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Saxon D, Alderman PJ, Sorrells SF, Vicini S, Corbin JG. Neuronal Subtypes and Connectivity of the Adult Mouse Paralaminar Amygdala. eNeuro 2024; 11:ENEURO.0119-24.2024. [PMID: 38811163 PMCID: PMC11208988 DOI: 10.1523/eneuro.0119-24.2024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2024] [Revised: 05/03/2024] [Accepted: 05/10/2024] [Indexed: 05/31/2024] Open
Abstract
The paralaminar nucleus of the amygdala (PL) comprises neurons that exhibit delayed maturation. PL neurons are born during gestation but mature during adolescent ages, differentiating into excitatory neurons. These late-maturing PL neurons contribute to the increase in size and cell number of the amygdala between birth and adulthood. However, the function of the PL upon maturation is unknown, as the region has only recently begun to be characterized in detail. In this study, we investigated key defining features of the adult mouse PL; the intrinsic morpho-electric properties of its neurons, and its input and output circuit connectivity. We identify two subtypes of excitatory neurons in the PL based on unsupervised clustering of electrophysiological properties. These subtypes are defined by differential action potential firing properties and dendritic architecture, suggesting divergent functional roles. We further uncover major axonal inputs to the adult PL from the main olfactory network and basolateral amygdala. We also find that axonal outputs from the PL project reciprocally to these inputs and to diverse targets including the amygdala, frontal cortex, hippocampus, hypothalamus, and brainstem. Thus, the adult mouse PL is centrally placed to play a major role in the integration of olfactory sensory information, to coordinate affective and autonomic behavioral responses to salient odor stimuli.
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Affiliation(s)
- David Saxon
- Center for Neuroscience Research, Children's Research Institute, Children's National Hospital, Washington, DC 20011
- Interdisciplinary Program in Neuroscience, Georgetown University Medical Center, Washington, DC 20007
| | - Pia J Alderman
- Department of Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
| | - Shawn F Sorrells
- Department of Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
- Center for the Neural Basis of Cognition, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
| | - Stefano Vicini
- Interdisciplinary Program in Neuroscience, Georgetown University Medical Center, Washington, DC 20007
- Department of Pharmacology and Physiology, Georgetown University Medical Center, Washington, DC 20007
| | - Joshua G Corbin
- Center for Neuroscience Research, Children's Research Institute, Children's National Hospital, Washington, DC 20011
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Saxon D, Alderman PJ, Sorrells SF, Vicini S, Corbin JG. Neuronal subtypes and connectivity of the adult mouse paralaminar amygdala. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.01.11.575250. [PMID: 38260244 PMCID: PMC10802617 DOI: 10.1101/2024.01.11.575250] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2024]
Abstract
The paralaminar nucleus of the amygdala (PL) is comprised of neurons which exhibit delayed maturation. PL neurons are born during gestation but mature during adolescent ages, differentiating into excitatory neurons. The PL is prominent in the adult amygdala, contributing to its increased neuron number and relative size compared to childhood. However, the function of the PL is unknown, as the region has only recently begun to be characterized in detail. In this study, we investigated key defining features of the adult PL; the intrinsic morpho-electric properties of its neurons, and its input and output connectivity. We identify two subtypes of excitatory neurons in the PL based on unsupervised clustering of electrophysiological properties. These subtypes are defined by differential action potential firing properties and dendritic architecture, suggesting divergent functional roles. We further uncover major axonal inputs to the adult PL from the main olfactory network and basolateral amygdala. We also find that axonal outputs from the PL project reciprocally to major inputs, and to diverse targets including the amygdala, frontal cortex, hippocampus, hypothalamus, and brainstem. Thus, the adult PL is centrally placed to play a major role in the integration of olfactory sensory information, likely coordinating affective and autonomic behavioral responses to salient odor stimuli. Significance Statement Mammalian amygdala development includes a growth period from childhood to adulthood, believed to support emotional and social learning. This amygdala growth is partly due to the maturation of neurons during adolescence in the paralaminar amygdala. However, the functional properties of these neurons are unknown. In our recent studies, we characterized the paralaminar amygdala in the mouse. Here, we investigate the properties of the adult PL in the mouse, revealing the existence of two neuronal subtypes that may play distinct functional roles in the adult brain. We further reveal the brain-wide input and output connectivity of the PL, indicating that the PL combines olfactory cues for emotional processing and delivers information to regions associated with reward and autonomic states.
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Proddutur A, Nguyen S, Yeh CW, Gupta A, Santhakumar V. Reclusive chandeliers: Functional isolation of dentate axo-axonic cells after experimental status epilepticus. Prog Neurobiol 2023; 231:102542. [PMID: 37898313 PMCID: PMC10842856 DOI: 10.1016/j.pneurobio.2023.102542] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2023] [Revised: 10/22/2023] [Accepted: 10/24/2023] [Indexed: 10/30/2023]
Abstract
Axo-axonic cells (AACs) provide specialized inhibition to the axon initial segment (AIS) of excitatory neurons and can regulate network output and synchrony. Although hippocampal dentate AACs are structurally altered in epilepsy, physiological analyses of dentate AACs are lacking. We demonstrate that parvalbumin neurons in the dentate molecular layer express PTHLH, an AAC marker, and exhibit morphology characteristic of AACs. Dentate AACs show high-frequency, non-adapting firing but lack persistent firing in the absence of input and have higher rheobase than basket cells suggesting that AACs can respond reliably to network activity. Early after pilocarpine-induced status epilepticus (SE), dentate AACs receive fewer spontaneous excitatory and inhibitory synaptic inputs and have significantly lower maximum firing frequency. Paired recordings and spatially localized optogenetic stimulation revealed that SE reduced the amplitude of unitary synaptic inputs from AACs to granule cells without altering reliability, short-term plasticity, or AIS GABA reversal potential. These changes compromised AAC-dependent shunting of granule cell firing in a multicompartmental model. These early post-SE changes in AAC physiology would limit their ability to receive and respond to input, undermining a critical brake on the dentate throughput during epileptogenesis.
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Affiliation(s)
- Archana Proddutur
- Department of Pharmacology, Physiology and Neuroscience, Rutgers New Jersey Medical School, Newark, NJ 07103, USA; Department of Molecular, Cell and Systems Biology, University of California Riverside, Riverside, CA 92521, USA
| | - Susan Nguyen
- Department of Molecular, Cell and Systems Biology, University of California Riverside, Riverside, CA 92521, USA
| | - Chia-Wei Yeh
- Department of Molecular, Cell and Systems Biology, University of California Riverside, Riverside, CA 92521, USA
| | - Akshay Gupta
- Department of Pharmacology, Physiology and Neuroscience, Rutgers New Jersey Medical School, Newark, NJ 07103, USA; Department of Molecular, Cell and Systems Biology, University of California Riverside, Riverside, CA 92521, USA
| | - Vijayalakshmi Santhakumar
- Department of Pharmacology, Physiology and Neuroscience, Rutgers New Jersey Medical School, Newark, NJ 07103, USA; Department of Molecular, Cell and Systems Biology, University of California Riverside, Riverside, CA 92521, USA.
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Corrubia L, Huang A, Nguyen S, Shiflett MW, Jones MV, Ewell LA, Santhakumar V. Early deficits in dentate circuit and behavioral pattern separation after concussive brain injury. Exp Neurol 2023; 370:114578. [PMID: 37858696 PMCID: PMC10712990 DOI: 10.1016/j.expneurol.2023.114578] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2023] [Revised: 09/28/2023] [Accepted: 10/16/2023] [Indexed: 10/21/2023]
Abstract
Traumatic brain injury leads to cellular and circuit changes in the dentate gyrus, a gateway to hippocampal information processing. Intrinsic granule cell firing properties and strong feedback inhibition in the dentate are proposed as critical to its ability to generate unique representation of similar inputs by a process known as pattern separation. Here we evaluate the impact of brain injury on cellular decorrelation of temporally patterned inputs in slices and behavioral discrimination of spatial locations in vivo one week after concussive lateral fluid percussion injury (FPI) in mice. Despite posttraumatic increases in perforant path evoked excitatory drive to granule cells and enhanced ΔFosB labeling, indicating sustained increase in excitability, the reliability of granule cell spiking was not compromised after FPI. Although granule cells continued to effectively decorrelate output spike trains recorded in response to similar temporally patterned input sets after FPI, their ability to decorrelate highly similar input patterns was reduced. In parallel, encoding of similar spatial locations in a novel object location task that involves the dentate inhibitory circuits was impaired one week after FPI. Injury induced changes in pattern separation were accompanied by loss of somatostatin expressing inhibitory neurons in the hilus. Together, these data suggest that the early posttraumatic changes in the dentate circuit undermine dentate circuit decorrelation of temporal input patterns as well as behavioral discrimination of similar spatial locations, both of which could contribute to deficits in episodic memory.
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Affiliation(s)
- Lucas Corrubia
- Department of Pharmacology, Physiology and Neuroscience, Rutgers New Jersey Medical School, Newark, NJ 07103, USA; Department of Molecular, Cell and Systems Biology, University of California Riverside, Riverside, CA 92521, USA
| | - Andrew Huang
- Department of Molecular, Cell and Systems Biology, University of California Riverside, Riverside, CA 92521, USA
| | - Susan Nguyen
- Department of Molecular, Cell and Systems Biology, University of California Riverside, Riverside, CA 92521, USA
| | | | - Mathew V Jones
- Department of Neuroscience, University of Wisconsin, Madison, WI 53705, USA
| | - Laura A Ewell
- Department of Anatomy and Neurobiology, University of California Irvine, Irvine, CA 92697, USA
| | - Vijayalakshmi Santhakumar
- Department of Pharmacology, Physiology and Neuroscience, Rutgers New Jersey Medical School, Newark, NJ 07103, USA; Department of Molecular, Cell and Systems Biology, University of California Riverside, Riverside, CA 92521, USA.
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Proddutur A, Nguyen S, Yeh CW, Gupta A, Santhakumar V. RECLUSIVE CHANDELIERS: FUNCTIONAL ISOLATION OF DENTATE AXO-AXONIC CELLS AFTER EXPERIMENTAL STATUS EPILEPTICUS. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.10.01.560378. [PMID: 37873292 PMCID: PMC10592856 DOI: 10.1101/2023.10.01.560378] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/25/2023]
Abstract
Axo-axonic cells (AACs) provide specialized inhibition to the axon initial segment (AIS) of excitatory neurons and can regulate network output and synchrony. Although hippocampal dentate AACs are structurally altered in epilepsy, physiological analyses of dentate AACs are lacking. We demonstrate that parvalbumin neurons in the dentate molecular layer express PTHLH, an AAC marker, and exhibit morphology characteristic of AACs. Dentate AACs show high-frequency, non-adapting firing but lack persistent firing in the absence of input and have higher rheobase than basket cells suggesting that AACs can respond reliably to network activity. Early after pilocarpine-induced status epilepticus (SE), dentate AACs receive fewer spontaneous excitatory and inhibitory synaptic inputs and have significantly lower maximum firing frequency. Paired recordings and spatially localized optogenetic stimulation revealed that SE reduced the amplitude of unitary synaptic inputs from AACs to granule cells without altering reliability, short-term plasticity, or AIS GABA reversal potential. These changes compromised AAC-dependent shunting of granule cell firing in a multicompartmental model. These early post-SE changes in AAC physiology would limit their ability to receive and respond to input, undermining a critical brake on the dentate throughput during epileptogenesis.
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Affiliation(s)
- Archana Proddutur
- Department of Pharmacology, Physiology and Neuroscience, Rutgers New Jersey Medical School, Newark, New Jersey 07103
- Department of Molecular, Cell and Systems Biology, University of California Riverside, Riverside, California 92521
| | - Susan Nguyen
- Department of Molecular, Cell and Systems Biology, University of California Riverside, Riverside, California 92521
| | - Chia-Wei Yeh
- Department of Molecular, Cell and Systems Biology, University of California Riverside, Riverside, California 92521
| | - Akshay Gupta
- Department of Pharmacology, Physiology and Neuroscience, Rutgers New Jersey Medical School, Newark, New Jersey 07103
- Department of Molecular, Cell and Systems Biology, University of California Riverside, Riverside, California 92521
| | - Vijayalakshmi Santhakumar
- Department of Pharmacology, Physiology and Neuroscience, Rutgers New Jersey Medical School, Newark, New Jersey 07103
- Department of Molecular, Cell and Systems Biology, University of California Riverside, Riverside, California 92521
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Corrubia L, Huang A, Nguyen S, Shiflett MW, Jones MV, Ewell LA, Santhakumar V. Early Deficits in Dentate Circuit and Behavioral Pattern Separation after Concussive Brain Injury. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.06.22.546120. [PMID: 37745454 PMCID: PMC10515770 DOI: 10.1101/2023.06.22.546120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/26/2023]
Abstract
Traumatic brain injury leads to cellular and circuit changes in the dentate gyrus, a gateway to hippocampal information processing. Intrinsic granule cell firing properties and strong feedback inhibition in the dentate are proposed as critical to its ability to generate unique representation of similar inputs by a process known as pattern separation. Here we evaluate the impact of brain injury on cellular decorrelation of temporally patterned inputs in slices and behavioral discrimination of spatial locations in vivo one week after concussive lateral fluid percussion injury (FPI) in mice. Despite posttraumatic increases in perforant path evoked excitatory drive to granule cells and enhanced ΔFosB labeling, indicating sustained increase in excitability, the reliability of granule cell spiking was not compromised after FPI. Although granule cells continued to effectively decorrelate output spike trains recorded in response to similar temporally patterned input sets after FPI, their ability to decorrelate highly similar input patterns was reduced. In parallel, encoding of similar spatial locations in a novel object location task that involves the dentate inhibitory circuits was impaired one week after FPI. Injury induced changes in pattern separation were accompanied by loss of somatostatin expressing inhibitory neurons in the hilus. Together, these data suggest that the early posttraumatic changes in the dentate circuit undermine dentate circuit decorrelation of temporal input patterns as well as behavioral discrimination of similar spatial locations, both of which could contribute to deficits in episodic memory.
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Affiliation(s)
- Lucas Corrubia
- Department of Pharmacology, Physiology and Neuroscience, Rutgers New Jersey Medical School, Newark, New Jersey 07103
- Department of Molecular, Cell and Systems Biology, University of California Riverside, Riverside, California 92521
| | - Andrew Huang
- Department of Molecular, Cell and Systems Biology, University of California Riverside, Riverside, California 92521
| | - Susan Nguyen
- Department of Molecular, Cell and Systems Biology, University of California Riverside, Riverside, California 92521
| | | | - Mathew V. Jones
- Department of Neuroscience, University of Wisconsin, Madison, WI, 53705
| | - Laura A. Ewell
- Department of Anatomy and Neurobiology, University of California Irvine, Irvine, California 92697
| | - Vijayalakshmi Santhakumar
- Department of Pharmacology, Physiology and Neuroscience, Rutgers New Jersey Medical School, Newark, New Jersey 07103
- Department of Molecular, Cell and Systems Biology, University of California Riverside, Riverside, California 92521
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Gupta A, Dovek L, Proddutur A, Elgammal FS, Santhakumar V. Long-Term Effects of Moderate Concussive Brain Injury During Adolescence on Synaptic and Tonic GABA Currents in Dentate Granule Cells and Semilunar Granule Cells. Front Neurosci 2022; 16:800733. [PMID: 35360164 PMCID: PMC8964009 DOI: 10.3389/fnins.2022.800733] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2021] [Accepted: 01/27/2022] [Indexed: 01/27/2023] Open
Abstract
Progressive physiological changes in the hippocampal dentate gyrus circuits following traumatic brain injury (TBI) contribute to temporal evolution of neurological sequelae. Although early posttraumatic changes in dentate synaptic and extrasynaptic GABA currents have been reported, and whether they evolve over time and remain distinct between the two projection neuron classes, granule cells and semilunar granule cells, have not been evaluated. We examined long-term changes in tonic GABA currents and spontaneous inhibitory postsynaptic currents (sIPSCs) and in dentate projection neurons 3 months after moderate concussive fluid percussion injury (FPI) in adolescent rats. Granule cell tonic GABA current amplitude remained elevated up to 1 month after FPI, but decreased to levels comparable with age-matched controls by 3 months postinjury. Granule cell sIPSC frequency, which we previously reported to be increased 1 week after FPI, remained higher than in age-matched controls at 1 month and was significantly reduced 3 months after FPI. In semilunar granule cells, tonic GABA current amplitude and sIPSC frequency were not different from controls 3 months after FPI, which contrast with decreases observed 1 week after injury. The switch in granule cell inhibitory inputs from early increase to subsequent decrease could contribute to the delayed emergence of cognitive deficits and seizure susceptibility after brain injury.
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Affiliation(s)
- Akshay Gupta
- Department of Pharmacology, Physiology and Neuroscience, Rutgers New Jersey Medical School, Newark, NJ, United States,Department of Molecular, Cell and Systems Biology, University of California, Riverside, Riverside, CA, United States
| | - Laura Dovek
- Department of Molecular, Cell and Systems Biology, University of California, Riverside, Riverside, CA, United States
| | - Archana Proddutur
- Department of Pharmacology, Physiology and Neuroscience, Rutgers New Jersey Medical School, Newark, NJ, United States,Department of Molecular, Cell and Systems Biology, University of California, Riverside, Riverside, CA, United States
| | - Fatima S. Elgammal
- Department of Pharmacology, Physiology and Neuroscience, Rutgers New Jersey Medical School, Newark, NJ, United States
| | - Vijayalakshmi Santhakumar
- Department of Pharmacology, Physiology and Neuroscience, Rutgers New Jersey Medical School, Newark, NJ, United States,Department of Molecular, Cell and Systems Biology, University of California, Riverside, Riverside, CA, United States,*Correspondence: Vijayalakshmi Santhakumar,
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Reduced hippocampal inhibition and enhanced autism-epilepsy comorbidity in mice lacking neuropilin 2. Transl Psychiatry 2021; 11:537. [PMID: 34663783 PMCID: PMC8523694 DOI: 10.1038/s41398-021-01655-6] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/23/2021] [Revised: 08/18/2021] [Accepted: 09/17/2021] [Indexed: 12/19/2022] Open
Abstract
The neuropilin receptors and their secreted semaphorin ligands play key roles in brain circuit development by regulating numerous crucial neuronal processes, including the maturation of synapses and migration of GABAergic interneurons. Consistent with its developmental roles, the neuropilin 2 (Nrp2) locus contains polymorphisms in patients with autism spectrum disorder (ASD). Nrp2-deficient mice show autism-like behavioral deficits and propensity to develop seizures. In order to determine the pathophysiology in Nrp2 deficiency, we examined the hippocampal numbers of interneuron subtypes and inhibitory regulation of hippocampal CA1 pyramidal neurons in mice lacking one or both copies of Nrp2. Immunostaining for interneuron subtypes revealed that Nrp2-/- mice have a reduced number of parvalbumin, somatostatin, and neuropeptide Y cells, mainly in CA1. Whole-cell recordings identified reduced firing and hyperpolarized shift in resting membrane potential in CA1 pyramidal neurons from Nrp2+/- and Nrp2-/- mice compared to age-matched wild-type controls indicating decrease in intrinsic excitability. Simultaneously, the frequency and amplitude of spontaneous inhibitory postsynaptic currents (sIPSCs) are reduced in Nrp2-deficient mice. A convulsive dose of kainic acid evoked electrographic and behavioral seizures with significantly shorter latency, longer duration, and higher severity in Nrp2-/- compared to Nrp2+/+ animals. Finally, Nrp2+/- and Nrp2-/- but not Nrp2+/+, mice have impaired cognitive flexibility demonstrated by reward-based reversal learning, a task associated with hippocampal circuit function. Together these data demonstrate a broad reduction in interneuron subtypes and compromised inhibition in CA1 of Nrp2-/- mice, which could contribute to the heightened seizure susceptibility and behavioral deficits consistent with an ASD/epilepsy phenotype.
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