A wireless and battery-less implant for multimodal closed-loop neuromodulation in small animals

Fully implantable wireless systems for the recording and modulation of neural circuits that do not require physical tethers or batteries allow for studies that demand the use of unconstrained and freely behaving animals in isolation or in social groups. Moreover, feedback-control algorithms that can be executed within such devices without the need for remote computing eliminate virtual tethers and any associated latencies. Here we report a wireless and battery-less technology of this type, implanted subdermally along the back of freely moving small animals, for the autonomous recording of electroencephalograms, electromyograms and body temperature, and for closed-loop neuromodulation via optogenetics and pharmacology. The device incorporates a system-on-a-chip with Bluetooth Low Energy for data transmission and a compressed deep-learning module for autonomous operation, that offers neurorecording capabilities matching those of gold-standard wired systems. We also show the use of the implant in studies of sleep-wake regulation and for the programmable closed-loop pharmacological suppression of epileptic seizures via feedback from electroencephalography. The technology can support a broader range of applications in neuroscience and in biomedical research with small animals.

A tool for monitoring cell type-specific focused ultrasound neuromodulation and control of chronic epilepsy

Focused ultrasound (FUS) is a powerful tool for noninvasive modulation of deep brain activity with promising therapeutic potential for refractory epilepsy; however, tools for examining FUS effects on specific cell types within the deep brain do not yet exist. Consequently, how cell types within heterogeneous networks can be modulated and whether parameters can be identified to bias these networks in the context of complex behaviors remains unknown. To address this, we developed a fiber Photometry Coupled focused Ultrasound System (PhoCUS) for simultaneously monitoring FUS effects on neural activity of subcortical genetically targeted cell types in freely behaving animals. We identified a parameter set that selectively increases activity of parvalbumin interneurons while suppressing excitatory neurons in the hippocampus. A net inhibitory effect localized to the hippocampus was further confirmed through whole brain metabolic imaging. Finally, these inhibitory selective parameters achieved significant spike suppression in the kainate model of chronic temporal lobe epilepsy, opening the door for future noninvasive therapies.

Altered sleep during spontaneous cannabinoid withdrawal in male mice

Cessation of cannabinoid use in humans often leads to a withdrawal state that includes sleep disruption. Despite important health implications, little is known about how cannabinoid abstention affects sleep architecture, in part because spontaneous cannabinoid withdrawal is difficult to model in animals. In concurrent work we report that repeated administration of the high-efficacy cannabinoid 1 (CB1) receptor agonist AM2389 to mice for 5 days led to heightened locomotor activity and paw tremor following treatment discontinuation, potentially indicative of spontaneous cannabinoid withdrawal. Here, we performed parallel studies to examine effects on sleep. Using implantable electroencephalography (EEG) and electromyography (EMG) telemetry we examined sleep and neurophysiological measures before, during, and after 5 days of twice-daily AM2389 injections. We report that AM2389 produces decreases in locomotor activity that wane with repeated treatment, whereas discontinuation produces rebound increases in activity that persist for several days. Likewise, AM2389 initially produces profound increases in slow-wave sleep (SWS) and decreases in rapid eye movement (REM) sleep, as well as consolidation of sleep. By the third AM2389 treatment, this pattern transitions to decreases in SWS and total time sleeping. This pattern persists following AM2389 discontinuation and is accompanied by emergence of sleep fragmentation. Double-labeling immunohistochemistry for hypocretin/orexin (a sleep-regulating peptide) and c-Fos (a neuronal activity marker) in lateral hypothalamus revealed decreases in c-Fos/orexin+ cells following acute AM2389 and increases following discontinuation, aligning with the sleep changes. These findings indicate that AM2389 profoundly alters sleep in mice and suggest that sleep disruption following treatment cessation reflects spontaneous cannabinoid withdrawal.

Preparation and use of wireless reprogrammable multilateral optogenetic devices for behavioral neuroscience

Wireless battery-free optogenetic devices enable behavioral neuroscience studies in groups of animals with minimal interference to natural behavior. Real-time independent control of optogenetic stimulation through near-field communication dramatically expands the realm of applications of these devices in broad contexts of neuroscience research. Dissemination of these tools with advanced functionalities to the neuroscience community requires protocols for device manufacturing and experimental implementation. This protocol describes detailed procedures for fabrication, encapsulation and implantation of recently developed advanced wireless devices in head- and back-mounted forms. In addition, procedures for standard implementation of experimental systems in mice are provided. This protocol aims to facilitate the application of wireless optogenetic devices in advanced optogenetic experiments involving groups of freely moving rodents and complex environmental designs. The entire protocol lasts ~3-5 weeks.

Wireless multilateral devices for optogenetic studies of individual and social behaviors

Advanced technologies for controlled delivery of light to targeted locations in biological tissues are essential to neuroscience research that applies optogenetics in animal models. Fully implantable, miniaturized devices with wireless control and power-harvesting strategies offer an appealing set of attributes in this context, particularly for studies that are incompatible with conventional fiber-optic approaches or battery-powered head stages. Limited programmable control and narrow options in illumination profiles constrain the use of existing devices. The results reported here overcome these drawbacks via two platforms, both with real-time user programmability over multiple independent light sources, in head-mounted and back-mounted designs. Engineering studies of the optoelectronic and thermal properties of these systems define their capabilities and key design considerations. Neuroscience applications demonstrate that induction of interbrain neuronal synchrony in the medial prefrontal cortex shapes social interaction within groups of mice, highlighting the power of real-time subject-specific programmability of the wireless optogenetic platforms introduced here.

Sleep in the United States Military

The military lifestyle often includes continuous operations whether in training or deployed environments. These stressful environments present unique challenges for service members attempting to achieve consolidated, restorative sleep. The significant mental and physical derangements caused by degraded metabolic, cardiovascular, skeletomuscular, and cognitive health often result from insufficient sleep and/or circadian misalignment. Insufficient sleep and resulting fatigue compromises personal safety, mission success, and even national security. In the long-term, chronic insufficient sleep and circadian rhythm disorders have been associated with other sleep disorders (e.g., insomnia, obstructive sleep apnea, and parasomnias). Other physiologic and psychologic diagnoses such as post-traumatic stress disorder, cardiovascular disease, and dementia have also been associated with chronic, insufficient sleep. Increased co-morbidity and mortality are compounded by traumatic brain injury resulting from blunt trauma, blast exposure, and highly physically demanding tasks under load. We present the current state of science in human and animal models specific to service members during- and post-military career. We focus on mission requirements of night shift work, sustained operations, and rapid re-entrainment to time zones. We then propose targeted pharmacological and non-pharmacological countermeasures to optimize performance that are mission- and symptom-specific. We recognize a critical gap in research involving service members, but provide tailored interventions for military health care providers based on the large body of research in health care and public service workers.

Dopamine D4 receptor excitation of lateral habenula neurons via multiple cellular mechanisms

Glutamatergic lateral habenula (LHb) output communicates negative motivational valence to ventral tegmental area (VTA) dopamine (DA) neurons via activation of the rostromedial tegmental nucleus (RMTg). However, the LHb also receives a poorly understood DA input from the VTA, which we hypothesized constitutes an important feedback loop regulating DA responses to stimuli. Using whole-cell electrophysiology in rat brain slices, we find that DA initiates a depolarizing inward current (I(DAi)) and increases spontaneous firing in 32% of LHb neurons. I(DAi) was also observed upon application of amphetamine or the DA uptake blockers cocaine or GBR12935, indicating involvement of endogenous DA. I(DAi) was blocked by D4 receptor (D4R) antagonists (L745,870 or L741,742), and mimicked by a selective D4R agonist (A412997). I(DAi) was associated with increased whole-cell conductance and was blocked by Cs+ or a selective blocker of hyperpolarization-activated cyclic nucleotide-gated (HCN) ion channel, ZD7288. I(DAi) was also associated with a depolarizing shift in half-activation voltage for the hyperpolarization-activated cation current (Ih) mediated by HCN channels. Recordings from LHb neurons containing fluorescent retrograde tracers revealed that I(DAi) was observed only in cells projecting to the RMTg and not the VTA. In parallel with direct depolarization, DA also strongly increased synaptic glutamate release and reduced synaptic GABA release onto LHb cells. These results demonstrate that DA can excite glutamatergic LHb output to RMTg via multiple cellular mechanisms. Since the RMTg strongly inhibits midbrain DA neurons, activation of LHb output to RMTg by DA represents a negative feedback loop that may dampen DA neuron output following activation.

Impaired nigrostriatal function precedes behavioral deficits in a genetic mitochondrial model of Parkinson's disease

Parkinson's disease (PD) involves progressive loss of nigrostriatal dopamine (DA) neurons over an extended period of time. Mitochondrial damage may lead to PD, and neurotoxins affecting mitochondria are widely used to produce degeneration of the nigrostriatal circuitry. Deletion of the mitochondrial transcription factor A gene (Tfam) in C57BL6 mouse DA neurons leads to a slowly progressing parkinsonian phenotype in which motor impairment is first observed at ~12 wk of age. L-DOPA treatment improves motor dysfunction in these "MitoPark" mice, but this declines when DA neuron loss is more complete. To investigate early neurobiological events potentially contributing to PD, we compared the neurochemical and electrophysiological properties of the nigrostriatal circuit in behaviorally asymptomatic 6- to 8-wk-old MitoPark mice and age-matched control littermates. Release, but not uptake of DA, was impaired in MitoPark mouse striatal brain slices, and nigral DA neurons lacked characteristic pacemaker activity compared with control mice. Also, hyperpolarization-activated cyclic nucleotide-gated (HCN) ion channel function was reduced in MitoPark DA neurons, although HCN messenger RNA was unchanged. This study demonstrates altered nigrostriatal function that precedes behavioral parkinsonian symptoms in this genetic PD model. A full understanding of these presymptomatic cellular properties may lead to more effective early treatments of PD.

NMDA receptors on non-dopaminergic neurons in the VTA support cocaine sensitization

BACKGROUND

The initiation of behavioral sensitization to cocaine and other psychomotor stimulants is thought to reflect N-methyl-D-aspartate receptor (NMDAR)-mediated synaptic plasticity in the mesolimbic dopamine (DA) circuitry. The importance of drug induced NMDAR mediated adaptations in ventral tegmental area (VTA) DA neurons, and its association with drug seeking behaviors, has recently been evaluated in Cre-loxp mice lacking functional NMDARs in DA neurons expressing Cre recombinase under the control of the endogenous dopamine transporter gene (NR1(DATCre) mice).

METHODOLOGY AND PRINCIPAL FINDINGS

Using an additional NR1(DATCre) mouse transgenic model, we demonstrate that while the selective inactivation of NMDARs in DA neurons eliminates the induction of molecular changes leading to synaptic strengthening, behavioral measures such as cocaine induced locomotor sensitization and conditioned place preference remain intact in NR1(DATCre) mice. Since VTA DA neurons projecting to the prefrontal cortex and amygdala express little or no detectable levels of the dopamine transporter, it has been speculated that NMDA receptors in DA neurons projecting to these brain areas may have been spared in NR1(DATCre) mice. Here we demonstrate that the NMDA receptor gene is ablated in the majority of VTA DA neurons, including those exhibiting undetectable DAT expression levels in our NR1(DATCre) transgenic model, and that application of an NMDAR antagonist within the VTA of NR1(DATCre) animals still blocks sensitization to cocaine.

CONCLUSIONS/SIGNIFICANCE

These results eliminate the possibility of NMDAR mediated neuroplasticity in the different DA neuronal subpopulations in our NR1(DATCre) mouse model and therefore suggest that NMDARs on non-DA neurons within the VTA must play a major role in cocaine-related addictive behavior.

Delta9-tetrahydrocannabinol is a full agonist at CB1 receptors on GABA neuron axon terminals in the hippocampus

Marijuana impairs learning and memory through actions of its psychoactive constituent, delta-9-tetrahydrocannabinol (Delta(9)-THC), in the hippocampus, through activation of cannabinoid CB1 receptors (CB1R). CB1Rs are found on glutamate and GABA neuron axon terminals in the hippocampus where they control neurotransmitter release. Previous studies suggest that Delta(9)-THC is a partial agonist of CB1Rs on glutamate axon terminals in the hippocampus, whereas its effects on GABA terminals have not been described. Using whole-cell electrophysiology in brain slices from C57BL6/J mice, we examined Delta(9)-THC effects on synaptic GABA IPSCs and postsynaptic GABA currents elicited by laser-induced photo-uncaging (photolysis) of alpha-carboxy-2-nitrobenzyl (CNB) caged GABA. Despite robust inhibition of synaptic IPSCs in wildtype mice by the full synthetic agonist WIN55,212-2, using a Tween-80 and DMSO vehicle, Delta(9)-THC had no effects on IPSCs in this, or in a low concentration of another vehicle, randomly-methylated beta-cyclodextrin (RAMEB, 0.023%). However, IPSCs were inhibited by Delta(9)-THC in 0.1% RAMEB, but not in neurons from CB1R knockout mice. Whereas Delta(9)-THC did not affect photolysis-evoked GABA currents, these responses were prolonged by a GABA uptake inhibitor. Concentration-response curves revealed that the maximal effects of Delta(9)-THC and WIN55,212-2 were similar, indicating that Delta(9)-THC is a full agonist at CB1Rs on GABA axon terminals. These results suggest that Delta(9)-THC inhibits GABA release, but does not directly alter GABA(A) receptors or GABA uptake in the hippocampus. Furthermore, full agonist effects of Delta(9)-THC on IPSCs likely result from a much higher expression of CB1Rs on GABA versus glutamate axon terminals in the hippocampus.

Properties of distinct ventral tegmental area synapses activated via pedunculopontine or ventral tegmental area stimulation in vitro

Anatomical studies indicate that synaptic inputs from many cortical and subcortical structures converge on neurons of the ventral tegmental area (VTA). Although in vitro electrophysiological studies have examined synaptic inputs to dopamine (DA) and non-DA neurons in the VTA, they have largely relied upon local electrical stimulation to activate these synapses. This provides little information regarding the distinct properties of synapses originating from different brain areas. Using whole-cell recordings in parasagittal rat brain slices that preserved subcortical axons from the pedunculopontine nucleus (PPN) to the VTA, we compared these synapses with those activated by intra-VTA stimulation. PPN-evoked currents demonstrated longer latencies than intra-VTA-evoked currents, and both VTA and PPN responses were mediated by GABA(A) and AMPA receptors. However, unlike VTA-evoked currents, PPN currents were exclusively mediated by glutamate in 25-40% of the VTA neurons. Consistent with a cholinergic projection from the PPN to the VTA, nicotinic acetylcholine receptors (nAChR) were activated by endogenous acetylcholine released during PPN, but not VTA, stimulation. This was seen as a reduction of PPN-evoked, and not VTA-evoked, synaptic currents by the alpha7-nAChR antagonist methyllycaconitine (MLA) and the agonist nicotine. The beta2-nAChR subunit antagonist dihydro-beta-erythroidine had no effect on VTA- or PPN-evoked synaptic currents. The effects of MLA on PPN-evoked currents were unchanged by the GABA(A) receptor blocker picrotoxin, indicating that alpha7-nAChRs presynaptically modulated glutamate and not GABA release. These differences in physiological and pharmacological properties demonstrate that ascending PPN and presumed descending inputs to VTA utilize distinct mechanisms to differentially modulate neuronal activity and encode cortical and subcortical information.

Muscarinic and nicotinic responses in the developing pedunculopontine nucleus (PPN)

The pedunculopontine nucleus (PPN), the cholinergic arm of the reticular activating system (RAS), is known to modulate waking and rapid eye movement (REM) sleep. REM sleep decreases between 10 and 30 days postnatally in the rat, with the majority occurring between 12 and 21 days. We investigated the possibility that changes in the cholinergic, muscarinic and/or nicotinic, input to PPN neurons could explain at least part of the developmental decrease in REM sleep. We recorded intracellularly from PPN neurons in 12-21 day rat brainstem slices maintained in artificial cerebrospinal fluid (aCSF) and found that application of the nicotinic agonist 1,1-dimethyl-4-phenyl-piperazinium iodide (DMPP) depolarized PPN neurons early in development, then hyperpolarized PPN neurons by day 21. Most of the effects of DMPP persisted following application of the sodium channel blocker tetrodotoxin (TTX), and in the presence of glutamatergic, serotonergic, noradrenergic and GABAergic antagonists, but were blocked by the nicotinic antagonist mecamylamine (MEC). The mixed muscarinic agonist carbachol (CAR) hyperpolarized all type II (A current) PPN cells and depolarized all type I (low threshold spike-LTS current) and type III (A+LTS current) PPN cells, but did not change effects during the period known for the developmental decrease in REM sleep. The effects of CAR persisted in the presence of TTX but were mostly blocked by the muscarinic antagonist atropine (ATR), and the remainder by MEC. We conclude that, while the nicotinic inputs to the PPN may help modulate the developmental decrease in REM sleep, the muscarinic inputs appear to modulate different types of cells differentially.

Alpha-2 adrenergic regulation of pedunculopontine nucleus neurons during development

Rapid eye movement sleep decreases between 10 and 30 days postnatally in the rat. The pedunculopontine nucleus is known to modulate waking and rapid eye movement sleep, and pedunculopontine nucleus neurons are thought to be hyperpolarized by noradrenergic input from the locus coeruleus. The goal of the study was to investigate the possibility that a change in alpha-2 adrenergic inhibition of pedunculopontine nucleus cells during this period could explain at least part of the developmental decrease in rapid eye movement sleep. We, therefore, recorded intracellularly in 12-21 day rat brainstem slices maintained in oxygenated artificial cerebrospinal fluid. Putative cholinergic vs. non-cholinergic pedunculopontine nucleus neurons were identified using nicotinamide adenine dinucleotide phosphate diaphorase histochemistry and intracellular injection of neurobiotin (Texas Red immunocytochemistry). Pedunculopontine nucleus neurons also were identified by intrinsic membrane properties, type I (low threshold spike), type II (A) and type III (A+low threshold spike), as previously described. Clonidine (20 microM) hyperpolarized most cholinergic and non-cholinergic pedunculopontine nucleus cells. This hyperpolarization decreased significantly in amplitude (mean+/-S.E.) from -6.8+/-1.0 mV at 12-13 days, to -3.0+/-0.7 mV at 20-21 days. However, much of these early effects (12-15 days) were indirect such that direct effects (tested following sodium channel blockade with tetrodotoxin (0.3 microM)) resulted in hyperpolarization averaging -3.4+/-0.5 mV, similar to that evident at 16-21 days. Non-cholinergic cells were less hyperpolarized than cholinergic cells at 12-13 days (-1.6+/-0.3 mV), but equally hyperpolarized at 20-21 days (-3.3+/-1.3 mV). In those cells tested, hyperpolarization was blocked by yohimbine, an alpha-2 adrenergic receptor antagonist (1.5 microM). These results suggest that the alpha-2 adrenergic receptor on cholinergic pedunculopontine nucleus neurons activated by clonidine may play only a modest role, if any, in the developmental decrease in rapid eye movement sleep. Clonidine blocked or reduced the hyperpolarization-activated inward cation conductance, so that its effects on the firing rate of a specific population of pedunculopontine nucleus neurons could be significant. In conclusion, the alpha-2 adrenergic input to pedunculopontine nucleus neurons appears to consistently modulate the firing rate of cholinergic and non-cholinergic pedunculopontine nucleus neurons, with important effects on the regulation of sleep-wake states.

Prenatal exposure to cigarette smoke affects the physiology of pedunculopontine nucleus (PPN) neurons in development

Prenatal exposure to cigarette smoke is known to produce lasting arousal, attentional and cognitive deficits in humans. The pedunculopontine nucleus (PPN), as the cholinergic arm of the reticular activating system (RAS), is known to modulate arousal, waking and rapid eye movement (REM) sleep. REM sleep decreases between 10 and 30 days postnatally in the rat, especially at 12-21 days. Pregnant dams were exposed to 350 ml of cigarette smoke for 15 min, 3 times per day, from day E14 until birth, and the pups allowed to mature. Intracellularly recorded PPN neurons in 12-21 day rat brainstem slices were tested for intrinsic membrane properties, including the hyperpolarization-activated cation current Ih, which is known to drive oscillatory activity. Type II (A-current) PPN cells from 12-16 day old offspring of treated animals had a 1/2max Ih amplitude of (mean +/- SE) 4.1 +/- 0.9 mV, while 17-21 day cells had a higher 1/2max Ih of 9.9 +/- 1.1 mV (p < 0.0001). Cells from 12-16 day old control brainstems had a 1/2max Ih of 1.3 +/- 0.1 mV, which was lower (p < 0.05) than in cells from prenatally treated offspring; while 17-21 day old cells from controls had a 1/2max Ih of 3.3 +/- 0.3 mV, which was also lower (p < 0.01) than in cells from prenatally treated offspring. In addition, changes in resting membrane potential [control -65. +/- 0.9 mV (n=32); exposed -55.0 +/- 1.4 mV (n = 27) (p < 0.0001)], and action potential (AP) threshold [control -56.5 +/- 0.7 mV (n = 32), exposed -47.0 +/- 1.4 mV (n = 27) (p < 0.0001)], suggest that prenatal exposure to cigarette smoke induced marked changes in cells in the cholinergic arm of the RAS, rendering them more excitable. Such data could partially explain the differences seen in individuals whose parents smoked during pregnancy, especially in terms of their hypervigilance and increased propensity for attentional deficits and cognitive/behavioral disorders.