Tacr1 Gene Variation and Neurokinin 1 Receptor Expression Is Associated with Antagonist Efficacy in Genetically Selected Alcohol-Preferring Rats

Abstract

Background Genetic deletion or antagonism of the neurokinin 1 receptor (NK1R) decreases alcohol intake, alcohol reward, and stress-induced alcohol relapse in rodents, while TACR1 variation is associated with alcoholism in humans. Methods We used L822429, a specific antagonist with high affinity for the rat NK1R, and examined whether sensitivity to NK1R blockade is altered in alcohol-preferring (P) rats. Operant alcohol self-administration and progressive ratio responding were analyzed in P-rats and their founder Wistar line. We also analyzed Tacr1 expression and binding and sequenced the Tacr1 promoter from both lines. Results Systemic L822429 decreased alcohol self-administration in P-rats but did not affect the lower rates of alcohol self-administration in Wistar rats. Tacr1 expression was elevated in the prefrontal cortex and the amygdala of P-rats. In central amygdala, elevated Tacr1 expression was accompanied by elevated NK1R binding. Central amygdala (but not prefrontal cortex) infusion of L822429 replicated the systemic antagonist effects on alcohol self-administration in P-rats. All P-rats, but only 18% of their founder Wistar population, were CC homozygous for a −1372G/C single nucleotide polymorphism. In silico analysis indicated that the Tacr1 −1372 genotype could modulate binding of the transcription factors GATA-2 and E2F-1. Electromobility shift and luciferase reporter assays suggested that the −1372C allele confers increased transcription factor binding and transcription. Conclusions Genetic variation at the Tacr1 locus may contribute to elevated rates of alcohol self-administration, while at the same time increasing sensitivity to NK1R antagonist treatment.

Wistar rats acquire and maintain self-administration of 20 % ethanol without water deprivation, saccharin/sucrose fading, or extended access training

“…In addition, BECs and rewards were positively correlated for a 30 minute SA session. Moreover, we verified the validity of our new SA paradigm by confirming the findings of Schank and colleagues (Schank et al, 2011, Schank et al, 2013), which used a classic WD and saccharin fading procedure to illustrate that 30 mg/kg of the NK1 antagonist L822429 blocks stress-induced reinstatement, but not baseline SA, of 10% EtOH. This distinction is important, as it demonstrates the ability of our model to specifically assess primary reinforcement for EtOH.…”

“…For example, Schank and colleagues have demonstrated that while alcohol SA in non-dependent Wistar rats is unaffected by L822429, escalated EtOH SA in alcohol preferring (P) rats is suppressed by even moderate doses of the compound (15 mg/kg, i.p. ; Schank et al, 2011, Schank et al, 2013). In contrast, stress-induced reinstatement of EtOH seeking is attenuated by L822429 pretreatment in non-dependent Wistars at a dose of 30 mg/kg (Schank et al, 2011).…”

Promising Pharmacogenetic Targets for Treating Alcohol Use Disorder: Evidence from Preclinical Models

“…Additionally, the NK 1 R seems to be particularly involved in the stressrelated aspects of alcohol consumption, as NK 1 R antagonism reduced stressinduced, but not cueinduced, reinstatement of alcohol seeking [143,144] and escalation of alcohol consumption [140]. Interestingly, it has recently been shown that the alcoholpreferring (P) rats, which are selectively bred for high alcohol preference, display increased sensi tivity to the effects of NK 1 R antagonism on alcohol selfadministration and motivation to work for alcohol compared with their Wistar parent strain [145]. What is more intriguing about the genetically selected P rats is that they show an upregulated NK 1 R system, that is, increased transcript levels of Tacr1 and Tac1 [145].…”

“…Interestingly, it has recently been shown that the alcoholpreferring (P) rats, which are selectively bred for high alcohol preference, display increased sensi tivity to the effects of NK 1 R antagonism on alcohol selfadministration and motivation to work for alcohol compared with their Wistar parent strain [145]. What is more intriguing about the genetically selected P rats is that they show an upregulated NK 1 R system, that is, increased transcript levels of Tacr1 and Tac1 [145]. Furthermore, Schank and colleagues also showed the presence of a G-C SNP in the transcriptional start sequence for Tacr1 and an increased transcription fac tor binding in the presence of the C allele, indicative of increased transcriptional activation of Tacr1.…”

The Neurokinin-1 Receptor in Addictive Processes

“…A hypothesis that remained to be addressed, therefore, was whether NK1R antagonists, while leaving basal alcohol intake unaffected, could suppress escalated alcohol consumption. In support of this idea, NK1R antagonists suppress alcohol consumption in a high alcohol preferring line of mice (C57/BL6J, see preceding) and attenuate escalated alcohol self-administration in alcohol-preferring (P) rats but do not affect alcohol self-administration in nondependent, nonpreferring rats (Thorsell et al, 2010;Schank et al, 2011Schank et al, , 2013. It was also demonstrated that P rats show an upregulated NK1R system, as evidenced by increased transcript levels of the Tacr1 gene, as well as increased receptor binding in specific brain regions.…”