Pineal system of desert rodents and its relationship to the epithalamus

The morphological relationships of the pineal complex to the epithalamic structures have been examined at light microscopic level in five desert rodent species, Meriones crassus, Meriones lybicus, Gerbillus gerbillus, Psammomys obesus and Ctenodactylus vali. The pineal complex is classified as type ABC in M. crassus and G. gerbillus, AC in M. lybicus, AbetaC in P. obesus and alphabetaC in C. vali. In these rodent species, the pineal is an elongated organ which is dumbbell-shaped in G. gerbillus and M. lybicus, and extends above the cerebral hemispheres in M. crassus, leaf-shaped in P. obesus and lancet-shaped in C. vali. In P. obesus, pigment-containing cells are noted in the superficial part of the gland. In all species examined, the suprahabenular recess which is an extension of the choroid plexus of the third ventricule establishes a close anatomical relationship with the deep pineal. In C. vali, the suprahabenular recess is also contiguous with the pineal stalk and the superficial pineal component. In M. lybicus, M. crassus, G. gerbillus and P. obesus, a prominent dorsal vessel, the vena cerebri magna, intervenes between the suprahabenular recess, the superficial portion and the stalk. The most striking feature noted in this study is the presence of numerous melanocytes in the connective tissue capsule of the pineal gland, in the connecting stalk and in the connective tissue core of the highly convoluted suprahabenular recess in M. lybicus and M. crassus. The location of melanocytes in the restricted pineal area may suggest that these cells have a morphosignificance in photoreception or photoprotection.