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Extracellular recordings were made from the neostriatum of rats anaesthetised with
halothane. Normal male and female animals were used as well as castrated animals with
implants containing oestradiol-17β (E<sub>2</sub>). In animals with high levels of
circulating oestrogen, intact pro-oestrous rats and females and males bearing an E2
implant, individual units could be recorded that were spontaneously active and with
axons that could be excited by stimulation in the crus cerebri. Such antidromically
identified striato-nigral neurones were invariably silent in male animals and in ovariectomised
females. In contrast to animals in pro-oestrus, intact female animals during metoestrus
showed the ‘male’ pattern of striatal cell activity. These results show that E<sub>2</sub>
can stimulate spontaneous firing of striato-nigral neurons, and that this action of
E2 is not sex-dependent.