PharmacologyBiochemistry&Behavh)r, Vol. 17, pp. 873-876, 1982. Printedin the U.S.A. A Quantitative Analysis of Stereotyped Gnawing Induced by Apomorphine P. REDGRAVE, P. DEAN AND G. LEWIS Department of Psychology, University of Sheffield, Sheffield, SIO 2TN, England Received 29 March 1982 REDGRAVE, P., P. DEAN AND G. LEWIS. A quantitative analysis of stereotyped gnawing induced by apomorphine. PHARMAC. BIOCHEM. BEHAV. 17(5)873-876, 1982.--An apparatus was designed and constructed to enable a quan- titative analysis of the stereotyped gnawing produced by the dopamine agonist apomorphine. Using this apparatus it was discovered that increasing the subcutaneous dose of apomorphine increased (1) the number of animals that gnawed, and (2) the duration of gnawing in those animals that gnawed at all doses. Other aspects of apomorphine-induced gnawing, in particular the latency to respond and the frequency and duration of individual gnaws, were relatively unaffected. Likely properties of the system responsible for the organization of stereotyped gnawing are discussed. Apomorphine Stereotyped gnawing Quantitative analysis BEHAVIOURAL stereotypies caused by increases in cen- tral dopamine (DA) transmission are characterised by the apparently purposeless repetition of relatively small se- quences of behaviour (for reviews see [9,11]). An analysis of the details of these individual behavioural sequences may provide important information concerning the mechanism whereby changes in DA transmission influence behaviour. Various procedures have been adopted to describe the types of stereotypy exhibited by rodents. Perhaps the most commonly used system is that of rating scales [1,2] which provide a qualitative description of stereotypy associated with different doses of drugs such as amphetamine and apomorphine. An alternative approach in which the presence or absence of different response categories is defined was reported recently [3]. These procedures have not, however, been able to provide satisfactory descriptions of quantitative aspects of individual stereotypies. When relatively large doses of DA-agonist are adminis- tered to rats the most common stereotyped behaviour is gnawing and biting. While there have been several attempts to automate the recording of this behaviour [5, 7, 8], so far none has provided a satisfactory quantitative description of it. We therefore designed and constructed an apparatus to meet the following requirements: (1) it should facilitate the expression of gnawing rather than some other form of stereo- typed behaviour; (2) gnawing should be exclusively directed to the part of the apparatus where it could be measured; (3) it should be capable of measuring characteristics of individual gnaws; (4) the process of detecting gnaws should be un- noticed by the animals and not triggered by events other than gnawing. Our solution to these problems was to use a small, smooth sided arena containing no suitable gnawing surface apart from two conspicuous metal plates. These plates were brought together only by gnawing; this completed an elec- trical circuit, an event which the animals could not detect. The apparatus was used to investigate quantitative changes in the stereotyped gnawing produced by different doses of the DA-receptor agonist apomorphine. METHOD Apparatus A small box (20×23×30 cm) was constructed out of 3 mm perspex sheet. A raised floor was placed approximately 7 cm from the bottom of the box. A slot 20/0.7 cm was cut in the floor 1 cm away from, and parallel to, one of the longest sides of the box. Through this slot a pair of parallel metal plates were admitted to which rats direct their stereotyped gnawing and biting (see Fig. 1). Biting or gnawing the plates caused one to touch the other, an event which switched a modified relay (see below). Relay closure was monitored continually by an ACT-N com- puter program (Campden Instruments) which indicated the frequency and duration of relay closures during specified time periods throughout a test session. Certain facilities were incorporated into the apparatus to ensure that (1) the animal was oblivious of the electrical events associated with plate closure, and (2) a high propor- tion of the bites and gnaws directed towards the plates re- sulted in detectable closure. These features of the apparatus are illustrated in Fig. 2. (1) Two measures were taken to prevent the animal being shocked while biting the plates. First, in order to reduce the current switched by the plates the original Campden relay module was modified by interposing a simple single transis- tor drive circuit between the metal plates and the relay. This alteration reduced the current through the plates to about 85 /xA. Secondly, the plates were constructed so that the live part of the equipment was normally inaccessible to the rat (see Fig. 2). (2) Three forms of adjustment were provided (see Fig. 2) to ensure that detection of gnaws and bites directed to the Copyright ~ 1982 ANKHO International Inc.--0091-3057/82/110873-04503.00/0