The basal ganglia output stage in the lamprey : a combined experimental and modeling study

• Based on previous immunohistochemical study Robertson et al., (J Comp Neurol, 2006) believed that a lamprey homolog of the primate globus pallidus interna (GPi) exists. They found GABAergic neurons in medial pallidum projecting to optic tectum, an area homologous to the superior colliculus in mammals. Medial pallidum in lamprey also receives GABAergic projections from striatum. This study aims to investigate the electrophysiological characteristics of the putative pallidal neurons.We have used lamprey brain slices and patch recordings to characterise neurons in the medial pallidum. The glutamate blockers CNQX and AP-V have been used to test spontaneous activity dependency of excitatory synaptic input. Projecting neurons in the pallidal area are sparsely scattered and do not form an easily detectable anatomical area. To record from projecting neurons we retrogradely labelled cell somas by tracer injections. The tracer (dextran 488 coupled ) was injected in optic tectum in the anaesthetized animal 12-24 hours before the experiment. Preliminary results show both tonically active and non active neurons in the medial pallidum. A majority of the neurons in rat entopeduncular nucleus, homologous of primate GPi, are persistently spontaneously active (Nakanishi et al., Brain Res, 1991). We have found neurons with frequency adaptation and with persistent spiking when depolarising current is injected.Recordings from labelled neurons display a subpopulation of spontaneously active neurons. These neurons were found in a narrow area near the border between the diencephalon and the mesencephalon. Results from blocking glutamatergic synaptic input indicate that intrinsic neuron properties generate the spontaneous activity. We have used the experimental findings to investigate a computer model of a lamprey pallidal neuron. The model have been tuned to replicate experimental data and characteristics of lamprey pallidal neurons.We therefore conclude that neurons with pallidal properties exist in lamprey and are homologous to primate globus pallidus interna, a output stage of basal ganglia.

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NATURVETENSKAP  -- Data- och informationsvetenskap (hsv//swe)

NATURAL SCIENCES  -- Computer and Information Sciences (hsv//eng)

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