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PubMed1988

Electrophysiology of the mammalian cerebellar cortex in organ culture.

A direct comparison was made between the electrical properties of rat Purkinje cells in cerebellar organotype cultures and those in acute slices from age-matched animals. Cultures were prepared from 9-11-day-old animals. Intracellular recordings were made 5-12 days later, at which time the folia architecture of the cerebellum was still well preserved. The resting membrane potentials and input resistances of Purkinje cells in cultured and acute slice preparations from young animals were comparable to those of mature Purkinje cells in slices. Neurons from animals younger than 14 days differed from mature Purkinje cells in that they fired at low frequencies in response to outward current pulses. The latter property was found in all cultured neurons studied, independent of their time in culture. These action potentials were generated by Na+ and Ca2+ conductances as shown by the application of selective channel blockers. Cultured or acute slice preparations from animals younger than 11 days shared other immature electroresponsive features. In both groups, Na+-dependent plateau depolarizations were observed in less than 10% of Purkinje cells unless K-conductances were blocked, and considerable membrane depolarization was often required to elicit Ca2+-dependent action potentials. These findings are compatible with the relative prominence of voltage-dependent outward currents in immature Purkinje cells, a property which may be enhanced in culture. The injection of hyperpolarizing current pulses revealed a marked time-dependent anomalous rectification in all Purkinje cells. At the breaks of such pulses, several events were observed. In all cells, a rebound conductance was identified which could generate post-anodal spike bursts. In cultured neurons, however, hyperpolarizing pulses were also followed by a slow return to resting potential. This membrane potential profile was similar to that produced by the activation of an A conductance. Experiments on acute slices from animals of different ages (P9-P17) showed that this A-like conductance was expressed only during a brief period in Purkinje cell development. A higher level of spontaneous synaptic activity was observed in cultured than in acute slice preparations. Both unitary excitatory postsynaptic potentials and inhibitory postsynaptic potentials could be elicited in the former by parallel fiber stimulation, and could be fully reversed by outward or inward transmembrane current injections, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMed2001

Unipolar brush cells form a glutamatergic projection system within the mouse cerebellar cortex.

Unipolar brush cells (UBCs) of the mammalian vestibulocerebellum receive mossy fiber projections primarily from the vestibular ganglion and vestibular nuclei. Recently, the axons of UBCs have been shown to generate an extensive system of cortex-intrinsic mossy fibers, which resemble traditional cerebellar mossy fiber afferents and synapse with granule cell dendrites and other UBCs. However, the neurotransmitter used by the UBC axon is still unknown. In this study, we used long-term organotypic slice cultures of the isolated nodulus (lobule X) from postnatal day 8 mouse cerebella to identify the neurotransmitter and receptors at synapses of the UBC axon terminals, relying on the notion that, in these cultures, all of the cortex-extrinsic fibers had degenerated during the first few days in vitro. Quantification of glutamate immunogold labeling showed that the UBC axon terminals have the same high gold-particle density as the glutamatergic parallel fiber varicosities. Furthermore, UBCs identified by calretinin immunoreactivity expressed the glutamate receptor subunits GluR2/3, NMDAR1, and mGluR2/3, like they do in the mature mouse cerebellum in situ. Evoked excitatory postsynaptic currents (EPSCs), spontaneous EPSCs, and burst discharges were demonstrated in UBCs and granule cells by patch-clamp recording. Both the evoked and spontaneous EPSCs were blocked by ionotropic glutamate receptor antagonists CNQX and D-AP5. We conclude that neurotransmission at the UBC axon terminals is glutamatergic. Thus, UBCs provide a powerful network of feedforward excitation within the granular layer, which may amplify vestibular signals and synchronize activity in clusters of functionally related granule cells which project vertically to patches of Purkinje cells.

2-Amino-5-phosphonovalerate↗