Involvement of the insular cortex in the consolidation and expression of contextual fear conditioning

Abstract

The insular cortex (IC) has been reported to be involved in the modulation of memory and autonomic and defensive responses. However, there is conflicting evidence about the role of the IC in fear conditioning. To explore the IC involvement in both behavioral and autonomic responses induced by contextual fear conditioning, we evaluated the effects of the reversible inhibition of the IC neurotransmission through bilateral microinjections of the non-selective synapse blocker CoCl2 (1 mm) 10 min before or immediately after the conditioning session or 10 min before re-exposure to the aversive context. In the conditioning session, rats were exposed to a footshock chamber (context) and footshocks were used as the unconditioned stimulus. Forty-eight hours later, the animals were re-exposed to the aversive context for 10 min, but no shock was given. Behavioral (freezing) as well as cardiovascular (arterial pressure and heart rate increases) responses induced by re-exposure to the aversive context were analysed. It was observed that the local IC neurotransmission inhibition attenuated freezing and the mean arterial pressure and heart rate increase of the groups that received the CoCl2 either immediately after conditioning or 10 min before re-exposure to the aversive context, but not when the CoCl2 was injected before the conditioning session. These findings suggest the involvement of the IC in the consolidation and expression of contextual aversive memory. However, the IC does not seem to be essential for the acquisition of memory associated with aversive context.

Both α1- and α2-adrenoceptors in the Insular Cortex Are Involved in the Cardiovascular Responses to Acute Restraint Stress in Rats

“…It has been described that the IC is involved in cardiovascular control [13]–[15] and baroreflex modulation [16]–[19]. Furthermore, previous results from our group demonstrated that bilateral microinjection of the unspecific neurotransmitter blocker CoCl 2 into the IC of rats reduced both cardiovascular and behavioral responses evoked by either conditioned (contextual fear conditioning) or unconditioned (acute restraint stress) aversive stimuli [2], [20]. These results provided the first evidence of a role of the IC in cardiovascular adjustments during stress.…”

“…A main mediator of these latter effects is corticosteroids acting through glucocorticoid receptors [1]. Since previous studies have demonstrated a role of the IC in the memory formation for aversive threat and hypothalamus-pituitary-adrenal axis control [2], [4], [9], further studies are necessary to investigate a possible role of IC in latter consequences of restraint stress.…”

“…After a 30 s period, the needle was removed and inserted into the second guide cannula for microinjection into the contralateral IC. Drugs were injected in a final volume of 100 nl [2], [20].…”

“…During stress a spectrum of physiological responses are evoked to maintain the physiologic integrity of the organism [1]. The physiological responses to stress are mainly characterized by autonomic nervous system alterations, increase in plasma catecholamine levels and activation of the hypothalamus-pituitary-adrenal (HPA) axis [1], [2]. Autonomic responses include increase on both blood pressure and heart rate (HR) [3], [4].…”

Locus coeruleus neuromodulation of memories encoded during negative or unexpected action outcomes

“…Previous studies also implicate the insula in memory consolidation of aversive events (Alves et al, 2013) and learning to avoid negative outcomes, including monetary punishment (Samanez-Larkin et al, 2007). One previous fMRI study demonstrated that human carriers of a genetic variant linked to elevated LC-NE system output exhibit increased insula activity during negative emotional memory encoding (Rasch et al, 2009).…”