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Ultrasonic vocalization as an indicator of emotional state during active avoidance learning in rats
Life Sciences, Vol. Printed in the USA
50, pp. 1049-1055
Pergamon Press
ULTRASONIC VOCALIZATION AS AN INDICATOR OF EMOTIONAL STATE DURING ACTIVE AVOIDANCE LEARNING IN RATS V. Cuomo, R. Cagiano, M.A. De Salvla, M. Mazzoccoli, M. Persichella and G. Renna Instltute of Pharmacology, Unlversity of Bari, Piazza G. Cesare, 70124 Barl, Italy. (Received in final form January 28, 1992)
Summary Adult male rats subjected to a two-way avoidance task emitted ultrasonlc vocalizations (20-30 k H z ) b o t h during the presentatlon of the conditioned stlmulus and the intertrial interval. The rate of ultrasonlc calling decreased durlng the 75-trlal sesslon Indicating that acquisltion of the condltloned avoidance response (CAR) was inversely correlated wlth the rate of vocalizatlon. The rate of acquisitlon of the CAR was most rapid in those rats that did not emlt any vocallzation durlng learning. These data suggest that ultrasonic calllng during stressful situations may be sensitive indicator of underlylng emotlonal states that Interfere with the acqulsition of a complex task. Ultrasonic vocalizations in animals have been recorded in a variety of behavloral situatlons and are thought to be expressions of emotional and motlvatlonal states, particularly durlng stressful situations (1, 2). These vocalizations, whlch differ somewhat in their physlcal characterlstics between species, have been associated with sexual behavior (3, 4, 5), agresslve and submissive behavior (6, 7, 8) and are thought to be a particularly Important method of communicatlon between mother and offsprlng in early Infancy (9, 10, 11). I t has been shown recently that ultrasonlc vocalizations are also emitted by rats in response to aversive stlmulatlon such as inescapable shock (12, 13). A reduction In the duratlon of ultrasonic vocalizations following the administration of benzodiazepine derivatives (diazepam and alprazolam) in an inescapable stress situation has been attributed to antl-anxlety properties of these compounds (14). Prellminary experiments In our laboratory have shown that during a learning task involving escapable averslve stimulation, rats also produce ultrasonic vocalizatlons. The purpose of the present studies therefore was to
Copyright
0024-3205/92 $5.00 + .00 © 1992 Pergamon Press plc All rights reserved.
1050
Ultrasonic Vocalization and Learning
vol. 50, No. 14, 1992
characterlze the emlsslon patterns of ultrasonic signals in rats to a two-way avoldance task.
subjected
Methods Animals: Male Wistar rats (Charles River Lab., Calco, Italy) welghing 250300g were used. Animals were allowed free access to f o o d and water,were housed in standard cages, and were exposed to a light cycle of 12 h/day (8 a.m. to 8 p.m.) for two weeks before the experiments. Apparatus and Procedures: The apparatus and procedure have been described in detail previously (14, 15). Briefly, the apparatus consisted of a two-way avoldance box housed inside a sound attenuating chamber (Ampllfon G-type cabin). Each avoidance box was dlvlded into two compartments connected by an openlng of 9 x 12 cm and operated by an electromechanlcal programmlng equipment. A llght (3W lamp) was alternately swltched on in each compartment and was the conditioned stimulus (CS). Onset of the CS was followed 12 sec later by the uncondltloned stlmulus (US) which was a 1 mA scrambled foot shock. The CS remained on durlng the presentatlon of the US, whlch lasted a maximum of 18 sec, when both the CS and US were turned off. A conditioned avoldance response (CAR) was recorded when an animal avoided the US by crosslng over to the opposite compartment during the f i r s t 12 sec when only the CS was on. An escape response consisted of the animal movlng into the opposlte compartment followlng the onset of the US. This response terminated both the CS and the US. Animals were subjected to 75 t r i a l s in three 25-trlal blocks, with a 60 sec i n t e r t r l a l interval (ITI). Ultrasonic calls (UC) emitted during the presentatlon of the CS or during the ITI were recorded by a ~MC ultrasonic mlcrophone (placed at the center of the shuttle-box cover) connected to a receiver (QMC Bat Detector $200) which trasformed, in real time, the UC into audlble sounds. Microphone signals were relayed, via the high frequency output socket, to a Bruel & Kjaer (2033) High Resolution Signal Analyzer (HRSA) in order to visualize the ultrasonic calls. The number of UC emitted by rats was counted manually by listening to the audible output of a headphone. The shuttle-box recording unit signalled the period (CS or ITI) In whlch ultrasounds occurred. In order to evaluate the acoustic characteristics of UC, the f i r s t call emitted by each rat was recorded on a Racal Store 4DS tape-recorder using a dlrect mode recording procedure with a tape-speed of 30 1.p.s. (76.2 cm/s); the frequency response range was f l a t between 200 Hz and 150 kHz. Ampex magnetic tapes (length: 3280 f t , width/O.25 in.) with precislon reels were used. The transducers employed were a calibrated Bruel & Kjaer (4135) 1/4 in. (0.64 cm) f r e e - f i e l d condenser microphone (frequency response f l a t within ~3 db, from 5 Hz to 100 kHz) a Bruel & Kjaer microphone preamplifier (2618) wlth a llnear frequency response from 10 Hz to 200 kHz which provided a 20 db ampllficatlon, a Rank Precision Ind. low noise amplifier whlch provlded 20 db ampllflcatlon steps and a Khron-Hite tunable band-pass f i l t e r
vol. 50, No. 14, 1992
Ultrasonic Vocalization
and Learning
1051
(3500) set at 20 to 120 kHz. The amplltude of the recoraed signals was monltored continually by a Tektronix oscilloscope and the input galns adjusted to prevent overload. Acoustic characterlstlcs of the signals were later analyzed on the HRSA. This required a reduction of tape speed from the original 30 i.p.s. (76.2 cm/s ) to 7.5 i.p.s. (19.05 cm/s). Followlng this analysis, shortened frequency values and the expanded tlme base were adjusted back to the original recording speed to estimate frequency and duratlon of slgnals. Results The results show that male rats subjected to a 75-trlal active avoldance session (three 25-trlal blocks) emltted UC both durlng the presentation of the CS and the ITI. The acqulsltlon of CARs was paralleled by a decrease in the rate of ultrasonic calling (Fig.l).
M e a n no. of U C / s e o 0.4
40
0.3
3O
0.2
20
M e a n %
C 10
0.1
0
I
I
I
1
2
3
25-trial
0
blocks
FIG. 1 Mean % conditioned avoldance responses, CAR ( ~ ) and mean number of ultrasonic calls (UC)/sec emitted by rats (21 anlmals) d u r l n g the presentatlon of the condltloned stimulus ( ( ) and the i n t e r t r l a l interval ( ÷ ) of a 75t r l a l session.
A R
1052
Ultrasonic Vocalizatlon and Learning
Vol. 50, No. 14, 1992
An ANOVA which took into account subjects as random variable (treated as blocks) showed a highly signlficant effect of the repeated measures variable (UC in the CS perlod: F = 18.31, df = 2/40, p < 0.0001; UC in the ITI: F = 22.12, df = 2/40, p < 0.0001; CARs: F = 10.19, df = 2/40, p < 0.0005). The acoustlc characteristics of UC are reported in Fig. 2.
2500
40
2000
I
30
|
1500
m
1000
8 e c
20
10
500
0
I ~1
J Mm Frequency Intensity peak Freq.
Max Frequency Duration
FIG. 2 Characteristlcs of the f i r s t ultrasonlc call emltted by rats (16 animals) during a 75-trlal session. Median values, Interquartile ( ) and f u l l range ( - - - 3 .
Moreover, the results of these experiments indicate that about 24% rats (5/21) did not emit any ultrasonlc vocallzatlon throughout the whole actlve avoidance session. Repeated measures ANOVAfor CARs performed by vocallzlng and non-vocallzlng rats durlng three 25-trial blocks gave the followlng results: ( i ) between groups (F = 14.20, df = 1/19, p < 0.002); ( i i ) between blocks (F = 9.89, df = 2/38, p < 0.001); (111) between groups x blocks (F = 0.87, df = 2/38 n.s). Individual between groups comparisons (Student's t - t e s t ) indicated that the percentage of CARs performed by non-vocalizing animals during the three 25t r l a ] blocks was s i g n l f i c a n t l y higher with respect to that exhlblted by
Vol. 50, No. 14, 1992
Ultrasonic Vocalization
and Learning
1053
vocallzing ones (Fig.3).
M e a n % CAR +__S.E. 80
60
40
20
T 0 1
2
3
25-trial blocks FIG. 3 Mean % (~ S.E.) conditioned avoidance responses (CAR) performed by vocalizing ( ~ ) and non-vocalizlng ( P T ~ ) rats during a 75-trial session. S1gnlflcant dlfferences (Student's t test): * p < 0.05; ** p < 0.01 vs vocalizlng group. Discussion Thls study indlcates that the rate of ultrasonic vocallzat~on durlng two-way avoldance learning in rats decreases durlng the acquisition of the CAR. Anlmals that vocalize during both the CS and the ITI period signlficantly reduce their vocallzation as learning progresses. There is, however, a proportion of animals (approximately 24%) that do not conform to this pattern. These animals do not vocallze throughout tralnlng. At the same tlme, the majority of these animals show the a b i l i t y to acquire the CAR much more rapidly than animals that vocalize. In view of the relationship between vocalization and the acquisition of the CAR, one might speculate that rate of vocalization may be a measure of the level of stress in the rat and that the greater the stress ( i . e . more vocalization) the more interference with the acquisition of the CAR. As learning progresses and the anlmals make avoidances, the stress levels decrease and the rate of vocalization declines as well. There is some evldence for thls hypothesls in previous studies by
1054
Ultrasonic Vocalization
and Learning
Vol. 50, No. 14, 1992
Kamln et al. (16). Anlmals removed from the two-way avoldance box following only escape or incomplete avoidance training and placed in a lever press operant sltuatlon, were progresslvely less dlsrupted by the presentatlon of the CS previously used in the avoidance box as tralnlng progressed and the animals began making avoidance responses. I t is not clear from these experlments why some animals do not vocalize at all In an avoldance tralnlng task. Nevertheless, I t seems that these animals are able to acquire the task more e f f i c l e n t l y t h a n t h o s e that vocalize,suggesting that vocallzatlon may not be a contlnuous phenomenon, but that only after certain levels of arousal are reached does I t occur. The d a t a derived from our prellmlnary experiments (Cuomo and Caglano, unpubllshed results) on the effects of dlazepam on ultrasonlc calllng during active avoidance learning in rats also seem to support these hypotheses. Treatment with this benzodlazeplne derivative (0.5 mg/Kg) not only reduced the rate of vocalizatlon, but also increased the rate of CAR, presumably by reducing the stress of the situatlon. Previous studies have shown a relatlonshlp between ultrasonic vocallzatlon and appetitive learning In infant rats. Rat pups separated from an anesthetized dam were'allowed to crawl to her and suck on a nlpple. Vocallzatlon decreased as a direct functlon of the response tlme in flndlng the nipple (17). During extinction of this response, vocalization increased agaln. Amsel et al. ( 1 7 ) hypotheslzed that in infant rats ultrasonlc vocalizatlon was an indlcator of arousal during appetitive learning and extinction. A comparative evaluatlon of the soclobiologlcal circumstances in whlch ultrasonlc signals ranging from 20 to 30 kHz (and commonly centering at about 22 kHz) occur indicates that these calls are emitted by male rats in condltlons whlch may have some analogous or homologous elements ( I . e . , behavioral inhlbltion): speclfically, durlng the post-ejaculatory refractory perlod, during submlsslve behavior or defeat, and in stressful situations Including painful and frustratlng condltlons (5, 12, 13, 14, 18, 19). Accordlng to Adler and Anlsko (18), i t may be that the organismic state that causes a male rat to generate 20-30 kHz calls is simllar In a wlde variety of psychologlcal contexts. In concluslon, our data suggest that ultrasonlc vocalization durlng averslve condltioning may be an useful measure of the emotional state of the rat and may provlde predlctive capab111ty in assesslng the outcome of condltionlng experiments in a variety of sltuatlons. References 1. G.D. SALES and D. PYE, Ultrasonlc communication Hall, London (1974).
by
animals. Chapman
Vol. 50, No. 14, 1992
Ultrasonic Vocalization and Learning
1055
2. K.A. MICZEK, W. TORNATZKY and J. VIVIAN, In: Animal Models in Psychopharmacology (B. OLIVER, J. MOS and J. SLANGEN, Eds), Birkhauser, Basel. (1991). 3. R.J. BARFIELD, L.A. GEYER, Sclence 176 1349 - 1350 (1972). 4. T.K. MclNTOSH and R.J. BARFIELD, Behav. Neural B i o l . 29 349 - 358 (1980). 5. R.J. BARFIELD and D.A. THOMAS, In: Reproductlon: A Behavioral and Neuroendocrlne Perspectlve (B.R. KOMISARUK, H . I . SIEGEL and H.H. FEDER, Eds.), Ann. N. Y. Acad. Sc1., Vol 475, New York Academy of Sciences, N. V., pp. 33-43 (1986). 6. G.D. SEWELL, Nature 215 512 - 514 (1967). 7. G.D. SALES, Anlmal Behaviour 20 88 - I00 (1972). 8. W. TORNATZKY and K.A. MICZEK, Soc. Neuroscl. Abstr. 16 432 (1990). 9. E. NOIROT, Anlmal Behavlor 14 459 - 462 (1966). i 0 . G.D. SEWELL, Nature 217 682 - 683 (1970). i i . T.R. INSEL and J.T. WINSLOW, In: Animals Models in Psychopharmacology 1991, Advances in Pharmacological Sciences (B. OLIVIER, J. MOS and J.L. SLANGEN, Eds.), B1rkhauser Verlag, Basel, pp. 15 - 36 (1991). 12. T. TONOUE, Y. ASHIDA, H. MAKINO and H. HATA, Psychoneuroendocrlnology i__11 177 - 184 (1986). 13. A.M. VAN DER POEL, E.J.K. NOACH and K.A. MICZEK, Psychopharmacology 97 147 - 148 (1989). 14. V. CUOMO, R. CAGIANO, M.A. DE SALVIA, M.A. MASELLI, G. RENNA and G. RACAGNI, L i f e Sc1. 43 485 - 491 (1988). 15. V. CUOMOand I . CORTESE, Experientla 36 1208 - 1210 (1980). 16. L.J. KAMIN, C.J. BRIMER and A.H. BLACK, J. Comp. Physiol. Psychol. 56(3) 497 - 501 (1963). 17. A. AMSEL, C.C. RADEK, M. GRAHAM and R. LETZ, Sclence 97 786 - 788 (1977). 18. N. ADLER and J. ANISKO, Amer. Zool. 19 493 - 508 (1979). 19. D.A. THOMAS, L.K. TAKAHASHI and R.J. BARFIELD, J. Comp. B i o l . 97 201 206 (1983).
50, pp. 1049-1055
Pergamon Press
ULTRASONIC VOCALIZATION AS AN INDICATOR OF EMOTIONAL STATE DURING ACTIVE AVOIDANCE LEARNING IN RATS V. Cuomo, R. Cagiano, M.A. De Salvla, M. Mazzoccoli, M. Persichella and G. Renna Instltute of Pharmacology, Unlversity of Bari, Piazza G. Cesare, 70124 Barl, Italy. (Received in final form January 28, 1992)
Summary Adult male rats subjected to a two-way avoidance task emitted ultrasonlc vocalizations (20-30 k H z ) b o t h during the presentatlon of the conditioned stlmulus and the intertrial interval. The rate of ultrasonlc calling decreased durlng the 75-trlal sesslon Indicating that acquisltion of the condltloned avoidance response (CAR) was inversely correlated wlth the rate of vocalizatlon. The rate of acquisitlon of the CAR was most rapid in those rats that did not emlt any vocallzation durlng learning. These data suggest that ultrasonic calllng during stressful situations may be sensitive indicator of underlylng emotlonal states that Interfere with the acqulsition of a complex task. Ultrasonic vocalizations in animals have been recorded in a variety of behavloral situatlons and are thought to be expressions of emotional and motlvatlonal states, particularly durlng stressful situations (1, 2). These vocalizations, whlch differ somewhat in their physlcal characterlstics between species, have been associated with sexual behavior (3, 4, 5), agresslve and submissive behavior (6, 7, 8) and are thought to be a particularly Important method of communicatlon between mother and offsprlng in early Infancy (9, 10, 11). I t has been shown recently that ultrasonlc vocalizations are also emitted by rats in response to aversive stlmulatlon such as inescapable shock (12, 13). A reduction In the duratlon of ultrasonic vocalizations following the administration of benzodiazepine derivatives (diazepam and alprazolam) in an inescapable stress situation has been attributed to antl-anxlety properties of these compounds (14). Prellminary experiments In our laboratory have shown that during a learning task involving escapable averslve stimulation, rats also produce ultrasonic vocalizatlons. The purpose of the present studies therefore was to
Copyright
0024-3205/92 $5.00 + .00 © 1992 Pergamon Press plc All rights reserved.
1050
Ultrasonic Vocalization and Learning
vol. 50, No. 14, 1992
characterlze the emlsslon patterns of ultrasonic signals in rats to a two-way avoldance task.
subjected
Methods Animals: Male Wistar rats (Charles River Lab., Calco, Italy) welghing 250300g were used. Animals were allowed free access to f o o d and water,were housed in standard cages, and were exposed to a light cycle of 12 h/day (8 a.m. to 8 p.m.) for two weeks before the experiments. Apparatus and Procedures: The apparatus and procedure have been described in detail previously (14, 15). Briefly, the apparatus consisted of a two-way avoldance box housed inside a sound attenuating chamber (Ampllfon G-type cabin). Each avoidance box was dlvlded into two compartments connected by an openlng of 9 x 12 cm and operated by an electromechanlcal programmlng equipment. A llght (3W lamp) was alternately swltched on in each compartment and was the conditioned stimulus (CS). Onset of the CS was followed 12 sec later by the uncondltloned stlmulus (US) which was a 1 mA scrambled foot shock. The CS remained on durlng the presentatlon of the US, whlch lasted a maximum of 18 sec, when both the CS and US were turned off. A conditioned avoldance response (CAR) was recorded when an animal avoided the US by crosslng over to the opposite compartment during the f i r s t 12 sec when only the CS was on. An escape response consisted of the animal movlng into the opposlte compartment followlng the onset of the US. This response terminated both the CS and the US. Animals were subjected to 75 t r i a l s in three 25-trlal blocks, with a 60 sec i n t e r t r l a l interval (ITI). Ultrasonic calls (UC) emitted during the presentatlon of the CS or during the ITI were recorded by a ~MC ultrasonic mlcrophone (placed at the center of the shuttle-box cover) connected to a receiver (QMC Bat Detector $200) which trasformed, in real time, the UC into audlble sounds. Microphone signals were relayed, via the high frequency output socket, to a Bruel & Kjaer (2033) High Resolution Signal Analyzer (HRSA) in order to visualize the ultrasonic calls. The number of UC emitted by rats was counted manually by listening to the audible output of a headphone. The shuttle-box recording unit signalled the period (CS or ITI) In whlch ultrasounds occurred. In order to evaluate the acoustic characteristics of UC, the f i r s t call emitted by each rat was recorded on a Racal Store 4DS tape-recorder using a dlrect mode recording procedure with a tape-speed of 30 1.p.s. (76.2 cm/s); the frequency response range was f l a t between 200 Hz and 150 kHz. Ampex magnetic tapes (length: 3280 f t , width/O.25 in.) with precislon reels were used. The transducers employed were a calibrated Bruel & Kjaer (4135) 1/4 in. (0.64 cm) f r e e - f i e l d condenser microphone (frequency response f l a t within ~3 db, from 5 Hz to 100 kHz) a Bruel & Kjaer microphone preamplifier (2618) wlth a llnear frequency response from 10 Hz to 200 kHz which provided a 20 db ampllficatlon, a Rank Precision Ind. low noise amplifier whlch provlded 20 db ampllflcatlon steps and a Khron-Hite tunable band-pass f i l t e r
vol. 50, No. 14, 1992
Ultrasonic Vocalization
and Learning
1051
(3500) set at 20 to 120 kHz. The amplltude of the recoraed signals was monltored continually by a Tektronix oscilloscope and the input galns adjusted to prevent overload. Acoustic characterlstlcs of the signals were later analyzed on the HRSA. This required a reduction of tape speed from the original 30 i.p.s. (76.2 cm/s ) to 7.5 i.p.s. (19.05 cm/s). Followlng this analysis, shortened frequency values and the expanded tlme base were adjusted back to the original recording speed to estimate frequency and duratlon of slgnals. Results The results show that male rats subjected to a 75-trlal active avoldance session (three 25-trlal blocks) emltted UC both durlng the presentation of the CS and the ITI. The acqulsltlon of CARs was paralleled by a decrease in the rate of ultrasonic calling (Fig.l).
M e a n no. of U C / s e o 0.4
40
0.3
3O
0.2
20
M e a n %
C 10
0.1
0
I
I
I
1
2
3
25-trial
0
blocks
FIG. 1 Mean % conditioned avoldance responses, CAR ( ~ ) and mean number of ultrasonic calls (UC)/sec emitted by rats (21 anlmals) d u r l n g the presentatlon of the condltloned stimulus ( ( ) and the i n t e r t r l a l interval ( ÷ ) of a 75t r l a l session.
A R
1052
Ultrasonic Vocalizatlon and Learning
Vol. 50, No. 14, 1992
An ANOVA which took into account subjects as random variable (treated as blocks) showed a highly signlficant effect of the repeated measures variable (UC in the CS perlod: F = 18.31, df = 2/40, p < 0.0001; UC in the ITI: F = 22.12, df = 2/40, p < 0.0001; CARs: F = 10.19, df = 2/40, p < 0.0005). The acoustlc characteristics of UC are reported in Fig. 2.
2500
40
2000
I
30
|
1500
m
1000
8 e c
20
10
500
0
I ~1
J Mm Frequency Intensity peak Freq.
Max Frequency Duration
FIG. 2 Characteristlcs of the f i r s t ultrasonlc call emltted by rats (16 animals) during a 75-trlal session. Median values, Interquartile ( ) and f u l l range ( - - - 3 .
Moreover, the results of these experiments indicate that about 24% rats (5/21) did not emit any ultrasonlc vocallzatlon throughout the whole actlve avoidance session. Repeated measures ANOVAfor CARs performed by vocallzlng and non-vocallzlng rats durlng three 25-trial blocks gave the followlng results: ( i ) between groups (F = 14.20, df = 1/19, p < 0.002); ( i i ) between blocks (F = 9.89, df = 2/38, p < 0.001); (111) between groups x blocks (F = 0.87, df = 2/38 n.s). Individual between groups comparisons (Student's t - t e s t ) indicated that the percentage of CARs performed by non-vocalizing animals during the three 25t r l a ] blocks was s i g n l f i c a n t l y higher with respect to that exhlblted by
Vol. 50, No. 14, 1992
Ultrasonic Vocalization
and Learning
1053
vocallzing ones (Fig.3).
M e a n % CAR +__S.E. 80
60
40
20
T 0 1
2
3
25-trial blocks FIG. 3 Mean % (~ S.E.) conditioned avoidance responses (CAR) performed by vocalizing ( ~ ) and non-vocalizlng ( P T ~ ) rats during a 75-trial session. S1gnlflcant dlfferences (Student's t test): * p < 0.05; ** p < 0.01 vs vocalizlng group. Discussion Thls study indlcates that the rate of ultrasonic vocallzat~on durlng two-way avoldance learning in rats decreases durlng the acquisition of the CAR. Anlmals that vocalize during both the CS and the ITI period signlficantly reduce their vocallzation as learning progresses. There is, however, a proportion of animals (approximately 24%) that do not conform to this pattern. These animals do not vocallze throughout tralnlng. At the same tlme, the majority of these animals show the a b i l i t y to acquire the CAR much more rapidly than animals that vocalize. In view of the relationship between vocalization and the acquisition of the CAR, one might speculate that rate of vocalization may be a measure of the level of stress in the rat and that the greater the stress ( i . e . more vocalization) the more interference with the acquisition of the CAR. As learning progresses and the anlmals make avoidances, the stress levels decrease and the rate of vocalization declines as well. There is some evldence for thls hypothesls in previous studies by
1054
Ultrasonic Vocalization
and Learning
Vol. 50, No. 14, 1992
Kamln et al. (16). Anlmals removed from the two-way avoldance box following only escape or incomplete avoidance training and placed in a lever press operant sltuatlon, were progresslvely less dlsrupted by the presentatlon of the CS previously used in the avoidance box as tralnlng progressed and the animals began making avoidance responses. I t is not clear from these experlments why some animals do not vocalize at all In an avoldance tralnlng task. Nevertheless, I t seems that these animals are able to acquire the task more e f f i c l e n t l y t h a n t h o s e that vocalize,suggesting that vocallzatlon may not be a contlnuous phenomenon, but that only after certain levels of arousal are reached does I t occur. The d a t a derived from our prellmlnary experiments (Cuomo and Caglano, unpubllshed results) on the effects of dlazepam on ultrasonlc calllng during active avoidance learning in rats also seem to support these hypotheses. Treatment with this benzodlazeplne derivative (0.5 mg/Kg) not only reduced the rate of vocalizatlon, but also increased the rate of CAR, presumably by reducing the stress of the situatlon. Previous studies have shown a relatlonshlp between ultrasonic vocallzatlon and appetitive learning In infant rats. Rat pups separated from an anesthetized dam were'allowed to crawl to her and suck on a nlpple. Vocallzatlon decreased as a direct functlon of the response tlme in flndlng the nipple (17). During extinction of this response, vocalization increased agaln. Amsel et al. ( 1 7 ) hypotheslzed that in infant rats ultrasonlc vocalizatlon was an indlcator of arousal during appetitive learning and extinction. A comparative evaluatlon of the soclobiologlcal circumstances in whlch ultrasonlc signals ranging from 20 to 30 kHz (and commonly centering at about 22 kHz) occur indicates that these calls are emitted by male rats in condltlons whlch may have some analogous or homologous elements ( I . e . , behavioral inhlbltion): speclfically, durlng the post-ejaculatory refractory perlod, during submlsslve behavior or defeat, and in stressful situations Including painful and frustratlng condltlons (5, 12, 13, 14, 18, 19). Accordlng to Adler and Anlsko (18), i t may be that the organismic state that causes a male rat to generate 20-30 kHz calls is simllar In a wlde variety of psychologlcal contexts. In concluslon, our data suggest that ultrasonlc vocalization durlng averslve condltioning may be an useful measure of the emotional state of the rat and may provlde predlctive capab111ty in assesslng the outcome of condltionlng experiments in a variety of sltuatlons. References 1. G.D. SALES and D. PYE, Ultrasonlc communication Hall, London (1974).
by
animals. Chapman
Vol. 50, No. 14, 1992
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