Development and Validation of Operant Cocaine Self-Administration in Rodents

Drug addiction is a debilitating psychiatric disorder characterized by compulsive drug seeking despite negative consequences. Due to its prevalence in our society, the development of reliable models to investigate its epidemiology is critical to itsconditional prevention. Here, it is shown that the development and validation of a self-administration model in rodents is an accurate depiction of cocaine abuse in a conditioned environment. Using stable cocaine self-administration and dose-response behavior in un-tampered with animals, the contribution of widespread influences can be assessed and identified as associated risk-factors of drug-seeking behavior. The establishment of a reputable model serves as the foundation for all behavioral research, and proves to be a key determinant for the controlled investigations of drug addiction. The development and validation of the cocaine self-administration model in rodents is an invaluable tool for the field of addiction research

Genetic dissection of an amygdala CRF circuit for fear and anxiety

Fear and anxiety are ethological responses to threats and danger in the environment. The central amygdala (CeA) is a brain structure important for fear responses to discrete cues that predict threat. Recent findings indicate that the CeA also contributes to states of sustained apprehension in the absence of discrete cues that characterize anxiety, although less is known about the neural circuitry involved. The stress neuropeptide corticotropin releasing factor (CRF) is anxiogenic and produced by subpopulations of neurons in the CeA and the dorsolateral bed nucleus of the stria terminalis (dlBNST), a structure with strong connections to the CeA. Early models of the neurobiology of fear and anxiety proposed that the CeA promotes fear behaviors but not anxiety behaviors, and the BNST mediates anxiety but not fear. Furthermore, these models also hypothesized that a CRF pathway from the CeA to the dlBNST could be important for anxiety behavior, but this prediction remained untested. Here, the function of CeA CRF (CeA [superscript CRF]) neurons in fear and anxiety was investigated using Cre-dependent viral-genetic tools and male rats that express Cre recombinase from a Crh promoter. CeA [superscript CRF] neurons mediated both stress-induced anxiety and fear behaviors, both of which were dependent on CRF signaling. Additionally, the neuropeptide dynorphin, but not neurotensin, produced by CeA [superscript CRF] neurons was critical for fear and anxiety behaviors. Neurotensin release had no effect on anxiety but dampened fear learning. GABA release from these neurons played a major role in setting the level of anxiety in the basal state. Finally, the CeA [superscript CRF] pathway to the dlBNST was tested for its role in anxiety and was found to be critical for these behaviors. This pathway also recruited CRF signaling and local CRF neurons in the dlBNST to engage anxiety-like behaviors. Collectively, these findings suggest that CeA [superscript CRF] neurons promote both fear and anxiety via the release of GABA and different neuropeptides and a projection to the dlBNST. The data presented here refine early neuroanatomical models of fear and anxiety and provide mechanistic support for recent human primate data suggesting that the CeA and BNST act together to generate negative emotional states.Neuroscienc

Cocaine self-administration in the mouse: A low-cost, chronic catheter preparation

Intravenous drug self-administration is the most valid animal model of human addiction because it allows volitional titration of the drug in the blood based on an individual’s motivational state together with the pharmacokinetic properties of the drug. Here we describe a reliable low-cost mouse self-administration catheter assembly and protocol that that can be used to assess a variety of drugs of abuse with a variety of protocols. We describe a method for intravenous catheter fabrication that allows for efficient and long-lasting intravenous drug delivery. The intravenous catheters remained intact and patent for several weeks allowing us to establish stable maintenance of cocaine acquisition. This was followed by a dose response study in the same mice. For collaborators interested in premade catheters for research please make a request at www.neuro-cloud.net/nature-precedings/pomerenze

Optogenetic control of genetically-targeted pyramidal neuron activity in prefrontal cortex

A salient feature of prefrontal cortex organization is the vast diversity of cell types that support the temporal integration of events required for sculpting future responses. A major obstacle in understanding the routing of information among prefrontal neuronal subtypes is the inability to manipulate the electrical activity of genetically defined cell types over behaviorally relevant timescales and activity patterns. To address these constraints, we present here a simple approach for selective activation of prefrontal excitatory neurons in both in vitro and in vivo preparations. Rat prelimbic pyramidal neurons were genetically targeted to express a light-­activated nonselective cation channel, channelrhodopsin-­2, or a light-­driven inward chloride pump, halorhodopsin, which enabled them to be rapidly and reversibly activated or inhibited by pulses of light. These light responsive tools provide a spatially and temporally precise means of studying how different cell types contribute to information processing in cortical circuits. Our customized optrodes and optical commutators for in vivo recording allow for efficient light delivery and recording and can be requested at www.neuro-­cloud.net/nature-precedings/baratta

High fidelity optogenetic control of individual prefrontal cortical pyramidal neurons in vivo

Precise spatial and temporal manipulation of neural activity in specific genetically defined cell populations is now possible with the advent of optogenetics. The emerging field of optogenetics consists of a set of naturally-occurring and engineered light-sensitive membrane proteins that are able to activate (e.g., channelrhodopsin-2, ChR2) or silence (e.g., halorhodopsin, NpHR) neural activity. Here we demonstrate the technique and the feasibility of using novel adeno-associated viral (AAV) tools to activate (AAV-CaMKll{\alpha}-ChR2-eYFP) or silence (AAV-CaMKll{\alpha}-eNpHR3.0-eYFP) neural activity of rat prefrontal cortical prelimbic (PL) pyramidal neurons in vivo. In vivo single unit extracellular recording of ChR2-transduced pyramidal neurons showed that delivery of brief (10 ms) blue (473 nm) light-pulse trains up to 20 Hz via a custom fiber optic-coupled recording electrode (optrode) induced spiking with high fidelity at 20 Hz for the duration of recording (up to two hours in some cases). To silence spontaneously active neurons we transduced them with the NpHR construct and administered continuous green (532 nm) light to completely inhibit action potential activity for up to 10 seconds with 100% fidelity in most cases. These versatile photosensitive tools combined with optrode recording methods provide experimental control over activity of genetically defined neurons and can be used to investigate the functional relationship between neural activity and complex cognitive behavior.Comment: 4 pages, 4 figures F1000Research articl

Cocaine self-administration in the mouse: A low- cost, chronic catheter preparation

Intravenous drug self-administration is the most valid animal model of human addiction because it allows volitional titration of the drug in the blood based on an individual’s motivational state together with the pharmacokinetic properties of the drug. Here we describe a reliable low-cost mouse self-administration catheter assembly and protocol that that can be used to assess a variety of drugs of abuse with a variety of protocols. We describe a method for intravenous catheter fabrication that allows for efficient and long-lasting intravenous drug delivery. The intravenous catheters remained intact and patent for several weeks allowing us to establish stable maintenance of cocaine acquisition. This was followed by a dose response study in the same mice. For collaborators interested in premade catheters for research please make a request at www.neuro-cloud.net/nature-precedings/pomerenze

Inactivation of a CRF-dependent amygdalofugal pathway reverses addiction-like behaviors in alcohol-dependent rats.

The activation of a neuronal ensemble in the central nucleus of the amygdala (CeA) during alcohol withdrawal has been hypothesized to induce high levels of alcohol drinking in dependent rats. In the present study we describe that the CeA neuronal ensemble that is activated by withdrawal from chronic alcohol exposure contains ~80% corticotropin-releasing factor (CRF) neurons and that the optogenetic inactivation of these CeA CRF+ neurons prevents recruitment of the neuronal ensemble, decreases the escalation of alcohol drinking, and decreases the intensity of somatic signs of withdrawal. Optogenetic dissection of the downstream neuronal pathways demonstrates that the reversal of addiction-like behaviors is observed after the inhibition of CeA CRF projections to the bed nucleus of the stria terminalis (BNST) and that inhibition of the CRFCeA-BNST pathway is mediated by inhibition of the CRF-CRF1 system and inhibition of BNST cell firing. These results suggest that the CRFCeA-BNST pathway could be targeted for the treatment of excessive drinking in alcohol use disorder

A Transgenic Rat for Investigating the Anatomy and Function of Corticotrophin Releasing Factor Circuits.

Corticotrophin-releasing factor (CRF) is a 41 amino acid neuropeptide that coordinates adaptive responses to stress. CRF projections from neurons in the central nucleus of the amygdala (CeA) to the brainstem are of particular interest for their role in motivated behavior. To directly examine the anatomy and function of CRF neurons, we generated a BAC transgenic Crh-Cre rat in which bacterial Cre recombinase is expressed from the Crh promoter. Using Cre-dependent reporters, we found that Cre expressing neurons in these rats are immunoreactive for CRF and are clustered in the lateral CeA (CeL) and the oval nucleus of the BNST. We detected major projections from CeA CRF neurons to parabrachial nuclei and the locus coeruleus, dorsal and ventral BNST, and more minor projections to lateral portions of the substantia nigra, ventral tegmental area, and lateral hypothalamus. Optogenetic stimulation of CeA CRF neurons evoked GABA-ergic responses in 11% of non-CRF neurons in the medial CeA (CeM) and 44% of non-CRF neurons in the CeL. Chemogenetic stimulation of CeA CRF neurons induced Fos in a similar proportion of non-CRF CeM neurons but a smaller proportion of non-CRF CeL neurons. The CRF1 receptor antagonist R121919 reduced this Fos induction by two-thirds in these regions. These results indicate that CeL CRF neurons provide both local inhibitory GABA and excitatory CRF signals to other CeA neurons, and demonstrate the value of the Crh-Cre rat as a tool for studying circuit function and physiology of CRF neurons