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1. Neurones of the globus pallidus (GP) have been classified into three subgroups based on the visual inspection of current clamp electrophysiological properties and morphology of biocytin-filled neurones. 2. Type A neurones (132Ï208; 63%) were identified by the presence of the time-and voltagedependent inward rectifier (Ih) and the low-threshold calcium current (It) giving rise to anodal break depolarisations. These cells were quiescent or fired regular spontaneous action potentials followed by biphasic AHPs. Current injection evoked regular activity up to maximum firing frequency of 350 Hz followed by moderate spike frequency adaptation. The somata of type A cells were variable in shape (20 ² 12 ìm) while their dendrites were highly varicose. 3. Type B neurones (66Ï208; 32%) exhibited neither Ih nor rebound depolarisations and only a fast monophasic AHP. These cells were spontaneously active while current injection induced irregular patterns of action potential firing up to a frequency of 440 Hz with weak spike frequency adaptation. Morphologically, these cells were the smallest encountered (15 ² 10 ìm), oval in shape with restricted varicose dendritic arborisations. 4. Type C neurones were much rarer (10Ï208; 5%). They were identified by the absence of Ih and rebound depolarisations, but did possess a prolonged biphasic AHP. They displayed large A-like potassium currents and ramp-like depolarisations in response to step current injections, which induced firing up to a maximum firing frequency of 310 Hz. These cells were the largest observed (27 ² 15 ìm) with extensive dendritic branching. 5. These results confirm neuronal heterogeneity in the adult rodent GP. The driven activity and population percentage of the three subtypes correlates well with the in vivo studies (Kita & Kitai, 1991). Type A cells appear to correspond to type II neurones of Nambu & Llinas (1994, 1997 while the small diameter type B cells display morphological similarities with those described by Millhouse (1986). The rarely encountered type C cells may well be large cholinergic neurones. These findings provide a cellular basis for the study of intercellular communication and network interactions in the adult rat in vitro. Keywords:

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A theoretical study investigating the effects of both anisotropic and isotropic surface roughness on the convective stability of the boundary-layer flow over a rotating disk is described. Surface roughness is modelled using a partial-slip approach, which yields steady-flow profiles for the relevant velocity components of the boundary-layer flow which are a departure from the classic von Kármán solution for a smooth disk. These are then subjected to a linear stability analysis to reveal how roughness affects the stability characteristics of the inviscid Type I (or cross-flow) instability and the viscous Type II instability that arise in the rotating disk boundary layer. Stationary modes are studied and both anisotropic (concentric grooves and radial grooves) and isotropic (general) roughness are shown to have a stabilizing effect on the Type I instability. For the viscous Type II instability, it was found that a disk with concentric grooves has a strongly destabilizing effect, whereas a disk with radial grooves or general isotropic roughness has a stabilizing effect on this mode. In order to extract possible underlying physical mechanisms behind the effects of roughness, and in order to reconfirm the results of the linear stability analysis, an integral energy equation for three-dimensional disturbances to the undisturbed three-dimensional boundary-layer flow is used. For anisotropic roughness, the stabilizing effect on the Type I mode is brought about by reductions in energy production in the boundary layer, whilst the destabilizing effect of concentric grooves on the Type II mode results from a reduction in energy dissipation. For isotropic roughness, both modes are stabilized by combinations of reduced energy production and increased dissipation.

A theoretical study into the effects of wall compliance on the stability of the rotating-disc boundary layer is described. A single-layer viscoelastic wall model is coupled to a sixth-order system of fluid stability equations which take into account the effects of viscosity, Coriolis acceleration, and streamline curvature. The coupled system of equations is integrated numerically by a spectral Chebyshev-tau technique.Travelling and stationary modes are studied and wall compliance is found to greatly increase the complexity of the eigenmode spectrum. It is effective in stabilizing the inviscid Type I (or cross-flow) instability. The effect on the viscous (Type II) eigenmode is more complex and can be strongly destabilizing. An analysis of the energy flux indicates that this destabilization arises as a result of a large degree of energy production by viscous stresses at the wall/flow interface.The Type I and II instabilities are shown to be negative and positive energy waves respectively. The co-existence of eigenmodes of opposite energy type indicates the possibility of modal interaction and coalescence. It is found that, compared with the rigid disc, wall compliance promotes the interaction and coalescence of the Type I and II eigenmodes. There is an associated strong instability which appears to be characterized by marked horizontal motion of the compliant surface. Modal coalescence is interpreted physically as producing local algebraic growth which could advance the onset of nonlinear effects.

The role of enkephalin and the opioid receptors in modulating GABA release within the rat globus pallidus (GP) was investigated using whole-cell patch recordings made from visually identified neurons. Two major GP neuronal subtypes were classified on the basis of intrinsic membrane properties, action potential characteristics, the presence of the anomalous inward rectifier (Ih), and anode break depolarizations. The mu opioid receptor agonist [D-Ala2-N-Me-Phe4-Glycol5]-enkephalin (DAMGO) (1 microM) reduced GABAA receptor-mediated IPSCs evoked by stimulation within the striatum. DAMGO also increased paired-pulse facilitation, indicative of presynaptic mu opioid receptor modulation of striatopallidal input. In contrast, the delta opioid agonist D-Pen-[D-Pen2, 5]-enkephalin (DPDPE) (1 microM) was without effect. IPSCs evoked by stimulation within the GP were depressed by application of [methionine 5']-enkephalin (met-enkephalin) (30 microM). Met-enkephalin also reduced the frequency, but not the amplitude, of miniature IPSCs (mIPSCs) and increased paired-pulse facilitation of evoked IPSCs, indicative of a presynaptic action. Both DAMGO and DPDPE reduced evoked IPSCs and the frequency, but not amplitude, of mIPSCs. However, spontaneous action potential-driven IPSCs were reduced in frequency by met-enkephalin and DAMGO, whereas DPDPE was without effect. Overall, these results indicate that presynaptic mu opioid receptors are located on striatopallidal terminals and pallidopallidal terminals of spontaneously firing GP neurons, whereas presynaptic delta opioid receptors are preferentially located on terminals of quiescent GP cells. Enkephalin, acting at both of these receptor subtypes, serves to reduce GABA release in the GP and may therefore act as an adaptive mechanism, maintaining the inhibitory function of the GP in basal ganglia circuitry.