Properties of developing lateral geniculate neurones in the mouse

This study describes the properties of neurones recorded in vitro from the dorsal lateral geniculate nucleus (dLGN) of the mouse between developmental stages El 6 and P36 and represents the first systematic study of the development of rodent thalamic neurones. The results demonstrate that thalamo‐cortical neurones in the mouse dLGN undergo a series of important changes as they mature. Prenatally recorded cells had low resting potentials and could not generate action potentials but as they mature, mouse dLGN neurones become more polarised and show an increase in membrane time constant and spike threshold, while action potentials increase in amplitude and decrease in width. The low‐threshold spike (LTS) complex appears at the time of birth, but does not show properties typical of adult cells until at least the third postnatal week. Immature action potentials are primarily sodium‐dependent but gain a significant calcium component in the second postnatal week, which is associated with a supra‐threshold oscillation of the membrane potential. The electrical activity during this critical period is strongly influenced by the interaction of powerful inward and outward rectification with calcium conductances which determines the appearance of voltage responses to intracellular current injection. The membrane potential in recordings from neurones during the first postnatal week was dominated by intense TTX‐sensitive depolarising synaptic‐like events which attained amplitudes of 60mV in several neurones at stages P5–P8. These changes are discussed in relationship to the formation of appropriate connections in the developing visual system.