Axonal patterns and sites of termination of cat superior colliculus neurons projecting in the tecto-bulbo-spinal tract

Abstract

Horseradish peroxidase was injected in the somata or axons of neurons located in the intermediate and deep layers of the superior colliculus. A group of 34 neurons with physiologically identified projection in the predorsal bundle (tectobulbo-spinal neurons, TBSNs) and two commissural tecto-tectal neurons were characterized with regard to soma-dendritic profiles, axon trajectories, collateral branching, and terminations. TBSNs belong to the class of large, multipolar, wide field neurons. They send axons through the deep white layer without generating local collaterals. Prior to decussation, all TBSNs bifurcate into an ascending branch which reaches the caudal diencephalon, and a main axon descending to the medulla or spinal cord. Regularly spaced collaterals supply a variety of structures at all rostro-caudal levels. In the midbrain, preterminal and terminal ramifications are present in the medial and lateral reticular tegmentum, in the central grey (including its supraoculo-motor zone), in the nuclei of Cajal and Dark-schewitsch and in the medial aspects of the prerubral area and the fields of Forel. Rhombencephalic targets of TBSNs include the medial pontine and bulbar reticular formation, the abducens nucleus, the nucleus reticularis tegmenti pontis and the nucleus prepositus hypoglossi. An increased density of terminal ramifications was found in several brain stem regions related to the control of eye and head movements. The widespread connections of each individual TBSN suggest that neurons of this type may provide a spatio-temporal pattern of facilitation which promotes rapid orientation of eyes, head and body towards the contralateral hemifield but does not specify the details of movement to be executed.

Tectal and tegmental excitation in dorsal neck motoneurones of the cat.

“…Thus, the observed shortening of the latencies described in Fig. 1 (Grantyn & Grantyn, 1982), then 0'7 ms is the required B. ALSTERMARK, M. J. PINTER AND S. SASAKI conduction time from tectum to the C2-C3 segments. Since the remaining 0-2-05 ms can only allow for one synaptic relay it is concluded that the shortest latencies of 1-51-6 ms from tectum to SPL and BCC motoneurones show a disynaptic linkage.…”

“…The anatomical study by Grantyn & Grantyn (1982) of tectofugal neurones labelled intracellularly with horseradish peroxidase demonstrated that their axons bifurcate into one descending and one ascending branch. The latter branch had terminal ramifications in the tegmentum, central grey, nuclei of Cajal and Darkschewitsch, prerubral area and in the fields of Forel.…”

Cross-modal links in exogenous covert spatial orienting between touch, audition, and vision

“…Moreover, these maps are in approximate spatiotopic register with each other and with the motor maps found in the deepest layers, which are associated with overt orienting of the eyes, head, and body (e.g., Groh & Sparks, 1996;Sparks, 1988;R E. Stein, 1984). Neurophysiological and neuropsychological studies have implicated SC involvement in the subcortical control ofboth overt and covert exogenous orienting both in animals (e.g., Dean, Redgrave, Sahibzada, & Tsuji, 1986;Grantyn & Grantyn, 1982;Knudsen, Knudsen, & Masino, 1993;Kustov & Robinson, 1996;Peck, 1987;Robinson & Kertzman, 1995) and in humans (e.g., Butter, 1987;Ladavas, 1993;Rafal et aI., 1991).…”

A physiological study of vestibular and prepositus hypoglossi neurones projecting to the abducens nucleus in the alert cat.

“…In view of the results presented here, a modified version of this hypothesis is now proposed, which is summarized in the diagram of Fig. 8 C. The first neural set in the chain could receive the velocity signal from excitatory reticular (Strassman et al 1986a;Grantyn, Ong-Meang Jacques & Berthoz, 1987) and/or from tecto-reticulo-spinal neurones (Grantyn & Grantyn, 1982). Each component of the rest of the chain projects on both the following and preceding one, forming an integrating loop (Escudero & Delgado-Garcia, 1988).…”