Research Report Strain differences in myenteric neuron number and CCK 1 receptor mRNA expression may account for differences in CCK induced c-Fos activation Stephen Gulley a , Sanjay K. Sharma a , Mahmoud Mansour a , Cherese N. Sullivan a , Timothy H. Moran b , Ayman I. Sayegh a, * a Gastroenterology Laboratory, Department of Biomedical Sciences, College of Veterinary Medicine, Tuskegee University, Tuskegee, AL 36088, USA b Department of Psychiatry and Behavioral Sciences, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA Accepted 28 July 2005 Available online 19 September 2005 Abstract We utilized a diaminobenzidine reaction enhanced with nickel to compare dorsal vagal complex (DVC) and myenteric neuronal Fos-Like immunoreactivity (Fos-LI), in response to sulfated cholecystokinin-8 (CCK-8) (5, 10, 20, 40 Ag/kg), among Sprague–Dawley (SD), Standard Long–Evans (SLE), Otsuka Long-Evans Tokushima Fatty (OLETF), and Long–Evans Tokushima Otsuka (LETO) rats. All rat strains but OLETF expressed Fos-LI in response to CCK-8. In addition, SD rats expressed more Fos-LI in the area postrema and myenteric neurons than SLE and LETO rats. To investigate the basis for these differences, we utilized cuprolinic blue staining, which stains neuronal cell bodies, to quantify the number of myenteric neurons, and a reverse transcriptase chain polymerase reaction to measure the gene expression of CCK 1 receptor in the gut. We found that SD rats have significantly more duodenal myenteric neurons than the other strains. In addition, this strain expressed significantly higher levels of the CCK 1 gene in both the duodenum and jejunum than the other strains. In conclusion, SD rats may express more myenteric Fos- LI in response to CCK due to increased numbers of myenteric neurons or more intestinal CCK 1 receptors than the other strains of rats. D 2005 Elsevier B.V. All rights reserved. Theme: Endocrine and autonomic regulation Topic: Neuroendocrine regulation Keywords: Sprague – Dawley; Long – Evans; LETO; OLETF; Fos; Myenteric plexus; Dorsal vagal complex; Cholecystokinin; CCK 1 receptor; NTS; Area postrema; Immunohistochemistry 1. Introduction Cholecystokinin (CCK) (reviewed recently in [14]) is a hormone secreted by the I cells of the gastrointestinal (GI) tract, and neurons in the central and enteric nervous systems (CNS and ENS, respectively). CCK plays a major role in the digestive process, evoking functions such as gallbladder contraction, the inhibition of gastric emptying, the stimulation of pancreatic secretion, and satiety. The actions of CCK are mediated through its interactions with two G-protein coupled receptors, CCK 1 and CCK 2 . These receptors are widely distributed throughout the GI tract and central and peripheral neurons. Recently, a line of rats lacking the CCK 1 receptor has been identified. From a spontaneous occurrence of diabetes and obesity in an outbred colony of Long–Evans rats, a line of rats that is characterized by diabetes, polyuria, polydipsia, and obesity was produced by selective mating. These rats are known as Otsuka Long–Evans Tokushima Fatty (OLETF) rats. These rats show increased rates of weight gain, hyperglycemia, and non-insulin dependent diabetes mellitus [5]. A control strain of rats, known as Long–Evans Tokushima Otsuka (LETO) does not show any of the clinical signs discussed above and these have been considered normal Long–Evans rats. In characterizing the pancreatic function of OLETF rats, it was noted that they did not respond to exogenous CCK [1]. This led to the demonstration that these rats lack CCK 1 receptors because of a 6.8 kb deletion in their CCK 1 receptor 0006-8993/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.brainres.2005.07.074 * Corresponding author. Fax: +1 334 727 8177. E-mail address: sayeghai@tuskegee.edu (A.I. Sayegh). Brain Research 1058 (2005) 109 – 119 www.elsevier.com/locate/brainres