Dynorphin inhibits basal forebrain cholinergic neurons by pre‐ and postsynaptic mechanisms

Abstract

Key pointsr The basal forebrain is an important component of the ascending arousal system and may be a key site through which the orexin neurons promote arousal.r It has long been known that orexin-A and -B excite basal forebrain cholinergic neurons, but orexin-producing neurons also make the inhibitory peptide dynorphin.r Using whole-cell recordings in brain slices, we found that dynorphin-A directly inhibits basal forebrain cholinergic neurons via κ-opioid receptors, and decreases afferent excitatory synaptic input to these neurons.r While the effects of dynorphin-A and orexin-A desensitize over multiple applications, co-application of dynorphin-A and orexin-A produces a sustained response that reverses depending on the membrane potential of basal forebrain cholinergic neurons. At −40 mV the net effect of the co-application is inhibition by dynorphin-A, whereas at −70 mV the excitatory response to orexin-A prevails.Abstract The basal forebrain (BF) is an essential component of the ascending arousal systems and may be a key site through which the orexin (also known as hypocretin) neurons drive arousal and promote the maintenance of normal wakefulness. All orexin neurons also make dynorphin, and nearly all brain regions innervated by the orexin neurons express kappa opiate receptors, the main receptor for dynorphin. This is remarkable because orexin excites target neurons including BF neurons, but dynorphin has inhibitory effects. We identified the sources of dynorphin input to the magnocellular preoptic nucleus and substantia innominata (MCPO/SI) in mice and determined the effects of dynorphin-A on MCPO/SI cholinergic neurons using patch-clamp recordings in brain slices. We found that the orexin neurons are the main source of dynorphin input to the MCPO/SI region, and dynorphin-A inhibits MCPO/SI cholinergic neurons through κ-opioid receptors by (1) activation of a G protein-coupled inwardly rectifying potassium current, (2) inhibition of a voltage-gated Ca 2+ current and (3) presynaptic depression of the glutamatergic input to these neurons. The responses both to dynorphin-A and to orexin-A desensitize, but co-application of dynorphin-A and orexin-A produces a sustained response. In addition, the polarity of the response to the co-application depends on the membrane potential of BF neurons; at −40 mV the net effect of the co-application is inhibition by dynorphin-A, whereas at −70 mV the excitatory response to orexin-A prevails. This suggests that depending on their state of activation, BF cholinergic neurons can be excited or inhibited by signals from the orexin neurons.

Dynorphin Counteracts Orexin in the Paraventricular Nucleus of the Thalamus: Cellular and Behavioral Evidence

“…neurons (Li and van den Pol, 2006) and counterbalance the response to Orx in basal forebrain neurons, preventing overexcitation (Ferrari et al, 2016). Importantly, our cellular findings are consistent with the behavioral data, indicating a functional interaction between the Orx and Dyn systems.…”

Galanin neurons in the ventrolateral preoptic area promote sleep and heat loss in mice

“…Three to eight weeks after AAV-ChR2-mCherry/AAV-ArchT-GFP virus injections into the VLPO, GAL-cre mice ( n = 3 for ChR2; n = 3 for ArchT) were anesthetized with isoflurane (>4%) and brain slices containing the VLPO (250 µm thick) were prepared for in vitro electrophysiological recordings 69 . Whole-cell current clamp recordings 69 were performed from VLPO GAL neurons expressing ChR2 or ArchT (identified by mCherry or GFP fluorescence, respectively) using a Multiclamp 700B amplifier (Molecular Devices, Foster City, CA, USA), a Digidata 1322 A interface, and Clampex 9.0 software (Molecular Devices).…”

Melanin-concentrating hormone neurons specifically promote rapid eye movement sleep in mice

“…4 weeks after these injections, these mice were sacrificed and LH slices (250 μm) were prepared for electrophysiological recordings as described earlier (Ferrari et al, 2016). Whole cell current clamp recordings were then performed on the mCherry+ neurons (n=8) using a Multiclamp 700B amplifier (Molecular Devices, Foster City, CA, USA), a Digidata 1322A interface and Clampex 9.0 software (Molecular Devices) as detailed in our previous publications (Ferrari et al, 2016). After achieving stable whole cell recordings from MCH neurons for 15 minutes, artificial cerebrospinal fluid (ACSF) solution containing 500 nM CNO was perfused through the chamber and recordings continued for 5 min before the CNO was washed out by ACSF.…”