Electrophysiological properties of in vitro hippocampal pyramidal cells from normal and staggerer mutant mice

Visuospatial abilities

The importance of the hippocampus and its anatomical connections, including the medial septum, thalamic nuclei, and neocortical regions in many spatial tasks including the Morris water maze, has been emphasized. Studies in mutant mice with cerebellar atrophy and in rats with electrolytic lesions of the cerebellum have indicated that the cerebellum has a role in visuospatial and visuomotor processes in the Morris maze. Directional deficits in the water have also been noted in rats whose cerebellum was exposed to X-rays during different developmental stages. Cerebellar interactions with the superior colliculus, the hippocampus, and the neocortex via thalamic nuclei are suggested to be the basis of the cerebellar modulation of directional sense in maze tests.

Development of ionic conductances in neurons of the inferior olive in the rat: an in vitro study

Neurons of the inferior olive of the rat were studied at different stages of their postnatal (PN) development by using the current clamp technique in slices maintained in vitro. Antidromic and synaptic activation of inferior olivary neurons could be achieved in preparations as young as PN day 2. Neurons at this age already exhibited a variety of ionic conductances which included fast sodium-dependent spikes, high-threshold and low-threshold calcium spikes, potassium-dependent currents, Ca-dependent after-hyperpolarizing potentials (AHPS), and both instantaneous and time-dependent inward rectification at hyperpolarized levels of membrane potential. The two types of Ca-dependent responses recorded in olivary neurons during the first postnatal week were graded with the magnitude of the depolarization imposed on the cells. Furthermore, the high-threshold Ca spikes were only clearly observed during this early period when K conductances were depressed by the injection of caesium into the cells or by bath application of 4-aminopyridine. In contrast, the high-threshold Ca spikes could be obtained without suppression of K currents and were all-or-none in character in some neurons after PN day 8 and in all neurons after PN day 11. The observations suggest that the balance between K and Ca currents changes throughout maturation and is largely in favour of the K current until about the end of the first PN week. At all ages studied, the low-threshold Ca spikes were much less sensitive to the Ca channel blocker cadmium than were the high-threshold Ca spikes. Finally, spontaneous, regular oscillations of the membrane potential were observed for the first time at PN day 16 and were only commonly observed after PN day 19, suggesting a late development of electrotonic coupling between olivary neurons.

Conditioning-specific membrane changes of rabbit hippocampal neurons measured in vitro

Intracellular recordings were made from hippocampal CA1 pyramidal neurons within brain slices of nictitating membrane conditioned, pseudoconditioned, and naive adult male albino rabbits. All neurons included (26 conditioned, 26 pseudoconditioned, and 28 naive) had stable penetration and at least 60 mV action potential amplitudes. Mean input resistances were approximately equal to 60 mu omega for the three groups. A marked reduction in the afterhyperpolarization (AHP) following an impulse was apparent for conditioned (x = -0.98 mV) as compared to the pseudoconditioned (x = -1.7 mV) and naive (x = -2.0 mV) neurons. The AHP has been attributed previously to activation of a Ca2+-dependent outward K+ current. The distribution of AHP amplitudes for the conditioned group included a new lower range of values for which there was little overlap with the other groups. The conditioning-specific reduction of AHP may be due to reduction of ICa2+-K+ as shown previously for conditioned Hermissenda neurons. This conditioning-induced biophysical alteration of the CA1 pyramidal cell must be stored by mechanisms intrinsic to the hippocampal slice and cannot be explained as a consequence of changes of presynaptic input arising elsewhere in the brain. Our experiments demonstrate the feasibility of analyzing cellular mechanisms of associative learning in mammalian brain with the in vitro brain slice technique.

Electrophysiological studies on the postnatal development of intracerebellar nuclei neurons in rat cerebellar slices maintained in vitro. II. Membrane conductances

The development of membrane conductances of intracerebellar nuclei neurons was studied in the rat since birth up to the weaning period by the use of thick sagittal cerebellar slices maintained in vitro. Mature nuclear neurons express fast sodium and slowly inactivating sodium conductances, as well as calcium conductances. As early as birth, fast sodium and calcium conductances appear well developed whereas slowly inactivating sodium conductances mature within the first postnatal week.