title: Cytoarchitectonic characterization of the parahippocampal region of the guinea pig.
abstract: The cytoarchitectonic features of the parahippocampal region (PHR) in the guinea pig are described, based on coronal, horizontal, and sagittal 50-microm sections stained for Nissl substance, zinc, parvalbumin, or calbindin. We differentiate between perirhinal (PRC), postrhinal (POR), and entorhinal (ERC) cortices. PRC is divided into areas 35 and 36 occupying the fundus and the dorsal bank of the rhinal fissure, respectively. POR is located caudal to the PRC. POR and area 36 show a dense, clustered cellular layer II and a thinner layer III in comparison to the adjacent neocortex, and they differ from each other with respect to the orientation of the somata of layer VI neurons. Area 35 is characterized by a thin layer II that is not very different from layer III. Layer IV is (dys)granular in area 36 and POR, and is absent in area 35 and ERC. ERC, located ventromedial to the PRC and POR, is subdivided in six fields, of which field 5 is adjacent to area 35. In both area 35 and field 5, no clear differentiation between layers II and III is present. Field 5 shows a darker cellular stain and exhibits a cell-free zone or lamina dissecans between layers III and V. Medial to field 5, an area characterized by large cell clusters in layer II is designated field 4. The latter field is replaced by field 3 rostromedially, which also typically shows clustering of layer II neurons. These cell clusters in field 3, however, are much more constant in size in spacing compared to those in field 4. The caudomedial portion of ERC is subdivided into fields 1, 1', and 2. The latter, characterized by a homogeneous distribution of neurons in all layers with large darkly stained neurons in layer V is positioned rostral to field 1 and caudomedial to fields 4 and 5. In field 1, layers V and VI are thinner, and layer II neurons are smaller then in field 1' and field 2. We conclude that the architectonic features of the guinea pig PHR are comparable to those described in other mammals, particularly the rat.
authors.affiliation: Department of Neurophysiology, Istituto Nazionale Neurologico Carlo Besta, Milano, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Uva
authors.forename: Sebastiaan
authors.initials: S
authors.lastname: Grüschke
authors.forename: Gerardo
authors.initials: G
authors.lastname: Biella
authors.forename: Marco
authors.initials: M
authors.lastname: De Curtis
authors.forename: Menno P
authors.initials: MP
authors.lastname: Witter
mesh_terms: D000818:Animals; D018728:Entorhinal Cortex / Q000166:cytology; D006168:Guinea Pigs; D007150:Immunohistochemistry; D000090204:Mesothelin; D009474:Neurons / Q000166:cytology*; D020534:Parahippocampal Gyrus / Q000166:cytology*