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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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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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Hernández-Frausto M, Bilash OM, Masurkar AV, Basu J. Local and long-range GABAergic circuits in hippocampal area CA1 and their link to Alzheimer's disease. Front Neural Circuits 2023; 17:1223891. [PMID: 37841892 PMCID: PMC10570439 DOI: 10.3389/fncir.2023.1223891] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2023] [Accepted: 09/08/2023] [Indexed: 10/17/2023] Open
Abstract
GABAergic inhibitory neurons are the principal source of inhibition in the brain. Traditionally, their role in maintaining the balance of excitation-inhibition has been emphasized. Beyond homeostatic functions, recent circuit mapping and functional manipulation studies have revealed a wide range of specific roles that GABAergic circuits play in dynamically tilting excitation-inhibition coupling across spatio-temporal scales. These span from gating of compartment- and input-specific signaling, gain modulation, shaping input-output functions and synaptic plasticity, to generating signal-to-noise contrast, defining temporal windows for integration and rate codes, as well as organizing neural assemblies, and coordinating inter-regional synchrony. GABAergic circuits are thus instrumental in controlling single-neuron computations and behaviorally-linked network activity. The activity dependent modulation of sensory and mnemonic information processing by GABAergic circuits is pivotal for the formation and maintenance of episodic memories in the hippocampus. Here, we present an overview of the local and long-range GABAergic circuits that modulate the dynamics of excitation-inhibition and disinhibition in the main output area of the hippocampus CA1, which is crucial for episodic memory. Specifically, we link recent findings pertaining to GABAergic neuron molecular markers, electrophysiological properties, and synaptic wiring with their function at the circuit level. Lastly, given that area CA1 is particularly impaired during early stages of Alzheimer's disease, we emphasize how these GABAergic circuits may contribute to and be involved in the pathophysiology.
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Affiliation(s)
- Melissa Hernández-Frausto
- Neuroscience Institute, New York University Langone Health, New York, NY, United States
- Department of Neuroscience and Physiology, New York University Grossman School of Medicine, New York, NY, United States
| | - Olesia M. Bilash
- Neuroscience Institute, New York University Langone Health, New York, NY, United States
- Meinig School of Biomedical Engineering, Cornell University, Ithaca, NY, United States
| | - Arjun V. Masurkar
- Neuroscience Institute, New York University Langone Health, New York, NY, United States
- Department of Neuroscience and Physiology, New York University Grossman School of Medicine, New York, NY, United States
- Center for Cognitive Neurology, Department of Neurology, New York University Grossman School of Medicine, New York, NY, United States
| | - Jayeeta Basu
- Neuroscience Institute, New York University Langone Health, New York, NY, United States
- Department of Neuroscience and Physiology, New York University Grossman School of Medicine, New York, NY, United States
- Department of Psychiatry, New York University Grossman School of Medicine, New York, NY, United States
- Center for Neural Science, New York University, New York, NY, United States
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Stöber TM, Batulin D, Triesch J, Narayanan R, Jedlicka P. Degeneracy in epilepsy: multiple routes to hyperexcitable brain circuits and their repair. Commun Biol 2023; 6:479. [PMID: 37137938 PMCID: PMC10156698 DOI: 10.1038/s42003-023-04823-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2022] [Accepted: 04/06/2023] [Indexed: 05/05/2023] Open
Abstract
Due to its complex and multifaceted nature, developing effective treatments for epilepsy is still a major challenge. To deal with this complexity we introduce the concept of degeneracy to the field of epilepsy research: the ability of disparate elements to cause an analogous function or malfunction. Here, we review examples of epilepsy-related degeneracy at multiple levels of brain organisation, ranging from the cellular to the network and systems level. Based on these insights, we outline new multiscale and population modelling approaches to disentangle the complex web of interactions underlying epilepsy and to design personalised multitarget therapies.
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Affiliation(s)
- Tristan Manfred Stöber
- Frankfurt Institute for Advanced Studies, 60438, Frankfurt am Main, Germany
- Institute for Neural Computation, Faculty of Computer Science, Ruhr University Bochum, 44801, Bochum, Germany
- Epilepsy Center Frankfurt Rhine-Main, Department of Neurology, Goethe University, 60590, Frankfurt, Germany
| | - Danylo Batulin
- Frankfurt Institute for Advanced Studies, 60438, Frankfurt am Main, Germany
- CePTER - Center for Personalized Translational Epilepsy Research, Goethe University, 60590, Frankfurt, Germany
- Faculty of Computer Science and Mathematics, Goethe University, 60486, Frankfurt, Germany
| | - Jochen Triesch
- Frankfurt Institute for Advanced Studies, 60438, Frankfurt am Main, Germany
| | - Rishikesh Narayanan
- Cellular Neurophysiology Laboratory, Molecular Biophysics Unit, Indian Institute of Science, Bangalore, 560012, India
| | - Peter Jedlicka
- ICAR3R - Interdisciplinary Centre for 3Rs in Animal Research, Faculty of Medicine, Justus Liebig University Giessen, 35390, Giessen, Germany.
- Institute of Clinical Neuroanatomy, Neuroscience Center, Goethe University, 60590, Frankfurt am Main, Germany.
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Stieve BJ, Smith MM, Krook-Magnuson E. LINCs Are Vulnerable to Epileptic Insult and Fail to Provide Seizure Control via On-Demand Activation. eNeuro 2023; 10:ENEURO.0195-22.2022. [PMID: 36725340 PMCID: PMC9933934 DOI: 10.1523/eneuro.0195-22.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2022] [Revised: 12/13/2022] [Accepted: 12/19/2022] [Indexed: 02/03/2023] Open
Abstract
Temporal lobe epilepsy (TLE) is notoriously pharmacoresistant, and identifying novel therapeutic targets for controlling seizures is crucial. Long-range inhibitory neuronal nitric oxide synthase-expressing cells (LINCs), a population of hippocampal neurons, were recently identified as a unique source of widespread inhibition in CA1, able to elicit both GABAA-mediated and GABAB-mediated postsynaptic inhibition. We therefore hypothesized that LINCs could be an effective target for seizure control. LINCs were optogenetically activated for on-demand seizure intervention in the intrahippocampal kainate (KA) mouse model of chronic TLE. Unexpectedly, LINC activation at 1 month post-KA did not substantially reduce seizure duration in either male or female mice. We tested two different sets of stimulation parameters, both previously found to be effective with on-demand optogenetic approaches, but neither was successful. Quantification of LINCs following intervention revealed a substantial reduction of LINC numbers compared with saline-injected controls. We also observed a decreased number of LINCs when the site of initial insult (i.e., KA injection) was moved to the amygdala [basolateral amygdala (BLA)-KA], and correspondingly, no effect of light delivery on BLA-KA seizures. This indicates that LINCs may be a vulnerable population in TLE, regardless of the site of initial insult. To determine whether long-term circuitry changes could influence outcomes, we continued testing once a month for up to 6 months post-KA. However, at no time point did LINC activation provide meaningful seizure suppression. Altogether, our results suggest that LINCs are not a promising target for seizure inhibition in TLE.
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Affiliation(s)
- Bethany J Stieve
- Graduate Program in Neuroscience, University of Minnesota, Minneapolis, Minnesota 55455
| | - Madison M Smith
- Department of Neuroscience, University of Minnesota, Minneapolis, Minnesota 55455
| | - Esther Krook-Magnuson
- Graduate Program in Neuroscience, University of Minnesota, Minneapolis, Minnesota 55455
- Department of Neuroscience, University of Minnesota, Minneapolis, Minnesota 55455
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Bryson A, Reid C, Petrou S. Fundamental Neurochemistry Review: GABA A receptor neurotransmission and epilepsy: Principles, disease mechanisms and pharmacotherapy. J Neurochem 2023; 165:6-28. [PMID: 36681890 DOI: 10.1111/jnc.15769] [Citation(s) in RCA: 11] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2022] [Revised: 12/12/2022] [Accepted: 01/04/2023] [Indexed: 01/23/2023]
Abstract
Epilepsy is a common neurological disorder associated with alterations of excitation-inhibition balance within brain neuronal networks. GABAA receptor neurotransmission is the most prevalent form of inhibitory neurotransmission and is strongly implicated in both the pathophysiology and treatment of epilepsy, serving as a primary target for antiseizure medications for over a century. It is now established that GABA exerts a multifaceted influence through an array of GABAA receptor subtypes that extends far beyond simply negating excitatory activity. As the role of GABAA neurotransmission within inhibitory circuits is elaborated, this will enable the development of precision therapies that correct the network dysfunction underlying epileptic pathology.
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Affiliation(s)
- Alexander Bryson
- The Florey Institute of Neuroscience and Mental Health, The University of Melbourne, Parkville, Victoria, Australia.,Department of Neurology, Austin Health, Heidelberg, Victoria, Australia
| | - Christopher Reid
- The Florey Institute of Neuroscience and Mental Health, The University of Melbourne, Parkville, Victoria, Australia
| | - Steven Petrou
- The Florey Institute of Neuroscience and Mental Health, The University of Melbourne, Parkville, Victoria, Australia.,Praxis Precision Medicines, Inc., Cambridge, Massachusetts, USA
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Proskurina EY, Zaitsev AV. Regulation of Potassium and Chloride Concentrations in Nervous Tissue as a Method of Anticonvulsant Therapy. J EVOL BIOCHEM PHYS+ 2022. [DOI: 10.1134/s0022093022050015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Abstract
Under some pathological conditions, such as pharmacoresistant
epilepsy, status epilepticus or certain forms of genetic abnormalities,
spiking activity of GABAergic interneurons may enhance excitation
processes in neuronal circuits and provoke the generation of ictal
discharges. As a result, anticonvulsants acting on the GABAergic
system may be ineffective or even increase seizure activity. This
paradoxical effect of the inhibitory system is due to ionic imbalances
in nervous tissue. This review addresses the mechanisms of ictal
discharge initiation in neuronal networks due to the imbalance of
chloride and potassium ions, as well as possible ways to regulate
ionic concentrations. Both the enhancement (or attenuation) of the
activity of certain neuronal ion transporters and ion pumps and
their additional expression via gene therapy can be effective in
suppressing seizure activity caused by ionic imbalances. The Na+–K+-pump,
NKCC1 and KCC2 cotransporters are important for maintaining proper
K+ and Cl– concentrations
in nervous tissue, having been repeatedly considered as pharmacological
targets for antiepileptic exposures. Further progress in this direction
is hampered by the lack of sufficiently selective pharmacological
tools and methods for providing effective drug delivery to the epileptic
focus. The use of the gene therapy techniques, such as overexpressing
of the KCC2 transporter in the epileptic focus, seems to be a more promising
approach. Another possible direction could be the use of optogenetic
tools, namely specially designed light-activated ion pumps or ion
channels. In this case, photon energy can be used to create the
required gradients of chloride and potassium ions, although these
methods also have significant limitations which complicate their
rapid introduction into medicine.
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Serpa A, Bento M, Caulino-Rocha A, Pawlak S, Cunha-Reis D. Opposing reduced VPAC 1 and enhanced VPAC 2 VIP receptors in the hippocampus of the Li 2+-pilocarpine rat model of temporal lobe epilepsy. Neurochem Int 2022; 158:105383. [PMID: 35787395 DOI: 10.1016/j.neuint.2022.105383] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2022] [Revised: 06/21/2022] [Accepted: 06/27/2022] [Indexed: 11/17/2022]
Abstract
VIP binding sites are upregulated in mesial temporal lobe epilepsy (MTLE) patients, also suffering from severe cognitive deficits. Although altered VIP and VIP receptor levels were described in rodent models of epilepsy, the VIP receptor subtype(s) were never identified. We now investigated how VPAC1 and VPAC2 receptor levels change in the Li2+-pilocarpine rat model of MTLE. Cognitive decline and altered synaptic plasticity as estimated from phosphorylation of AMPA GluA1 subunit on Ser831 and Ser845 and AMPA GluA1/GluA2 ratio was also probed. Animals showing spontaneous recurrent seizures (SRSs) for at least 4 weeks showed impaired learning in the radial arm maze (RAM) and presented decreased VPAC1 and increased VPAC2 receptor levels. In addition, SRSs rats showed increased AMPA GluA1 phosphorylation in Ser831 and Ser845, marked decrease in GluA1 levels and a milder decrease in GluA2 levels. Consequently, the GluA1/GluA2 ratio was also decreased in SRSs rats. Altered VIP receptor levels may differentially prevent or contribute to MTLE pathology, since VPAC1 receptors promote the endogenous control of LTP, mediate endogenous VIP neuroprotection against altered synaptic plasticity following epileptiform activity, and mediate anti-inflammatory actions in microglia, while VPAC2 receptors mediate VIP endogenous neuroprotection against neonatal excitotoxicity and prevent reactive astrogliosis. This discovery imposes a different mindset for considering VIP receptors as therapeutic targets in MTLE, allowing a differential targeting of the cellular events contributing to epileptogenesis.
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Affiliation(s)
- André Serpa
- Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, 1749-016, Lisboa, Portugal; BioISI - Instituto de Biossistemas e Ciências Integratives, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, 1749-016, Lisboa, Portugal
| | - Marta Bento
- Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, 1749-016, Lisboa, Portugal; BioISI - Instituto de Biossistemas e Ciências Integratives, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, 1749-016, Lisboa, Portugal
| | - Ana Caulino-Rocha
- Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, 1749-016, Lisboa, Portugal; BioISI - Instituto de Biossistemas e Ciências Integratives, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, 1749-016, Lisboa, Portugal
| | - Seweryn Pawlak
- Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, 1749-016, Lisboa, Portugal; BioISI - Instituto de Biossistemas e Ciências Integratives, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, 1749-016, Lisboa, Portugal
| | - Diana Cunha-Reis
- Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, 1749-016, Lisboa, Portugal; BioISI - Instituto de Biossistemas e Ciências Integratives, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, 1749-016, Lisboa, Portugal.
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Seelman A, Vu K, Buckmaster P, Mackie K, Field C, Johnson S, Wyeth M. Cannabinoid receptor 1-labeled boutons in the sclerotic dentate gyrus of epileptic sea lions. Epilepsy Res 2022; 184:106965. [PMID: 35724601 DOI: 10.1016/j.eplepsyres.2022.106965] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2021] [Revised: 05/13/2022] [Accepted: 06/10/2022] [Indexed: 11/03/2022]
Abstract
Pathology in the dentate gyrus, including sclerosis, is a hallmark of temporal lobe epilepsy, and reduced inhibition to dentate granule cells may contribute to epileptogenesis. The perisomatic-targeting axonal boutons of parvalbumin-expressing interneurons decrease in proportion with granule cells in temporal lobe epilepsy. In contrast, dendrite-targeting axonal boutons of somatostatin-expressing interneurons sprout exuberantly in temporal lobe epilepsy. A third major class of GABAergic interneurons expresses cannabinoid receptor type 1 (CB1) on their terminal boutons, but there is conflicting evidence as to whether these boutons are increased or decreased in temporal lobe epilepsy. Naturally occurring temporal lobe epilepsy in California sea lions, with unilateral or bilateral sclerosis, offers the benefit of neuroanatomy and neuropathology akin to humans, but with the advantage that the entirety of both hippocampi from control and epileptic brains can be studied. Stereological quantification in the dentate gyrus revealed that sclerotic hippocampi from epileptic sea lions had fewer CB1-labeled boutons than controls. However, the reduction in the number of granule cells was greater, resulting in increased CB1-labeled boutons per granule cell in sclerotic hippocampi at temporal levels. This suggests that although CB1-expressing boutons are decreased in sclerotic dentate gyri, surviving cells have enhanced innervation from these boutons in epileptic sea lions.
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Affiliation(s)
- Amanda Seelman
- Department of Comparative Medicine, School of Medicine, Stanford University, 300 Pasteur Drive, Stanford, CA 94305, USA; College of Veterinary Medicine, Western University of Health Sciences, East 2nd Street, Pomona, CA 91766, USA
| | - Kristina Vu
- Department of Comparative Medicine, School of Medicine, Stanford University, 300 Pasteur Drive, Stanford, CA 94305, USA; College of Veterinary Medicine, Cornell University, 602 Tower Rd, Ithaca, NY 14853, USA
| | - Paul Buckmaster
- Department of Comparative Medicine, School of Medicine, Stanford University, 300 Pasteur Drive, Stanford, CA 94305, USA
| | - Ken Mackie
- Department of Psychological & Brain Sciences, Indiana University, 1101 E 10th Street, Bloomington, IN 47405, USA; Gill Centre for Biomolecular Science, Indiana University, 702 North Walnut Grove Avenue, Bloomington, IN 47405, USA
| | - Cara Field
- The Marine Mammal Center, 2000 Bunker Road, Sausalito, CA 94965, USA
| | - Shawn Johnson
- The Marine Mammal Center, 2000 Bunker Road, Sausalito, CA 94965, USA
| | - Megan Wyeth
- Department of Comparative Medicine, School of Medicine, Stanford University, 300 Pasteur Drive, Stanford, CA 94305, USA.
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