HISTOLOGICAL IDENTIFICATION OF PREMOTOR NEURONS FOR HORIZONTAL SACCADES IN MONKEY AND MAN BY PARVALBUMIN IMMUNOSTAINING

The premotor excitatory and inhibitory burst neurons are essential for horizontal saccades. In the monkey, excitatory burst neurons lie in t he ipsilateral paramedian pontine reticular formation, and the inhibit ory burst neurons lie more caudally in the contralateral nucleus parag igantocellularis dorsalis. For a neuropathological analysis of degener ative changes in saccadic disorders of patients, the histological iden tification of the burst neuron areas in man is important. Here, we sho w that this is possible with parvalbumin immunostaining as a histologi cal marker. First, in monkeys, the premotor burst neurons were backlab eled by injections of wheat germ agglutinin-horseradish peroxidase or cholera toxin subunit B into the abducens nucleus or tetanus toxin fra gment C into the lateral rectus muscle and shown by double labeling to contain parvalbumin. Then, human brainstem sections were immunoreacte d for parvalbumin, and, by comparing the resulting staining pattern to that in the monkey, the homologous burst neuron areas were defined in man. In the monkey, excitatory burst neurons were confined to the nuc leus reticularis pontis caudalis and did not extend farther rostrally into the nucleus reticularis pontis oralis. All retrogradely labeled c ells in both burst neuron areas were parvalbumin positive, and approxi mately 70% of the parvalbumin-positive cells were retrogradely labeled . Both burst neuron areas were highlighted by their parvalbumin staini ng pattern and could be outlined in man as well. The putative excitato ry burst neuron area in man is in the medial part of the nucleus retic ularis pontis caudalis (extending 2.5 mm mediolaterally), immediately rostral (250 mu m) to the omnipause neurons and extending 2.2 mm rostr ally, and the putative inhibitory burst neuron area lies in the medial part of the paragigantocellular nucleus caudal to the abducens nucleu s, extending 1.8 mm caudally. The location of the burst neuron areas, including the burst neurons themselves, via parvalbumin immunostaining will help in the analysis of clinical cases with slow saccades. (C) 1 995 Wiley-Liss, Inc.