Ake. Horn et al., SACCADIC PREMOTOR NEURONS IN THE BRAIN-STEM - FUNCTIONAL NEUROANATOMYAND CLINICAL IMPLICATIONS, Neuro-ophthalmology, 16(4), 1996, pp. 229-240
Saccadic eye movements are generated by immediate premotor excitatory
(EBN) and inhibitory (IBN) medium-lead burst neurons, long-lead burst
neurons (LBN), and omnipause neurons (OPN) in the brainstem. The histo
logical identification of the functional neuron populations is essenti
al for performing any neuropathological analysis of clinical cases wit
h saccadic disorders. This paper describes the localization of some pr
emotor saccadic neurons in human brain and their neurochemistry, based
on monkey data. In humans, the EBNs for horizontal saccades (EBN(H))
lie in the paramedian pontine reticular formation in the nucleus retic
ularis pontis caudalis (nrpc) and form a compact group of medium-sized
neurons. The medium-sized IBNs lie caudal to the nucleus abducens in
the nucleus paragigantocellularis dorsalis (pgd). The EBNs for vertica
l saccades (EBN(V)) are medium-sized neurons in the rostral interstiti
al nucleus of the medial longitudinal fasciculus (riMLF) in the rostra
l mesencephalon. The OPNs are located at the midline of the pontine re
ticular formation, in the nucleus raphe interpositus, bordered by the
EBN area rostrally and the IBN area caudally. The OPNs use glycine as
an inhibitory transmitter. These cell groups (EBN(H), EBN(V), IBN, and
OPN) were first identified experimentally in monkeys, and all were sh
own to express parvalbumin immunoreactivity. The parvalbumin immunorea
ctivity was then used as a marker to help identify the homologous neur
ons in man.