Brain Research, 624 (1993) 19-28 19 © 1993 Elsevier Science Publishers B.V. All rights reserved 0006-8993/93/$06.00 BRES 19249 Autonomic areas of rat brain exhibit increased Fos-like immunoreactivity during opiate withdrawal in rats Ruth L. Stornetta, Frederick E. Norton and Patrice G. Guyenet Department of Pharmacology, Universityof Virginia Health Sciences Center, Charlottesville, VA 22908 (USA) (Accepted 5 May 1993) Key words: c-los; Fos; Opiate withdrawal; Dependence and withdrawal; Rostral ventrolaterai medulla; Autonomic nervous system; Nucleus tractus solitarius; Locus coeruleus; Amygdala; Paraventricular nucleus; A5; Catecholamine We sought to identify the brain areas that might contribute to the increased autonomic activity seen during morphine withdrawal by mapping neuronal expression of c-los protein (Fos) and Fos-related antigens. Rats were implanted with morphine pellets or placebo pellets over a 5 day regimen and injected on day 6 with either saline or naltrexone (100 mg/kg). After a standard PAP immunocytochemical protocol, Fos-like immunoreactivity (Fos-LIR) was observed in medullary nuclei including the NTS (nucleus of the solitary tract), caudal (CVL) and rostral ventrolateral medulla (RVL). Although some Fos-LIR was seen in these areas in control rats (either morphine-implanted, saline injected, or placebo-implanted, saline or naltrexone injected), a significantly higher number of Fos-LIR-positive cells in NTS, CVL and RVL were seen after morphine withdrawal. Large numbers of Fos-like immunoreactive cells were also seen in the A5 area, the parabrachial nuclei of the pons and the locus coeruleus. Increased Fos-LIR was also detected in the paraventricular nucleus of the hypothalamus and the amygdala of morphine withdrawn rats. The Fos-LIR was co-localized with tyrosine hydroxylase immunoreactivity in many of the cells in caudal and rostral ventrolateral medulla, A5 and locus coeruleus. These data support the conclusion that autonomic areas in brain and noradrenergic/adrenergic cells in these areas are activated during morphine withdrawal and may contribute to the autonomic symptoms of opiate withdrawal. INTRODUCTION Opiate withdrawal is a multi-faceted phenomenon characterized by behavioral and physiological symp- toms involving many different areas of the b r a i n 2'46'47'52'62. Most studies examining the brain re- gions involved in morphine withdrawal have concen- trated on behavioral symptoms of withdrawal rather than autonomic s y m p t o m s 9'47'52'81. The autonomic symptoms of withdrawal include an increase in arterial pressure. This must, at least in part, be neurogenic and of central origin since it is accompanied by an increase in adrenal and lumbar sympathetic nerve activity as well as increases in plasma catecholamines and argi- nine vasopressin 21. Buccafusco n notes that the in- crease in arterial pressure is a reliable, objective and quantitative measure of withdrawal in morphine-de- pendent rats. The existing studies on medullary cir- cuitry involved in the autonomic effects of acutely administered opiates point to the involvement of NTS (nucleus of the solitary t r a c t ) 13'36'37'40'53'76, caudal ven- trolateral medulla 58'59, and rostral ventrolateral medulla58'59'64'84. These findings suggest that these and possibly other autonomic areas of brain involved in sympathetic nervous system control are particularly activated during morphine withdrawal. The presence of c-los protein (Fos) and Fos-related antigens or c-fos precursor mRNA have been used repeatedly as a measure of cell activation in the central n e r v o u s s y s t e m 1,8,12,42,43,68,74,77,79. In the present study we sought to determine whether autonomic areas of brain and particularly catecholaminergic autonomic ar- eas are activated during naltrexone-precipitated mor- phine withdrawal in conscious animals. The presence of Fos and Fos-related antigens detected by an anti- body to Fos was used as a measure of cell activation. A preliminary report of this work has been published in abstract form 82. Correspondence: R.L. Stornetta, Department of Pharmacology, University of Virginia Health Sciences Center, Jordan Hall, 1300 Jefferson Park Ave., Charlottesville, VA 22908, USA. Fax: (1) (804) 982-3878.