Fiber Photometry publications

Tissue inflammation or nerve injury at the periphery can cause chronic pain. Although the spinal-cord-projecting neurons in the rostral ventromedial medulla (RVMSC neurons) can promote pain chronification1-4, the pathway by which peripheral injury signals drive these neurons is poorly understood1-3,5. Here we report a circuit loop that extends from the spinal cord to the ventral posterolateral thalamus and posterior complex of the thalamus, proceeds to the primary somatosensory cortex and returns to the spinal cord via the lateral superior colliculus, which in turn connects to μ-opioid-receptor-expressing RVMSC neurons. Silencing any node along this multisynaptic circuit has minimal effects on nociception in healthy mice, but can eliminate mechanical hypersensitization and restore normal nociceptive response thresholds in mouse models of inflammatory and neuropathic pain. In healthy mice, repetitive-but not acute-activation of each node in this circuit is sufficient to cause robust chronic mechanical hypersensitization. Our findings reveal a spino-brain-spinal cord circuit loop that links ascending and descending pathways and specifically drives chronic mechanical pain. This could enable the identification of cellular targets for treating chronic pain.

The lateral preoptic area (LPO) is a functionally heterogeneous hypothalamic structure that is increasingly recognised for its role in motivated and drug‐seeking behaviours. Although prior studies have shown that LPO neurons exhibit diverse activity patterns during cocaine self‐administration, the specific contributions of glutamatergic and GABAergic populations to conditioned responses to cocaine remain unclear. In this study, we recorded the activity of LPO glutamatergic ( vglut2 ‐expressing) and GABAergic ( vgat ‐expressing) neuronal subpopulations during cocaine conditioning to identify how these cell types respond to drug‐associated cues in awake, behaving mice. Our results revealed that, after cocaine conditioning, both glutamatergic and GABAergic populations showed reduced activity upon entry into the cocaine‐paired chamber. However, only glutamatergic neurons exhibited increased activity when mice entered the saline‐paired chamber. The magnitude of these activity changes was also correlated with behavioural outcomes: reduced GABAergic activity was associated with greater preference for the cocaine‐paired chamber, whereas stronger glutamatergic responses were associated with greater preference for the saline‐paired chamber. These findings indicate that LPO GABAergic and glutamatergic neurons exhibit distinct, cell type–specific patterns during cocaine‐conditioned place preference. Rather than indicating opposing motivational states, the results highlight that LPO activity relates to conditioned behaviours in a cell type– and context‐dependent manner. By linking activity in glutamatergic and GABAergic neurons with conditioned responses, this work provides initial evidence for how LPO circuits may contribute to drug‐associated learning.

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.

The dopaminergic system is crucial for affect regulation. Melanocortin 4 receptors (MC4R) in the ventral striatum have been shown to be necessary for establishing aversive states. Here, we functionally characterize MC4R-expressing striatal neurons in mice. MC4Rs were enriched in atypical dopamine receptor 1 (D1) neurons in the lateral stripe of the striatum (LSS), an understudied area in the ventrolateral striatum. Fiber photometry recordings showed that MC4R neuron activity and local dopamine release in the LSS increased in response to both rewarding and aversive stimuli. Moreover, MC4R neuronal activity and glutamate release in the LSS correlated with body movement. Optogenetic activation of MC4R-LSS neurons was rewarding in a real-time place preference test and a self-stimulation paradigm, increased locomotor activity, and induced striatal dopamine release. Collectively, our findings suggest that MC4R-LSS neurons are activated by stimuli of both rewarding and aversive character and that they induce positive affect, dopamine release and locomotion.

Animals learn the value of foods on the basis of their postingestive effects and thereby develop aversions to foods that are toxic 1–10 and preferences to those that are nutritious 11–13 . However, it remains unclear how the brain is able to assign credit to flavours experienced during a meal with postingestive feedback signals that can arise after a substantial delay. Here we reveal an unexpected role for the postingestive reactivation of neural flavour representations in this temporal credit-assignment process. To begin, we leverage the fact that mice learn to associate novel 14,15 , but not familiar, flavours with delayed gastrointestinal malaise signals to investigate how the brain represents flavours that support aversive postingestive learning. Analyses of brain-wide activation patterns reveal that a network of amygdala regions is unique in being preferentially activated by novel flavours across every stage of learning (consumption, delayed malaise and memory retrieval). By combining high-density recordings in the amygdala with optogenetic stimulation of malaise-coding hindbrain neurons, we show that delayed malaise signals selectively reactivate flavour representations in the amygdala from a recent meal. The degree of malaise-driven reactivation of individual neurons predicts the strengthening of flavour responses upon memory retrieval, which in turn leads to stabilization of the population-level representation of the recently consumed flavour. By contrast, flavour representations in the amygdala degrade in the absence of unexpected postingestive consequences. Thus, we demonstrate that postingestive reactivation and plasticity of neural flavour representations may support learning from delayed feedback.

Dopamine (DA) signals to the striatum play critical roles in shaping and sustaining stimulus-reward associations. In primates, however, the dynamics of the DA signals remain unknown since conventional methods are not necessarily appropriate in terms of the spatiotemporal resolution or chemical specificity sufficient for detecting the DA signals. In our study, fiber photometry with a fluorescent DA sensor was employed to identify reward-related DA transients in the monkey striatum. This technique, which directly monitors local DA release, reveals a reward prediction error signal in the anterior putamen originating from midbrain DA neurons. Further, DA transients in the head of the caudate nucleus exhibit a value-based response to reward-predicting stimuli. These signals have been found to arise from two separate groups of DA neurons in the substantia nigra pars compacta. The present results demonstrate that fluorescence DA monitoring is applicable to detect DA signals in the primate striatum for investigating their roles.

High-frequency stimulation (HFS)-induced long–term potentiation (LTP) is generally regarded as a homosynaptic Hebbian-type LTP, where synaptic changes are thought to occur at the synapses that project from the stimulation site and terminate onto the neurons at the recording site. In this study, we first investigated HFS-induced LTP on urethane-anesthetized rats and found that cortical HFS enhances neural responses at the recording site through the strengthening of local connectivity with nearby neurons at the stimulation site rather than through synaptic strengthening at the recording site. This enhanced local connectivity at the stimulation site leads to increased output propagation, resulting in signal potentiation at the recording site. Additionally, we discovered that HFS can also nonspecifically strengthen distant afferent synapses at the HFS site, thereby expanding its impact beyond local neural connections. This form of plasticity exhibits a neo-Hebbian characteristic as it exclusively manifests in the presence of cholecystokinin release, induced by HFS. The cortical HFS-induced local LTP was further supported by a behavioral task, providing additional evidence. Our results unveil a previously overlooked mechanism underlying cortical plasticity: synaptic plasticity is more likely to occur around the soma site of strongly activated cortical neurons rather than solely at their projection terminals.

Objective . Intracortical microelectrode arrays often fail to deliver reliable signal quality over chronic recordings, and the effect of an implanted recording array on local neural circuits is not completely understood. Approach . In this work we examined the degree of correlation and the spatial dependence of that relationship between widefield calcium imaging and electrophysiology in awake mice from 4 to 44 d post-implantation. Both correlation maps and spike-triggered averaging (STA) are used to characterize the relationship. Main results . We find that calcium imaging and electrophysiological signal are highly correlated in all animals, however, spatial variability in the correlation is affected by inherent correlation in the calcium imaging signal. Some animals exhibit a high degree of apparent neuronal synchrony in the vicinity of the probe at 4 d, while more diversity of response is detected at later time points. Significance . Degree of synchrony appears to be related to the acute injury response to the implanted electrode, with later time points displaying less synchrony. STA may be used to uncover the diverse cortical connections of spiking units.

The entorhinal cortex is involved in establishing enduring visuo-auditory associative memory in the neocortex. Here we explored the mechanisms underlying this synaptic plasticity related to projections from the visual and entorhinal cortices to the auditory cortex in mice using optogenetics of dual pathways. High-frequency laser stimulation (HFS laser) of the visuo-auditory projection did not induce long-term potentiation. However, after pairing with sound stimulus, the visuo-auditory inputs were potentiated following either infusion of cholecystokinin (CCK) or HFS laser of the entorhino-auditory CCK-expressing projection. Combining retrograde tracing and RNAscope in situ hybridization, we show that Cck expression is higher in entorhinal cortex neurons projecting to the auditory cortex than in those originating from the visual cortex. In the presence of CCK, potentiation in the neocortex occurred when the presynaptic input arrived 200 ms before postsynaptic firing, even after just five trials of pairing. Behaviorally, inactivation of the CCK + projection from the entorhinal cortex to the auditory cortex blocked the formation of visuo-auditory associative memory. Our results indicate that neocortical visuo-auditory association is formed through heterosynaptic plasticity, which depends on release of CCK in the neocortex mostly from entorhinal afferents.

The lateral hypothalamus (LH) is involved in feeding behavior and defense responses by interacting with different brain structures, including the Ventral Tegmental Area (VTA). Emerging evidence indicates that LH-glutamatergic neurons infrequently synapse on VTA-dopamine neurons but preferentially establish multiple synapses on VTA-glutamatergic neurons. Here, we demonstrated that LH-glutamatergic inputs to VTA promoted active avoidance, long-term aversion, and escape attempts. By testing feeding in the presence of a predator, we observed that ongoing feeding was decreased, and that this predator-induced decrease in feeding was abolished by photoinhibition of the LH-glutamatergic inputs to VTA. By VTA specific neuronal ablation, we established that predator-induced decreases in feeding were mediated by VTA-glutamatergic neurons but not by dopamine or GABA neurons. Thus, we provided evidence for an unanticipated neuronal circuitry between LH-glutamatergic inputs to VTA-glutamatergic neurons that plays a role in prioritizing escape, and in the switch from feeding to escape in mice.

Absence seizures are characterized by brief periods of unconsciousness accompanied by lapses in motor function that can occur hundreds of times throughout the day. Outside of these frequent moments of unconsciousness, approximately a third of people living with the disorder experience treatment-resistant attention impairments. Convergent evidence suggests prefrontal cortex (PFC) dysfunction may underlie attention impairments in affected patients. To examine this, we use a combination of slice physiology, fiber photometry, electrocorticography (ECoG), optogenetics, and behavior in the Scn8a +/- mouse model of absence epilepsy. Attention function was measured using a novel visual attention task where a light cue that varied in duration predicted the location of a food reward. In Scn8a +/- mice, we find altered parvalbumin interneuron (PVIN) output in the medial PFC (mPFC) in vitro and PVIN hypoactivity along with reductions in gamma power during cue presentation in vivo. This was associated with poorer attention performance in Scn8a +/- mice that could be rescued by gamma-frequency optogenetic stimulation of PVINs. This highlights cue-related PVIN activity as an important mechanism for attention and suggests PVINs may represent a therapeutic target for cognitive comorbidities in absence epilepsy.

Excessive fear is a hallmark of anxiety disorders, a major cause of disease burden worldwide. Substantial evidence supports a role of prefrontal cortex-amygdala circuits in the regulation of fear and anxiety, but the molecular mechanisms that regulate their activity remain poorly understood. Here, we show that downregulation of the histone methyltransferase PRDM2 in the dorsomedial prefrontal cortex enhances fear expression by modulating fear memory consolidation. We further show that Prdm2 knock-down (KD) in neurons that project from the dorsomedial prefrontal cortex to the basolateral amygdala (dmPFC-BLA) promotes increased fear expression. Prdm2 KD in the dmPFC-BLA circuit also resulted in increased expression of genes involved in synaptogenesis, suggesting that Prdm2 KD modulates consolidation of conditioned fear by modifying synaptic strength at dmPFC-BLA projection targets. Consistent with an enhanced synaptic efficacy, we found that dmPFC Prdm2 KD increased glutamatergic release probability in the BLA and increased the activity of BLA neurons in response to fear-associated cues. Together, our findings provide a new molecular mechanism for excessive fear responses, wherein PRDM2 modulates the dmPFC -BLA circuit through specific transcriptomic changes.

How are actions linked with subsequent outcomes to guide choices? The nucleus accumbens, which is implicated in this process, receives glutamatergic inputs from the prelimbic cortex and midline regions of the thalamus. However, little is known about whether and how representations differ across these input pathways. By comparing these inputs during a reinforcement learning task in mice, we discovered that prelimbic cortical inputs preferentially represent actions and choices, whereas midline thalamic inputs preferentially represent cues. Choice-selective activity in the prelimbic cortical inputs is organized in sequences that persist beyond the outcome. Through computational modeling, we demonstrate that these sequences can support the neural implementation of reinforcement-learning algorithms, in both a circuit model based on synaptic plasticity and one based on neural dynamics. Finally, we test and confirm a prediction of our circuit models by direct manipulation of nucleus accumbens input neurons.

Mu opioid receptor (MOR) agonists are potent analgesics, but also cause sedation, respiratory depression, and addiction risk. The epithalamic lateral habenula (LHb) signals aversive states including pain, and here we found that it is a potent site for MOR-agonist analgesia-like responses in rats. Importantly, LHb MOR activation is not reinforcing in the absence of noxious input. The LHb receives excitatory inputs from multiple sites including the ventral tegmental area, lateral hypothalamus, entopeduncular nucleus, and the lateral preoptic area of the hypothalamus (LPO). Here we report that LHb-projecting glutamatergic LPO neurons are excited by noxious stimulation and are preferentially inhibited by MOR selective agonists. Critically, optogenetic stimulation of LHb-projecting LPO neurons produces an aversive state that is relieved by LHb MOR activation, and optogenetic inhibition of LHb-projecting LPO neurons relieves the aversiveness of ongoing pain.

Although fear memory formation is essential for survival and fear-related mental disorders, the neural circuitry and mechanism are incompletely understood. Here, we utilized trace fear conditioning to study the formation of trace fear memory in mice. We identified the entorhinal cortex (EC) as a critical component of sensory signaling to the amygdala. We adopted both loss-of-function and gain-of-function experiments to demonstrate that release of the cholecystokinin (CCK) from the EC is required for trace fear memory formation. We discovered that CCK-positive neurons project from the EC to the lateral nuclei of the amygdala (LA), and inhibition of CCK-dependent signaling in the EC prevented long-term potentiation of the auditory response in the LA and formation of trace fear memory. In summary, high-frequency activation of EC neurons triggers the release of CCK in their projection terminals in the LA, potentiating auditory response in LA neurons. The neural plasticity in the LA leads to trace fear memory formation.

The combined development of new technologies for neuronal recordings and the development of novel sensors for recording both cellular activity and neurotransmitter binding has ushered in a new era for the field of neuroscience. Among these new technologies is fiber photometry, a technique wherein an implanted fiber optic is used to record signals from genetically encoded fluorescent sensors in bulk tissue. Fiber photometry has been widely adapted due to its cost-effectiveness, ability to examine the activity of neurons with specific anatomical or genetic identities, and the ability to use these highly modular systems to record from one or more sensors or brain sites in both superficial and deep-brain structures. Despite these many benefits, one major hurdle for laboratories adopting this technique is the steep learning curve associated with the analysis of fiber photometry data. This has been further complicated by a lack of standardization in analysis pipelines. In the present communication, we present pMAT, a ‘photometry modular analysis tool’ that allows users to accomplish common analysis routines through the use of a graphical user interface. This tool can be deployed in MATLAB and edited by more advanced users, but is also available as an independently deployable, open-source application.

Rats have the ability to learn and perform sophisticated behavioral tasks, making them very useful for investigating neural circuit functions. In contrast to the extensive mouse genetic toolkit, the paucity of recombinase-expressing rat models has limited the ability to monitor and manipulate molecularly-defined neural populations in this species. Here we report the generation and validation of two knock-in rat strains expressing either Cre or Flp recombinase under the control of Parvalbumin (Pvalb) , a gene expressed in the critical “fast-spiking” subset of inhibitory interneurons (FSIs). These strains were generated with CRISPR-Cas9 gene editing and show highly specific and penetrant labeling of Pvalb -expressing neurons, as demonstrated by in situ hybridization and immunohistochemistry. We validated these models in both prefrontal cortex and striatum using both ex vivo and in vivo approaches, including whole-cell recording, optogenetics, extracellular physiology and photometry. Our results demonstrate the utility of these new transgenic models for a wide range of neuroscience experiments.