Projections from the medial agranular cortex to brain stem visuomotor centers in rats

Abstract

Projections from medial agranular cortex to brain stem in rat were determined by use of the anterograde tracers Phaseolus vulgaris leucoagglutinin, or wheat germ agglutinin conjugated horseradish peroxidase. Axonal trajectories were also followed by means of the Wiitanen modification of the Fink-Heimer degeneration technique. AGm was identified on the basis of its cytoarchitectonics. AGm projected to the anterior pretectal nucleus, the rostral interstitial nucleus of the medial longitudinal fasciculus, the medial accessory oculomotor nucleus of Bechterew, the interstitial nucleus of Cajal, the nucleus of Darkschewitsch, the nucleus cuneiformis and subcuneiformis, intermediate and deep superior collicular layers, the paramedian pontine reticular formation (reticularis pontis oralis and caudalis, and reticularis gigantocellularis), and raphe centralis superior. Differences in connections between rostral and caudal injections were observed: pontine and medullary projections were lighter from the rostral portion of AGm than from the more caudal portions of AGm. The heaviest projections to the anterior pretectal nucleus were from the caudal portion of AGm. The subcortical projections were very similar to those described for the frontal eye field in monkeys, and the majority of them targeted areas thought to be involved in coordination of gaze with head and neck movements. Thus AGm in rats may contain the homologue of the primate frontal eye fields.

Nigrothalamic projections and nigrothalamocortical pathway to the medial agranular cortex in the rat: Single- and double-labeling light and electron microscopic studies

“…Microstimulation of the rat AGm has resulted in eyelid and eye movements (Hall and Lindholm, 1974;Donoghue and Wise, 1982;Sanderson et al, 1984;Neafsey et al, 1986b). Moreover, efferents of the AGm preferentially target visuomotor structures, including the visual cortices (Reep et al, 1990;VanEden et al, 1992), superior colliculus (Neafsey et al, 1986a;Leichnetz and GonzaloRuiz, 1987;Reep et al, 1987;Sesack et al, 1989;Zeng and Steusse, 1993), and brainstem visuomotor nuclei Steusse and Newman, 1990). Taken together with our own findings of nigral input by way of the thalamus to the AGm, these observations support the view that the AGm has a role in visuomotor function.…”

“…Alternatively, Reep et al (1990) suggested that the AGm as a whole consists of a frontal eye field, whereas others have suggested that the AGm consists of two separate, functionally distinct subdivisions: a rostral AGm, as a somatomotor field, and a caudal AGm, concerned with both somatomotor and visuomotor functions (Sesack et al, 1989;Neafsey et al, 1986a;Neafsey, 1990;Steusse and Newman, 1990;Hicks and Huerta, 1991). The rostral and caudal AGm subdivisions are hypothesized to be hodologically distinct based on differential corticocortical projections and efferent connections to visually related structures (Sesack et al, 1989;Neafsey et al, 1990;Reep et al, 1990;Stuesse and Newman, 1990;VanEden et al, 1992).…”

“…However, the functional role of the rat AGm remains unclear. Several studies using a variety of techniques have suggested that the rat AGm contains the homologue of the primate frontal eye field (Leonard, 1969;Hall and Lindholm, 1974;Leichnetz and Gonzalo-Ruiz, 1987;Reep et al, 1990;Steusse and Newman, 1990). Microstimulation of the rat AGm has resulted in eyelid and eye movements (Hall and Lindholm, 1974;Donoghue and Wise, 1982;Sanderson et al, 1984;Neafsey et al, 1986b).…”

Efferents from the lateral frontal cortex to spinomedullary target areas, trigeminal nuclei, and spinally projecting brainstem regions in the hedgehog tenrec

“…The cortical projections, however, were mainly to the stratum griseum intermedium, while the tectospinal cells are found predominantly in the stratum griseum profundum. Regarding the presumed projections from the frontal cortex to the superficial collicular layers in tenrec, it might be mentioned that such superficial projections are clearly present in monkey (Kunzle and Akert, 1977;Huerta et al, 1986;Stanton et al, 19881, but could not be demonstrated so far in the rat (Leichnetz et al, 1987;Stuesse and Newman, 1990;Preuss, 1995).…”

Optogenetics in the behaving rat: integration of diverse new technologies in a vital animal model

“…For example, organic dye-based imaging has been combined with optogenetic control [121][122][123] [19,169]. Over the last few decades, increasing anatomical [170][171][172], lesion [173][174][175], and microstimulation [176] evidence has continued to support assignment of this homology, and recent electrophysiological evidence [19] has lent further credence to this hypothesis. To directly test the role of the rodent FOF in behavior, a recent rat optogenetic study [177] utilized a memory-guided orienting task, in which rats were trained to distinguish between a "long" and a "short" series of clicks.…”