Nicotine disrupts safety learning by enhancing fear associated with a safety cue via the dorsal hippocampus

Abstract

Learned safety, a learning process in which a cue becomes associated with the absence of threat, is disrupted in individuals with post-traumatic stress disorder (PTSD). A bi-directional relationship exists between smoking and PTSD and one potential explanation is that nicotine-associated changes in cognition facilitate PTSD emotional dysregulation by disrupting safety associations. Therefore, we investigated whether nicotine would disrupt learned safety by enhancing fear associated with a safety cue. In the present study, C57BL/6 mice were administered acute or chronic nicotine and trained over three days in a differential backward trace conditioning paradigm consisting of five trials of a forward conditioned stimulus (CS)+ (Light) coterminating with a footshock unconditioned stimulus followed by a backward CS− (Tone) presented 20 s after cessation of the unconditioned stimulus. Summation testing found that acute nicotine disrupted learned safety, but chronic nicotine had no effect. Another group of animals administered acute nicotine showed fear when presented with the backward CS (Light) alone, indicating the formation of a maladaptive fear association with the backward CS. Finally, we investigated the brain regions involved by administering nicotine directly into the dorsal hippocampus, ventral hippocampus, and prelimbic cortex. Infusion of nicotine into the dorsal hippocampus disrupted safety learning.

Nicotine modulates contextual fear extinction through changes in ventral hippocampal GABAergic function

“…Our results have several implications for anxiety and stress disorders in humans. In conjunction with the results of our previous studies (e.g., (Connor et al , 2017; Kutlu et al , 2014, 2016a, 2016b; Kutlu and Gould, 2014), the results of the present study strongly suggest that nicotine exposure might be a contributing factor to fundamental maladaptive behaviors such as inability to inhibit and extinguish fear observed in these psychopathologies. In line with this hypothesis, we recently showed that chronic nicotine exposure both in mice and humans is associated with a decreased ability to learn cues signaling safety (Kutlu et al , 2018a).…”

“…However, the effects of nicotine are not limited to enhancing fear memories. Previous studies from our laboratory have demonstrated that nicotine administration impaired fear extinction and safety learning in mice (Connor et al , 2017; Kutlu et al , 2014, 2016a, 2017a, 2017b, 2018a; Kutlu and Gould, 2014). Specifically, acute nicotine administration was shown to cause deficits in encoding, consolidation, and retrieval of contextual fear extinction memories (Kutlu et al , 2016a, 2016b; Kutlu and Gould, 2014; Oliver et al , 2018), as well as deficits in contextual safety discrimination (Kutlu and Gould, 2014).…”

Bed nucleus of the stria terminalis regulates fear to unpredictable threat signals

“…Specifically, we arranged a brief (10 s) auditory CS to either precede (forward conditioning, FW) or follow (backward conditioning, BW) a footshock US in rats. Although extensively-trained BW CSs become conditioned inhibitors that dampen responding to other first-order excitatory cues (Andreatta et al, 2012; Ayres et al, 1976; Christianson et al, 2011; Gerber et al, 2014; Moscovitch and LoLordo, 1968; Siegel and Domjan, 1971), minimally-trained BW CSs elicit excitatory conditioned responses that transfer across contexts (Ayres et al, 1987; Barnet and Miller, 1996; Bevins and Ayres, 1992; Chang et al, 2003; Connor et al, 2017; Heth, 1976; Mahoney and Ayres, 1976; Prével et al, 2018; Prével et al, 2016; Rescorla, 1968). After conditioning, we examined the effect of pharmacological inactivation of the BNST on freezing to FW or BW CSs.…”

Digital Delivery of Meditative Movement Training Improved Health of Cigarette-Smoke-Exposed Subjects

“…Animal studies have shown that nicotine caused extended fear responses, enhanced fear conditioning ( 22 ), delayed extinction of fear memories ( 23 , 24 ), and disrupted safety learning ( 17 , 25 ). In humans, children exposed to SHCS had higher rates of major depressive disorder and attention-deficit/hyperactivity disorder ( 20 ).…”

“…Studies in laboratory rodents show that nicotine is a causal agent of extended fear response. In mice, nicotine enhanced fear conditioning ( 22 ), delayed extinction of fear memories ( 23 , 24 ), and disrupted safety learning ( 17 , 25 ). While not directly tested, these effects of nicotine on fear learning and extinction could be related to altered hypothalamic-pituitary-adrenal function in those exposed to second hand smoke as well as active smokers.…”