Amphetamine injections into the nucleus accumbens affect neither acquisition/expression of conditioned fear nor baseline startle response

65 years of research on dopamine's role in classical fear conditioning and extinction: A systematic review

Dopamine, a catecholamine neurotransmitter, has historically been associated with the encoding of reward, whereas its role in aversion has received less attention. Here, we systematically gathered the vast evidence of the role of dopamine in the simplest forms of aversive learning: classical fear conditioning and extinction. In the past, crude methods were used to augment or inhibit dopamine to study its relationship with fear conditioning and extinction. More advanced techniques such as conditional genetic, chemogenic and optogenetic approaches now provide causal evidence for dopamine's role in these learning processes. Dopamine neurons encode conditioned stimuli during fear conditioning and extinction and convey the signal via activation of D1-4 receptor sites particularly in the amygdala, prefrontal cortex and striatum. The coordinated activation of dopamine receptors allows for the continuous formation, consolidation, retrieval and updating of fear and extinction memory in a dynamic and reciprocal manner. Based on the reviewed literature, we conclude that dopamine is crucial for the encoding of classical fear conditioning and extinction and contributes in a way that is comparable to its role in encoding reward.

Pain-relief learning in flies, rats, and man: basic research and applied perspectives

Memories relating to a painful, negative event are adaptive and can be stored for a lifetime to support preemptive avoidance, escape, or attack behavior. However, under unfavorable circumstances such memories can become overwhelmingly powerful. They may trigger excessively negative psychological states and uncontrollable avoidance of locations, objects, or social interactions. It is therefore obvious that any process to counteract such effects will be of value. In this context, we stress from a basic-research perspective that painful, negative events are "Janus-faced" in the sense that there are actually two aspects about them that are worth remembering: What made them happen and what made them cease. We review published findings from fruit flies, rats, and man showing that both aspects, respectively related to the onset and the offset of the negative event, induce distinct and oppositely valenced memories: Stimuli experienced before an electric shock acquire negative valence as they signal upcoming punishment, whereas stimuli experienced after an electric shock acquire positive valence because of their association with the relieving cessation of pain. We discuss how memories for such punishment- and relief-learning are organized, how this organization fits into the threat-imminence model of defensive behavior, and what perspectives these considerations offer for applied psychology in the context of trauma, panic, and nonsuicidal self-injury.

Modulation of neuropeptide FF (NPFF) receptors influences the expression of amphetamine-induced conditioned place preference and amphetamine withdrawal anxiety-like behavior in rats

Many data indicate that endogenous opioid system is involved in amphetamine-induced behavior. Neuropeptide FF (NPFF) possesses opioid-modulating properties. The aim of the present study was to determine whether pharmacological modulation of NPFF receptors modify the expression of amphetamine-induced conditioned place preference (CPP) and amphetamine withdrawal anxiety-like behavior, both processes relevant to drug addiction/abuse. Intracerebroventricular (i.c.v.) injection of NPFF (5, 10, and 20 nmol) inhibited the expression of amphetamine CPP at the doses of 10 and 20 nmol. RF9, the NPFF receptors antagonist, reversed inhibitory effect of NPFF (20 nmol, i.c.v.) at the doses of 10 and 20 nmol and did not show any effect in amphetamine- and saline conditioned rats. Anxiety-like effect of amphetamine withdrawal was measured 24h after the last (14 days) amphetamine (2.5mg/kg, i.p.) treatment in the elevated plus-maze test. Amphetamine withdrawal decreased the percent of time spent by rats in the open arms and the percent of open arms entries. RF9 (5, 10, and 20 nmol, i.c.v.) significantly reversed these anxiety-like effects of amphetamine withdrawal and elevated the percent of time spent by rats in open arms at doses of 5 and 10 nmol, and the percent of open arms entries in all doses used. NPFF (20 nmol) pretreatment inhibited the effect of RF9 (10 nmol). Our results indicated that stimulation or inhibition of NPFF receptors decrease the expression of amphetamine CPP and amphetamine withdrawal anxiety, respectively. These findings may have implications for a better understanding of the processes involved in amphetamine dependence.

Adrenergic receptors in the nucleus accumbens shell differentially modulate dopamine and acetylcholine receptor-mediated turning behaviour

The role of alpha- and beta-adrenoceptors in the nucleus accumbens shell in turning behaviour of rats was investigated. Unilateral injections of the alpha-adrenoceptor agonist (phenylephrine; 10 microg) and antagonist (phentolamine; 10 microg) as well as the beta-adrenoceptor agonist (isoprenaline; 1 microg) and antagonist (propranolol; 5 microg) into the nucleus accumbens shell did not produce turning behaviour more than that of control vehicle injection. Unilateral injection of a mixture of dopamine D(1) ((+/-)-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine-7,8-diol, SKF 38393; 5 microg) and D(2) (quinpirole; 10 microg) receptor agonists into the nucleus accumbens shell has been found to elicit contraversive pivoting. Such pivoting was dose-dependently inhibited by phenylephrine (5, 10 microg), injected into the nucleus accumbens shell, and the inhibitory effect of phenylephrine (10 microg) was antagonised by phentolamine (10 microg) that per se had no effect on this pivoting. Isoprenaline (0.5, 1 microg) dose-dependently increased the contraversive pivoting induced by the mixture of SKF 38393 (1 microg) and quinpirole (10 microg) injected into the nucleus accumbens shell. The effect of isoprenaline (1 microg) was antagonised by propranolol (5 microg) that per se had no effect on this pivoting. It is concluded that stimulation of accumbal alpha-adrenoceptors inhibits the dopamine-dependent pivoting in contrast to stimulation of accumbal beta-adrenoceptors that facilitates this dopamine-dependent pivoting. Unilateral injection of the acetylcholine receptor agonist carbachol (5 microg) into the nucleus accumbens shell has been found to elicit contraversive circling. Such circling was significantly reduced by accumbal administration of either phenylephrine (10, 20 microg) or phentolamine (5, 10 microg) in a dose-independent manner; moreover, both drugs potentiated, but did not counteract, each other's effects. Carbachol-induced circling was also reduced by propranolol (2.5, 5 microg), but again in an aspecific manner. It is concluded that alpha- and beta-adrenergic agents have an effect on accumbal acetylcholine receptor-mediated circling through a non-adrenergic mechanism. The impact of the present study for putative new treatments of various neuropsychiatric and neurological disorders is discussed.

Distribution characteristics of methamphetamine and amphetamine in urine and hair specimens collected from alleged methamphetamine users in northern Taiwan

This study was conducted to better understand the distribution characteristics of methamphetamine and amphetamine in urine and hair specimens collected from alleged methamphetamine users in the local population. It is anticipated that the data hereby obtained will be helpful to the interpretation of the time and pattern of drug use. Eight alleged methamphetamine-using arrestees from Keelung Police Department (north of Taipei, Taiwan) consented to contribute both urine and hair specimens. Each arrestee contributed seven urine specimens collected at 0, 12, 24, 48, 72, 96, and 120 h, respectively, after the arrest. Hair specimens were cut into 2-cm sections. The limits of detection and quantitation of the urine protocol were 40 and 50 ng/mL, respectively, for both amphetamine and methamphetamine, while the corresponding limits of detection and quantitation for the hair protocol were 0.8 and 1.0 ng/mg, respectively. The concentration variations of methamphetamine and amphetamine in the urine specimens exhibited three distinct patterns: (a) continuous decrease in the analytes' concentrations for specimens collected at hours 0-120; (b) increase in the analytes' concentrations in specimens collected at hours 0-12, followed by decrease; (c) increase in analytes' concentrations in specimens collected at later times. Together with the amphetamine/methamphetamine concentration ratios found in these urine specimens, the observed trends in the changes of the analytes' concentrations are helpful for the interpretation on the time of drug use. Unlike urine specimens, amphetamine/methamphetamine concentration ratios in various hair specimens and hair sections remain relatively constant.

Carbachol injections into the nucleus accumbens disrupt acquisition and expression of fear-potentiated startle and freezing in rats

The nucleus accumbens is involved in different types of emotional learning, ranging from appetitive instrumental learning to Pavlovian fear conditioning. In previous studies, we found that temporary inactivation of the nucleus accumbens blocked both the acquisition and expression of conditioned fear. This was not due to altered dopaminergic activity as we have also found that intra-nucleus accumbens infusions of the dopamine agonist amphetamine do not affect either the acquisition or the expression of conditioned fear. Therefore, in the present study we examined whether cholinergic activity in the nucleus accumbens is involved in the acquisition and expression of conditioned fear. Specifically, the effect of intra-nucleus accumbens infusions of the unselective cholinergic agonist carbachol on the acquisition and expression of conditioned fear was assessed. Across several experiments, we measured fear to visual and acoustic conditioned stimuli and to the experimental context. Further, two different measures of conditioned fear were recorded: fear potentiation of startle and freezing. Intra-nucleus accumbens carbachol infusions disrupted acquisition as well as expression of conditioned fear, regardless of the modality of the fear-eliciting stimulus or of the specific measure of conditioned fear. This disruption of conditioned fear was not simply a by-product of enhanced motor activity which also occurred after intra-nucleus accumbens carbachol infusions. Interestingly, despite the substantial effect of intra-nucleus accumbens carbachol on expression of conditioned fear, the results of the final experiment suggest that these rats extinguish similarly to control rats. Taken together, the present results indicate that acetylcholine within the nucleus accumbens is important for the learning and retrieval of conditioned fear.

Modulation of memory consolidation by the basolateral amygdala or nucleus accumbens shell requires concurrent dopamine receptor activation in both brain regions

Previous findings indicate that the basolateral amygdala (BLA) and the nucleus accumbens (NAc) interact in influencing memory consolidation. The current study investigated whether this interaction requires concurrent dopamine (DA) receptor activation in both brain regions. Unilateral, right-side cannulae were implanted into the BLA and the ipsilateral NAc shell or core in male Sprague-Dawley rats ( approximately 300 g). One week later, the rats were trained on an inhibitory avoidance (IA) task and, 48 h later, they were tested for retention. Drugs were infused into the BLA and NAc shell or core immediately after training. Post-training intra-BLA infusions of DA enhanced retention, as assessed by latencies to enter the shock compartment on the retention test. Infusions of the general DA receptor antagonist cis-Flupenthixol (Flu) into the NAc shell (but not the core) blocked the memory enhancement induced by the BLA infusions of DA. In the reverse experiment, post-training intra-NAc shell infusions of DA enhanced retention and Flu infusions into the BLA blocked the enhancement. These findings indicate that BLA modulation of memory consolidation requires concurrent DA receptor activation in the NAc shell but not the core. Similarly, NAc shell modulation of memory consolidation requires concurrent DA receptor activation in the BLA. Together with previous findings, these results suggest that the dopaminergic innervation of the BLA and NAc shell is critically involved in the modulation of memory consolidation.