No abstract

The cells arising in the anterior part of the subventricular zone (SVZa) migrate along a well-demarcated pathway which lacks radial glial fibers to the olfactory bulb where they differentiate into interneurons of the granule cell layer or glomerular layer (Luskin, 1993, Neuron 11, 173). To analyze the mechanisms underlying this highly directed migration, we have compared the migratory behavior of unmanipulated SVZa-derived cells to that of homotopically transplanted SVZa cells and of heterotopically transplanted telencephalic ventricular zone (VZ) cells that ordinarily migrate in association with radial glial fibers. To identify the phenotype of the SVZa progenitor cells prior to their transplantation, we characterized them in vitro using cell type-specific markers. After 1 day in culture nearly all the SVZa cells were stained with TuJ1, a neuron-specific marker; only an occasional cell exhibited a glial phenotype as judged by the presence of GFAP-immunoreactivity. This indicates that SVZa cells express a neuronal phenotype. To reveal the spatiotemporal distribution of homotopically transplanted neonatal SVZa cells in a host brain, dissociated SVZa cells from Postnatal Day 0 (P0)-P2 animals were labeled with the lipophilic dye PKH26 or the cell proliferation marker BrdU and implanted into the SVZa of host animals of the same age. Within the first week after transplantation there were vast numbers of labeled cells throughout the pathway. Over the next 2 weeks the labeled cells migrated into the overlying cellular layer of the olfactory bulb and began to differentiate, and within 4 weeks the transplanted cells had reached their final positions in the granule cell and glomerular layers of the olfactory bulb in the same proportions as for unmanipulated SVZa-derived cells. While en route to the olfactory bulb the homotopically transplanted cells never strayed from the migratory pathway. In contrast, heterotopically transplanted VZ cells from the embryonic telencephalon did not undergo migration although they did differentiate. These results demonstrate that the homotopically transplanted SVZa-derived cells adopt a mode of migration indistinguishable from that ordinarily utilized by SVZa-derived neurons and that the VZ cells are unable to decipher the same set of guidance cues.

The purpose of this experiment was to compare the problem-solving performance of rats allowed to explore either one or two tables of Maier's three-table-problem apparatus on successive days. The feeding &xperience and test trial were administered on the day after all tables and runways had been explored in this piecemeal fashion. No rat that explored only one table and runway per day was able to solve the problem, whereas 60% of the rats that explored two tables and their interconnecting runways did solve the problem. All rats that explored the entire apparatus on each exploratory day were able to solve the problem. These data support the notion that animals can conceptually link objects experienced successively into cognitive representations which specify the constant relationships existing between those objects. The existence of such an absolute spatial mechanism makes it unnecessary for an organism to depend upon relative spatial mechanisms such as routes or cues.In recent years the concept of a cognitive map has become a major theoretical construct in theories of spatial cognition. Although first introduced by Tolman (1948), the cognitive map concept received its most sophisticated treatment by O' Keefe and Nadel (1978), inasmuch as they elaborated a number of major properties of cognitive maps. Specifically, cognitive maps were differentiated from systems that relied on extant cues and orientations in the guidance of behavior. For example, a cognitive map allows an animal to react to stimuli that are not immediately present (i.e., act at a distance). Additionally, it is an information structure in which the distance and direction between various environmental objects are specified. Another property of a cognitive map is that it allows organisms "to link together conceptually parts of an environment which have never been experienced at the same time" (O'Keefe & Nadel, 1978, p. 2). It is to this latter property of a cognitive map that this paper is addressed.Inasmuch as organisms acquire information about a region by virtue of exploratory activity (O'Keefe & Nadel, 1978) and inasmuch as this process involves a series of successive experiences, such information must be transformed into a cognitive structure in which the distance and direction between the various successively experienced objects are indicated before it can be used in the solving of problems such as the A version of this paper was presented at the Seventy-Fifth Annual Meeting of the Southern Society for Philosophy and Psychology, Atlanta, GA, March 3I-April 2, 1983, and at the Sixtieth Annual Meeting of the Georgia Academy of Science, April 22-23, 1983. The patience of Martha Turner and Majella Hardie in the typing of various versions of this manuscript is appreciated. The authors' mailing address is: Department of Psychology, Georgia State University, University Plaza, Atlanta, GA 30303.taking of the shortest route to food, etc. Spatial information results when various objects in a cognitive representation exist as a simultaneous pattern rat...