Reciprocal connectivity between the glutamatergic subthalamic nucleus (STN) and GABAergic globus pallidus (GP) appears essential for oscillatory activity and rhythmic bursting in the GP -STN network (Plenz and Kitai. 1999). This central pattern generator could play a prominent role in driving the oscillatory neuronal activity observed in several basal ganglia nuclei seen both in idiopathic Parkinson’s disease and animal models thereof. Indeed, the frequency and pattern of this activity may be related to resting tremor. Here, we describe a brain slice preparation that maintains the functional connectivity between the GP and STN.

300-400 µm thick brain slices were obtained from 21-40 day old CB57BL/6JCrL mice. The animals were anaesthetised with fluorothane 4 % in O₂ and humanely killed. Slices were continuously superfused with ACSF at 32-34 °C. Pellets of biocytin were implanted in either the GP or STN in slices prepared in the horizontal, saggital or parasaggital plane. After 8-10 h slices were fixed and processed to reveal the reaction product.

Extensive labelling, including fibres in the internal capsule and cell bodies in the GP and STN, together with labelling in substantia nigra and striatum, was best observed in parasagittal slices, reflecting both retrograde and anterograde biocytin transport. To show functional connectivity, whole-cell recordings were made in parasaggital slices cut 20^o to the midline. Single shock stimulation in the GP evoked GABA_A receptor-mediated IPSCs in the STN (44/59 cells) that reversed around E_Cl and were blocked by bicuculline (10 µM, n = 7). Stimulation of the STN evoked EPSCs in the GP (22/33 cells), which were blocked by CNQX (10 µM) and DL-AP5 (100 µM, n = 5). In 2/2 slices, both GP to STN and STN to GP connectivity was demonstrated. In current clamp, evoked EPSPs (from the STN) were able to trigger action potentials in the GP (n = 3), while evoked IPSPs (from the GP) caused a cessation of STN firing activity followed by a rebound depolarisation that was able to elicit further action potential firing (n = 2). Such rebound depolarisations in STN neurones could play a role in oscillatory activity.

In summary, the parasaggital mouse brain slice maintains functional GP-STN connectivity and provides a suitable model for future pharmacological and mechanistic studies of this basal ganglia neuronal network.

This work was supported by a Parkinson’s Disease Society (UK) Research Studentship (CLW), and the Wellcome Trust (Grant nos. 063461 & 068818).