Nucleus incertus promotes cortical desynchronization and behavioral arousal

Abstract

Arousal and vigilance are essential for survival and relevant regulatory neural circuits lie within the brainstem, hypothalamus and forebrain. The nucleus incertus (NI) is a distinct site within the pontine periventricular gray, containing a substantial population of GABAergic neurons with long-range, ascending projections. Existing neuroanatomical data and functional studies in anesthetized rats, suggest the NI is a central component of a midline behavioral control network well positioned to modulate arousal, vigilance and exploratory navigation, yet none of these roles have been established experimentally. We used a chemogenetic approach-clozapine-N-oxide (CNO) activation of virally delivered excitatory hM3Dq-DREADDs-to activate the NI in rats and examined the behavioral and physiological effects, relative to effects in naïve rats and appropriate viral-treated controls. hM3Dq activation by CNO resulted in long-lasting depolarization of NI neurons with action potentials, in vitro. Peripheral injection of CNO significantly increased c-Fos immunoreactivity in the NI and promoted cortical electroencephalograph (EEG) desynchronization. These brain changes were associated with heightened arousal, and increased locomotor activity in the homecage and in a novel environment. Furthermore, NI activation altered responses in a fear conditioning paradigm, reflected by increased head-scanning, vigilant behaviors during conditioned fear recall. These findings provide direct evidence that the NI promotes general arousal via a broad behavioral activation circuit and support early hypotheses, based on its connectivity, that the NI is a modulator of cognition and attention, and emotional and motivated behaviors.

Chronic activation of the relaxin‐3 receptor on GABA neurons in rat ventral hippocampus promotes anxiety and social avoidance

“…Recent studies have established a role for relaxin-3/RXFP3 signaling in the regulation of the septohippocampal system, hippocampal theta rhythm, and spatial memory, via actions in the MS and dorsal hippocampus (Albert-Gasco et al, 2017;Haidar et al, 2017;Ma, Blasiak, Olucha-Bordonau, Verberne, & Gundlach, 2013;Ma, Olucha-Bordonau, et al, 2009). Furthermore, chemogenetic activation of NI neurons altered hippocampal activity and theta rhythm, and increased risk assessment behavior, consistent with an influence of NI GABA and relaxin-3 transmission on affective and cognitive processes (Ma et al, 2017). Notably, all clinically effective anxiolytic drugs reduce the average frequency of brain theta activity, despite their substantial neurochemical dissimilarities (McNaughton & Gray, 2000;McNaughton, Kocsis, & Hajos, 2007), suggesting that relaxin-3 modulation of hippocampal theta rhythm may also impact anxiety.…”

“…Therefore, in the future, it will be of interest to determine which SST/GABA and PV/GABA neuron populations are altered by endogenous RXFP3 signaling and how this underlies different behavioral states. It will also be important to further assess the effect of RXFP3 activation on the neurophysiological activity of the hippocampus under conditions such as the home cage and in tests of anxiety or social interaction, including recordings of local field potentials and hippocampal theta (Klausberger et al, , ), since suppression of hippocampal theta is a well‐established feature of anxiolytic agents, while its elevation is associated with anxiety; and recent evidence confirms a strong association between a major group of relaxin‐3 neurons in the NI and likely relaxin‐3/RXFP3‐mediated modulation of hippocampal theta (Ma & Gundlach, ; Ma, Shen, Sang, Lanciego, & Gundlach, ; Ma et al, ; Martínez‐Bellver et al, ).…”

Muscarinic receptors regulate auditory and prefrontal cortical communication during auditory processing

“…To address this, we characterized the strength of cortical desynchrony during the ITI as a proxy for engagement to the stimulus. Cortical desynchrony is associated with increased locomotion and generalized activity (Ma et al, 2017;Poulet and Petersen, 2008) and has been used as a measure of general arousal (Ma et al, 2017;Shinba et al, 2000). Given that cortical desynchrony has also been implicated in improving sensory responses (Goard and Dan, 2009;Kalmbach and Waters, 2014;Metherate and Ashe, 1993;Pinto et al, 2013), we assessed the strength of cortical desynchrony across mice, and across trials, to determine how the strength of cortical desynchrony preceding sound onset may influence the strength of the PFC response.…”

CRF and the nucleus incertus: a node for integration of stress signals

“…Electrolytic lesioning of the NI 8 and selective ablation of CRFR1-positive NI neurons using CRFsaporin 9 cause deficits in fear extinction without impairing initial conditioning. Moreover, selective pharmacogenetic activation of NI neurons causes enhanced arousal, locomotion, vigilance and active responding behaviours during fear conditioning 10 . CRF infusion into, or electrical stimulation of, the NI impairs long-term potentiation (LTP) of hippocampal-medial prefrontal cortical synapses 11 , whereas intra-NI infusion of the CRFR1 antagonist antalarmin reversed stress-induced suppression of LTP in this pathway 12 .…”

“…Intra-NI infusion of the CRFR1 antagonist CP-376395, but not the CRFR2 antagonist astressin 2B, considerably reduced the reinstatement of alcohol seeking in rats that was induced by administration of the pharmacological stressor yohimbine 13 -an effect that is probably mediated by CRFR1 activation of relaxin-3-positive NI neurons 6,14 . The NI is therefore a stressresponsive nucleus and, through CRFR1, contributes to memory and learning, stressinduced reward seeking, impairments in neuronal plasticity, and arousal behaviours [9][10][11][12][13] .…”