A biophysical minimal model to investigate age-related changes in CA1 pyramidal cell electrical activity.

Aging is a physiological process that is still poorly understood, especially with respect to effects on the brain. There are open questions about aging that are difficult to answer with an experimental approach. Underlying challenges include the difficulty of recording in vivo single cell and network activity simultaneously with submillisecond resolution, and brain compensatory mechanisms triggered by genetic, pharmacologic, or behavioral manipulations. Mathematical modeling can help address some of these questions by allowing us to fix parameters that cannot be controlled experimentally and investigate neural activity under different conditions. We present a biophysical minimal model of CA1 pyramidal cells (PCs) based on general expressions for transmembrane ion transport derived from thermodynamical principles. The model allows directly varying the contribution of ion channels by changing their number. By analyzing the dynamics of the model, we find parameter ranges that reproduce the variability in electrical activity seen in PCs. In addition, increasing the L-type Ca2+ channel expression in the model reproduces age-related changes in electrical activity that are qualitatively and quantitatively similar to those observed in PCs from aged animals. We also make predictions about age-related changes in PC bursting activity that, to our knowledge, have not been reported previously. We conclude that the model's biophysical nature, flexibility, and computational simplicity make it a potentially powerful complement to experimental studies of aging.

Cell-specific effects of temporal interference stimulation on cortical function.

Temporal interference (TI) stimulation is a popular non-invasive neurostimulation technique that utilizes the following salient neural behavior: pure sinusoid (generated in off-target brain regions) appears to cause no stimulation, whereas modulated sinusoid (generated in target brain regions) does. To understand its effects and mechanisms, we examine responses of different cell types, excitatory pyramidal (Pyr) and inhibitory parvalbumin-expressing (PV) neurons, to pure and modulated sinusoids, in intact network as well as in isolation. In intact network, we present data showing that PV neurons are much less likely than Pyr neurons to exhibit TI stimulation. Remarkably, in isolation, our data shows that almost all Pyr neurons stop exhibiting TI stimulation. We conclude that TI stimulation is largely a network phenomenon. Indeed, PV neurons actively inhibit Pyr neurons in the off-target regions due to pure sinusoids (in off-target regions) generating much higher PV firing rates than modulated sinusoids in the target regions. Additionally, we use computational studies to support and extend our experimental observations.

Organizing the coactivity structure of the hippocampus from robust to flexible memory.

New memories are integrated into prior knowledge of the world. But what if consecutive memories exert opposing demands on the host brain network? We report that acquiring a robust (food-context) memory constrains the mouse hippocampus within a population activity space of highly correlated spike trains that prevents subsequent computation of a flexible (object-location) memory. This densely correlated firing structure developed over repeated mnemonic experience, gradually coupling neurons in the superficial sublayer of the CA1 stratum pyramidale to whole-population activity. Applying hippocampal theta-driven closed-loop optogenetic suppression to mitigate this neuronal recruitment during (food-context) memory formation relaxed the topological constraint on hippocampal coactivity and restored subsequent flexible (object-location) memory. These findings uncover an organizational principle for the peer-to-peer coactivity structure of the hippocampal cell population to meet memory demands.

Input specificity of NMDA-dependent GABAergic plasticity in the hippocampus.

Sensory experiences and learning induce long-lasting changes in both excitatory and inhibitory synapses, thereby providing a crucial substrate for memory. However, the co-tuning of excitatory long-term potentiation (eLTP) or depression (eLTD) with the simultaneous changes at inhibitory synapses (iLTP/iLTD) remains unclear. Herein, we investigated the co-expression of NMDA-induced synaptic plasticity at excitatory and inhibitory synapses in hippocampal CA1 pyramidal cells (PCs) using a combination of electrophysiological, optogenetic, and pharmacological approaches. We found that inhibitory inputs from somatostatin (SST) and parvalbumin (PV)-positive interneurons onto CA1 PCs display input-specific long-term plastic changes following transient NMDA receptor activation. Notably, synapses from SST-positive interneurons consistently exhibited iLTP, irrespective of the direction of excitatory plasticity, whereas synapses from PV-positive interneurons predominantly showed iLTP concurrent with eLTP, rather than eLTD. As neuroplasticity is known to depend on the extracellular matrix, we tested the impact of metalloproteinases (MMP) inhibition. MMP3 blockade interfered with GABAergic plasticity for all inhibitory inputs, whereas MMP9 inhibition selectively blocked eLTP and iLTP in SST-CA1PC synapses co-occurring with eLTP but not eLTD. These findings demonstrate the dissociation of excitatory and inhibitory plasticity co-expression. We propose that these mechanisms of plasticity co-expression may be involved in maintaining excitation-inhibition balance and modulating neuronal integration modes.

Gestational CBD Shapes Insular Cortex in Adulthood.

Many expectant mothers use CBD to alleviate symptoms like nausea, insomnia, anxiety, and pain, despite limited research on its long-term effects. However, CBD passes through the placenta, affecting fetal development and impacting offspring behavior. We investigated how prenatal CBD exposure affects the insular cortex (IC), a brain region involved in emotional processing and linked to psychiatric disorders. The IC is divided into two territories: the anterior IC (aIC), processing socioemotional signals, and the posterior IC (pIC), specializing in interoception and pain perception. Pyramidal neurons in the aIC and pIC exhibit sex-specific electrophysiological properties, including variations in excitability and the excitatory/inhibitory balance. We investigated IC's cellular properties and synaptic strength in the offspring of both sexes from mice exposed to low-dose CBD during gestation (E5-E18; 3 mg/kg, s.c.). Prenatal CBD exposure induced sex-specific and territory-specific changes in the active and passive membrane properties, as well as intrinsic excitability and the excitatory/inhibitory balance, in the IC of adult offspring. The data indicate that in utero CBD exposure disrupts IC neuronal development, leading to a loss of functional distinction between IC territories. These findings may have significant implications for understanding the effects of CBD on emotional behaviors in offspring.

Gain control of sensory input across polysynaptic circuitries in mouse visual cortex by a single G protein-coupled receptor type (5-HT2A).

Response gain is a crucial means by which modulatory systems control the impact of sensory input. In the visual cortex, the serotonergic 5-HT2A receptor is key in such modulation. However, due to its expression across different cell types and lack of methods that allow for specific activation, the underlying network mechanisms remain unsolved. Here we optogenetically activate endogenous G protein-coupled receptor (GPCR) signaling of a single receptor subtype in distinct mouse neocortical subpopulations in vivo. We show that photoactivation of the 5-HT2A receptor pathway in pyramidal neurons enhances firing of both excitatory neurons and interneurons, whereas 5-HT2A photoactivation in parvalbumin interneurons produces bidirectional effects. Combined photoactivation in both cell types and cortical network modelling demonstrates a conductance-driven polysynaptic mechanism that controls the gain of visual input without affecting ongoing baseline levels. Our study opens avenues to explore GPCRs neuromodulation and its impact on sensory-driven activity and ongoing neuronal dynamics.

Distinct ventral hippocampal inhibitory microcircuits regulating anxiety and fear behaviors.

In emotion research, anxiety and fear have always been interconnected, sharing overlapping brain structures and neural circuitry. Recent investigations, however, have unveiled parallel long-range projection pathways originating from the ventral hippocampus, shedding light on their distinct roles in anxiety and fear. Yet, the mechanisms governing the emergence of projection-specific activity patterns to mediate different negative emotions remain elusive. Here, we show a division of labor in local GABAergic inhibitory microcircuits of the ventral hippocampus, orchestrating the activity of subpopulations of pyramidal neurons to shape anxiety and fear behaviors in mice. These findings offer a comprehensive insight into how distinct inhibitory microcircuits are dynamically engaged to encode different emotional states.

MeCP2 Deficiency Alters the Response Selectivity of Prefrontal Cortical Neurons to Different Social Stimuli.

Rett syndrome (RTT), a severe neurodevelopmental disorder caused by mutations in the MeCP2 gene, is characterized by cognitive and social deficits. Previous studies have noted hypoactivity in the medial prefrontal cortex (mPFC) pyramidal neurons of MeCP2-deficient mice (RTT mice) in response to both social and nonsocial stimuli. To further understand the neural mechanisms behind the social deficits of RTT mice, we monitored excitatory pyramidal neurons in the prelimbic region of the mPFC during social interactions in mice. These neurons' activity was closely linked to social preference, especially in wild-type mice. However, RTT mice showed reduced social interest and corresponding hypoactivity in these neurons, indicating that impaired mPFC activity contributes to their social deficits. We identified six mPFC neural ensembles selectively tuned to various stimuli, with RTT mice recruiting fewer neurons to ensembles responsive to social interactions and consistently showing lower stimulus-ON ensemble transient rates. Despite these lower rates, RTT mice exhibited an increase in the percentage of social-ON neurons in later sessions, suggesting a compensatory mechanism for the decreased firing rate. This highlights the limited plasticity in the mPFC caused by MeCP2 deficiency and offers insights into the neural dynamics of social encoding. The presence of multifunctional neurons and those specifically responsive to social or object stimuli in the mPFC emphasizes its crucial role in complex behaviors and cognitive functions, with selective neuron engagement suggesting efficiency in neural activation that optimizes responses to environmental stimuli.

A hippocampal circuit mechanism to balance memory reactivation during sleep.

Memory consolidation involves the synchronous reactivation of hippocampal cells active during recent experience in sleep sharp-wave ripples (SWRs). How this increase in firing rates and synchrony after learning is counterbalanced to preserve network stability is not understood. We discovered a network event generated by an intrahippocampal circuit formed by a subset of CA2 pyramidal cells to cholecystokinin-expressing (CCK+) basket cells, which fire a barrage of action potentials ("BARR") during non-rapid eye movement sleep. CA1 neurons and assemblies that increased their activity during learning were reactivated during SWRs but inhibited during BARRs. The initial increase in reactivation during SWRs returned to baseline through sleep. This trend was abolished by silencing CCK+ basket cells during BARRs, resulting in higher synchrony of CA1 assemblies and impaired memory consolidation.

Temporal dynamics of neocortical development in organotypic mouse brain cultures: a comprehensive analysis.

Murine organotypic brain slice cultures have been widely used in neuroscientific research and are offering the opportunity to study neuronal function under normal and disease conditions. Despite the broad application, the mechanisms governing the maturation of immature cortical circuits in vitro are not well understood. In this study, we present a detailed investigation into the development of the neocortex in vitro. Using a holistic approach, we studied organotypic whole hemisphere brain slice cultures from postnatal mice and tracked the development of the somatosensory area over a 5-wk period. Our analysis revealed the maturation of passive and active intrinsic properties of pyramidal cells together with their morphology, closely resembling in vivo development. Detailed multielectrode array (MEA) electrophysiological assessments and RNA expression profiling demonstrated stable network properties by 2 wk in culture, followed by the transition of spontaneous activity toward more complex patterns including high-frequency oscillations. However, culturing weeks 4 and 5 exhibited increased variability and initial signs of neuronal loss, highlighting the importance of considering developmental stages in experimental design. This comprehensive characterization is vital for understanding the temporal dynamics of the neocortical development in vitro, with implications for neuroscientific research methodologies, particularly in the investigation of diseases such as epilepsy and other neurodevelopmental disorders.NEW & NOTEWORTHY The development of the mouse neocortex in vitro mimics the in vivo development. Mouse brain cultures can serve as a model system for cortical development for the first 2 wk in vitro and as a model system for the adult cortex from 2 to 4 wk in vitro. Mouse organotypic brain slice cultures develop high-frequency network oscillations at γ frequency after 2 wk in vitro. Mouse brain cultures exhibit increased heterogeneity and variability after 4 wk in culture.

Chronic morphine treatment induces sex- and synapse-specific cellular tolerance on thalamo-cortical mu opioid receptor signaling.

How cellular adaptations give rise to opioid analgesic tolerance to opioids like morphine is not well understood. For one, pain is a complex phenomenon comprising both sensory and affective components, largely mediated through separate circuits. Glutamatergic projections from the medial thalamus (MThal) to the anterior cingulate cortex (ACC) are implicated in processing of affective pain, a relatively understudied component of the pain experience. The goal of this study was to determine the effects of chronic morphine exposure on mu-opioid receptor (MOR) signaling on MThal-ACC synaptic transmission within the excitatory and feedforward inhibitory pathways. Using whole cell patch-clamp electrophysiology and optogenetics to selectively target these projections, we measured morphine-mediated inhibition of optically evoked postsynaptic currents in ACC layer V pyramidal neurons in drug-naïve and chronically morphine-treated mice. We found that morphine perfusion inhibited the excitatory and feedforward inhibitory pathways similarly in females but caused greater inhibition of the inhibitory pathway in males. Chronic morphine treatment robustly attenuated morphine presynaptic inhibition within the inhibitory pathway in males, but not females, and mildly attenuated presynaptic inhibition within the excitatory pathway in both sexes. These effects were not observed in MOR phosphorylation-deficient mice. This study indicates that chronic morphine treatment induces cellular tolerance to morphine within a thalamo-cortical circuit relevant to pain and opioid analgesia. Furthermore, it suggests this tolerance may be driven by MOR phosphorylation. Overall, these findings improve our understanding of how chronic opioid exposure alters cellular signaling in ways that may contribute to opioid analgesic tolerance.NEW & NOTEWORTHY Opioid signaling within the anterior cingulate cortex (ACC) is important for opioid modulation of affective pain. Glutamatergic medial thalamus (MThal) neurons synapse in the ACC and opioids, acting through mu opioid receptors (MORs), acutely inhibit synaptic transmission from MThal synapses. However, the effect of chronic opioid exposure on MThal-ACC synaptic transmission is not known. Here, we demonstrate that chronic morphine treatment induces cellular tolerance at these synapses in a sex-specific and phosphorylation-dependent manner.

Reducing Filamin A Restores Cortical Synaptic Connectivity and Early Social Communication Following Cellular Mosaicism in Autism Spectrum Disorder Pathways.

Communication in the form of nonverbal, social vocalization, or crying is evolutionary conserved in mammals and is impaired early in human infants that are later diagnosed with autism spectrum disorder (ASD). Defects in infant vocalization have been proposed as an early sign of ASD that may exacerbate ASD development. However, the neural mechanisms associated with early communicative deficits in ASD are not known. Here, we expressed a constitutively active mutant of Rheb (RhebS16H), which is known to upregulate two ASD core pathways, mTOR complex 1 (mTORC1) and ERK1/2, in Layer (L) 2/3 pyramidal neurons of the neocortex of mice of either sex. We found that cellular mosaic expression of RhebS16H in L2/3 pyramidal neurons altered the production of isolation calls from neonatal mice. This was accompanied by an expected misplacement of neurons and dendrite overgrowth, along with an unexpected increase in spine density and length, which was associated with increased excitatory synaptic activity. This contrasted with the known decrease in spine density in RhebS16H neurons of 1-month-old mice. Reducing the levels of the actin cross-linking and adaptor protein filamin A (FLNA), known to be increased downstream of ERK1/2, attenuated dendrite overgrowth and fully restored spine properties, synaptic connectivity, and the production of pup isolation calls. These findings suggest that upper-layer cortical pyramidal neurons contribute to communicative deficits in a condition known to affect two core ASD pathways and that these mechanisms are regulated by FLNA.

A dendritic mechanism for balancing synaptic flexibility and stability.

Biological and artificial neural networks learn by modifying synaptic weights, but it is unclear how these systems retain previous knowledge and also acquire new information. Here, we show that cortical pyramidal neurons can solve this plasticity-versus-stability dilemma by differentially regulating synaptic plasticity at distinct dendritic compartments. Oblique dendrites of adult mouse layer 5 cortical pyramidal neurons selectively receive monosynaptic thalamic input, integrate linearly, and lack burst-timing synaptic potentiation. In contrast, basal dendrites, which do not receive thalamic input, exhibit conventional NMDA receptor (NMDAR)-mediated supralinear integration and synaptic potentiation. Congruently, spiny synapses on oblique branches show decreased structural plasticity in vivo. The selective decline in NMDAR activity and expression at synapses on oblique dendrites is controlled by a critical period of visual experience. Our results demonstrate a biological mechanism for how single neurons can safeguard a set of inputs from ongoing plasticity by altering synaptic properties at distinct dendritic domains.

Chronic Stress Alters Synaptic Inhibition/Excitation Balance of Pyramidal Neurons But Not PV Interneurons in the Infralimbic and Prelimbic Cortices of C57BL/6J Mice.

The medial prefrontal cortex (mPFC) plays a pivotal role in regulating working memory, executive function, and self-regulatory behaviors. Dysfunction in the mPFC circuits is a characteristic feature of several neuropsychiatric disorders including schizophrenia, depression, and post-traumatic stress disorder. Chronic stress (CS) is widely recognized as a major triggering factor for the onset of these disorders. Although evidence suggests synaptic dysfunction in mPFC circuits following CS exposure, it remains unclear how different neuronal populations in the infralimbic (IL) and prelimbic (PL) cortices are affected in terms of synaptic inhibition/excitation balance (I/E ratio). Here, using neuroproteomic analysis and whole-cell patch-clamp recordings in pyramidal neurons (PNs) and parvalbumin (PV) interneurons within the PL and IL cortices, we examined the synaptic changes after 21 d of chronic unpredictable stress, in male mice. Our results reveal distinct impacts of CS on PL and IL PNs, resulting in an increased I/E ratio in both subregions but through different mechanisms: CS increases inhibitory synaptic drive in the PL while decreasing excitatory synaptic drive in the IL. Notably, the I/E ratio and excitatory and inhibitory synaptic drive of PV interneurons remained unaffected in both PL and IL circuits following CS exposure. These findings offer novel mechanistic insights into the influence of CS on mPFC circuits and support the hypothesis of stress-induced mPFC hypofunction.

Bidirectional fear modulation by discrete anterior insular circuits in male mice.

The brain's ability to appraise threats and execute appropriate defensive responses is essential for survival in a dynamic environment. Humans studies have implicated the anterior insular cortex (aIC) in subjective fear regulation and its abnormal activity in fear/anxiety disorders. However, the complex aIC connectivity patterns involved in regulating fear remain under investigated. To address this, we recorded single units in the aIC of freely moving male mice that had previously undergone auditory fear conditioning, assessed the effect of optogenetically activating specific aIC output structures in fear, and examined the organization of aIC neurons projecting to the specific structures with retrograde tracing. Single-unit recordings revealed that a balanced number of aIC pyramidal neurons' activity either positively or negatively correlated with a conditioned tone-induced freezing (fear) response. Optogenetic manipulations of aIC pyramidal neuronal activity during conditioned tone presentation altered the expression of conditioned freezing. Neural tracing showed that non-overlapping populations of aIC neurons project to the amygdala or the medial thalamus, and the pathway bidirectionally modulated conditioned fear. Specifically, optogenetic stimulation of the aIC-amygdala pathway increased conditioned freezing, while optogenetic stimulation of the aIC-medial thalamus pathway decreased it. Our findings suggest that the balance of freezing-excited and freezing-inhibited neuronal activity in the aIC and the distinct efferent circuits interact collectively to modulate fear behavior.

Net synaptic drive of fast-spiking interneurons is inverted towards inhibition in human FCD I epilepsy.

Focal cortical dysplasia type I (FCD I) is the most common cause of pharmaco-resistant epilepsy with the poorest prognosis. To understand the epileptogenic mechanisms of FCD I, we obtained tissue resected from patients with FCD I epilepsy, and from tumor patients as control. Using whole-cell patch clamp in acute human brain slices, we investigated the cellular properties of fast-spiking interneurons (FSINs) and pyramidal neurons (PNs) within the ictal onset zone. In FCD I epilepsy, FSINs exhibited lower firing rates from slower repolarization and action potential broadening, while PNs had increased firing. Importantly, excitatory synaptic drive of FSINs increased progressively with the scale of cortical activation as a general property across species, but this relationship was inverted towards net inhibition in FCD I epilepsy. Further comparison with intracranial electroencephalography (iEEG) from the same patients revealed that the spatial extent of pathological high-frequency oscillations (pHFO) was associated with synaptic events at FSINs.

Developmental Cajal-Retzius cell death contributes to the maturation of layer 1 cortical inhibition and somatosensory processing.

The role of developmental cell death in the formation of brain circuits is not well understood. Cajal-Retzius cells constitute a major transient neuronal population in the mammalian neocortex, which largely disappears at the time of postnatal somatosensory maturation. In this study, we used mouse genetics, anatomical, functional, and behavioral approaches to explore the impact of the early postnatal death of Cajal-Retzius cells in the maturation of the cortical circuit. We find that before their death, Cajal-Retzius cells mainly receive inputs from layer 1 neurons, which can only develop their mature connectivity onto layer 2/3 pyramidal cells after Cajal-Retzius cells disappear. This developmental connectivity progression from layer 1 GABAergic to layer 2/3 pyramidal cells regulates sensory-driven inhibition within, and more so, across cortical columns. Here we show that Cajal-Retzius cell death prevention leads to layer 2/3 hyper-excitability, delayed learning and reduced performance in a multi-whisker-dependent texture discrimination task.

Cl--dependent amplification of excitatory synaptic potentials at distal dendrites revealed by voltage imaging.

The processing of synaptic signals in somatodendritic compartments determines neuronal computation. Although the amplification of excitatory signals by local voltage-dependent cation channels has been extensively studied, their spatiotemporal dynamics in elaborate dendritic branches remain obscure owing to technical limitations. Using fluorescent voltage imaging throughout dendritic arborizations in hippocampal pyramidal neurons, we demonstrate a unique chloride ion (Cl-)-dependent remote computation mechanism in the distal branches. Excitatory postsynaptic potentials triggered by local laser photolysis of caged glutamate spread along dendrites, with gradual amplification toward the distal end while attenuation toward the soma. Tour de force subcellular patch-clamp recordings from thin branches complemented by biophysical model simulations revealed that the asymmetric augmentation of excitation relies on tetrodotoxin-resistant sodium ion (Na+) channels and Cl- conductance accompanied by a more hyperpolarized dendritic resting potential. Together, this study reveals the cooperative voltage-dependent actions of cation and anion conductance for dendritic supralinear computation, which can locally decode the spatiotemporal context of synaptic inputs.

Adolescent Thalamoprefrontal Inhibition Leads to Changes in Intrinsic Prefrontal Network Connectivity.

Adolescent inhibition of thalamocortical projections from postnatal days P20 to 50 leads to long-lasting deficits in prefrontal cortex function and cognition in the adult mouse. While this suggests a role of thalamic activity in prefrontal cortex maturation, it is unclear how inhibition of these projections affects prefrontal circuitry during adolescence. Here, we used chemogenetic tools to inhibit thalamoprefrontal projections in male/female mice from P20 to P35 and measured synaptic inputs to prefrontal pyramidal neurons by layer (either II/III or V/VI) and projection target (mediodorsal thalamus (MD), nucleus accumbens (NAc), or callosal prefrontal projections) 24 h later using slice physiology. We found a decrease in the frequency of excitatory and inhibitory currents in layer II/III NAc and layer V/VI MD-projecting neurons while layer V/VI NAc-projecting neurons showed an increase in the amplitude of excitatory and inhibitory currents. Regarding cortical projections, the frequency of inhibitory but not excitatory currents was enhanced in contralateral mPFC-projecting neurons. Notably, despite these complex changes in individual levels of excitation and inhibition, the overall balance between excitation and inhibition in each cell was only altered in the contralateral mPFC projections. This finding suggests homeostatic regulation occurs within subcortically but not intracortical callosal-projecting neurons. Increased inhibition of intraprefrontal connectivity may therefore be particularly important for prefrontal cortex circuit maturation. Finally, we observed cognitive deficits in the adult mouse using this narrowed window of thalamocortical inhibition.

Multiple layers of diversity govern the cell type specificity of GABAergic input received by mouse subicular pyramidal neurons.

The subiculum is a key region of the brain involved in the initiation of pathological activity in temporal lobe epilepsy, and local GABAergic inhibition is essential to prevent subicular-originated epileptiform discharges. Subicular pyramidal cells may be easily distinguished into two classes based on their different firing patterns. Here, we have compared the strength of the GABAa receptor-mediated inhibitory postsynaptic currents received by regular- vs. burst-firing subicular neurons and their dynamic modulation by the activation of µ opioid receptors. We have taken advantage of the sequential re-patching of the same cell to initially classify pyramidal neurons according to their firing patters, and then to measure GABAergic events triggered by the optogenetic stimulation of parvalbumin- and somatostatin-expressing interneurons. Activation of parvalbumin-expressing cells generated larger responses in postsynaptic burst-firing neurons whereas the opposite was observed for currents evoked by the stimulation of somatostatin-expressing interneurons. In all cases, events depended critically on ω-agatoxin IVA- but not on ω-conotoxin GVIA-sensitive calcium channels. Optogenetic GABAergic input originating from both parvalbumin- and somatostatin-expressing cells was reduced in amplitude following the exposure to a µ opioid receptor agonist. The kinetics of this pharmacological sensitivity was different in regular- vs. burst-firing neurons, but only when responses were evoked by the activation of parvalbumin-expressing neurons, whereas no differences were observed when somatostatin-expressing cells were stimulated. In conclusion, our results show that a high degree of complexity regulates the organizing principles of subicular GABAergic inhibition, with the interaction of pre- and postsynaptic diversity at multiple levels. KEY POINTS: Optogenetic stimulation of parvalbumin- and somatostatin-expressing interneurons (PVs and SOMs) triggers inhibitory postsynaptic currents (IPSCs) in both regular- and burst-firing (RFs and BFs) subicular pyramidal cells. The amplitude of optogenetically evoked IPSCs from PVs (PV-opto IPSCs) is larger in BFs whereas IPSCs generated by the light activation of SOMs (SOM-opto IPSCs) are larger in RFs. Both PV- and SOM-opto IPSCs critically depend on ω-agatoxin IVA-sensitive P/Q type voltage-gated calcium channels, whereas no major effects are observed following exposure to ω-conotoxin GVIA, suggesting no significant involvement of N-type channels. The amplitude of both PV- and SOM-opto IPSCs is reduced by the probable pharmacological activation of presynaptic µ opioid receptors, with a faster kinetics of the effect observed in PV-opto IPSCs from RFs vs. BFs, but not in SOM-opto IPSCs. These results help us understand the complex interactions between different layers of diversity regulating GABAergic input onto subicular microcircuits.