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Organization of anterior dorsal ventricular ridge in snakes
Author(s) -
Ulinski Philip S.
Publication year - 1978
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.901780303
Subject(s) - biology , anatomy , forebrain , efferent , commissure , population , neuroscience , central nervous system , afferent , demography , sociology
Anterior dorsal ventricular ridge (ADVR) is a major telencephalic structure in reptiles. The intrinsic, efferent, and afferent connections of ADVR were studied in water snakes ( Natrix sipedon ) and garter snakes ( Thamnophis sirtalis ) using orthograde degeneration and Golgi techniques. ADVR in these snakes contains four zones oriented concentric with the ventricular surface and named zones A, B, C, and D, with zone A being the most peripheral. Each zone contains a characteristic population of neurons. Zone A neurons have dendrites which extend obliquely through zone A and into zone B. Zone B neurons have dendrites with a high density of dendritic spines and axons which ramify in zone A concentric with the ventricle, typically bearing large varicosities about 5 μ in length. Zone C neurons have dendrites with a low density of dendritic spines and axons which ramify within about 300 μ of the soma, typically bearing small varicosities about 3 μ in length. Zone D neurons resemble those in zone C, except that their axons may course ventrally out of ADVR into the subjacent striatum. Lesions placed superficially in ADVR produce terminal degeneration which is restricted to ADVR in Fink‐Heimer preparations. Lesions which damage the ventral part of ADVR produce degeneration in striatal nuclei (medial striatal nucleus, intrapeduncular nucleus, and perifascicular complex) as well as in the ventral two‐thirds of the posterior dorsal ventricular ridge. Unilateral transections of the midbrain produce degeneration in a system of thick caliber axons, with thin collaterals, which enters ADVR caudally behind the anterior commissure and rostrally through the lateral forebrain bundle. These fibers are oriented primarily along the radii of ADVR and confined predominantly to zones B, C, and D. Lesions of the dorsal thalamus produce degeneration in a system of thin caliber axons which enters ADVR rostrally through the lateral forebrain bundle. These fibers course radially through zones C and D and then turn to run concentric with the ventricle in zone B. These observations suggest that snake ADVR consists of two fundamentally different parts. Neurons in zones A and B interact strongly with neighboring neurons through somatosomatic and axodendritic contacts and participate in connections which run concentric with the ventricle. Neurons in zones C and D participate in connections which run radially. Some of the neurons in zone D, and possibly some in zone C, project to the striatum. Neurons situated near the ventral border of ADVR are the only source of ADVR efferents. Neurons in each zone interact with those in neighboring zones.