Fiber Photometry publications

Drugs of abuse in adolescence impact brain maturation and increase psychiatric risk, with differences in sensitivity between males and females. Amphetamine in early adolescence (postnatal day; PND 21 ± 1–32 ± 1) in male, but not female mice, causes dopamine axons intended to innervate the nucleus accumbens and to grow ectopically to the prefrontal cortex (PFC). This is mediated by drug-induced downregulation of the Netrin-1 receptor DCC. How off-target dopamine axons function in the adult PFC remains to be determined. Here we report that males and females show place preference for amphetamine in early adolescence. However, only in males, amphetamine increases PFC dopamine transporter expression in adulthood (PND 101 ± 15): leading to aberrant baseline dopamine transients, faster dopamine release, and exaggerated responses to acute methylphenidate. Upregulation of DCC in adolescence, using CRISPRa, prevents all these changes. Mesolimbic dopamine axons rerouted to the PFC in adolescence retain anatomical and functional phenotypes of their intended target, rendering males enduringly vulnerable to the harmful effects of drugs of abuse.

The hypothalamus is critical for regulating behaviors essential for survival and locomotion, but how it integrates internal needs and transmits locomotion commands to the spinal cord (SC) remains unclear. We found that glutamatergic neurons in lateral hypothalamic area (LHA) are essential for regulating motivated locomotor activity. Using single-neuron projectome analysis, trans-synaptic tracing, and optogenetic manipulation, we showed that LHA facilitates motivated locomotion during food seeking via pontine reticular nucleus, oral part (PnO) projection neurons, rather than direct SC projections or indirect stress signaling via medial septum and diagonal band. Activating PnO-SC projection neurons also initiated locomotion. Importantly, LHA-PnO projection neurons were crucial for regulating locomotor recovery following mouse spinal cord injury (SCI). Motor cortex signals gated LHA deep brain stimulation treatment markedly promoted long-term restoration of hindlimb motor functions after severe SCI. Thus, we have identified a hypothalamic-pontine-spinal pathway and the stimulation paradigm for potential therapeutic intervention after SCI.

Memory consolidation enables animals to draw on past experiences to guide future behavior. This process involves system- and synaptic-level changes and predominantly occurs during sleep. While hippocampal-cortical circuits are well studied in this context, the contributions of other systems, including dopaminergic circuits—key players in learning-related processes—remain poorly understood. Ventral tegmental area dopaminergic (VTA DA ) neurons are active during sleep and suggested to participate in memory consolidation processes; however, causal evidence for this is lacking. Using calcium-dependent fiber photometry, electrophysiology, and chemogenetic and optogenetic manipulations across learning paradigms, we explore the functions of VTA DA neuronal activity during sleep. We show that VTA DA activity during nonrapid eye movement sleep is experience dependent, is enhanced by motor skill and associative learning, facilitates motor skill memory consolidation, and exhibits a motor learning–dependent increase in temporal coordination with cortical spindle oscillations. Our findings uncover a previously unidentified function for VTA DA neurons in consolidating memories during sleep, advancing understanding of this central neuromodulator’s functions in regulating fundamental biological processes.

Maternal obesity predisposes offspring to metabolic diseases. Here, we show that non-nutritive sensory components of a high-fat diet (HFD), beyond its hypercaloric, obesogenic effects, are sufficient to alter metabolic health in the offspring. To dissociate the caloric and sensory components of HFD, we fed dams a bacon-flavoured diet, isonutritional to a normal chow diet but enriched with fat-related odours. Offspring exposed to these fat-related odours during development display metabolic inflexibility and increased adiposity when fed HFD in adulthood independently of maternal metabolic health. Developmental exposure to fat-related odours shifts mesolimbic dopaminergic circuits and Agouti-related peptide (AgRP) hunger neurons’ responses to phenocopy those of obese mice, including a desensitization of AgRP neurons to dietary fat. While neither neonatal optogenetic activation of sensory circuits nor passive exposure to fat-related odours is sufficient to alter metabolic responses to HFD, coupling optogenetic stimulation of sensory circuits with caloric intake exacerbates obesity. Collectively, we report that fat-related sensory cues during development act as signals that can prime central responses to food cues and whole-body metabolism regulation.

The anterior-lateral motor cortex (ALM) has been extensively studied as a model for understanding the cortical mechanisms involved in planning directional movements. ALM neurons show preparatory activity that predict whether the mouse will produce a left- or right-directed lick. While the neural mechanisms underlying ALM dynamics and their links to behavior are beginning to be elucidated, the sources of this directional activity remain unclear. Here, we examined the role of ALM dopaminergic circuits in mice performing a directional licking task. We report that dopamine (DA) signals and the activity of neurons expressing D1 receptors (D1R + ) tracked the preparation and execution of licking and demonstrated a bias for planning of licks aimed at the direction contralateral to the recording site. Unilateral optogenetic manipulations of D1R + neurons or DA afferents affected lateral licking in a way consistent with their role in planning contralateral movements. Together, these results show that cortical DA modulation plays an important role in the motor preparation of directional movements.

The lateral habenula (LHb) integrates cortical and basal forebrain (BF) input to control monoaminergic outflow and is implicated in depression, anxiety, impulsivity, and aversion. Although cannabis withdrawal is associated with negative affect and heightened anxiety, LHb involvement is not established. Here, effects of withdrawal from the psychoactive cannabis constituent Δ 9 -tetrahydrocannabinol (Δ 9 -THC) on LHb neurons were assessed with photometric calcium measurement during fear conditioning and in vitro electrophysiology. LHb calcium signals were larger during footshock, and presentation of a tone paired with footshock in Δ 9 -THC withdrawn rats. Fear-induced freezing to the tone was also larger during Δ 9 -THC withdrawal. Electrophysiology revealed larger LHb excitatory-inhibitory (E-I) ratios during Δ 9 -THC withdrawal, resulting from impaired synaptic GABA release. Moreover, GABA release via optogenetic activation of BF-LHb inputs was impaired during Δ 9 -THC withdrawal, whereas no changes occurred at ventral tegmental area-LHb inputs. Recovery of BF-LHb GABA release and cannabinoid CB1 receptor desensitization were incomplete at 30 days of Δ 9 -THC withdrawal. The data show that LHb responsivity to primary aversive and conditioned stimuli are increased during Δ 9 -THC withdrawal, and that this is likely mediated by altered E-I balance. We propose negative affect experienced during cannabis withdrawal is related to LHb hypersensitivity to aversive stimuli and this facilitates encoding of associated environmental cues.

The ventral tegmental area (VTA) is classically linked to learning and reinforcement via the actions of dopamine neurons. Intermingled VTA GABA neurons are positioned to regulate dopamine, but we lack detailed insight into how this population contributes to behavior. Recording calcium activity in VTA dopamine and GABA neurons, we show that, while dopamine neurons were only responsive to appetitive events, GABA neurons actively encoded both appetitive and aversive stimuli. Critically, GABA neuron activity selectively integrated events when both valences were present. In a motivational conflict task, where rats weighed decisions to avoid shock or seek reward, GABA neuron activity scaled with escalating cost and predicted reward seeking. Optogenetic inhibition of GABA neurons disrupted reward seeking specifically under conditions of motivational conflict. Together, our data show that VTA GABA neurons reflect a broader learning signal, compared to dopamine neurons, that is important for directing economic decision making in complex, multivalent environments.

The thalamocortical pathways exhibit neuroplasticity not only during the critical period but also in adulthood. In this study, we investigated how cholecystokinin (CCK) modulates age-dependent thalamocortical plasticity. Our findings demonstrated that CCK is expressed in thalamocortical neurons and that high-frequency stimulation (HFS) of the thalamocortical pathway triggers the release of CCK in auditory cortex (ACx), as detected by a CCK sensor. HFS of the medial geniculate body (MGB) induced thalamocortical long-term potentiation (LTP) in wild-type young adult mice. However, knockdown of CCK expression in MGB neurons or blockade of the CCK-B receptor (CCKBR) in the ACx abolished HFS-induced LTP. Interestingly, this LTP could not be elicited in juvenile (3-week-old) or aged mice (over 18-month-old) due to distinct mechanisms: the absence of CCKBR in juveniles and the inability to release CCK in aged mice. Notably, exogenous administration of CCK into the ACx rescued LTP in aged mice and significantly improved frequency discrimination. These findings highlight the potential of CCK as a therapeutic intervention for ameliorating neuroplasticity deficits associated with thalamocortical connectivity.

Dopamine release in the nucleus accumbens is classically linked to associative learning, signaling relationships between predictive cues and outcomes. Yet, dopamine is also strongly modulated by novelty, a nonassociative factor that has received comparatively little attention. Here, we used optical dopamine sensors in awake, behaving male and female mice to define how novelty alters the temporal dynamics of dopamine release during aversive learning. We manipulated novelty in three ways: (1) omitting expected footshocks, (2) introducing novel neutral cues concurrently with shock-predictive stimuli, and (3) presenting novel stimuli in an unpaired fashion within a context. Across all conditions, manipulations robustly increased dopamine release and in some cases altered the directionality of cue-evoked dopamine responses. Notably, these effects extended beyond the immediate stimulus window, altering subsequent responses to both conditioned cues and footshocks. Together, these findings demonstrate that changes in the environment that extend beyond prediction-based learning can exert a powerful and sustained influence on dopamine signaling, reshaping how aversive cues and outcomes are represented in the brain.

Anxiety disorders impose a substantial global burden, yet current pharmacotherapies often lack sustained efficacy and carry risks of dependence. Dexmedetomidine (Dex), a selective α2 adrenergic receptor agonist primarily used for sedation, demonstrates promising anxiolytic properties, but its long-term neural mechanisms remain unclear. Here, using a chronic restraint stress (CRS) mouse model, we reveal that tyrosine hydroxylase (TH)-positive neurons in the locus coeruleus (LC) are persistently hyperactivated during chronic anxiety states, driving elevated norepinephrine (NE) release in the medial prefrontal cortex (mPFC). A single low dose of Dex (50 µg/kg) produced anxiolytic effects lasting ≥3 days, evidenced by improved performance in open-field, light-dark box, and elevated plus maze tests. In vivo fiber photometry and chemogenetic approaches demonstrated that Dex suppresses LC-NE neuronal hyperactivity and normalizes mPFC NE levels. Crucially, neuron-specific knockdown of α2 receptors in the LC abolished Dex's anxiolytic effects, confirming their essential role. These findings elucidate a neural mechanism wherein Dex sustains anxiety relief via α2 receptor-mediated inhibition of the LC-NE-mPFC circuit, highlighting its potential as a novel long-acting therapeutic strategy for anxiety disorders.

Background CLN3 disease, also known as juvenile Batten disease, is a recessively inherited neurodevelopmental disorder caused by mutations in the CLN3 gene. It represents the most common form of Neuronal Ceroid Lipofuscinoses (NCLs), a group of lysosomal storage disorders that impair brain function. Clinical features include progressive vision loss, language impairment, and cognitive decline. The early onset of visual deficits complicates the neurological assessment of cognitive dysfunction, while the rarity of CLN3 cases limits the study of sex-specific disease trajectories in humans. Therefore, there is a critical need for objective, translational biomarkers to monitor disease progression and support therapeutic development in preclinical animal models. Methods Building on our recent studies in individuals with CLN3 disease, we developed a parallel experimental paradigm using high-density electroencephalography (EEG) in Cln3 knockout ( Cln3-/-) mice to longitudinally assess auditory neurophysiological changes. We applied a duration-based mismatch negativity (MMN) paradigm, similar to that used in our human studies, to evaluate automatic detection of auditory pattern changes in male and female mice between 3 and 9 months of age. Results Wild-type (WT) mice of both sexes showed robust and stable duration MMN responses across this age range. In contrast, Cln3-/- mice showed marked sex- and age-dependent deficits: female mutants displayed persistent MMN deficits, whereas male mutants exhibited early MMN abnormalities that unexpectedly improved with age. Auditory brainstem responses confirmed intact peripheral hearing in Cln3-/- mice, indicating a central origin for the observed abnormalities. Further analyses revealed that MMN impairments were driven by age- and sex-specific alterations in auditory evoked potentials to both standard and deviant stimuli. Conclusions These findings demonstrate sex- and age-dependent disruptions in central auditory processing in Cln3-/- mice and support auditory duration MMN as a sensitive, translational biomarker of brain dysfunction in CLN3 disease. This approach offers a functional, cross-species measure for tracking disease progression and evaluating therapeutic interventions in Batten disease.

A central mechanism of exposure-based cognitive behavioral therapy for anxiety and trauma-related disorders is fear extinction. However, the mechanisms underlying fear extinction are deficient in some individuals, leading to treatment resistance. Recent animal studies demonstrate that upon omission of the aversive, unconditioned stimulus (US) during fear extinction, dopamine (DA) neurons in the ventral tegmental area (VTA) produce a prediction error (PE)-like signal. However, whether this VTA-DA neuronal PE-like signal is altered in animals exhibiting deficient fear extinction has not been studied. Here, we used a mouse model of impaired fear extinction [129S1/SvImJ (S1) inbred mouse strain] to monitor and manipulate VTA-DA neurons during extinction. Male DAT-Cre mice backcrossed onto an S1 background (S1-DAT-Cre) exhibited impaired extinction but normal VTA-DA neuron number, as compared with BL6-DAT-Cre mice. In vivo fiber photometry showed that impaired extinction in male S1-DAT-Cre mice was associated with abnormally sustained US omission-related VTA-DA neuronal calcium activity during extinction training and retrieval. Neither in vivo optogenetic photoexcitation of VTA-DA neuronal cell bodies nor their axons in the infralimbic cortex was sufficient to rescue deficient extinction in male S1-DAT-Cre mice, at least within the optogenetic and behavioral parameters used. These data suggest that alterations in the activity of VTA-DA neurons during extinction learning and retrieval may be associated with deficient fear extinction in male S1 mice and could potentially contribute to extinction impairments in patient populations.

Long-term sustained pain following acute physical injury is a prominent feature of chronic pain conditions1. Populations of neurons that rapidly respond to noxious stimuli or tissue damage have been identified in the spinal cord and several nuclei in the brain2-4. Understanding the central mechanisms that signal ongoing sustained pain, including after tissue healing, remains a challenge5. Here we use spatial transcriptomics, neural manipulations, activity recordings and computational modelling to demonstrate that activity in an ensemble of anatomically and molecularly diverse parabrachial neurons that express the neuropeptide Y (NPY) receptor Y1 (Y1R neurons) is increased following injury and predicts functional coping behaviour. Hunger, thirst or predator cues suppressed sustained pain, regardless of the injury type, by inhibiting parabrachial Y1R neurons via the release of NPY. Together, our results demonstrate an endogenous analgesic hub at pain-responsive parabrachial Y1R neurons.

Classical neuromodulators regulate arousal states, spanning deep sleep to vigilant wakefulness, primarily by activating cortical neurons. However, cortical astrocytes also express neuromodulatory G-protein-coupled receptors (GPCRs). While astrocytic noradrenergic receptors have been shown to modulate two critical regulators of arousal—cortical synchrony and extracellular adenosine levels—how other neuromodulatory signaling pathways similarly shape arousal remains unclear. Astrocytes in mammalian cortex express particularly high levels of the wake-promoting, Gq-coupled histamine-1-receptor (H1R), yet little is known about how astrocytic H1R contributes to regulation of arousal. To address this gap, we used pharmacological and genetic approaches in murine cortex to test how astrocyte-H1R signaling affects astrocyte calcium (Ca 2+ ), cortical neural activity across sleep/wake, and extracellular adenosine—an astrocytic output that regulates cortical arousal. Using ex vivo two-photon Ca 2+ imaging in acute cortical slices, we show that H1R mediates cell-autonomous astrocyte Ca 2+ responses to histamine (HA) and attenuates responses to norepinephrine (NE). Next, in vivo fiber photometry and electrophysiology results show that H1R deletion in cortical astrocytes disrupts local astrocyte Ca 2+ during wake and extracellular adenosine dynamics specifically around REM sleep transitions, when HA release is minimal. Further, astrocyte-specific H1R deletion in cortex promotes wakefulness and reduces REM sleep time. Our results indicate that H1R activity modulates astrocyte responses to non-histaminergic inputs by inducing lasting changes in astrocyte physiology that modulate extracellular adenosine and REM sleep. Our findings contribute to an emerging model in which neuromodulator GPCRs synergistically shape astrocyte physiology to regulate arousal behavior and adenosine signaling in the cortex.

Basolateral amygdala (BLA) GABAergic interneurons (INs) are critical for associative learning; however, the comparative synaptic organization and learning-related activity of BLA IN types have not been systematically evaluated. Here, we show somatostatin (SOM) INs provide inhibition onto, and are excited by, local pyramidal cells (PCs), whereas vasoactive intestinal peptide (VIP) INs are driven by extrinsic afferents. Parvalbumin (PV) INs inhibit PCs and are activated by local and extrinsic inputs. Thus, SOM and VIP INs exhibit complementary roles in feedback and feedforward inhibition, respectively, while PV INs contribute to both microcircuit motifs. Functionally, each IN subtype exhibits unique activity patterns across fear and extinction learning, with SOM and VIP INs showing most divergent characteristics, and PV INs display an intermediate phenotype. Finally, SOM and PV INs dynamically track behavioral-state transitions across learning. These data provide insight into the synaptic microcircuit organization and activity of distinct BLA IN classes across aversive associative learning.

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.

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.