Interoceptive insular cortex participates in sensory processing of gastrointestinal malaise and associated behaviors

Endocannabinoid signaling in stress, nausea, and vomiting

BACKGROUND

Classical antiemetics that target the serotonin system may not be effective in treating certain nausea and vomiting conditions like cyclic vomiting syndrome (CVS) and cannabinoid hyperemesis syndrome (CHS). As a result, there is a need for better therapies to manage the symptoms of these disorders, including nausea, vomiting, and anxiety. Cannabis is often used for its purported antiemetic and anxiolytic effects, given regulation of these processes by the endocannabinoid system (ECS). However, there is considerable evidence that cannabinoids can also produce nausea and vomiting and increase anxiety in certain instances, especially at higher doses. This paradoxical effect of cannabinoids on nausea, vomiting, and anxiety may be due to the dysregulation of the ECS, altering how it maintains these processes and contributing to the pathophysiology of CVS or CHS.

PURPOSE

The purpose of this review is to highlight the involvement of the ECS in the regulation of stress, nausea, and vomiting. We discuss how prolonged cannabis use, such as in the case of CHS or heightened stress, can dysregulate the ECS and affect its modulation of these functions. The review also examines the evidence for the roles of ECS and stress systems' dysfunction in CVS and CHS to better understand the underlying mechanisms of these conditions.

Bilateral insular cortical lesions reduce sensitivity to the adverse consequences of acute ethanol intoxication in Pavlovian conditioning procedures

BACKGROUND

Sensitivity to the adverse post-ingestive effects of ethanol likely serves as a deterrent to initiate alcohol consumption early in drinking and later may contribute to efforts to remain abstinent. Administering ethanol to naïve rats prior to Pavlovian conditioning procedures elicits robust ethanol-conditioned taste and place avoidance (CTA; CPA) mediated by its subjective interoceptive properties. The insular cortex (IC) has been implicated as a region involved in mediating sensitivity to the interoceptive properties of ethanol. Here, we examined whether bilateral lesions of the IC affect the acquisition and expression of taste and place avoidance in ethanol-induced CTA and CPA paradigms.

METHODS

Adult male and female Wistar rats received bilateral excitotoxic lesions (ibotenic acid; 20 mg/mL; 0.3 μL) of the IC prior to conditioning procedures. Subsequently, rats were conditioned to associate a novel taste stimulus (0.1% saccharin) and context with the effects of ethanol (1.0 g/kg) in a combined CTA/CPP procedure. Conditioning occurred over 8 alternating CS+/CS- days, followed by tests for expression of taste and place preferences. Data from IC-lesioned rats were compared with neurologically intact rats.

RESULTS

Our findings revealed that neurologically intact rats showed a significantly stronger ethanol-induced CTA than IC-lesioned rats. There were no significant differences in total fluid intake when rats consumed water (CS-). As with CTA effects, intact rats showed a strong CPA, marked by a greater reduction in time spent on the drug-paired context, while IC-lesioned rats failed to display CPA to ethanol.

CONCLUSION

These results indicate that proper IC functioning is necessary for responding to the adverse interoceptive properties of ethanol regardless of which Pavlovian paradigm is used to assess interoceptive responsivity to ethanol. Blunted IC functioning from chronic ethanol use may reduce interoceptive signaling specifically of ethanol's adverse effects thus contributing to increased alcohol use.

Chemogenetic Modulation of Posterior Insula CaMKIIa Neurons Alters Pain and Thermoregulation

The posterior insular cortex (PIC) is well positioned to perform somatosensory-limbic integration; yet, the function of neuronal subsets within the PIC in processing the sensory and affective dimensions of pain remains unclear. Here, we employ bidirectional chemogenetic modulation to characterize the function of PIC CaMKIIa-expressing excitatory neurons in a comprehensive array of sensory, affective, and thermoregulatory behaviors. Excitatory pyramidal neurons in the PIC were found to be sensitized under inflammatory pain conditions. Chemogenetic activation of excitatory CaMKIIa-expressing PIC neurons in non-injured conditions produced an increase in reflexive and affective pain- and anxiety-like behaviors. Moreover, activation of PIC CaMKIIa-expressing neurons during inflammatory pain conditions exacerbated hyperalgesia and decreased pain tolerance. However, Chemogenetic activation did not alter heat nociception via hot plate latency or body temperature. Conversely, inhibiting CaMKIIa-expressing neurons did not alter either sensory or affective pain-like behaviors in non-injured or under inflammatory pain conditions, but it did decrease body temperature and decreased hot plate latency. Our findings reveal that PIC CaMKIIa-expressing neurons are a critical hub for producing both sensory and affective pain-like behaviors and important for thermoregulatory processing. PERSPECTIVE: The present study reveals that activation of the posterior insula produces hyperalgesia and negative affect, and has a role in thermal tolerance and thermoregulation. These findings highlight the insula as a key player in contributing to the multidimensionality of pain.

The basolateral amygdala to posterior insular cortex tract is necessary for social interaction with stressed juvenile rats

Vocalizations, chemosignals, and behaviors are influenced by one's internal affective state and are used by others to shape social behaviors. A network of interconnected brain structures, often called the social behavior network or social decision-making network, integrates these stimuli and coordinates social behaviors, and in-network connectivity deficits underlie several psychiatric disorders such as schizophrenia and autism spectrum disorders. Here, we investigated the role of the basolateral amygdala (BLA) and its projections to the posterior insular cortex, regions independently implicated in a range of sociocognitive processes, in a social affective preference (SAP) test. Viral vectors containing the gene coding for inhibitory chemogenetic receptors (AAV5-hSyn-hM4Di-mCherry) were injected into the BLA. SAP tests, which allow for the observation of unconditioned behavioral responses to the affective states of others, were conducted after inhibition of the BLA by systemic administration of the hM4Di agonist clozapine-n-oxide (CNO), or inhibition of BLA-insula terminals by direct infusion of CNO to the insula. After vehicle infusions, rats displayed preference for interactions with stressed juvenile conspecifics. However, CNO treatment eliminated preference behavior. The current results suggest that social decision making involves the transfer of emotional information from the BLA to the insula which represents a previously unrecognized anatomical substrate for social cognition.

Functional brain-wide network mapping during acute stress exposure in rats: Interaction between the lateral habenula and cortical, amygdalar, hypothalamic and monoaminergic regions

Upon stress exposure, a broad network of structures comes into play in order to provide adequate responses and restore homeostasis. It has been known for decades that the main structures engaged during the stress response are the medial prefrontal cortex, the amygdala, the hippocampus, the hypothalamus, the monoaminergic systems (noradrenaline, dopamine and serotonin) and the periaqueductal gray. The lateral habenula (LHb) is an epithalamic structure directly connected to prefrontal cortical areas and to the amygdala, whereas it functionally interacts with the hippocampus. Also, it is a main modulator of monoaminergic systems. The LHb is activated upon exposure to basically all types of stressors, suggesting it is also involved in the stress response. However, it remains unknown if and how the LHb functionally interacts with the broad stress response network. In the current study we performed in rats a restraint stress procedure followed by immunohistochemical staining of the c-Fos protein throughout the brain. Using graph theory-based functional connectivity analyses, we confirm the principal hubs of the stress network (e.g., prefrontal cortex, amygdala and periventricular hypothalamus) and show that the LHb is engaged during stress exposure in close interaction with the medial prefrontal cortex, the lateral septum and the medial habenula. In addition, we performed DREADD-induced LHb inactivation during the same restraint paradigm in order to explore its consequences on the stress response network. This last experiment gave contrasting results as the DREADD ligand alone, clozapine-N-oxide, was able to modify the network.

LiCl-induced sickness modulates rat gustatory cortical responses

Gustatory cortex (GC), a structure deeply involved in the making of consumption decisions, presumably performs this function by integrating information about taste, experiences, and internal states related to the animal's health, such as illness. Here, we investigated this assertion, examining whether illness is represented in GC activity, and how this representation impacts taste responses and behavior. We recorded GC single-neuron activity and local field potentials (LFPs) from healthy rats and rats made ill (via LiCl injection). We show (consistent with the extant literature) that the onset of illness-related behaviors arises contemporaneously with alterations in 7 to 12 Hz LFP power at approximately 12 min following injection. This process was accompanied by reductions in single-neuron taste response magnitudes and discriminability, and with enhancements in palatability-relatedness-a result reflecting the collapse of responses toward a simple "good-bad" code visible in the entire sample, but focused on a specific subset of GC neurons. Overall, our data show that a state (illness) that profoundly reduces consumption changes basic properties of the sensory cortical response to tastes, in a manner that can easily explain illness' impact on consumption.

Fear balance is maintained by bodily feedback to the insular cortex in mice

[Figure: see text].

Cellular activity in insular cortex across seconds to hours: Sensations and predictions of bodily states

Our wellness relies on continuous interactions between our brain and body: different organs relay their current state to the brain and are regulated, in turn, by descending visceromotor commands from our brain and by actions such as eating, drinking, thermotaxis, and predator escape. Human neuroimaging and theoretical studies suggest a key role for predictive processing by insular cortex in guiding these efforts to maintain bodily homeostasis. Here, we review recent studies recording and manipulating cellular activity in rodent insular cortex at timescales from seconds to hours. We argue that consideration of these findings in the context of predictive processing of future bodily states may reconcile several apparent discrepancies and offer a unifying, heuristic model for guiding future work.