Fiber Photometry publications

Medial Forebrain Bundle Deep Brain Stimulation (MFB‐DBS) can have rapid and long lasting antidepressant effects in Treatment Resistant Depression (TRD) patients. The mechanisms are not well understood, but one hypothesis stipulates that modulation of the dopaminergic (DAergic) fibers contribute to the therapeutic outcome. Acute DBS effects on DA release have been studied; however, longitudinal studies with acute‐repetitive DBS are lacking. Long‐Evans accumbal DA release and Ventral Tegmental Area (VTA) calcium tonic and phasic signaling to different mfb‐DBS parameters were measured using fiber photometry over 8 weeks, following acute and repetitive stimulation in behaving and non‐behaving animals. DBS‐induced release was observed in both targets, with increased frequency and DBS duration. 130 Hz stimulation increased phasic and tonic DA response over time, with the latter being a potential mechanism for its long‐term clinical effectiveness. VTA calcium transients decreased, while phasic activity increased with frequency. Pulse width (PW)‐mediated differential peak release timing also suggests potential parallel activation of diverse fiber types. Additionally, decreased DA transients rate during Elevated Plus Maze (EPM) suggests context and stimulation duration‐dependent DA release. The data confirm chronic antidromic/orthodromic DAergic responses with stimulation parameter dependent variability, providing novel insights into temporal adaptations, connectivity and fiber recruitment on mfb DBS. image

Anatomical connectivity and lesion-deficit studies have shown that the dorsal and ventral hippocampi contribute to cognitive and emotional processes, respectively. However, the role of the dorsal hippocampus (dHP) in emotional or stress-related behaviors remains unclear. Here, we showed that neuronal activity in the dHP affects stress-coping behaviors in mice via excitatory projections to the medial prefrontal cortex (mPFC). The antidepressant ketamine rapidly induced c-Fos expression in both the dorsal and ventral hippocampi. The suppression of GABAergic transmission in the dHP-induced molecular changes similar to those induced by ketamine administration, including eukaryotic elongation factor 2 (eEF2) dephosphorylation, brain-derived neurotrophic factor (BDNF) elevation, and extracellular signal-regulated kinase (ERK) phosphorylation. These synaptic and molecular changes in the dHP induced a reduction in the immobility time of the mice in the tail-suspension and forced swim tests without affecting anxiety-related behavior. Conversely, pharmacological and chemogenetic potentiation of inhibitory neurotransmission in the dHP CA1 region induced passive coping behaviors during the tests. Transneuronal tracing and electrophysiology revealed monosynaptic excitatory connections between dHP CA1 neurons and mPFC neurons. Optogenetic stimulation of dHP CA1 neurons in freely behaving mice produced c-Fos induction and spike firing in the mPFC neurons. Chemogenetic activation of the dHP-recipient mPFC neurons reversed the passive coping behaviors induced by suppression of dHP CA1 neuronal activity. Collectively, these results indicate that neuronal activity in the dHP modulates stress-coping strategies to inescapable stress and contributes to the antidepressant effects of ketamine via the dHP-mPFC circuit.

Social recognition is an essential part of social function and often promotes specific social behaviors based on prior experience. Social and defensive behaviors in particular often emerge with prior experiences of familiarity or novelty/stress, respectively. This is also commonly seen in rodents toward same-strain and interstrain conspecifics. Medial amygdala (MeA) activity guides social choice based on age and sex recognition and is sensitive to social experiences. However, little is known about whether the MeA exhibits differential responses based on strain or how this is impacted by experience. Social stress impacts posterior MeA (MeAp) function and can shift measures of social engagement. However, it is unclear how stress impacts MeAp activity and contributes to altered social behavior. The primary goal of this study in adult male Sprague Dawley rats was to determine whether prior stress experience with a different-strain (Long–Evans) rat impacts MeAp responses to same-strain and different-strain conspecifics in parallel with a change in behavior using in vivo fiber photometry. We found that MeAp activity was uniformly activated during social contact with a novel same-strain rat during a three-chamber social preference test following control handling but became biased toward a novel different-strain rat following social stress. Socially stressed rats also showed initially heightened social interaction with novel same-strain rats but showed social avoidance and fragmented social behavior with novel different-strain rats relative to controls. These results indicate that heightened MeAp activity may guide social responses to novel, threatening, rather than non-threatening, social stimuli after stress.

Orchestrating complex behaviors, such as approaching and consuming food, is critical for survival. In addition to hypothalamus neuronal circuits, the nucleus accumbens (NAc) also controls appetite and satiety. However, specific neuronal subtypes of the NAc that are involved and how the humoral and neuronal signals coordinate to regulate feeding remain incompletely understood. Here we decipher the spatial diversity of neuron subtypes of the NAc shell (NAcSh) and define a dopamine receptor D1-expressing and Serpinb2- expressing subtype controlling food consumption in male mice. Chemogenetics and optogenetics-mediated regulation of Serpinb2 + neurons bidirectionally regulate food seeking and consumption specifically. Circuitry stimulation reveals that the NAcSh Serpinb2 →LH LepR projection controls refeeding and can overcome leptin-mediated feeding suppression. Furthermore, NAcSh Serpinb2 + neuron ablation reduces food intake and upregulates energy expenditure, resulting in reduced bodyweight gain. Our study reveals a neural circuit consisting of a molecularly distinct neuronal subtype that bidirectionally regulates energy homeostasis, providing a potential therapeutic target for eating disorders.

Females exhibit complex, dynamic behaviours during mating with variable sexual receptivity depending on hormonal status 1–4 . However, how their brains encode the dynamics of mating and receptivity remains largely unknown. The ventromedial hypothalamus, ventrolateral subdivision contains oestrogen receptor type 1-positive neurons that control mating receptivity in female mice 5,6 . Here, unsupervised dynamical system analysis of calcium imaging data from these neurons during mating uncovered a dimension with slow ramping activity, generating a line attractor in neural state space. Neural perturbations in behaving females demonstrated relaxation of population activity back into the attractor. During mating, population activity integrated male cues to ramp up along this attractor, peaking just before ejaculation. Activity in the attractor dimension was positively correlated with the degree of receptivity. Longitudinal imaging revealed that attractor dynamics appear and disappear across the oestrus cycle and are hormone dependent. These observations suggest that a hypothalamic line attractor encodes a persistent, escalating state of female sexual arousal or drive during mating. They also demonstrate that attractors can be reversibly modulated by hormonal status, on a timescale of days.

Current concepts of corticothalamic organization in the mammalian brain are mainly based on sensory systems, with less focus on circuits for higher-order cognitive functions. In sensory systems, first-order thalamic relays are driven by subcortical inputs and modulated by cortical feedback, while higher-order relays receive strong excitatory cortical inputs. The applicability of these principles beyond sensory systems is uncertain. We investigated mouse prefronto-thalamic projections to the midline thalamus, revealing distinct top-down control. Unlike sensory systems, this pathway relies on indirect modulation via the thalamic reticular nucleus (TRN). Specifically, the prelimbic area, which influences emotional and motivated behaviors, impacts instrumental avoidance responses through direct and indirect projections to the paraventricular thalamus. Both pathways promote defensive states, but the indirect pathway via the TRN is essential for organizing avoidance decisions through disinhibition. Our findings highlight intra-thalamic circuit dynamics that integrate cortical cognitive signals and their role in shaping complex behaviors.

Experiencing a single severe stressor is sufficient to drive sexually dimorphic psychiatric disease development. The ventral subiculum (vSUB) emerges as a site where stress may induce sexually dimorphic adaptations due to its sex-specific organization and pivotal role in stress integration. Using a 1-hr acute restraint stress model, we uncover that stress causes a net decrease in vSUB activity in females that is potent, long-lasting, and driven by adrenergic receptor signaling. By contrast, males exhibit a net increase in vSUB activity that is transient and driven by corticosterone signaling. We further identified sex-dependent changes in vSUB output to the bed nucleus of the stria terminalis and in anxiety-like behavior in response to stress. These findings reveal striking changes in psychiatric disease-relevant brain regions and behavior following stress with sex-, cell-type, and synapse-specificity that contribute to our understanding of sex-dependent adaptations that may shape stress-related psychiatric disease risk. Highlights vSUB BS cells are uniquely stress sensitive Stress causes sex-dependent changes to BS cell E/I balance Stress causes sex-dependent changes to vSUB activity to aBNST in vivo Stress causes anxiety-like behavior in females, but not males

The presence of valence coding neurons in the basolateral amygdala (BLA) that form distinct projections to other brain regions implies functional opposition between aversion and reward during learning. However, evidence for opponent interactions in fear learning is sparse and may only be apparent under certain conditions. Here we test this possibility by studying the roles of the BLA→central amygdala (CeA) and BLA→nucleus accumbens (Acb) pathways in fear learning in male rats. First, we assessed the organisation of these pathways in the rat brain. BLA→CeA and BLA→Acb pathways were largely segregated in the BLA but shared overlapping molecular profiles. Then we assessed activity of the BLA→CeA and BLA→Acb pathways during two different forms of fear learning - fear learning in a neutral context and fear learning in a reward context. BLA → CeA neurons were robustly recruited by footshock regardless of where fear learning occurred whereas recruitment of BLA→Acb neurons was state-dependent because footshock only recruited this pathway in a reward context. Finally, we assessed the causal roles of activity in these pathways in fear learning. Photoinhibition of the BLA→CeA pathway during the footshock US impaired fear learning, regardless of where fear learning occurred. In contrast, photoinhibition of the BLA→Acb pathway augmented fear learning, but only in the reward context. Taken together, our findings show circuit- and state-dependent opponent processing of fear. Footshock activity in the BLA → Acb pathway limits how much fear is learned. Significance Statement Here we identify a fear opponent process in the brain. We show that an aversive event can recruit distinct populations of neurons in the rat basolateral amygdala. One population projects to the central amygdala to promote fear learning. A second population projects to the nucleus accumbens to oppose fear learning. These nucleus accumbens projecting neurons limit how much fear is learned and are candidates for therapeutic targeting to minimize the amount of fear learned after a traumatic experience.

Reactive astrocytes are associated with neuroinflammation and cognitive decline in diverse neuropathologies; however, the underlying mechanisms are unclear. We used optogenetic and chemogenetic tools to identify the crucial roles of the hippocampal CA1 astrocytes in cognitive decline. Our results showed that repeated optogenetic stimulation of the hippocampal CA1 astrocytes induced cognitive impairment in mice and decreased synaptic long-term potentiation (LTP), which was accompanied by the appearance of inflammatory astrocytes. Mechanistic studies conducted using knockout animal models and hippocampal neuronal cultures showed that lipocalin-2 (LCN2), derived from reactive astrocytes, mediated neuroinflammation and induced cognitive impairment by decreasing the LTP through the reduction of neuronal NMDA receptors. Sustained chemogenetic stimulation of hippocampal astrocytes provided similar results. Conversely, these phenomena were attenuated by a metabolic inhibitor of astrocytes. Fiber photometry using GCaMP revealed a high level of hippocampal astrocyte activation in the neuroinflammation model. Our findings suggest that reactive astrocytes in the hippocampus are sufficient and required to induce cognitive decline through LCN2 release and synaptic modulation. This abnormal glial–neuron interaction may contribute to the pathogenesis of cognitive disturbances in neuroinflammation-associated brain conditions.

The synaptojanin-1 ( SYNJ1 ) gene is known to be important for dopamine-related disorders. Recent evidence has demonstrated that Synj1 deficient mice ( Synj1 +/− ) have impairments in dopaminergic synaptic vesicular recycling. However, less is known about how Synj1 deficits affect the mesolimbic system, reward processing, and motivated behavior. To examine the role of the Synj1 gene in motivated behavior, we subjected male and female Synj1 +/− and Synj1 +/+ mice to a battery of behavioral tests evaluating hedonic responses, effortful responding, and responses to psychomotor stimulants. We observed that Synj1 +/− mice exhibit few differences in reward processing and motivated behavior, with normal hedonic responses and motivated responding for sucrose. However, male but not female Synj1 +/− demonstrated an attenuated conditioned place preference for cocaine that could not be attributed to deficits in spatial memory. To further understand the dopamine signaling underlying the attenuated response to cocaine in these mutant mice, we recorded nucleus accumbens dopamine in response to cocaine and observed that Synj1 +/− male and female mice took longer to reach peak dopamine release following experimenter-administered cocaine. However, female mice also showed slower decay in accumbens dopamine that appear to be linked to differences in cocaine-induced DAT responses. These findings demonstrate that SYNJ1 deficiencies result in abnormal mesolimbic DA signaling which has not previously been demonstrated. Our work also highlights the need to develop targeted therapeutics capable of restoring deficits in DAT function, which may be effective for reversing the pathologies associated with Synj1 mutations.

Sleep is indispensable for health and wellbeing, but its basic function remains elusive. The locus coeruleus (LC) powerfully promotes arousal by releasing noradrenaline. We found that noradrenaline transmission is reduced by prolonged wakefulness and restored during sleep. Fiber-photometry imaging of noradrenaline using its biosensor showed that its release evoked by optogenetic LC neuron activation was strongly attenuated by three hours of sleep deprivation and restored during subsequent sleep. This is accompanied by the reduction and recovery of the wake-promoting effect of the LC neurons. The reduction of both LC evoked noradrenaline release and wake-inducing potency is activity dependent, and the rate of noradrenaline transmission recovery depends on mammalian target of rapamycin (mTOR) signaling. The decline and recovery of noradrenaline transmission also occur in spontaneous sleep-wake cycles on a timescale of minutes. Together, these results reveal an essential role of sleep in restoring transmission of a key arousal-promoting neuromodulator.

Genetically-encoded dopamine (DA) sensors enable high-resolution imaging of DA release, but their ability to detect a wide range of extracellular DA levels, especially tonic versus phasic DA release, is limited by their intrinsic affinity. Here we show that a human-selective dopamine receptor positive allosteric modulator (PAM) can be used to boost sensor affinity on-demand. The PAM enhances DA detection sensitivity across experimental preparations (in vitro, ex vivo and in vivo) via one-photon or two-photon imaging. In vivo photometry-based detection of optogenetically-evoked DA release revealed that DETQ administration produces a stable 31 minutes window of potentiation without effects on animal behavior. The use of the PAM revealed region-specific and metabolic state-dependent differences in tonic DA levels and enhanced single-trial detection of behavior-evoked phasic DA release in cortex and striatum. Our chemogenetic strategy can potently and flexibly tune DA imaging sensitivity and reveal multi-modal (tonic/phasic) DA signaling across preparations and imaging approaches.

Failure to appropriately predict and titrate reactivity to threat is a core feature of fear and anxiety-related disorders and is common following early life adversity (ELA). A population of neurons in the lateral central amygdala (CeAL) expressing corticotropin releasing factor (CRF) have been proposed to be key in processing threat of different intensities to mediate active fear expression. Here, we use in vivo fiber photometry to show that ELA results in sex-specific changes in the activity of CeAL CRF+ neurons, yielding divergent mechanisms underlying the augmented startle in ELA mice, a translationally relevant behavior indicative of heightened threat reactivity and hypervigilance. Further, chemogenic inhibition of CeAL CRF+ neurons selectively diminishes startle and produces a long-lasting suppression of threat reactivity. These findings identify a mechanism for sex-differences in susceptibility for anxiety following ELA and have broad implications for understanding the neural circuitry that encodes and gates the behavioral expression of fear.

The claustrum has been linked to attention and sleep. We hypothesized that this reflects a shared function, determining responsiveness to stimuli, which spans the axis of engagement. To test this hypothesis, we recorded claustrum population dynamics from male mice during both sleep and an attentional task (‘ENGAGE’). Heightened activity in claustrum neurons projecting to the anterior cingulate cortex (ACCp) corresponded to reduced sensory responsiveness during sleep. Similarly, in the ENGAGE task, heightened ACCp activity correlated with disengagement and behavioral lapses, while low ACCp activity correlated with hyper-engagement and impulsive errors. Chemogenetic elevation of ACCp activity reduced both awakenings during sleep and impulsive errors in the ENGAGE task. Furthermore, mice employing an exploration strategy in the task showed a stronger correlation between ACCp activity and performance compared to mice employing an exploitation strategy which reduced task complexity. Our results implicate ACCp claustrum neurons in restricting engagement during sleep and goal-directed behavior.

Nociceptin/orphanin-FQ (N/OFQ) is a recently appreciated critical opioid peptide with key regulatory functions in several central behavioral processes including motivation, stress, feeding, and sleep. The functional relevance of N/OFQ action in the mammalian brain remains unclear due to a lack of high-resolution approaches to detect this neuropeptide with appropriate spatial and temporal resolution. Here we develop and characterize NOPLight, a genetically encoded sensor that sensitively reports changes in endogenous N/OFQ release. We characterized the affinity, pharmacological profile, spectral properties, kinetics, ligand selectivity, and potential interaction with intracellular signal transducers of NOPLight in vitro. Its functionality was established in acute brain slices by exogeneous N/OFQ application and chemogenetic induction of endogenous N/OFQ release from PNOC neurons. In vivo studies with fibre photometry enabled direct recording of NOPLight binding to exogenous N/OFQ receptor ligands, as well as detection of endogenous N/OFQ release within the paranigral ventral tegmental area (pnVTA) during natural behaviors and chemogenetic activation of PNOC neurons. In summary, we show here that NOPLight can be used to detect N/OFQ opioid peptide signal dynamics in tissue and freely behaving animals.

Rapid eye movement sleep (REMs) is characterized by activated electroencephalogram (EEG) and muscle atonia, accompanied by vivid dreams. REMs is homeostatically regulated, ensuring that any loss of REMs is compensated by a subsequent increase in its amount. However, the neural mechanisms underlying the homeostatic control of REMs are largely unknown. Here, we show that GABAergic neurons in the preoptic area of the hypothalamus projecting to the tuberomammillary nucleus (POA GAD2 →TMN neurons) are crucial for the homeostatic regulation of REMs in mice. POA GAD2 →TMN neurons are most active during REMs, and inhibiting them specifically decreases REMs. REMs restriction leads to an increased number and amplitude of calcium transients in POA GAD2 →TMN neurons, reflecting the accumulation of REMs pressure. Inhibiting POA GAD2 →TMN neurons during REMs restriction blocked the subsequent rebound of REMs. Our findings reveal a hypothalamic circuit whose activity mirrors the buildup of homeostatic REMs pressure during restriction and that is required for the ensuing rebound in REMs.

All drugs of abuse induce long-lasting changes in synaptic transmission and neural circuit function that underlie substance-use disorders 1,2 . Another recently appreciated mechanism of neural circuit plasticity is mediated through activity-regulated changes in myelin that can tune circuit function and influence cognitive behaviour 3–7 . Here we explore the role of myelin plasticity in dopaminergic circuitry and reward learning. We demonstrate that dopaminergic neuronal activity-regulated myelin plasticity is a key modulator of dopaminergic circuit function and opioid reward. Oligodendroglial lineage cells respond to dopaminergic neuronal activity evoked by optogenetic stimulation of dopaminergic neurons, optogenetic inhibition of GABAergic neurons, or administration of morphine. These oligodendroglial changes are evident selectively within the ventral tegmental area but not along the axonal projections in the medial forebrain bundle nor within the target nucleus accumbens. Genetic blockade of oligodendrogenesis dampens dopamine release dynamics in nucleus accumbens and impairs behavioural conditioning to morphine. Taken together, these findings underscore a critical role for oligodendrogenesis in reward learning and identify dopaminergic neuronal activity-regulated myelin plasticity as an important circuit modification that is required for opioid reward.

Learning causal relationships relies on understanding how often one event precedes another. To investigate how dopamine neuron activity and neurotransmitter release change when a retrospective relationship is degraded for a specific pair of events, we used outcome-selective Pavlovian contingency degradation in rats. Conditioned responding was attenuated for the cue-reward contingency that was degraded, as was dopamine neuron activity in the midbrain and dopamine release in the ventral striatum in response to the cue and subsequent reward. Contingency degradation also abolished the trial-by-trial history dependence of the dopamine responses at the time of trial outcome. This profile of changes in cue- and reward-evoked responding is not easily explained by a standard reinforcement learning model. An alternative model based on learning causal relationships was better able to capture dopamine responses during contingency degradation, as well as conditioned behavior following optogenetic manipulations of dopamine during noncontingent rewards. Our results suggest that mesostriatal dopamine encodes the contingencies between meaningful events during learning.

Binge alcohol consumption during adolescence can produce lasting deficits in learning and memory while also increasing the susceptibility to substance use disorders. The adolescent intermittent ethanol (AIE) rodent model mimics human adolescent binge drinking and has identified the nucleus basalis magnocellularis (NbM) as a key site of pathology. The NbM is a critical regulator of prefrontal cortical (PFC) cholinergic function and attention. The cholinergic phenotype is controlled pro/mature neurotrophin receptor activation. We sought to determine if p75NTR activity contributes to the loss of cholinergic phenotype in AIE by using a p75NTR modulator (LM11A-31) to inhibit prodegenerative signaling during ethanol exposure. Male and female rats underwent 5 g/kg ethanol (AIE) or water (CON) exposure following 2-day-on 2-day-off cycles from postnatal day 25–57. A subset of these groups also received a protective dose of LM11A-31 (50 mg/kg) during adolescence. Rats were trained on a sustained attention task (SAT) and behaviorally relevant acetylcholine (ACh) activity was recorded in the PFC with a fluorescent indicator (AChGRAB 3.0). AIE produced learning deficits on the SAT, which were spared with LM11A-31. In addition, PFC ACh activity was blunted by AIE, which LM11A-31 corrected. Investigation of NbM ChAT+ and TrkA+ neuronal expression found that AIE led to a reduction of ChAT+TrkA+ neurons, which again LM11A-31 protected. Taken together, these findings demonstrate the p75NTR activity during AIE treatment is a key regulator of cholinergic degeneration.

Fentanyl is a powerful painkiller that elicits euphoria and positive reinforcement 1 . Fentanyl also leads to dependence, defined by the aversive withdrawal syndrome, which fuels negative reinforcement 2,3 (that is, individuals retake the drug to avoid withdrawal). Positive and negative reinforcement maintain opioid consumption, which leads to addiction in one-fourth of users, the largest fraction for all addictive drugs 4 . Among the opioid receptors, µ-opioid receptors have a key role 5 , yet the induction loci of circuit adaptations that eventually lead to addiction remain unknown. Here we injected mice with fentanyl to acutely inhibit γ-aminobutyric acid-expressing neurons in the ventral tegmental area (VTA), causing disinhibition of dopamine neurons, which eventually increased dopamine in the nucleus accumbens. Knockdown of µ-opioid receptors in VTA abolished dopamine transients and positive reinforcement, but withdrawal remained unchanged. We identified neurons expressing µ-opioid receptors in the central amygdala (CeA) whose activity was enhanced during withdrawal. Knockdown of µ-opioid receptors in CeA eliminated aversive symptoms, suggesting that they mediate negative reinforcement. Thus, optogenetic stimulation caused place aversion, and mice readily learned to press a lever to pause optogenetic stimulation of CeA neurons that express µ-opioid receptors. Our study parses the neuronal populations that trigger positive and negative reinforcement in VTA and CeA, respectively. We lay out the circuit organization to develop interventions for reducing fentanyl addiction and facilitating rehabilitation.