Compulsive alcohol seeking, where intake persists despite serious adverse economic, social, and physical consequences, represents a major and pernicious clinical obstacle to successful treatment of alcoholism, but little is known about the molecular and circuit mechanisms that drive compulsive aspects of alcohol intake. Thus, we have pioneered the study of the circuitry of compulsive-like ethanol drinking in rodents, where intake persists despite pairing with the aversive, bitter-tasting quinine, since this aversion-resistant drinking is considered to model aspects of compulsive drinking in humans. Here, we study projections from corticotropin-releasing factor (CRF)-expressing cells of the central amygdala (CeA) that impact upon neurons within the locus coeruleus (LC) and adjacent parabrachial areas (PB), which we call the LCPB. CRF activation of the LCPB and increased NE release (through indirect action on PB cells or direct action on LC cells) is a critical mediato of many arousal- and stress-related behaviors. Also, there is considerable interest in whether the CeA is the source of CRF that activates the LCPB, since the CeA itself is a central regulator of emotional and cognitive responses to stressors. Importantly, CRF receptors (CRFRs) and norepinephrine receptors (NERs) are known to promote pathological ethanol drinking (drinking after dependence, binge intake) with little impact on more moderate consumption. Thus, our central hypothesis is that CRF+-CeA inputs activate LCPB neurons, leading to increased NE release which then promotes compulsion-like ethanol drinking.
Aim 1 will examine whether inhibiting CRF+-CeA inputs to the LCPB reduces aversion-resistant ethanol drinking. Our methods are pioneering, significant, and innovative, since we use state-of-the-art opto- and chemo- genetic techniques in a novel transgenic CRF-Cre rat, where CRF-expressing neurons can be specifically targeted. We will selectively inhibit CeA-LCPB inputs with halorhodopsin, a light-activated inhibitory protein, and the inhibitory DREADD hMd4i, an engineered receptor activated by intra-LCPB injection of the selective ligand CNO. The G-protein-linked DREADDs are pharmacologically activated, obviating the need for long laser stimulation during optogenetics which could damage tissue, but many critical technical questions remain, including possible off-target effects of CNO and very few studies addressing intra-cranial injection of CNO.
Aim 2 examines whether stimulating CRF+-CeA inputs to the LCPB with the excitatory hM3Dq enhances compulsive ethanol drinking, and whether enhanced intake is prevented by inhibiting CRFRs in the LCPB or NERs systemically. Our use of opto- and chemo-genetics with intracranial pharmacology in a novel transgenic CRF-Cre rat is likely to provide critical and therapeutically relevant information about the mechanisms underlying compulsive ethanol intake, and also will deliver important technical advances to study specific connections between CRF+ cells and target regions (the CeA and LCPB in the present study) which are likely relevant to many neuropsychiatric conditions including addiction, stress, depression, and anxiety.
The results of these experiments in animal models will provide critical new information about the brain regions and molecules that drive compulsive ethanol intake, where intake continues despite aversive consequences. Since compulsive intake is a major clinical hurdle in the treatment of alcoholism, our experiments investigating the molecular bases of aversion-resistant, compulsive ethanol intake will help identify novel therapeutic targets for the treatment of human alcoholism and other human diseases involving compulsion.
| Pomrenze, Matthew B; Millan, E Zayra; Hopf, F Woodward et al. (2015) A Transgenic Rat for Investigating the Anatomy and Function of Corticotrophin Releasing Factor Circuits. Front Neurosci 9:487 |
