Nicotine Self-Administration in Adolescent Male and Female Rats

Tobacco product use is the leading preventable cause of death in the United States. Nearly 90% of current daily smokers initiated use during adolescence. Moreover, although national rates of tobacco use by adults have declined in recent years, adolescent initiation remains high. Despite this, little is known about adolescent initiation and use. The present study sought to determine the effects of sex and developmental stage in the acquisition of nicotine self-administration, across a range of doses paired with different nonpharmacological cues. Adolescent (postnatal day [P] 30) and adult (P90) male and female rats with unlimited access to food were allowed to nosepoke on a fixed ratio 2 schedule to intravenously self-administer nicotine (3, 10, 30, or 100 μg/kg/infusion) paired with a moderately reinforcing visual reinforcer (VS) or an initially neutral stimulus light presentation (conditioned stimulus; CS), during daily 1-h sessions. The lowest doses of nicotine (3 or 10 μg/kg) paired with CS presentations did not support acquisition of self-administration in adolescents; however, when paired with VS both low doses engendered acquisition. While adolescents did not acquire at 10 μg/kg + CS, both male and female adults acquired self-administration in this condition. All four sex and age groups acquired self-administration, and earned a similar number of infusions when responding for 30 μg/kg nicotine paired with CS presentations. When paired with VS, adolescents, particularly males, responded more for 30 μg/kg nicotine than adults. Cue condition did not affect adult acquisition for either 10 or 30 μg/kg. Finally, 100 μg/kg supported the acquisition of self-administration for male and female adolescents when paired with either CS or VS, at rates comparable to 30 μg/kg. These results demonstrate that adolescent rats will respond for low doses of nicotine when combined with a moderate reinforcer (VS), but do not respond more than adults for a moderate dose of nicotine. Our finding that a low nicotine dose may enhance responding for VS during adolescence suggests that combination of nicotine exposure with mild rewards may lead to increased exposure to nicotine, and result in nicotine self-administration

Auditory communication in domestic dogs: vocal signalling in the extended social environment of a companion animal

Domestic dogs produce a range of vocalisations, including barks, growls, and whimpers, which are shared with other canid species. The source–filter model of vocal production can be used as a theoretical and applied framework to explain how and why the acoustic properties of some vocalisations are constrained by physical characteristics of the caller, whereas others are more dynamic, influenced by transient states such as arousal or motivation. This chapter thus reviews how and why particular call types are produced to transmit specific types of information, and how such information may be perceived by receivers. As domestication is thought to have caused a divergence in the vocal behaviour of dogs as compared to the ancestral wolf, evidence of both dog–human and human–dog communication is considered. Overall, it is clear that domestic dogs have the potential to acoustically broadcast a range of information, which is available to conspecific and human receivers. Moreover, dogs are highly attentive to human speech and are able to extract speaker identity, emotional state, and even some types of semantic information

Nicotine enhances footshock- and lithium chloride-conditioned place avoidance in male rats

Introduction: Numerous studies have shown that nicotine (NIC) can enhance the reinforcing effects of non-NIC stimuli through a nonassociative mechanism. To date, it is unclear whether NIC reinforcement enhancement serves to increase behaviors motivated by rewarding stimuli only, or whether NIC potentiates behavior motivated by all stimuli, regardless of valence. Methods: The current study used a place conditioning procedure to examine whether acute NIC injection modulates avoidance of an environment previously associated with an aversive stimulus. Separate groups of rats underwent place conditioning using either lithium chloride (125 mg/kg/ml, i.p.) or footshock (0.75 mA) as the aversive stimulus. Other rats served as nonconditioned controls. The magnitude of place avoidance was assessed after acute NIC (0.1 or 0.4 mg/kg/ml, s.c.) or saline. Results: Rats avoided chambers previously paired with either lithium chloride or footshock, and conditioned place avoidance was significantly enhanced by NIC pre-treatment. Conclusions: These results demonstrate that the ability of NIC to enhance motivated behavior extends to behaviors elicited by aversive stimuli, evidence that NIC affects behavior motivated by a broader range of stimuli than previously appreciated. Implications: The current study examined whether the reinforcement enhancement properties of NIC apply to aversive stimuli by testing NIC enhancement of conditioned place avoidance in rats. The results demonstrate that NIC enhances the motivational impact of these distinct aversive stimuli, providing novel evidence that NIC affects behavior motivated by a broader range of stimuli than has previously been demonstrated

What role does dopamine really play in tobacco addiction?

Editoria

Differentiating the Primary Reinforcing and Reinforcement-Enhancing Effects of Varenicline

Rationale: Varenicline (VAR), a smoking cessation aid that is a partial agonist at nicotinic receptors, mimics the reinforcement-enhancing effects of nicotine. Varenicline, when accompanied by non-drug cues, is self-administered by rats, though it is unclear whether this results from varenicline acting as a primary reinforcer or a reinforcement enhancer of the cues. Objectives: This study sought to disentangle these two potential actions. Methods: Rats were allowed to self-administer intravenous nicotine, saline, or varenicline during 1-h sessions in operant chambers equipped with two levers. Five groups had concurrent access to drug infusions and a moderately reinforcing visual stimulus (VS) for responding on separate levers. Meeting the reinforcement schedule on one lever was reinforced with VAR (0.01, 0.06, 0.1 mg/kg/infusion), nicotine (0.06 mg/kg/infusion), or saline, while meeting the same schedule on the other lever delivered the VS. Additional groups were reinforced for pressing a single active lever and received VAR paired with the VS, the VS with response-independent infusions of VAR, or VAR alone (0.1 mg/kg/infusion). Results: Rats readily responded for VAR paired with VS on a single lever. However, when VAR was the only reinforcer contingent on a response, rats did not respond more than for saline. Conclusions: These findings show that VAR does not serve as a primary reinforcer in rats at doses that increase responding for non-drug reinforcers. These data are consistent with research showing that the primary reinforcing effects of VAR are weak, at best, and that the primary reinforcing and reinforcement-enhancing actions of nicotinic drugs are pharmacologically distinct