Electrophysiologic effects of systemic and locally infused epibatidine on locus coeruleus neurons

Novel agonist of α4β2* neuronal nicotinic receptor with antinociceptive efficacy in rodent models of acute and chronic pain

Objective

To demonstrate the antinociceptive and antihypersensitivity mechanisms of Cris-104 (1-{2-[5-(4-fluorophenyl)-1H-pyrazol-4-yl]ethyl}piperidine), a novel selective α₄β₂* nicotinic acetylcholine receptor (nAChR) agonist, in rodent acute/inflammatory and chronic pain models.

Materials and methods

Hot-plate and formalin tests in mice were used to examine Cris-104-induced antinociceptive effects on thermal/inflammatory pain. Cris-104 effects on hypersensitivity, norepinephrine (NE) release in the spinal dorsal horn, and neuronal activity in the locus coeruleus (LC) were examined in rats with lumbar spinal nerve ligation using behavioral, microdialysis, and extracellular recording methods. Cris-104 effects on spontaneous locomotion were examined in an open-field test.

Results

Cris-104 induced dose-dependent antinociception effects in hot-plate and formalin tests, and these effects were blocked by the general nAChR antagonist mecamylamine, the selective α₄β₂* nAChR antagonist dihydro-beta-erythroidine, and the α₂-adrenoceptor antagonist yohimbine, but not by the α₁-adrenoceptor antagonist prazosin. Systemic and spinally perfused Cris-104 increased NE concentrations in microdialysates from the spinal cord in both normal and SNL rats. Systemic Cris-104 increased neuronal activity in the LC of normal rats. Mecamylamine blocked the effects of Cris-104 on spinal NE release and LC neuronal activity. Systemic Cris-104 did not affect locomotor activity significantly.

Conclusion

The α₄β₂ neuronal nAChR agonist, Cris-104, was effective for treatment of pain via descending noradrenergic inhibition of pain signaling.

Antinociceptive effect of tebanicline for various noxious stimuli-induced behaviours in mice

Tebanicline (ABT-594), an analogue of epibatidine, exhibits potent antinociceptive effects and high affinity for the nicotinic acetylcholine receptor in the central nervous system. We assessed whether tebanicline exerts an effect on various noxious stimuli and mediates the nicotine receptor or opioid receptor through stimulation. The antinociceptive effects of tebanicline were determined by noxious chemical, thermal and mechanical stimuli-induced behaviours in mice. Tebanicline had dose-dependent analgesic effects in formalin, hot-plate and tail-pressure tests. By contrast, the antinociceptive effect of tebanicline was not demonstrated in the tail-flick assay. Pre-treatment with mecamylamine, a nicotinic acetylcholine receptor antagonist, blocked the effects of tebanicline in formalin, tail-pressure and hot-plate tests. Moreover, pre-treatment with naloxone, an opioid receptor antagonist, only partially inhibited the effects of tebanicline in formalin and tail-pressure tests. Tebanicline produced antinociception in persistent chemical (formalin), acute thermal (hot-plate, but not tail-flick) and mechanical (tail-pressure) pain states. Moreover, tebanicline stimulated the nicotinic acetylcholine receptor and opioid receptor.

Regulation of neurological and neuropsychiatric phenotypes by locus coeruleus-derived galanin

Decades of research confirm that noradrenergic locus coeruleus (LC) neurons are essential for arousal, attention, motivation, and stress responses. While most studies on LC transmission focused unsurprisingly on norepinephrine (NE), adrenergic signaling cannot account for all the consequences of LC activation. Galanin coexists with NE in the vast majority of LC neurons, yet the precise function of this neuropeptide has proved to be surprisingly elusive given our solid understanding of the LC system. To elucidate the contribution of galanin to LC physiology, here we briefly summarize the nature of stimuli that drive LC activity from a neuroanatomical perspective. We go on to describe the LC pathways in which galanin most likely exerts its effects on behavior, with a focus on addiction, depression, epilepsy, stress, and Alzheimer׳s disease. We propose a model in which LC-derived galanin has two distinct functions: as a neuromodulator, primarily acting via the galanin 1 receptor (GAL1), and as a trophic factor, primarily acting via galanin receptor 2 (GAL2). Finally, we discuss how the recent advances in neuropeptide detection, optogenetics and chemical genetics, and galanin receptor pharmacology can be harnessed to identify the roles of LC-derived galanin definitively. This article is part of a Special Issue entitled SI: Noradrenergic System.

The neural and genetic basis of executive function: attention, cognitive flexibility, and response inhibition

Executive function is a collection of cognitive processes essential for higher order mental function. Processes involved in executive function include, but are not limited to, working memory, attention, cognitive flexibility, and impulse control. These complex behaviors are largely mediated by prefrontal cortical function but are modulated by dopaminergic, noradrenergic, serotonergic, and cholinergic input. The ability of these neurotransmitter systems to modulate executive function allows for adaptation in cognitive behavior in response to changes in the environment. Because of the important role these neurotransmitter systems play in regulating executive function, changes in these systems can also have a grave impact on executive function. In addition, polymorphisms in genes associated with these neurotransmitters are associated with phenotypic differences in executive function. Understanding how these naturally occurring polymorphisms contribute to different executive function phenotypes will advance basic knowledge of cognition and potentially further understanding and treatment of mental illness that involve changes in executive function. In this review, we will examine the influence of dopamine, norepinephrine, serotonin, and acetylcholine on the following measures of executive function: attention, cognitive flexibility, and impulse control. We will also review the effects of polymorphisms in genes associated with these neurotransmitter systems on these measures of executive function.