Journal of Neurophysiology, Vol 39, Issue 1 102-108, Copyright © 1976 by APS
Medial reticular and perihypoglossal neurons projecting to cerebellum
J. C. Eccles, R. A. Nicoll, D. W. Schwarz, H. Taborkova and T. J. Willey
Almost 10% of neurons in the medial reticular nucleus or adjacent thereto
were invaded antidromically in response to stimulation of the fastigial and
interpositus nuclei. The fraction was 77/835 for the bulbar and caudal
pontine levels, but 0/167 for rostral pontine levels. The mahority, 49, of
the neurons projecting to the cerebellum were superficially located in the
region of the perihypoglossal nucleus, but 23 were scattered through the
medial reticular nucleus, being 2.5-5.0 mm below the bulbopontine dorsum.
Both classes of cerebellopetal neurons had a similar range of antidromic
latencies, usually from 0.8 to 2.0 ms, but some were ober 3 ms. Both
classes responded to volleys from limb nerves and inputs from cutaneous
mechanoreceptors, with ranges of excitatory and inhibitory latencies that
were similar to those for other medial reticular neurons. It is conjectured
that the axonal projection is primarily to the cerebellar cortex and that
the branches to the nuclei are often slender, hence the long antidromic
latencies; 31 of 59 neurons tested projected to cerebellar nuclei on both
sides, often with a considerable latency differential. Rarely, there were
also axonal branches projecting up the central tegmental tract. The
experimental findings are in very good accord with the anatomical
descriptions of Brodal and associates (4, 5, 8, 19). It is suggested that
the paramedian reticular and the perihypoglossal nuclei may provide a
background excitatory input to the interpositus nuclei.
