PET study of the [¹¹C]raclopride binding in the striatum of the awake cat: effects of anaesthetics and role of cerebral blood flow

Abstract.

Cats were trained to stay in a containment box, without developing any signs of behavioural stress, while their head was maintained in a position that allowed positron emission tomography (PET) experiments to be performed. The binding potential for [¹¹C]raclopride (BP_raclo), a radioligand with good specificity for dopamine (DA) receptors of the D₂ type, was measured in the striatum and in three experimental situations: awake, anaesthetised with ketamine (50 mg kg^–1 h^–1; i.m.) and anaesthetised with halothane (1.5%). Non-specific binding was evaluated in the cerebellum. In the striatum of both sides, the BP_raclo was unmodified by ketamine anaesthesia when compared with awake animals. In contrast, a large increase in BP_raclo was observed under halothane anaesthesia. The non-specific binding of [¹¹C]raclopride, evaluated in the cerebellum, was also unchanged under ketamine anaesthesia but greatly increased under halothane anaesthesia. To evaluate whether changes in the cerebral blood flow (CBF) resulting from the different experimental situations could be at the root of these discrepancies, injections of [¹⁵O]H₂O were performed; measurements revealed a drastically increased CBF under halothane anaesthesia and a slight enhancement under ketamine anaesthesia, when compared with the waking state. These results are the first to be obtained on this topic in awake cats, and show that the BP_raclo is greatly dependent on alterations in the CBF.