[Show abstract][Hide abstract] ABSTRACT: The mesencephalic (or midbrain) locomotor region (MLR) was first described in 1966 by Shik and colleagues, who demonstrated that electrical stimulation of this region induced locomotion in decerebrate (intercollicular transection) cats. The pedunculopontine tegmental nucleus (PPT) cholinergic neurons and midbrain extrapyramidal area (MEA) have been suggested to form the neuroanatomical basis for the MLR, but direct evidence for the role of these structures in locomotor behavior has been lacking. Here, we tested the hypothesis that the MLR is composed of non-cholinergic spinally projecting cells in the lateral pontine tegmentum. Our results showed that putative MLR neurons medial to the PPT and MEA in rats were non-cholinergic, glutamatergic, and express the orexin (hypocretin) type 2 receptors. Fos mapping correlated with motor behaviors revealed that the dorsal and ventral MLR are activated, respectively, in association with locomotion and an erect posture. Consistent with these findings, chemical stimulation of the dorsal MLR produced locomotion, whereas stimulation of the ventral MLR caused standing. Lesions of the MLR (dorsal and ventral regions together) resulted in cataplexy and episodic immobility of gait. Finally, trans-neuronal tracing with pseudorabies virus demonstrated disynaptic input to the MLR from the substantia nigra via the MEA. These findings offer a new perspective on the neuroanatomic basis of the MLR, and suggest that MLR dysfunction may contribute to the postural and gait abnormalities in Parkinsonism.
Frontiers in Neurology 06/2015; 6:140. DOI:10.3389/fneur.2015.00140
[Show abstract][Hide abstract] ABSTRACT: We have reported that glutamatergic signaling in the lateral parabrachial area that includes both the lateral crescent and external lateral PB (PBel) regulates cortical arousals to hypercapnia1. The majority of the PBel neurons express calcitonin gene-related peptide (CGRP), and are possibly a necessary relay for the hypercapnic signal to cause arousal.
Methods: We conducted optogenetic inhibition of CGRP PBel neurons selectively in CGRP-CreER mice (n=5) and tested their arousal responses to 10% CO2. On one side of the brain, we injected an adeno-associated virus containing the gene for Archaerhodopsin TP009 T in a Cre-inducible FLEX cassette (AAV-FLEX-ArchT-GFP), that expressed ArchT in CGRP+ PBel cells. On the other side we deleted the CGRP neurons by injecting a Cre dependent virus expressing the diphtheria toxin subunit A (AAV-FLEX-DTA). Mice were also instrumented for sleep recording and optogenetics. To model cyclic hypercapnia as seen during sleep apnea, we investigated EEG arousals to 10% CO2 given for 30s every 300s. We compared the cortical arousals to 10% CO2 in these mice, with and without the 593nm laser light that hyperpolarizes the CGRP-PBel neurons.
Results: Without the laser, mice showed normal responses to CO2 (arousal latency- 16.8 ± 0.6sec), and woke-up on every CO2 trial (0% failure to arouse). With 593nm laser-ON, the arousal latency increased five- fold (74.4 ± 6.9sec) and in 43.7 ± 5.2% of the trials the mice did not wake up to CO2 stimulus. ArchT-induced inhibition of CGRP-PBel had no effect on sleep and wake percentages, and on their responses to acoustic stimuli.
Conclusions: These results suggest that CGRP-PBel neurons mediate cortical EEG arousals to hypercapnia, by projecting to the lateral hypothalamus, basal forebrain, and central nucleus of amygdala. Current studies are underway to dissect the role of these targets of the CGRP-PBel neurons in CO2 arousal.
1. Kaur S et al., J.Neurosci. 2013, 33:7627-7640.
[Show abstract][Hide abstract] ABSTRACT: In the last eight years optogenetic tools have been widely used to identify functional synaptic connectivity between specific neuronal populations. Most of our knowledge comes from the photo-activation of channelrhodopsin-2 (ChR2) expressing inputs that release glutamate and GABA. More recent studies have been reporting releases of acetylcholine and biogenic amines but direct evidence for photo-evoked released of neuropeptides is still limited particularly in brain slice studies. The high fidelity in the responses with photo-evoked amino-acid transmission is ideal for ChR2-assisted circuit mapping and this approach has been successfully used in different fields of neuroscience. Conversely, neuropeptides employ a slow mode of communication and might require higher frequency and prolonged stimulations to be released. These factors may have contributed to the apparent lack of success for optogenetic release of neuropeptides. In addition, once released, neuropeptides often act on multiple sites and at various distances from the site of release resulting in a greater complexity of postsynaptic responses. Here, we focus on what optogenetics is telling us — and failing to tell us — about fast neurotransmitters and neuropeptides.
Current Opinion in Neurobiology 12/2014; 29:165–171. DOI:10.1016/j.conb.2014.07.016 · 6.63 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Since I began reading the scientific literature when I was a student, I have had a bucket list of journals that published work I admired, and in which I eventually wanted to see some of my own work published. Getting papers into some of those journals (no, I have not yet completed the list…) has been a very satisfying part of my career. Along the way, as an author, reviewer, and editor, I have learned a great deal about how to prepare a paper so that it has the best chance of making it into my journal of choice. In the first two segments of this series, we explored the peer-review process and how to choose a journal in which to publish your work. In this article, we will discuss the process of writing a research paper to maximize the chance of its being accepted in your first-choice journal. This article is protected by copyright. All rights reserved.
Annals of Neurology 11/2014; 77(1). DOI:10.1002/ana.24317 · 9.98 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Work in animals and humans has suggested the existence of a slow wave sleep (SWS)-promoting/electroencephalogram (EEG)-synchronizing center in the mammalian lower brainstem. Although sleep-active GABAergic neurons in the medullary parafacial zone (PZ) are needed for normal SWS, it remains unclear whether these neurons can initiate and maintain SWS or EEG slow-wave activity (SWA) in behaving mice. We used genetically targeted activation and optogenetically based mapping to examine the downstream circuitry engaged by SWS-promoting PZ neurons, and we found that this circuit uniquely and potently initiated SWS and EEG SWA, regardless of the time of day. PZ neurons monosynaptically innervated and released synaptic GABA onto parabrachial neurons, which in turn projected to and released synaptic glutamate onto cortically projecting neurons of the magnocellular basal forebrain; thus, there is a circuit substrate through which GABAergic PZ neurons can potently trigger SWS and modulate the cortical EEG.
[Show abstract][Hide abstract] ABSTRACT: Armodafinil is the pharmacologically active R-enantiomer of modafinil, a widely prescribed wake-promoting agent used to treat several sleep-related disorders including excessive daytime sleepiness associated with narcolepsy, shift work sleep disorder, and obstructive sleep apnea/hypopnea syndrome. Remarkably, however, the neuronal circuitry through which modafinil exerts its wake-promoting effects remains unresolved. In the present study, we sought to determine if the wake-promoting effects of armodafinil are mediated, at least in part, by inhibiting the sleep-promoting neurons of the ventrolateral preoptic (VLPO) nucleus. To do so, we measured changes in waking following intraperitoneal administration of armodafinil (200 mg/kg) or the psychostimulant methamphetamine (1 mg/kg) in rats with cell-body specific lesion of the VLPO. Rats with histologically confirmed lesions of the VLPO demonstrated a sustained increase in wakefulness at baseline, but the increase in wakefulness following administration of both armodafinil and methamphetamine was similar to that of intact animals. These data suggest that armodafinil increases wakefulness by mechanisms that extend beyond inhibition of VLPO neurons.
Nature and Science of Sleep 05/2014; 6:57-63. DOI:10.2147/NSS.S53132