Colchicine Differentially Induces the Expressions of Nitric Oxide Synthases in Central and Peripheral Catecholaminergic Neurons Sampsa Vanhatalo,* , † Aki Lumme,* , ‡ and Seppo Soinila* , ‡ *Department of Anatomy, Institute of Biomedicine, †Unit of Child Neurology, Hospital for the Children and Adolescent, and ‡Department of Neurology, University of Helsinki, P.O. Box 9, 00014 University of Helsinki, Finland Received July 1, 1997; accepted October 24, 1997 This study was aimed at elucidating differences in nerve injury induced expression of nitric oxide syn- thases (NOS) between the peripheral and central cate- cholaminergic neurons. Colchicine was used to dis- rupt chemically the neuronal cytoskeletal integrity. A marked increase in the expression of neuronal NOS-IR and NADPH-diaphorase activity, a marker of neuronal NOS (nNOS), was seen in distinct populations of post- ganglionic sympathetic neurons of the superior cervi- cal ganglion after intraganglionic colchicine injection. Similarly, immunoreactivity for the inducible form of NOS (iNOS) was induced in some sympathetic neuron somata. However, this immunoreactivity did not coin- cide with nNOS-IR. In contrast to the sympathetic neurons, hypothalamic arcuate and periventricular dopaminergic neurons did not show NOS-IR or NADPH-DA either in intact animals or in animals treated with an intracerebroventricular injection of colchicine. Immunoreactivity for the inducible form of NOS revealed no neuronal staining in the hypotha- lamic neurons in either group, while a large number of glia-resembling cells around the third ventricle showed slight expression of iNOS-IR. The present results show that expression of both neuronal and inducible forms of NOS may be induced by colchicine in some catechol- aminergic neurons. It is suggested that these in- ductions are specific to certain catecholaminergic neuronal systems, like the sympathetic neurons, rather than a general property of catecholaminergic neurons.  1998 Academic Press INTRODUCTION Since its discovery as a cellular transmitter, nitric oxide (NO) has been implicated in a vast array of different physiological as well as pathophysiological functions in the nervous system (17). Recently, an interest has arised in the obvious role of nitric oxide as an important mediator of neurotoxic mechanisms (19, 25), as well as in the neuronal response to injury (24, 35, 55). We have previously shown that the postgangli- onic sympathetic neurons, which do not naturally express nitric oxide synthase (NOS), begin to express it after various challenges, e.g., colchicine treatment (48). A number of investigators have increasingly reported induction of or increase in expression of NOS or NADPH-diaphorase activity (NADPH-DA), a marker of neural form of NOS (27), by colchicine, many other toxins, or neuronal injury in both central and periph- eral neurons (10, 24, 40, 47, 52, 55). Up till now it is known that the type of injury, e.g., peripheral nerve root avulsion vs distal axonal transsection, somehow dictates the NOS-related responses (55). Thus, as NO inevidently appears to play a role in neuronal injury mechanisms, the question arises whether NO is a ubiqui- tos mediator of neuronal response to these challenges or whether there are differences between neuronal popula- tions in terms of these NO-related mechanisms. A recent study on axotomy-induced NOS expression in the motor neurons suggested that even within function- ally similar (motor) neurons fundamental differences in their NOS expression may exist (57). There are, however, no studies on whether neurons sharing other features, e.g., transmitter phenotype, do differ in their NO- related responses to cellular injury. To address this question we set out to study induction of NOS expres- sion by colchicine in two well known catecholaminergic neuronal populations: one peripheral, superior cervical ganglion (SCG) sympathetic noradrenergic postgangli- onic neurons, the other central, hypothalamic arcuate, and periventricular dopaminergic neurons (9). We also investigated separately the expressions of neuronal (nNOS) and inducible (iNOS) forms of NOS, since both of these have recently been implicated in various types of neuronal injury mechanisms (25, 38, 52). As common features, (i) both of these catecholaminergic systems studied express tyrosine hydroxylase (TH), (ii) neither of them expresses NOS in intact situation (5, 45), and (iii) they both partly project to the pituitary gland (21, 23, 49), having thus one common target organ. MATERIAL AND METHODS Adult male Wistar rats (n = 15, weighing 200–300 g) were anesthesized with a combination of Hypnorm (0.8 ml/kg, Janssen Pharmaceutica) and Dormicum (0.8 EXPERIMENTAL NEUROLOGY 150, 107–114 (1998) ARTICLE NO. EN976733 107 0014-4886/98 $25.00 Copyright  1998 by Academic Press All rights of reproduction in any form reserved.