Ž . Developmental Brain Research 109 1998 51–58 Research report Striatal cholinergic interneurons: birthdates predict compartmental localization Eileen H.S. van Vulpen, Derek van der Kooy ) Neurobiology Research Group, Department of Anatomy and Cell Biology, UniÕersity of Toronto, Toronto, Ontario, Canada M5S 1A8 Accepted 6 January 1998 Abstract The striatal patch and matrix compartment neurons are born at different times during rat development. The majority of the early born neurons preferentially end up in the patch compartment, while the majority of the later born neurons end up in the matrix compartment. Ž . Although the cholinergic interneurons are all born early in neurogenesis between embryonic day E12 and E17 , and we would therefore expect them to be located mainly in the patches, they are relatively homogeneously distributed in the adult, with a preference for the Ž . matrix area just outside the patches the intermediate zone . To ask if birthdate can predict the compartmental localization of cholinergic Ž . neurons in the striatum, we marked new postmitotic neurons in the embryo with a maternal injection of bromodeoxyuridine BrdU on E13, E15 or E17 and labeled the patch compartment with an injection of the retrograde tracer True Blue into the substantia nigra on Ž. postnatal day P 1. The pups were sacrificed at P40 and the tissue was processed for BrdU, choline acetyltransferase, and True Blue triple labeling. Cholinergic neurons that became postmitotic at E13, had a higher chance of ending up in the patch compartment compared to either the intermediate zone or the rest of the matrix compartment. On the other hand cholinergic neurons that became postmitotic at Ž . E17 had a higher chance of ending up in the matrix compartment including the intermediate zone . We conclude that birthdate can predict compartmental localization, with the cholinergic neurons in the intermediate zone following the same pattern as the cholinergic neurons in the rest of the matrix compartment. Cholinergic neurons show the same relative birthdatercompartment relationship as do other striatal neurons, although the absolute birthdates of cholinergic neurons are shifted earlier in neurogenesis. q 1998 Elsevier Science B.V. All rights reserved. Keywords: Cholineacetyltransferase; Bromodeoxyuridine; Patch; Matrix 1. Introduction The mammalian striatum is a heterogeneous structure that can be divided into two complementary and function- ally distinct compartments, the patches and the matrix w x 8,9,11 . Communication between the two compartments is thought to be mediated mainly by the striatal interneurons, which can extend their dendrites across compartmental w x boundaries 20,25 . One electrophysiologically identifiable Ž class of neurons in the striatum the tonically active neu- . rons, or TANs is thought to be involved directly in collecting reinforcement related information from the patches and influencing the activity of the projection neu- w x rons in the matrix 12 . These TANs show learning-depen- dent plasticity, are distributed over broad regions in the ) Corresponding author. Fax: q1-416-978-3488; E-mail: derek.van.der.kooy@utoronto.ca striatum and respond in a temporally coordinated way after behavioral conditioning. Based on their electrophysiologi- w x cal properties 14,33 and their tendency to reside on patchrmatrix borders, these cells are thought to be the wx cholinergic interneurons of the striatum 1 . The cholinergic neurons in the rat striatum are born Ž Ž. early during neurogenesis between embryonic E days . w x 12–17 26,28 , and are distributed homogeneously among the patch and matrix compartments in the adult rat, but with a preference for the matrix area just outside the w x patches, termed the intermediate zone 31 . Striatal neurons as a whole show compartmental preferences, depending on w x the time that they leave the mitotic cycle 2,7,10,21,29 . The earliest striatal neurons to become postmitotic in the Ž . rat embryo between E12–E16 become restricted mainly to the patch compartment, while neurons that are born later Ž Ž. . E18-postnatal P day 2 end up primarily in the matrix w x compartment 7,21,29 . The cholinergic neurons in the striatum appear not to follow this general rule, as they are 0165-3806r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved.