Quantitation of operant nose press force maintained in CD-1, BALB/c and C57BL/6 mice

T.J. Zarcone and S. C. Fowler

Life Span Institute, University of Kansas, Lawrence, KS, U.S.A.

Measurement of operant behavior in laboratory rodents is usually accomplished with a lever-switch ensemble that detects lever depressions of sufficient force to close the switch. These manipulanda only register the occurrence of a response, thereby ignoring many of the motor features of the response itself, such as the force applied to the manipulandum during the response. We have constructed a manipulandum that uses an isometric force transducer to measure the force of operant response as the mouse presses it nose against a smooth, flat disk.

The force-sensitive disk is serviced by a computerized data collection system, allowing on-line, real-time measurement of the applied force at a 100 Hz sampling rate. In-house software permits the force data to be used in real-time to provide auditory or visual feedback or to be used to control other environmental events (e.g. food delivery). Data stored on the computer can be reviewed in its original integer form or can be transformed to text for importation and processing by graphics (see Figure 1) or statistical packages. Combining this manipulandum with an operant-conditioning chamber has allowed us to measure nose presses directly reinforced with food presentation (Fixed Ratio 1), as well as anticipatory nose presses made during signaled conditions prior to the reinforcement period. With these methods we have observed mouse strain differences in capacity to emit appropriately high force as force requirements for reinforcement are increased. Specifically, force production by the C57BL/6 mouse was lower than that seen for the other two strains (CD-1, BALB/c). Our preliminary neurochemical analyses have suggested that the low force production in the C57BL/6 strain is associated with lower levels of brain dopamine and lower dopamine turnover in this strain compared to the other two strains studied.

Figure 1. The top panel shows a sample record of the transition from two non-reinforcement conditions ("10min Cued No Milk" and "30 s COD to a reinforcement condition ("30 min Operant Milk", Fixed Ratio 1,8 gram requirement). The three bottom panels show 2 s samples from each of the conditions shown in the upper panel highligthed by the blue squares, expanded to show real-time in seconds. Head Entries (HE) into the feeding hopper are shown by the deflection of the signal line (red) below the zero value. The vertical dashed lines (upper panel) show changes in conditions. The horizontal dashed line (all panels) shows the force requirement for reinforcement in the last condition.

The force-sensitive manipulandum provides an additional quantitative level of analysis that can be incorporated into current operant-conditioning paradigms to yield measures reflective of the dynamic nature of motor responses in laboratory mice.

Supported by R21 DA12508.


Poster presented at Measuring Behavior 2000, 3rd International Conference on Methods and Techniques in Behavioral Research, 15-18 August 2000, Nijmegen, The Netherlands

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