Fiber Photometry publications

Deep Brain Stimulation (DBS) of the superolateral medial forebrain bundle has shown promising long-term anti-depressant effects in treatment-resistant depression patients, although the mechanisms are not clear. The study explored medial forebrain bundle DBS mediated modulation of central noradrenaline transmission in a rodent depression model, the Flinders Sensitive Line (FSL), and in controls, Sprague Dawley (SD) rats. In vivo noradrenergic signaling in the prefrontal cortex (PFC) and nucleus accumbens (NAc) and ultrasonic vocalization were monitored during unilateral mfb-DBS across diverse stimulation parameters. The fiber amount, myelination status, and the activation of ascending projected noradrenergic cell groups (A1, A2, A6) were quantified. Moreover, stimulation induced changes in the parvalbumin-mediated feedforward microcircuitry and neuron activation at PFC and NAc were assessed. FSL rats showed decrease in NA fibers in mfb. Stimulation increased PFC noradrenergic signaling similarly across both groups compared to baseline, but in the NAc, the FSLs had notably higher signaling compared with SDs. FSLs demonstrated more positive affective ultrasonic vocalizations post-DBS than SDs. Brainstem nuclei A1 and A2 had similar noradrenergic neuron density across the experimental groups, and mfb DBS increased neuronal activation in both groups. FSLs had fewer noradrenergic neurons in the A6 nuclei, fewer unmyelinated noradrenergic fibers traversing the mfb, and decreased parvalbumin interneuron activity in both PFC and NAc. DBS normalized parvalbumin interneuron activity in the FSL rats. The study proposes that mfb DBS, via the modulation of the central NA system and the GABAergic inhibitory control of neural excitability, likely contributes to the anti-depressant therapeutic mechanisms reported in both clinical and experimental studies.

How Δ 9 -tetrahydrocannabinol (THC) impairs natural behaviors in mice remains unknown. We developed a video-monitored behavioral platform with machine learning classifiers to unravel discrete changes in natural mouse behaviors. THC infusion into the medial prefrontal cortex (mPFC) disrupted walking kinematic features characteristic of impairment responses. THC predominantly increased mPFC GABAergic activity preceding walk initiation shifting the mPFC excitatory/inhibitory (E/I) balance. Pose-defined closed loop photo-stimulation of mPFC GABAergic neurons demonstrated that THC exacerbates selected parameters of motor impairment. Surprisingly, THC also induced a time locked, movement-induced, transient potentiation of mPFC endocannabinoid (eCB) release and ensuing CB 1 R-mediated synaptic inhibition. Here we establish that THC-modifies mPFC E/I balance to excitation via dynamic changes in eCB release which acts to induce behavioral impairment.

The locus coeruleus–norepinephrine (LC-NE) system regulates arousal and awakening; however, it remains unclear whether the LC does this in a global or circuit-specific manner. We hypothesized that sensory-evoked awakenings are predominantly regulated by specific LC-NE efferent pathways. Anatomical, physiological, and functional modularities of LC-NE pathways involving the mouse basal forebrain (BF) and pontine reticular nucleus (PRN) were tested. We found partial anatomical segregation between the LC → PRN and LC → BF circuits. Extracellular NE dynamics in BF and PRN exhibited distinct sound-evoked activation during sleep, including a fast sound-evoked NE peak specific to PRN. Causal optogenetic interrogation of LC efferent pathways, by retro-channelrhodopsin (ChR2) activation or Platynereis dumerilii ciliary opsin (PdCO) silencing of synapses in target regions, revealed a role for early LC → PRN activity in driving arousal and sound-evoked awakenings. Together, our results uncover a role for early LC-NE PRN activity in connecting sensory and arousal pathways and establish LC heterogeneity in regulating arousal.

In the hippocampal formation, cholinergic modulation from the medial septum/diagonal band of Broca is known to correlate with the speed of an animal's movements at subsecond timescales and also supports spatial memory formation. Yet, the extent to which subsecond cholinergic dynamics, if at all, align with transient behavioral and cognitive states supporting the encoding of novel spatial information remains unknown. In this study, we used fiber photometry to record the temporal dynamics in the population activity of septo-hippocampal cholinergic neurons at subsecond resolution during a hippocampus-dependent object location memory task using ChAT-Cre mice of both sexes. Using a linear mixed-effects model, we quantified the extent to which cholinergic dynamics were explained by changes in movement speed; behavioral states such as locomotion, grooming, and rearing; and hippocampus-dependent cognitive states such as recognizing a novel location of a familiar object. The data show that cholinergic dynamics contain a multiplexed code of fast and slow signals (1) coding for the logarithm of movement speed at subsecond timescales, (2) providing a phasic spatial novelty signal during the brief periods of exploring a novel object location, and (3) coding for recency of environmental change at a seconds-long timescale. Furthermore, behavioral event-related phasic cholinergic activity demonstrates that fast cholinergic transients correlate with a switch in cognitive and behavioral states. These findings enhance understanding of the mechanisms by which cholinergic modulation contributes to the coding of movement speed and encoding of novel spatial information.

Behavioural adaptations to environmental threats are crucial for survival1,2 and necessitate rapid deployment of energy reserves3-5. The amygdala coordinates behavioural adaptations to threats6, but little is known about its involvement in underpinning metabolic adaptations. Here we show that acute stress activates medial amygdala (MeA) neurons that innervate the ventromedial hypothalamus (MeAVMH neurons), which precipitates hyperglycaemia and hypophagia. The glycaemic actions of MeAVMH neurons occur independently of adrenal or pancreatic glucoregulatory hormones. Using whole-body virus tracing, we identify a polysynaptic connection from MeA to the liver that promotes the rapid synthesis of glucose by hepatic gluconeogenesis. Repeated stress exposure disrupts MeA control of blood glucose, resulting in diabetes-like dysregulation of glucose homeostasis. Our findings reveal an amygdala-liver axis that regulates rapid glycaemic adaptations to stress and links recurrent stress to metabolic dysfunction.

Internal motive states, such as sexual arousal, drive behaviour in response to social cues. However, little is known about how internal states and external cues are integrated to release appropriate behaviours at the correct moment during a social interaction, such as the transition from the appetitive to the consummatory phases of mating 1,2 . Here we identify a neural circuit in male mice that gates the onset of consummatory reproductive behaviours on contact with a mating partner. Stimulating MPOA Esr1 ∩ Vgat hypothalamic neurons promotes mounting of conspecifics and three-dimensional dummy objects 3 . We find that such mounting depends on mechanosensory but not visual cues. Through a large-scale electrophysiological screen, we identify neurons in the subparafascicular thalamic nucleus that nonlinearly integrate medial preoptic area of the hypothalamus (MPOA) and mechanosensory input to encode contact with a potential mate. Circuit tracing and perturbations demonstrated that this conjunctive coding occurs by means of convergent disinhibition from MPOA and excitation from the spinal trigeminal nucleus. Functional manipulations and calcium recordings showed these social-contact neurons, marked by parathyroid hormone 2, were essential for and able to promote mounting. These data indicate that subparafascicular thalamic nucleus-parathyroid hormone 2 neurons integrate internal drive with social touch to trigger mounting at opportune moments during mating. More generally, our findings uncover a brain mechanism whereby an internal state can attribute a social quality to a generic touch to initiate purposeful reproductive actions.

An adverse gestational environment is a risk factor for the development of psychiatric disorders. Although studies have implicated modifications in neuronal DNA and chromatin, how these changes come about and lead to abnormal behaviors is not known. We sought to identify persistent DNA/chromatin and transcriptomic signatures induced by a proinflammatory gestational environment in the ventral dentate gyrus (vDG), a hippocampal region linked to anxiety. A proinflammatory environment shifted DNA methylation of enhancers and promoters and altered synapse-related gene expression, resulting in transcriptional heterogeneity in the vDG. In animals with prior adversity, exposure to a threatening environment recruited vDG neurons with the greatest transcriptional changes, notably in synapse-relevant genes that also tended to be differentially methylated. Finally, vDG activity was increased during transition from a safe to a threatening environment in animals with prior adversity but not in controls, suggesting their enhanced perception of a potential threat. Our data outline a proinflammatory gestational environment-induced neurobiological sequence that leads to anxiety.

Nicotine is one of the most widely used addictive substances, yet its primary reinforcing effects are relatively weak. Nicotine's ability to potentiate responding for conditioned reinforcers is thought to drive persistent drug use. Here, we show that nicotine failed to alter responding maintained by a primary sucrose reinforcer (under a variable-ratio [VR] 11 schedule) across a broad dose range (0.01-1.0 mg/kg). Yet, nicotine enhanced operant behavior under a second-order reinforcement schedule in which responses produced sucrose-associated cues and were only intermittently reinforced by sucrose itself. Together, we demonstrate that nicotine selectively augments behavior maintained by conditioned reinforcers (sucrose-associated cues) in a rate-dependent manner, increasing responding only in mice with low rates of reinforcement behavior at baseline. Using fiber photometry, we demonstrate that nicotine selectively amplified cue-evoked dopamine release in the dorsolateral striatum-but only in low baseline responders-while having no effect on dopamine signaling in the nucleus accumbens. These effects were blocked by the nicotinic receptor antagonist mecamylamine. Further, nicotine's influence on behavior was abolished when the contingency between action and conditioned stimuli was disrupted, indicating that nicotine strengthens cue control of behavior rather than increasing motivation generally. Collectively, these findings reveal that nicotine's behavioral actions emerge through an interaction between pharmacological mechanisms, behavioral contingencies, and individual differences in baseline behavioral control. SIGNIFICANCE STATEMENT: Nicotine strengthens the impact of environmental cues on behavior by amplifying dopamine signals in specific projection targets, but only in individuals with specific behavioral traits. This reveals how nicotine hijacks learning processes to promote persistent, cue-driven actions.

Chemical feedback is ubiquitous in physiology but is challenging to study without perturbing basal functions. One example is addictive drugs, which elicit a positive-feedback cycle of drug-seeking and ingestion by acting on the brain to increase dopamine signalling 1–3 . However, interfering with this process by altering basal dopamine also adversely affects learning, movement, attention and wakefulness 4 . Here, inspired by physiological control systems, we developed a highly selective synthetic physiology approach to interfere with the positive-feedback cycle of addiction by installing a cocaine-dependent opposing signalling process into this body–brain signalling loop. We used protein engineering to create cocaine-gated ion channels that are selective for cocaine over other drugs and endogenous molecules. Expression of an excitatory cocaine-gated channel in the rat lateral habenula, a brain region that is normally inhibited by cocaine, suppressed cocaine self-administration without affecting food motivation. This artificial cocaine-activated chemogenetic process reduced the cocaine-induced extracellular dopamine rise in the nucleus accumbens. Our results show that cocaine chemogenetics is a selective approach for countering drug reinforcement by clamping dopamine release in the presence of cocaine. In the future, chemogenetic receptors could be developed for additional addictive drugs or hormones and metabolites, which would facilitate efforts to probe their neural circuit mechanisms using a synthetic physiology approach. As these chemogenetic ion channels are specific for cocaine over natural rewards, they may also offer a route towards gene therapies for cocaine addiction.

Olfactory perception of food odors is a key determinant of eating behavior, including triggering appetite, facilitating food seeking and influencing food choice. While transient food-related olfactory cues stimulate appetite and provoke cravings in states of hunger, emerging evidence implies that prolonged and sustained exposure to food-derived odor (FO) suppresses feeding. However, the mechanisms by which olfaction induces hypophagia remain elusive. In this study, we show that prolonged FO exposure significantly suppresses food intake in male mice. We identified a subset of neurons in the ventral subiculum (vSub) that are specifically activated by FO. We further discovered that these FO-activated neurons in the vSub receive excitatory inputs from the olfactory bulb (OB) and send glutamatergic projections to the ventromedial hypothalamus (VMH). Inhibition of the OB → vSub → VMH circuit abolished the FO-induced reduction in food intake, while activation of this circuit suppressed feeding and reduced body weight. Together, these findings reveal a neurobiological circuitry that mediates the influence of olfactory signals on food intake regulation.

Maternal defense, a hallmark of motherhood, often involves protecting offspring at personal risk. However, the neural mechanisms underlying the emergence and modulation of this behavior remain not-well understood. Here, we introduce a novel paradigm in which mother mice under threat prioritize offspring protection over self-preservation by approaching, collecting, and retreating pups to safety, a risk-associated behavior that also develops in virgin females following maternal experience. Microendoscopic calcium imaging reveals sequential activation of distinct corticofugal neuronal populations in the medial prefrontal cortex (mPFC) during maternal defense. Specifically, layer (L)6 dopamine receptor D1-expressing (D1) neurons are active during pup approach, while L5 neurons are engaged during pup collection and retreat. Activation of the L6 neurons bidirectionally modulates maternal defense via projections to the medial preoptic area. These findings suggest that mPFC L6 D1 neurons may facilitate the transition to maternal behavior by influencing behavioral selection and initiating maternal defense response under threat.

Fluorescent sensors have revolutionized the measurement of molecules in the brain, and the dLight dopamine sensor has been used extensively to examine reward- and cue-evoked dopamine release, but only recently has the field turned its attention to spontaneous release events. Analysis of spontaneous events typically requires evaluation of hundreds of events over minutes to hours, and the most common method of analysis, z-scoring, was not designed for this purpose. Here, we compare the accuracy and reliability of three different analysis methods to identify pharmacologically induced changes in dopamine release and uptake in the nucleus accumbens core of freely moving C57BL/6J mice. The D1-like receptor antagonist SCH23390 was used to prevent dLight sensors from interacting with dopamine in the extracellular space, while cocaine was used to inhibit uptake and raclopride to increase the release of dopamine. We examined peak-to-peak frequency, peak amplitude, and width, the time spent above an established cutoff. The three methods were (1) the "Z-score method", which automatically smooths baseline drift and normalizes recordings using signal-to-noise ratios; (2) a "manual method", in which local baselines were adjusted manually and individual cutoffs were determined for each subject; and (3) the "prominence method" that combines z-scoring with prominence assessment to tag individual peaks and then returns to the preprocessed data for kinetic analysis. First, SCH23390 reduced the amplitude of release, but this effect was diminished using the Z-score method, and there was a variable effect on frequency between methods. Cocaine increased signal width as expected using the manual and prominence methods but not the Z-score method. Finally, raclopride-induced increases in amplitude were correctly identified by all three methods, but this effect was again diminished by using the Z-score method. Thus, analysis of spontaneous dopamine signals requires assessment of the %ΔF/F values, and the use of z-scoring is not appropriate.

Alcohol use disorder (AUD) is a chronic disease that poses significant economic burden and health risks. It is pivotal to better understand brain mechanisms engaged by alcohol that promote misuse. The central amygdala (CeA) has emerged as a key mediator of excessive alcohol consumption in preclinical models. A dynorphin-expressing subpopulation within the CeA (CeADyn) has been implicated in excessive alcohol drinking, yet how cellular activity of CeADyn neurons relates to ongoing alcohol drinking is not well-understood. The current study interrogated the engagement of CeADyn neurons in male and female mice during voluntary alcohol consumption using fiber photometry and compared this cellular response with that of other solutions having similar motivational and/or taste characteristics. Activity of a calcium sensor, GCaMP7f, expressed in mouse CeADyn neurons was recorded and time-locked to drinking bouts. Advanced fiber photometry normalization and mixed modeling methods were developed to better resolve effects, revealing relatively large increases in CeADyn neuron calcium transients after bouts of alcohol drinking compared to water or sucrose drinking. This indicates that these neurons are uniquely engaged during alcohol consumption. Alcohol-specific drinking behavior (i.e., longer bout durations) did not fully explain signal differences between alcohol and other solutions nor did the relatively increased alcohol response diminish over time. No other conditions or solutions tested reproduced the pronounced change in CeADyn activity associated with alcohol drinking. These findings support the presence of a unique functional signature for alcohol in a cell population known to control excessive alcohol drinking and further advance fiber photometric normalization and analytical methods.

Glutamatergic neuronal activity promotes proliferation of both oligodendrocyte precursor cells (OPCs) and gliomas, including diffuse midline glioma (DMG). However, the role of neuromodulatory brainstem neurons projecting to midline structures where DMGs arise remains unexplored. Here, we demonstrate that midbrain cholinergic neuronal activity modulates OPC and DMG proliferation in a circuit-dependent manner. Optogenetic stimulation of the cholinergic pedunculopontine nucleus (PPN) promotes glioma growth in pons, while stimulation of the laterodorsal tegmentum nucleus (LDT) drives proliferation in thalamus. DMG-bearing mice exhibit higher acetylcholine release and increased cholinergic neuronal activity over the disease course. In co-culture, cholinergic neurons enhance DMG proliferation, and acetylcholine directly acts on DMG cells. Single-cell RNA sequencing revealed high CHRM1 and CHRM3 expression in primary DMG samples. Pharmacological or genetic blockade of M1/M3 receptors abolished cholinergic activity-driven DMG proliferation. Taken together, these findings demonstrate that midbrain cholinergic long-range projections promote activity-dependent DMG growth, mirroring a parallel proliferative effect on healthy OPCs.

Objective: The bed nucleus of the stria terminalis (BNST) is involved in feeding, reward, aversion, and anxiety-like behavior. We identify BNST neurons defined by the expression of vesicular glutamate transporter 3, VGluT3. Methods: A combination of in situ hybridization, tract tracing, ex vivo whole-cell electrophysiology, in vivo recording, optogenetic, and behavioral approaches were used. Results: VGluT3 neurons were localized to anteromedial BNST, were molecularly distinct from accumbal VGluT3 neurons, and co-express vesicular GABA transporter (VGaT). BNST VGluT3 neurons projected to arcuate nucleus (ARC) and paraventricular nucleus of the hypothalamus (PVN), regions critical for feeding and homeostatic regulation. Most single BNST VGluT3 neurons projected to either PVN or ARC and a subset projected to both. BNST VGluT3 neurons functionally transmit GABA to both ARC and PVN, with rare glutamate co-transmission to ARC. In vivo, VGluT3 BNST neurons showed greater neuronal activity in response to sucrose consumption while sated compared with fasted. When fasted, optogenetic stimulation of BNST VGluT3 neurons decreased sucrose consumption using several stimulation conditions but not when stimulation occurred prior to sucrose access, suggesting that BNST VGluT3 activation concurrent with consumption in the fasted state reduces feeding. BNST VGluT3 activation had no effect on anxiety-like behavior in several paradigms (novelty-suppressed feeding, open field, and elevated zero maze). BNST VGluT3 activation also did not result in real-time place preference or aversion. Conclusions: We interpret these data such that VGluT3 BNST neurons represent a unique cellular population within the BNST that provides inhibitory input to hypothalamic regions to decrease sucrose consumption.

The role of the dynorphin/kappa opioid receptor (KOR) system in dopamine (DA) regulation has been extensively investigated. KOR activation reduces extracellular DA concentrations, but the exact mechanism(s) through which this is accomplished are not fully elucidated. To explore KOR influences on real-time DA fluctuations, we used the photosensor dLight1.2 with fiber photometry in the nucleus accumbens (NAc) core of freely moving male and female C57BL/6J mice. First, we established that the rise and fall of spontaneously arising DA signals were due to DA release and reuptake, respectively. Next, mice were systemically administered the KOR agonist U50,488H in the presence or absence of the KOR antagonist aticaprant. U50,488H reduced both the amplitude and width of spontaneous signals in both sexes. Further, the slope of the correlation between amplitude and width was increased, indicating that DA uptake rates were increased. U50,488H also reduced the frequency of occurrence of signals in males and females. The effects of KOR activation were stronger in males, while effects of KOR antagonism were stronger in females. Overall, KORs exerted significant inhibitory control over spontaneous DA signaling, acting through at least three mechanisms - inhibiting DA release, promoting DA transporter-mediated uptake, and reducing the frequency of signals.

Dopaminergic signaling is essential for regulating movement, learning, and reward. Disruptions in this system are linked to neuropsychiatric disorders such as ADHD. ADGRL3, an adhesion G protein-coupled receptor highly expressed in the brain, is genetically associated with increased ADHD risk. ADGRL3 knockout in animals alters expression of dopaminergic markers and induces dopamine-related behavioral changes. However, its precise role in modulating dopamine signaling remains unclear. We investigated how ADGRL3 knockout affects striatal dopamine release in mice using ex vivo fast-scan cyclic voltammetry and in vivo fiber photometry with a dopamine sensor. Ex vivo measurements showed increased electrically-evoked dopamine release across the striatum. Conversely, in vivo recordings revealed reduced task-induced dopamine signals in the nucleus accumbens during an operant fixed interval task. This reduction was not due to impaired dopamine availability, as amphetamine-evoked release was unchanged. These findings suggest ADGRL3 modulates dopamine release in complex ways via different pre- and postsynaptic mechanisms.

The stress axis is always active, even in the absence of any threat. This manifests as hourly pulses of corticosteroid stress hormone secretion over the day. Corticotropin-releasing hormone (CRH) neurons in the paraventricular nucleus of the hypothalamus (CRH PVN ) control both the neuroendocrine stress axis as well as stress-associated behaviors. However, it is currently unclear how the resting activity of these neurons is coordinated with both spontaneous behavior and ultradian pulses of corticosteroid secretion. To investigate this, we performed fiber photometry recordings of CRH PVN neuron activity in Crh-Ires-Cre mice and a newly generated line of Crh-Ires-Cre rats. In both mice and rats, CRH PVN neurons displayed an ultradian rhythm of activity with reoccurring upstates of activity approximately once per hour over the 24-h day. Upstates in activity were coordinated with increases in animal activity/arousal. Chemogenetic activation of CRH PVN neurons was also sufficient to induce behavioral arousal. In rats, increases in CRH neural activity preceded some pulses of corticosteroid secretion but not others. Thus, while CRH PVN neurons display an ultradian rhythm of activity over the 24-h day that is coordinated with behavioral arousal, the relationship between CRH PVN activity and pulses of corticosteroid secretion is not one-to-one.

In dynamic environments where stimuli predicting reward or punishment unexpectedly change, it is critical to flexibly update behavior while preserving recollection of previous associations. Dopamine and gamma-aminobutyric acid (GABA) neurons in the ventral tegmental area (VTA) are implicated in reward and punishment learning, yet little is known about how each population adapts when the predicted outcome valence changes. To address this, VTA GABA and dopamine population calcium activity fluctuations were measured with fiber photometry while male and female rats learned to associate three discrete auditory cues with three distinct outcomes: reward, punishment, or no outcome within the same session. Contingency learning was determined by quantifying conditioned responding and probability of approach behaviors. After learning, the reward and punishment cue-outcome contingencies were reversed and subsequently re-reversed. The dopamine population displayed the expected adaptation to learning and contingency reversals by increasing the response to appetitive stimuli and decreasing the response to aversive stimuli. By contrast, the GABA population increased activity to all sensory events regardless of valence. Reversing learned contingencies selectively influenced GABA responses to the reward-predictive cue, prolonging increased activity both within and across sessions. Trial-by-trial analysis further confirmed that sustained GABA activity tracks contingency reversal. The valence-specific dissociations in the directionality and temporal progression of VTA GABA and dopamine neuronal activity suggest that these populations serve distinct roles during reward or punishment associative learning and reversal. These findings also describe a novel role for VTA GABA in behavioral flexibility.

The basolateral amygdala (BLA) assigns valence to sensory stimuli, with a dedicated nociceptive ensemble encoding the negative valence of pain. However, the effects of chronic pain on the transcriptomic signatures and projection architecture of this BLA nociceptive ensemble are not well understood. Here, we show that optogenetic inhibition of the nociceptive BLA ensemble reduces affective-motivational behaviors in chronic neuropathic pain. Single-nucleus RNA sequencing revealed peripheral injury–induced changes in genetic pathways involved in axonal and presynaptic organization in nociceptive BLA neurons. Next, we identified a previously uncharacterized nociceptive hotspot in the nucleus accumbens shell that is innervated by BLA nociceptive neurons. Axonal calcium imaging of BLA projections to the accumbens and chemogenetic inhibition of this pathway revealed pain-related transmission from the amygdala to the medial nucleus accumbens, facilitating both acute and chronic pain affective-motivational behaviors. Together, this work defines a critical nociceptive amygdala-striatal circuit underlying pain unpleasantness across pain states.