Mono- and disynaptic excitatory inputs from the superior colliculus to vertical saccade-related neurons in the cat Forel's field H

Abstract

Excitatory inputs to neurons in the Forel's field H (FFH) related to visually induced vertical saccades from the ipsilateral superior colliculus (SC) were investigated in chronically prepared alert cats. By stimulation of the deep or intermediate layer of the SC, upward augmenting neurons (ANs) and one long-lead downward burst neuron (BN) were found to be activated monosynaptically, while medium-lead BNs were activated disynaptically. The monosynaptically activated neurons were not antidromically activated from the oculomotor nucleus, whereas disynaptically activated neurons were also activated antidromically from the inferior rectus subdivision of the nucleus. These results suggest that an excitatory input to the FFH from the SC for inducing vertical saccades of visual origin first reaches upward ANs and/or long-lead downward BNs in the FFH, which in turn drive medium-lead BNs in the same area synapsing with motoneurons related to vertical eye movements.

Morphological study of the rostral interstitial nucleus of the medial longitudinal fasciculus in the monkey, Macaca mulatta by Nissl, Golgi, and computer reconstruction and rotation methods

“…Reports in which riMLF cells were intracellularly injected with horseradish peroxidase (Moschovakis et al, 1991b) illustrate multipolar cells, some of which appear similar to our type I cells. These burst neurons project to both iC and OC (Moschovakis et al, 1991a), which is consistent with the findings of Nakao et al (1990) that burst neurons project to OC monosynaptically.…”

“…The introduction of new tract-tracing techniques in the past 20 years has revealed that the ND has no direct connection with the oculomotor system (Graybiel and Hartwieg, 1974;Steiger and Buttner-Ennever, 1979). However, another region has been revealed at the rostral end of the MLF, contiguous with the rostral iC (Buttner-Ennever and Buttner, 1978;Graybiel, 1977b), which contains neurons that discharge before and during vertical saccadic eye movements (Buttner et al, 1977;King and Fuchs, 1979;King et al, 1981;Nakao et al, 1990). This region has received different designations (for review, see Buttner-Ennever and Biittner, 19881, but it is most commonly termed the "rostral interstitial nucleus of the MLF" (riMLF).…”

“…The riMLF has been described in the pioneering work of Buttner-Ennever, Buttner, and colleagues as a collection of neurons situated among the rostralmost fascicles of the MLF rostral to the iC, dorsal to the rostral pole of the red nucleus, ventral and medial to branches of the posterior thalamosubthalamic artery, and medial to the nucleus of the Field of Fore1 Buttner, 1978, 1988). The riMLF receives prominent afferent projections from the superior colliculus (Harting, 1977;Grantyn and Grantyn, 1982;Nakao et al, 1990) and paramedian pontine reticular formation (PPRF; Graybiel, 1977a;Buttner-Ennever and Buttner, 1978;Langer and Kaneko, 1983;Ohgaki et al, 1989;Nakao et al, 19911, both closely linked to the production of saccadic eye movements (Fuchs et al, 1985). Leichnetz et al (1984) and Huerta et al (1986), but not Stanton et al (1988), reported input from the frontal eye fields.…”

“…Electrophysiological studies of riMLF neurons (Buttner et al, 1977;King and Fuchs, 1979;Vilis et al, 1989;Nakao et al, 1990;Moschovakis et al, 1991a,b) have demonstrated that some riMLF neurons fire bursts of action potentials before the eyes make vertical or torsional saccadic movements. Nakao et al (1990) studied two groups of neurons in the cat riMLF region. One group of neurons, which fires with relatively long leads before saccades, receives monosynaptic input from the superior colliculus but does not project monosynaptically to the oculomotor centers.…”

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

“…The ascending projection from tectofugal neurones is interesting also with respect to eye motor control since it has been shown that the target neurones project to the frontal eye field (area 8) and the inferior parietal lobule (area 7; Harting, Huerta, Frankfurter, Strominger & Royce, 1980). Mono-and disynaptic excitatory connections from tectofugal neurones to vertical saccade-related neurones have recently been observed in the fields of Forel (Nakao, Shiraishi, Li & Oikawa, 1990). Furthermore, it has been shown by Isa, litouji, Nakao & Sasaki (1988a) and Isa, litouji & Sasaki (1988b) that excitatory neurones in the fields of Forel project monosynaptically or disynaptically via reticulospinal neurones to dorsal neck motoneurones.…”