic vocalizations: effects of amphetamine and social context

  • Jennifer M. Wright
  • Jim C. Gourdon
  • Paul B. S. Clarke
Original Investigation

Abstract

Rationale

50-kHz ultrasonic vocalizations (USVs) emitted by adult rats are heterogeneous; they occur over a wide frequency range, show varying degrees of frequency modulation, and appear to differ in their behavioral significance. However, they have not been extensively categorized.

Objectives

The main objective of this study was to identify subtypes of 50-kHz USVs emitted by adult rats and to determine how amphetamine (AMPH) or social testing condition affects their relative and absolute production rate and acoustic characteristics. A second objective was to determine the extent of individual differences in call rate, call subtype profile, and acoustic parameters (i.e., duration, bandwidth, and mean peak frequency).

Methods

Adult male Long–Evans rats were administered systemic amphetamine (0.25–2 mg/kg, IP) and tested individually or with a cage mate for 20 min. Call categories were defined based on visual inspection of over 20,000 USV spectrograms. Surgical devocalization was performed on a subset of AMPH-tested rats in order to confirm the authenticity of call subtypes.

Results

Fourteen categories of 50-kHz USVs were recognized. Call subtypes were differentially affected by social context, AMPH dose, and time within session. In contrast, the acoustic characteristics of call subtypes were notably stable. Marked and stable inter-individual differences occurred with respect to overall 50-kHz call rate, acoustic parameters, and call profile.

Conclusions

The present findings, obtained under saline and amphetamine test conditions, provide the first detailed classification of adult rat 50-kHz USVs. Consideration of 50-kHz USV subtypes may advance our understanding of inter-rat communication and affective state.

Keywords

Ultrasonic vocalizations Amphetamine Reward Frequency-modulated Trill Dose–response Individual differences 

Supplementary material

213_2010_1859_MOESM1_ESM.pdf (58 kb)
Table S1Correlation between the average proportion of each call subtype across all test conditions (PDF 57 kb)
213_2010_1859_MOESM2_ESM.pdf (76 kb)
Table S2ANOVA results for the effect of AMPH, social testing condition, and call category on acoustic parameters (PDF 75 kb)
213_2010_1859_MOESM3_ESM.pdf (166 kb)
Figure S1The mean ± SEM number of USVs (per minute) during each of the sampled time intervals during the 20-min session for each of the drug conditions (a), and for the AMPH-SAL difference scores for each AMPH dose (b). (PDF 165 kb)
213_2010_1859_MOESM4_ESM.pdf (1.1 mb)
Figure S2Individual differences in call rate were maintained within test sessions and across AMPH doses. Each rat (panels a and b) or rat pair (panels b and d) was ranked with respect to the total number of USVs emitted, either during particular 1-min time intervals within test sessions (panels a and c) or at different AMPH doses (panels b and d). For the purposes of illustration, the time course data (panels a and c) are from AMPH 1 mg/kg test sessions only. Dose–response data are from numbers of calls averaged across minutes 3, 8, 13, and 18 of the session. Cronbach’s alpha = 0.844–0.979 (see text) (PDF 1114 kb)
213_2010_1859_MOESM5_ESM.pdf (99 kb)
Figure S3Individual differences in call profile across test sessions. The number of flats, step-ups, trills, and flat–trill combinations as a percentage (+SEM) of the total number of calls (i.e. all subtypes) is shown for three singly-tested rats (n = 5 dose levels). Across test sessions, individual rats exhibit higher or lower proportions of the various subtypes compared to other rats. These rats were chosen to illustrate this phenomenon based on clear differences in tendency to emit the four most frequent call categories. (PDF 98 kb)
213_2010_1859_MOESM6_ESM.pdf (418 kb)
Figure S4Amphetamine dose-dependently increased the proportion of trill calls and suppressed flat calls. The proportion (mean ± SEM) of each call category for singly- and pair-tested rats is plotted against increasing AMPH dose. Note also the overall higher proportion of trills and trills with jumps in the pair-tested rats compared to the singly-tested rats. Caveat: some call categories were emitted very infrequently, namely the upward and downward ramps, the split, and the inverted U. For example, 1% in the saline condition for singly-tested rats corresponds to approximately three calls. Amphetamine-induced changes with respect to flat, short, and trill calls were not significantly group-dependent (Table 1); pooling the two groups (i.e., single and pair-tested), significant differences from the saline condition are indicated by asterisks (*p < 0.05, **p < 0.01, ***p < 0.001, paired t tests, n = 16) (PDF 418 kb)

Copyright information

© Springer-Verlag 2010

Authors and Affiliations

  • Jennifer M. Wright
    • 1
  • Jim C. Gourdon
    • 2
  • Paul B. S. Clarke
    • 1
    • 3
  1. 1.Department of Pharmacology and TherapeuticsMcGill UniversityMontrealCanada
  2. 2.Comparative Medicine and Animal Resources CenterMcGill UniversityMontrealCanada
  3. 3.Center for Studies in Behavioral NeurobiologyConcordia UniversityMontrealCanada

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