A Genetically Defined Compartmentalized Striatal Direct Pathway for Negative Reinforcement.

The striosome compartment within the dorsal striatum has been implicated in reinforcement learning and regulation of motivation, but how striosomal neurons contribute to these functions remains elusive. Here, we show that a genetically identified striosomal population, which expresses the Teashirt family zinc finger 1 (Tshz1) and belongs to the direct pathway, drives negative reinforcement and is essential for aversive learning in mice. Contrasting a "conventional" striosomal direct pathway, the Tshz1 neurons cause aversion, movement suppression, and negative reinforcement once activated, and they receive a distinct set of synaptic inputs. These neurons are predominantly excited by punishment rather than reward and represent the anticipation of punishment or the motivation for avoidance. Furthermore, inhibiting these neurons impairs punishment-based learning without affecting reward learning or movement. These results establish a major role of striosomal neurons in behaviors reinforced by punishment and moreover uncover functions of the direct pathway unaccounted for in classic models.

A serotonergic circuit regulates aversive associative learning under mitochondrial stress in C. elegans.

SignificancePhysiological stress triggers avoidance behavior, allowing the animals to stay away from potential threats and optimize their chance of survival. Mitochondrial disruption, a common physiological stress in diverse species, induces the nematode Caenorhabditis elegans to avoid non-pathogenic bacteria through a serotonergic neuronal circuit. We find that distinct neurons, communicated through serotonin and a specific serotonin receptor, are required for the formation and retrieval of this learned aversive behavior. This learned avoidance behavior is associated with increased serotonin synthesis, altered neuronal response property, and reprogramming of locomotion patterns. The circuit and neuromodulatory mechanisms described here offer important insights for stress-induced avoidance behavior.

Brain state-dependent responses of midbrain dopaminergic neurons to footshock under urethane anaesthesia.

For a long time, it has been assumed that dopaminergic (DA) neurons in both the ventral tegmental area (VTA) and the substantia nigra pars compacta (SNc) uniformly respond to rewarding and aversive stimuli by either increasing or decreasing their activity, respectively. This response was believed to signal information about the perceived stimuli's values. The identification of VTA&SNc DA neurons that are excited by both rewarding and aversive stimuli has led to the categorisation of VTA&SNc DA neurons into two subpopulations: one signalling the value and the other signalling the salience of the stimuli. It has been shown that the general state of the brain can modulate the electrical activity of VTA&SNc DA neurons, but it remains unknown whether this factor may also influence responses to aversive stimuli, such as a footshock (FS). To address this question, we have recorded the responses of VTA&SNc DA neurons to FSs across cortical activation and slow wave activity brain states in urethane-anaesthetised rats. Adding to the knowledge of aversion signalling by midbrain DA neurons, we report that significant proportion of VTA&SNc DA neurons can change their responses to an aversive stimulus in a brain state-dependent manner. The majority of these neurons decreased their activity in response to FS during cortical activation but switched to increasing it during slow wave activity. It can be hypothesised that this subpopulation of DA neurons may be involved in the 'dual signalling' of both the value and the salience of the stimuli, depending on the general state of the brain.

Electroacupuncture alleviates the relapse of pain-related aversive memory by activating KOR and inhibiting GABAergic neurons in the insular cortex.

Pain-related aversive memory is common in chronic pain patients. Electroacupuncture has been demonstrated to block pain-related aversive memory. The insular cortex is a key region closely related to aversive behaviors. In our study, a potential mechanism underlying the effect of electroacupuncture treatment on pain-related aversive memory behaviors relative to the insular cortex was investigated. Our study used the chemogenetic method, pharmacological method, electroacupuncture intervention, and behavioral detection. Our study showed that both inhibition of gamma-aminobutyric acidergic neurons and activation of the kappa opioid receptor in the insular cortex blocked the pain-related aversive memory behaviors induced by 2 crossover injections of carrageenan in mice; conversely, both the activation of gamma-aminobutyric acidergic neurons and inhibition of kappa opioid receptor in the insular cortex play similar roles in inducing pain-related aversive memory behaviors following 2 crossover injections of carrageenan. In addition, activation of gamma-aminobutyric acidergic neurons in the insular cortex reversed the effect of kappa opioid receptor activation in the insular cortex. Moreover, electroacupuncture effectively blocked pain-related aversive memory behaviors in model mice, which was reversed by both activation of gamma-aminobutyric acidergic neurons and inhibition of kappa opioid receptor in the insular cortex. The effect of electroacupuncture on blocking pain-related aversive memory behaviors may be related to the activation of the kappa opioid receptor and inhibition of gamma-aminobutyric acidergic neurons in the insular cortex.

Temporal association activates projections from the perirhinal cortex and ventral CA1 to the prelimbic cortex and from the prelimbic cortex to the basolateral amygdala.

In trace fear conditioning, the prelimbic cortex exhibits persistent activity during the interval between the conditioned and unconditioned stimuli, which maintains a conditioned stimulus representation. Regions cooperating for this function or encoding the conditioned stimulus before the interval could send inputs to the prelimbic cortex, supporting learning. The basolateral amygdala has conditioned stimulus- and unconditioned stimulus-responsive neurons, convergently activated. The prelimbic cortex could directly project to the basolateral amygdala to associate the transient memory of the conditioned stimulus with the unconditioned stimulus. We investigated the neuronal circuit supporting temporal associations using contextual fear conditioning with a 5-s interval, in which 5 s separates the contextual conditioned stimulus from the unconditioned stimulus. Injecting retrobeads, we quantified c-Fos in prelimbic cortex- or basolateral amygdala-projecting neurons from 9 regions after contextual fear conditioning with a 5-s interval or contextual fear conditioning, in which the conditioned and unconditioned stimuli overlap. The contextual fear conditioning with a 5-s interval activated ventral CA1 and perirhinal cortex neurons projecting to the prelimbic cortex and prelimbic cortex neurons projecting to basolateral amygdala. Both fear conditioning activated ventral CA1 and lateral entorhinal cortex neurons projecting to basolateral amygdala and basolateral amygdala neurons projecting to prelimbic cortex. The perirhinal cortex â†’ prelimbic cortex and ventral CA1 â†’ prelimbic cortex connections are the first identified prelimbic cortex afferent projections participating in temporal associations. These results help to understand time-linked memories, a process required in episodic and working memories.

Counterirritation by pain inhibits the responsiveness to aversive loud tones: the role of state anxiety and state fear triggered in the NPU paradigm.

AIM OF THE STUDY: The application of a noxious stimulus reduces the perception and responsiveness to other pain stimuli. This inhibition can be experimentally assessed with a method called 'counterirritation'. The question arises if counterirritation acts also on the perception and responsiveness to aversive but non-nociceptive stimuli (e.g., loud tones). Since aversive stimulation is often associated with state anxiety or state fear, we investigated in addition the modulatory effects of these emotions on counterirritation. MATERIAL AND METHODS: 51 subjects participated in our study. We presented tones with aversive loudness (105 dB), first alone then during counterirritation (immersion of the hand in a hot water bath of 46 °C) to assess inhibition of loudness perception and responsiveness. Influences of state anxiety and state fear on counterirritation were investigated by using the Neutral-Predictable(fear)- Unpredictable(anxiety) Paradigm (NPU), which is based on classical conditioning. Loudness ratings (perception of the aversive tones) and startle reflex (defensive reaction to aversive tones) were assessed. RESULTS: Counterirritation reduced startle reflex amplitudes, but not the loudness ratings. Although state anxiety and state fear were successfully induced, counterirritation remained unaffected. CONCLUSIONS: Our study showed that pain inhibits the responsiveness to aversive stimuli (loud tones). Thus, the postulate that 'pain inhibits pain' might be better changed to 'pain inhibits aversiveness'. Consequently, our findings may also question the assumption of a clear pain specificity in inhibitory action as assumed by theoretical approaches like 'conditioned pain modulation' (CPM). Furthermore, counterirritation appeared one more time resistant to the influence of negative emotions.

Effects of omega-3 supplementation on anxiety-like behaviors and neuroinflammation in Wistar rats following cafeteria diet-induced obesity.

ABSTRACTObjetives: Omega-3 (n3) fatty acids have been studied as an option to alleviate the harmful effects of obesity. However, its role in obesity-related behavioral changes is still controversial. This study aimed to evaluate the effects of n3 on behavior and neuroinflammation in obese animals. Methods: Male Wistar rats were divided into four groups: control diet (CT), CT+n3, cafeteria diet (CAF), and CAF+n3. Diet was administered for 13 weeks, and n3 was supplemented during the last 5 weeks. Metabolic and biochemical parameters were evaluated, as well as anxiety-like behaviors. Immunoblots were conducted in the animals' cerebral cortex and hippocampus to assess changes in neuroinflammatory markers.Results: CAF-fed animals showed higher weight gain, visceral adiposity, fasting glucose, total cholesterol, triglycerides, and insulin levels, and n3 improved the lipid profile and restored insulin sensitivity. CAF-fed rats showed anxiety-like behaviors in the open field and light-dark box tasks but not in the contextual aversive conditioning. Omega-3 did not exert any effect on these behaviors. Regarding neuroinflammation, diet and supplementation acted in a region-specific manner. In the hippocampus, CAF reduced claudin-5 expression with no effect of n3, indicating a brain-blood barrier disruption following CAF. Furthermore, in the hippocampus, the glial fibrillary acidic protein (GFAP) and toll-like receptor 4 (TLR-4) were reduced in treated obese animals. However, n3 could not reverse the TLR-4 expression increase in the cerebral cortex.Discussion: Although n3 may protect against some neuroinflammatory manifestations in the hippocampus, it does not seem sufficient to reverse the increase in anxiolytic manifestations caused by CAF.

Testing the equivalence of the aversive core of personality and a blend of agreeableness(-related) items.

OBJECTIVE: There is an ongoing debate in personality research whether the common core of aversive ("dark") traits can be approximated by or even considered equivalent to one of the constructs that have been labeled "Agreeableness". In particular, it has been suggested that the low pole of (what we term) AG+, a broad blend of Big Five Agreeableness and the HEXACO factors Honesty-Humility, Agreeableness, and Altruism, is essentially equivalent to the Dark Factor of Personality (D). Based on theoretical differences, we herein test empirically whether D and AG+ are isomorphic. METHODS: Self-report data on D, AG+, and eight criterion measures reflecting justifying beliefs, inflicting disutility on others, and affiliative tendencies were collected in a pre-registered study (N = 1156) and analyzed via confirmatory factor modeling. RESULTS: Results speak against unity of D and AG+ (35% shared variance) and support the notion that D subsumes a broader range of aversive content (i.e., justifying beliefs and inflicting disutility on others) than AG+, which, in turn, subsumes a slightly broader range of non-aversive, affiliative tendencies. CONCLUSION: We conclude that AG+ is non-equivalent to the common core of aversive traits, D.

Dual roles of dopaminergic pathways in olfactory learning and memory in the oriental fruit fly, Bactrocera dorsalis.

Dopamine (DA) is a key regulator of associative learning and memory in both vertebrates and invertebrates, and it is widely believed that DA plays a key role in aversive conditioning in invertebrates. However, the idea that DA is involved only in aversive conditioning has been challenged in recent studies on the fruit fly (Drosophila melanogaster), ants and crabs, suggesting diverse functions of DA modulation on associative plasticity. Here, we present the results of DA modulation in aversive olfactory conditioning with DEET punishment and appetitive olfactory conditioning with sucrose reward in the oriental fruit fly, Bactrocera dorsalis. Injection of DA receptor antagonist fluphenazine or chlorpromazine into these flies led to impaired aversive learning, but had no effect on the appetitive learning. DA receptor antagonists impaired both aversive and appetitive long-term memory retention. Interestingly, the impairment on appetitive memory was rescued not only by DA but also by octopamine (OA). Blocking the OA receptors also impaired the appetitive memory retention, but this impairment could only be rescued by OA, not by DA. Thus, we conclude that in B. dorsalis, OA and DA pathways mediate independently the appetitive and aversive learning, respectively. These two pathways, however, are organized in series in mediating appetitive memory retrieval with DA pathway being at upstream. Thus, OA and DA play dual roles in associative learning and memory retrieval, but their pathways are organized differently in these two cognitive processes - parallel organization for learning acquisition and serial organization for memory retrieval.

Aversive conditioning, anxiety, and the strategic control of attention.

What we pay attention to is influenced by both reward learning and aversive conditioning. Although early attention tends to be biased toward aversively conditioned stimuli, sustained ignoring of such stimuli is also possible. How aversive conditioning influences how a person chooses to search, or the strategic control of attention, has not been explored. In the present study, participants learned an association between a colour and an aversive outcome during a training phase, and in a subsequent test phase searched for one of two targets presented on each trial; one target was rendered in the aversively conditioned colour (CS+) and the other in a neutral colour (CS-). Given the distribution of colour stimuli in the search array, it was more optimal to search for and report a target in one of the two colours on some trials. Our results demonstrate that participants were biased away from the CS+ target, which resulted in non-optimal search on some trials. Surprisingly, rather than accentuate this bias, greater state anxiety was associated with a stronger tendency to find and report the CS+ target. Our findings have implications for our understanding of the learning-dependent control of attention and abnormal attentional biases observed in high-anxious individuals.

Temporal memory for threatening events encoded in a haunted house.

Despite the salient experience of encoding threatening events, these memories are prone to distortions and often non-veridical from encoding to recall. Further, threat has been shown to preferentially disrupt the binding of event details and enhance goal-relevant information. While extensive work has characterised distinctive features of emotional memory, research has not fully explored the influence threat has on temporal memory, a process putatively supported by the binding of event details into a temporal context. Two primary competing hypotheses have been proposed; that threat can impair or enhance temporal memory. We analysed two datasets to assess temporal memory for an in-person haunted house experience. In study 1, we examined the temporal structure of memory by characterising memory contiguity in free recall as a function of individual levels of heart rate as a proxy of threat. In study 2, we replicated marginal findings of threat-related increases in memory contiguity found in study 1. We extended these findings by showing threat-related increases in recency discriminations, an explicit test of temporal memory. Together, these findings demonstrate that threat enhances temporal memory regarding free recall structure and during explicit memory judgments.

Observational learning of threat-related attentional bias.

Attentional bias to threat has been almost exclusively examined after participants experienced repeated pairings between a conditioned stimulus (CS) and an aversive unconditioned stimulus (US). This study aimed to determine whether threat-related attentional capture can result from observational learning, when participants acquire knowledge of the aversive qualities of a stimulus without themselves experiencing aversive outcomes. Non-clinical young-adult participants (N = 38) first watched a video of an individual (the demonstrator) performing a Pavlovian conditioning task in which one colour was paired with shock (CS+) and another colour was neutral (CS-). They then carried out visual search for a shape-defined target. Oculomotor measures evidenced an attentional bias toward the CS+ colour, suggesting that threat-related attentional capture can ensue from observational learning. Exploratory analyses also revealed that this effect was positively correlated with empathy for the demonstrator. Our findings extend empirical and theoretical knowledge about threat-driven attention and provide valuable insights to better understand the formation of anxiety disorders.

The challenges of diversity in nursing faculty recruitment: the case of Finland.

BACKGROUND: Diversity considerations in hiring faculty in higher education have garnered significant attention globally in recent years. However, analyses of faculty recruitment dynamics outside the United States, particularly in schools and colleges of nursing, have been limited. PURPOSE: This paper explores how concepts related to racism apply to recruitment in nursing education, focusing on the specific context of Finland. METHODS: Discourse Approach. DISCUSSION: Despite the increased admission of foreign students to English-language nursing programs, potential biases against the recruitment of nurse educators from foreign backgrounds could exist in Finland. Local data, anecdotes, and an analysis of the broader literature suggest that robust diversity, equity, and inclusion (DEI) policies and guidelines are necessary to enhance the experiences of both instructors and students. Additionally, training and support mechanisms may be needed to enable nursing faculty members from foreign backgrounds to thrive and fully participate in shared governance within academic institutions. CONCLUSION: By examining the challenges and proposing strategies for increasing diversity in Finnish nursing education, this paper aims to contribute to the broader discourse on diversity in nursing as a profession.

[Patient and quality characteristics in the treatment with disulfiram (Antabus) in the German "Network for Alcohol Aversive Pharmacotherapy"]. / Patienten- und Qualitätsmerkmale bei der Behandlung mit Disulfiram ("Antabus") im deutschsprachigen "Netzwerk alkoholaversive Pharmakotherapie".

BACKGROUND: More than a decade ago disulfiram lost its approval for use in Germany. Nonetheless, a considerable number of psychiatric hospital outpatient departments as well as practicing physicians continue to prescribe it. These professionals have formed the "Network for Alcohol Aversive Pharmacotherapy" (NAP) to maintain a high quality of this treatment approach. OBJECTIVE: To describe the current use of disulfiram with respect to patient numbers and characteristics, side effects, and use of concomitant multimodal treatment forms. MATERIAL AND METHODS: Since 2019 the NAP has conducted an annual retrospective survey among its members regarding the aforementioned parameters. RESULTS: From 2019 to 2023 a total of 1579 treatment cases were described by 33 centers, 152 patients reported a total of 241 drinking events, 26 of them resulting in hospitalization but none causing complications or permanent harm. The most frequent side effects, in descending order, were unpleasant body odor (2.5%), fatigue, male sexual dysfunction, mildly elevated liver enzymes, allergic skin reactions and polyneuropathy (0.8%). More than one quarter of the patients suffered from comorbid depression, and approximately 5% from ADHD, borderline or other personality disorders, trauma-related disorders and anxiety disorders, respectively. Of the patients 33% were treated with antidepressants and 12% with sedating antipsychotics. Various forms of concomitant group therapy were offered to 66% of the patients. CONCLUSION: Treatment with disulfiram is legally possible, generally well-tolerated and safe. It is offered in most treatment centers as part of a comprehensive treatment plan that includes multimodal treatment of comorbid psychiatric disorders.

Understanding the concurrence of environmental characteristics in Latino youth: A person-centered approach.

The current study aimed to identify profiles of youth presenting with a unique combination of environmental characteristics and understand the differential relationship between profile membership, anxiety, and depression symptoms. Data were drawn from 158 Latino youth between the ages of 11 and 13. Youth provided information on community violence exposure, acculturative stress, familial and peer support, and parental supervision. Main analyses included Latent Profile Analysis and Multivariate Analysis of Variance. Support for a four-profile model was found. Profiles are distinguished by mean levels of community violence exposure, acculturative stress, familial and peer support, and parental supervision. Profile membership was significantly associated with anxiety and depression, separately. Those belonging to the profile with the highest levels of environmental risk reported the highest levels of anxiety and depression. Findings contribute to a personalized understanding of risk and protective experiences in the environment for Latino youth.

Contextual fear conditioning with a time interval induces CREB phosphorylation in the dorsal hippocampus and amygdala nuclei that depend on prelimbic cortex activity.

In temporal associations, a conditioned stimulus (CS) is separated by a time interval from the unconditioned stimulus (US), which activates the prelimbic cortex (PL) to maintain a CS representation over time. However, it is unknown whether the PL participates, besides the encoding, in the memory consolidation, and thus directly, with activity-dependent changes or indirectly, by modulation of activity-dependent changes in other brain regions. We investigated brain regions supporting the consolidation of associations with intervals and the influence of PL activity in this consolidation process. For this, we observed in Wistar rats the effect of pre-training PL inactivation by muscimol in CREB (cAMP response element-binding protein) phosphorylation, which is essential for memory consolidation, in subdivisions of the medial prefrontal cortex (mPFC), hippocampus, and amygdala 3 h after the training in the contextual fear conditioning (CFC) or CFC with 5-s interval (CFC-5s), fear associations without or with an interval between the CS and US, respectively. Both the CFC-5s and CFC training increased phosphorylation of CREB in the PL and infralimbic cortex (IL); lateral (LA) and basolateral (BLA) amygdala; dorsal CA1 (dCA1); dorsal (dDG), and ventral dentate gyrus, and the CFC-5s training in the central amygdala (CEA). PL activity was necessary for the CREB phosphorylation in the PL, BLA, CEA, dCA1, and dDG only in animals trained in the CFC-5s. The cingulate cortex, ventral CA1, and ventral subiculum did not have learning-induced phosphorylation of CREB. These results suggest that the mPFC, hippocampus, and amygdala support the consolidation of associations with or without intervals and that PL activity influences consolidation in the dorsal hippocampus and amygdala in temporal associations. Thereby, the PL contributes directly and indirectly by modulation to memory consolidation. The time interval engaged the PL early in recent memory consolidation. Results expanded PL's role beyond the time interval and remote memory consolidation.

Neuroproteomic mapping of kinases and their substrates downstream of acetylcholine: finding and implications.

INTRODUCTION: Since the emergence of the cholinergic hypothesis of Alzheimer's disease (AD), acetylcholine has been viewed as a mediator of learning and memory. Donepezil improves AD-associated learning deficits and memory loss by recovering brain acetylcholine levels. However, it is associated with side effects due to global activation of acetylcholine receptors. Muscarinic acetylcholine receptor M1 (M1R), a key mediator of learning and memory, has been an alternative target. The importance of targeting a specific pathway downstream of M1R has recently been recognized. Elucidating signaling pathways beyond M1R that lead to learning and memory holds important clues for AD therapeutic strategies. AREAS COVERED: This review first summarizes the role of acetylcholine in aversive learning, one of the outputs used for preliminary AD drug screening. It then describes the phosphoproteomic approach focused on identifying acetylcholine intracellular signaling pathways leading to aversive learning. Finally, the intracellular mechanism of donepezil and its effect on learning and memory is discussed. EXPERT OPINION: The elucidation of signaling pathways beyond M1R by phosphoproteomic approach offers a platform for understanding the intracellular mechanism of AD drugs and for developing AD therapeutic strategies. Clarifying the molecular mechanism that links the identified acetylcholine signaling to AD pathophysiology will advance the development of AD therapeutic strategies.

Social buffering reduces fear expression in Wistar rats when tested in pairs, but not when retested alone.

Social buffering is a phenomenon in which the stress response of an individual can be reduced by the presence of another individual. However, little is known about the effect of social buffering on aversive after memory extinction, especially when animals are tested alone afterwards. The aim of this study was to verify the social buffering effect in rats during the extinction session of the contextual fear conditioning model and the fear response when animals are tested alone in the following day. Animals were divided into subjects and associates, with the subjects undergoing the fear conditioning protocol and the associates paired with the subjects during the fear extinction session. Across five different experiments, we tested moderate and high intensity contextual fear conditioning protocols, as well four variations of pairs: (i) two conditioned subjects, (ii) a conditioned subject and a non-conditioned associate, (iii) a conditioned subject and an associate who observed the conditioning of the partner and (iv) two conditioned subjects, with one treated with diazepam. The social buffering effect was found efficient to reduce the fear memory expression during the fear extinction session. In the moderate intensity protocol, the reduction in freezing time occurred only in subjects accompanied by non-conditioned associates and observer associates. In the high intensity protocol, the social buffering effect occurred in subjects accompanied by either conditioned or non-conditioned associates, although the effect was more evident in the presence of non-conditioned subjects. Treatment of the conditioned associates with diazepam did not improve the social buffering effect. Moreover, social buffering effects were not correlated with self-grooming or prosocial behaviors, which indicates that the presence of another animal might decrease freezing by promotion of exploratory activity. Finally, the social buffering effect was not observed in the extinction test, either because the extinction was too effective in the moderate intensity protocol or because the extinction was equally ineffective in the high intensity protocol. Our results suggest that social buffering does not improve fear extinction consolidation.

Synergistic photoactivation of VTA-catecholaminergic and BLA-glutamatergic projections induces long-term potentiation in the insular cortex.

The presentation of novel stimuli induces a reliable dopamine release in the insular cortex (IC) from the ventral tegmental area (VTA). The novel stimuli could be associated with motivational and emotional signals induced by cortical glutamate release from the basolateral amygdala (BLA). Dopamine and glutamate are essential for acquiring and maintaining behavioral tasks, including visual and taste recognition memories. In this study, we hypothesize that the simultaneous activation of dopaminergic and glutamatergic projections to the neocortex can underlie synaptic plasticity. High-frequency stimulation of the BLA-IC circuit has demonstrated a reliable long-term potentiation (LTP), a widely acknowledged synaptic plasticity that underlies memory consolidation. Therefore, the concurrent optogenetic stimulation of the insula's glutamatergic and dopaminergic terminal fibers would induce reliable LTP. Our results confirmed that combined photostimulation of the VTA and BLA projections to the IC induces a slow-onset LTP. We also found that optogenetically-induced LTP in the IC relies on both glutamatergic NMDA receptors and dopaminergic D1/D5 receptors, suggesting that the combined effects of these neurotransmitters can trigger synaptic plasticity in the neocortex. Overall, our findings provide compelling evidence supporting the essential role of both dopaminergic and glutamatergic projections in modulating synaptic plasticity within the IC. Furthermore, our results suggest that the synergistic actions of these projections have a pivotal influence on the formation of motivational memories.

Role of nitric oxide on defensive behavior and long-term aversive learning induced by chemical stimulation of the dorsolateral periaqueductal gray matter.

The midbrain periaqueductal gray matter, especially the dorsolateral portion (dlPAG), coordinates immediate defensive responses (DR) to threats, but also ascends forebrain information for aversive learning. The synaptic dynamics in the dlPAG regulate the intensity and type of behavioral expression, as well as long-term processes such as memory acquisition, consolidation, and retrieval. Among several neurotransmitters and neural modulators, nitric oxide seems to play an important regulatory role in the immediate expression of DR, but it remains unclear if this gaseous on-demand neuromodulator contributes to aversive learning. Therefore, the role of nitric oxide in the dlPAG was investigated, during conditioning in an olfactory aversive task. The behavioral analysis consisted of freezing and crouch-sniffing in the conditioning day after glutamatergic NMDA agonist injection into the dlPAG. Two days later, rats were re-exposed to the odor cue and avoidance was measured. 7NI, a selective neuronal nitric oxide synthase inhibitor (40 and 100 nmol), injected before NMDA (50 pmol) impaired immediate DR and consequent aversive learning. The scavenging of extrasynaptic nitric oxide by C-PTIO (1 and 2 nmol) induced similar results. Moreover, spermine NONOate, a nitric oxide donor (5, 10, 20, 40, and 80 nmol), produced DR by itself, but only the low dose also promoted learning. The following experiments utilized a fluorescent probe, DAF-FM diacetate (5 µM), directly into the dlPAG, to quantify nitric oxide in the three previous experimental situations. Nitric oxide levels were increased after NMDA stimulation, decreased after 7NI, and increased after spermine NONOate, in line with alterations in defensive expression. Altogether, the results indicate that nitric oxide plays a modulatory and decisive role in the dlPAG regarding immediate DR and aversive learning.