Norepinephrine Infusion into Nucleus Basalis Elicits Microarousal in Desflurane-anesthetized Rats

Abstract

Background The nucleus Basalis of Meynert of the basal forebrain has been implicated in the regulation of the state of consciousness across normal sleep-wake cycles. Here we investigated its role in the modulation of general anesthesia. Methods Rats were chronically implanted with bilateral infusion cannulae in the nucleus Basalis of Meynert and epidural electrodes to record the electroencephalogram in frontal and visual cortices. Animals were anesthetized with desflurane at a concentration required for the loss of righting reflex (4.6 ± 0.5%). Norepinephrine (17.8 nmol), or artificial cerebrospinal fluid was infused at 0.2 µl/min (1 µl total). Behavioral response to infusion was measured by scoring the orofacial, limb and head movements, and postural changes. Results Behavioral responses were higher after norepinephrine (2.1 ± 1) than artificial cerebrospinal fluid (0.63 ± 0.8) infusion (p < 0.01, t-test). Responses were brief (1–2 minutes), repetitive and more frequent after norepinephrine infusion (p < 0.0001, chi-square test). Electroencephalogram δ power decreased after norepinephrine in frontal (70 ± 7%) but not in visual cortex (p < 0.05, t-test). Simultaneously, electroencephalogram cross-approximate entropy between frontal and visual cortices increased from 3.17 ± 0.56 to 3.85 ± 0.29 after norepinephrine infusion (p < 0.01, t-test). Behavioral activation was predictable by the decrease in frontal δ power (logistic regression, p < 0.05). Conclusions Norepinephrine infusion into the nucleus Basalis of Meynert can modulate anesthetic depth presumably by ascending activation of the cortex. The transient nature of the responses suggests a similarity with micro-arousals normally observed during natural sleep, and may imply a mechanism for transient awareness under light anesthesia.

α2-Adrenergic Stimulation of the Ventrolateral Preoptic Nucleus Destabilizes the Anesthetic State

“…It is possible that norepinephrine itself failed to induce arousal in mice as a result of opposing actions within the VLPO microenvironment, which was the intended target of cannula drug delivery. Such an effect could potentially be mediated by the isoflurane-non-activated subset of VLPO cells or by off-target actions of the single, high concentration of norepinephrine chosen based on the literature (Pillay et al, 2011). A complete neurotransmitter receptor profile would be required to determine all of the VLPO targets on which norepinephrine may be working along with a full dose-response curve, but it is beyond the scope of this study.…”

“…When dexmedetomidine was administered during the deeper plane of 1.0% isoflurane, corresponding to an EC 1 for spontaneous return of righting, no arousing response was seen despite the ability of dexmedetomidine to reverse isoflurane-induced activation of VLPO neurons in vitro at an even higher anesthetic concentration. This suggests that the VLPO may contribute to the transition between arousal states but that recruitment of other brain regions, neurotransmitter systems, and protein targets are likely necessary to enact a full return to arousal (Alkire et al, 2007(Alkire et al, , 2009Kelz et al, 2008;Pillay et al, 2011;Solt et al, 2011;Taylor et al, 2013;van Swinderen and Kottler, 2014). Although global modulation of adrenergic signaling affects both anesthesia induction and emergence and local activation of the locus ceruleus powerfully facilitates emergence, local modulation of adrenergic signaling within the basal forebrain could only elicit transient microarousals (Mason et al, 1983;Kushikata et al, 2011;Pillay et al, 2011;Hu et al, 2012; Vazey and Aston-Jones, 2014).…”

“…This suggests that the VLPO may contribute to the transition between arousal states but that recruitment of other brain regions, neurotransmitter systems, and protein targets are likely necessary to enact a full return to arousal (Alkire et al, 2007(Alkire et al, , 2009Kelz et al, 2008;Pillay et al, 2011;Solt et al, 2011;Taylor et al, 2013;van Swinderen and Kottler, 2014). Although global modulation of adrenergic signaling affects both anesthesia induction and emergence and local activation of the locus ceruleus powerfully facilitates emergence, local modulation of adrenergic signaling within the basal forebrain could only elicit transient microarousals (Mason et al, 1983;Kushikata et al, 2011;Pillay et al, 2011;Hu et al, 2012; Vazey and Aston-Jones, 2014). Hence, a major unanswered question remains regarding the adrenoceptive neuronal targets capable of eliciting a complete response.…”

“…The qualitative test relied on the return of the righting reflex, a common surrogate readout for restoration of consciousness in rodents. Although the definition of this test was expanded to consider mice that made a clear effort to right as responsive, the readout was still binary and failed to address the significance of smaller behaviors that may be associated with arousal, such as facial grooming and tail swinging (Pillay et al, 2011). For this reason, the percentage of time spent moving before and after drug injections was also examined.…”

Optogenetic activation of dopamine neurons in the ventral tegmental area induces reanimation from general anesthesia

“…A variety of experimental approaches have been used to study the neural circuits that underlie anesthetic-induced unconsciousness and recovery of consciousness in rodents, including designer receptors exclusively activated by designer drugs (DREADDs) (35), genetic manipulations (36), local and systemic drug administration (10,(37)(38)(39), microdialysis (40,41), targeted brain lesions (42,43), and electrical stimulation (34). Optogenetics is a novel tool that provides distinct advantages over previous techniques used to study anesthetic-induced unconsciousness and recovery of consciousness in rodents.…”