Fos immunoreactivity in the rat forebrain induced by electrical stimulation of the dorsolateral periaqueductal gray matter Lee Wei Lim a,b,d,e, *, Yasin Temel a,b,d,e , Veerle Visser-Vandewalle b,d , Arjan Blokland c,e , Harry Steinbusch a,e a Department of Neuroscience, Maastricht University, Maastricht, The Netherlands b Department of Neurosurgery, Maastricht University Medical Center, Maastricht, The Netherlands c Department of Neurocognition, Faculty of Psychology, Maastricht University, Maastricht, The Netherlands d Maastricht Institute of Neuromodulative Development (MIND), The Netherlands e European Graduate School of Neuroscience (EURON), The Netherlands 1. Introduction Electrical stimulation of the dorsolateral periaqueductal gray (dlPAG) evokes a typical reaction which is generally described as escape or defensive behaviour (Bandler and Shipley, 1994; De Oca et al., 1998). This behaviour consists of a spontaneous flight reaction characterized by wild running, galloping, and jumping accompanied by hypertension, tachycardia, tachypnoea, freezing, and fear (Bittencourt et al., 2005; Hogg et al., 2006; Lim et al., 2008a). It is now widely accepted that this escape behaviour has similarities with a panic attack in humans (Deakin and Graeff, 1991; Nashold et al., 1969; Schenberg et al., 1998). In clinical practice, panic attack occurs spontaneously and produces intense emotional distress with significant changes in autonomic and neurological functions including palpitation, chest strains, sweat- ing, dyspnoe, feeling of choking, trembling, nausea, dizziness, paresthesia, chills or hot flushes, depersonalization or derealiza- tion, and fear of dying or losing control (American-Psychiatric- Association, 1994; Cassano and Savino, 1993). Importantly, panic attack can be induced both in humans and rodents by electrical stimulation of the dorsal parts of the PAG (Hogg et al., 2006; Hunsperger, 1956; Nashold et al., 1969). Despite several studies, the pathophysiology of fear and panic related to the PAG is relatively unknown probably due to a complex interplay between anatomical circuits, neurotransmitters, and neuropeptides (Borelli et al., 2005; de Bortoli et al., 2006; Lim et al., 2008a,b). This type of fear-like behaviour is complex and requires higher cortical connections to process the acquired defensive information of external threats. The PAG, however, is involved in the coordination of defensive behaviour (Maren and Quirk, 2004; Mobbs et al., 2007). Recent preclinical studies have demonstrated that electrical stimulation of the dlPAG with stimulation parameters which causes an escape reaction, led to a significant increase in the number of c-Fos immunoreactive (c-Fos- ir) cells in specific brain regions (Borelli et al., 2005; Lim et al., 2008a). This neural activation highlights the existence of a brain network controlling defensive behaviour (Coimbra et al., 2006; McNaughton and Corr, 2004; Vianna and Branda ˜o, 2003). More specifically, electrical or chemical stimulation of the dlPAG induced significant c- Fos expression in the ventromedial hypothalamus, dorsal premam- Journal of Chemical Neuroanatomy 38 (2009) 83–96 ARTICLE INFO Article history: Received 17 July 2008 Received in revised form 29 June 2009 Accepted 29 June 2009 Available online 7 July 2009 Keywords: Periaqueductal gray Escape behaviour Panic-like behaviour Fear-like behaviour c-Fos immunoreactivity Neuroanatomy Forebrain ABSTRACT Electrical stimulation of the dorsolateral periaqueductal gray (dlPAG) matter induces panic- or fear-like responses with intense emotional distress and severe anxiety. In this study, we evoked panic-like behaviour by dlPAG stimulation and evaluated the effect on neuronal activation in different brain regions. The number of c-Fos immunoreactive (c-Fos-ir) cells was measured semi-quantitatively through series of stained rat brain sections. Our results demonstrate strong neural activation in the medial prefrontal cortex, orbital cortex, anterior olfactory nuclei, secondary motor cortex, and the somatosensory cortex. Moderate increases in the number of c-Fos-ir cells were detected in various regions, including the hypothalamus, amygdala, and striatum. Additionally, there was mild expression of c-Fos-ir cells in the hippocampus, thalamus, and habenula regions. In conclusion, we have shown that deep brain stimulation of the dlPAG produced a distinctive pattern of neuronal activation across forebrain regions as compared to the sham and control animals. ß 2009 Elsevier B.V. All rights reserved. * Corresponding author at: Department of Neuroscience and Neurosurgery, Maastricht University, Universiteitssingel 50 (Box 38), 6229 ER, Maastricht, The Netherlands. E-mail address: lw.lim@maastrichtuniversity.nl (L.W. Lim). Contents lists available at ScienceDirect Journal of Chemical Neuroanatomy journal homepage: www.elsevier.com/locate/jchemneu 0891-0618/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jchemneu.2009.06.011