Excitatory and inhibitory processes acting upon cerebellar Purkinje cells during maturation in the rat; influence of hypothyroidism

Electrophysiological study on the postnatal development of neuronal mechanisms in the rat cerebellar cortex

(1) Functional commencements of the neuronal elements in the cerebellar cortex of young rats were studied electrophysiologically by means of laminar field potential analyses in the cortex on stimulation of the cerebellar surface (Loc) and the white matter (WM). (2) The antidromic action potential of Purkinje cells on the WM stimulation was observed at one day after birth. The climbing fiber excitation of Purkinje cells on the stimulation was noted at 3 days after birth. (3) The mossy fiber-granule cell synapses were found to function at 10 days after birth and the Golgi cell inhibition of granule cells could be proved at the same time. The excitatory action of parallel fibers and the inhibitory action of basket-stellate cells on Purkinje cells appeared simultaneously at about 12 days after birth. The transverse distribution across the cerebellar folium of the basket-stellate cell inhibitory action on Purkinje cells was found to be narrow up to 60 days after birth. (4) These results concerning the dates of commencement of excitatory and inhibitory synaptic actions in the cerebellar cortex were compared with those of synaptogenesis studied morphologically, and some implications of the dates in the functional development of the cerebellar cortex were discussed.

Anatomical, physiological and biochemical studies of the cerebellum from mutant mice. I. Electrophysiological analysis of cerebellar cortical neurons in the staggerer mouse

An electrophysiological analysis of cerebellar cortical neurons was performed in staggerer mutant mice on postnatal days 18 to 22, and data were compared with cerebellar activities in normal mice of the same age. Bioelectrical activities were elicited through local (LOC) and juxtafastigial (JF) stimulation. In staggerer mice, parallel fibers (PF) exhibited no major alterations, i.e. they conducted impulses and they activated most of the cerebellar cortical units encountered, but some minor differences existed in comparison with normal mice, i.e. their excitability was reduced, as tested by their refractory period and conduction velocity. On the contrary, Purkinje cell (PC) responses presented marked abnormalities. (1) Depth profiles during antidromic invasion of PC and unitary antidromic responses revealed a lower safety factor than normal in the invasion of the somatodendritic region of PC. In particular, a marked IS-SD delay or block occurred in about 60% of unitary antidromic responses of the mutant mouse. (2) Spontaneous or evoked typical climbing fiber responses (CFR) were never recorded in staggerer mice, despite functional synapses between climbing fibers (CF) and PC disclosed with harmaline injections. Activation of PC via CF under harmaline consisted of rhythmical trains of simple spikes, Finally, most of the PC studies in the staggerer mice were certainly activated via PF but with a low efficacy. The results suggest that PC are directly affected by the mutation.