Loss of Neuron Connectors in the Brains of Sea Lions with Epilepsy
- Domoic acid
- Epilepsy
Abstract
One in 26 people develop epilepsy and in these temporal lobe epilepsy (TLE) is common. Many patients display a pattern of neuron loss called hippocampal sclerosis. Seizures usually start in the hippocampus but underlying mechanisms remain unclear. One possibility is insufficient inhibition of dentate granule cells. Normally parvalbumin‐immunoreactive (PV) interneurons strongly inhibit granule cells. Humans with TLE display loss of PV interneurons in the dentate gyrus but questions persist. To address this, we evaluated PV interneuron and bouton numbers in California sea lions (Zalophus californianus) that naturally develop TLE after exposure to domoic acid, a neurotoxin that enters the marine food chain during harmful algal blooms. Sclerotic hippocampi were identified by the loss of Nissl‐stained hilar neurons. Stereological methods were used to estimate the number of granule cells and PV interneurons per dentate gyrus. Sclerotic hippocampi contained fewer granule cells, fewer PV interneurons, and fewer PV synaptic boutons, and the ratio of granule cells to PV interneurons was higher than in controls. To test whether fewer boutons was attributable to loss versus reduced immunoreactivity, expression of synaptotagmin‐2 (syt2) was evaluated. Syt2 is also expressed in boutons of PV interneurons. Sclerotic hippocampi displayed proportional losses of syt2‐immunoreactive boutons, PV boutons, and granule cells. There was no significant difference in the average numbers of PV‐ or syt2‐positive boutons per granule cell between control and sclerotic hippocampi. These findings do not address functionality of surviving synapses but suggest reduced granule cell inhibition in TLE is not attributable to anatomical loss of PV boutons.
Cameron, S., Lopez A., Glabman, R., Abrams, E., Johnson, S., Field, C., Gulland, F.M., Buckmaster, P.S. 2019. Proportional loss of parvlbumin-immunoreacitve synaptic boutons and granule cells from the hippocampus of sea lions with temporal lobe epilepsy. J. Comp Neurology Mar. 12 doi:10.1002/cne.24680
epilepsy
Cara Field
Meet The Experts
{"image":"\/People\/Portrait\/cara-field.jpg","alt":"Cara Field","title":"Cara Field","text":"Director, Conservation Medicine","link_url":"https:\/\/www.marinemammalcenter.org\/person\/cara-field","link_text":"Read Bio"}
Related Publications
{"image":"\/Animals\/Patients\/California sea lions\/cropped-images\/csl-eeg-frances-gulland-photo-c-the-marine-mammal-center-33-0-806-630-1685576701.jpg","alt":"","title":"Pinniped Electroencephalography: Methodology and Findings in California sea lions","link_url":"https:\/\/www.marinemammalcenter.org\/publications\/pinniped-electroencephalography-methodology-and-findings-in-california-sea-lions","label":"Research Paper"}
Pinniped Electroencephalography: Methodology and Findings in California sea lions
Read MoreRecent News
{"image":"\/Animals\/Wild\/Gray whale\/stranded-gray-whale-july-2025.jpg","alt":"stranded gray whale","title":"Scientists respond to dead gray whale in San Francisco Bay as species faces population recovery challenges","link_url":"https:\/\/www.marinemammalcenter.org\/news\/scientists-respond-to-dead-gray-whale-in-san-francisco-bay-as-species-faces-population-recovery-challenges","label":"Press Release","date":"2025-07-17 02:00:00"}
Scientists respond to dead gray whale in San Francisco Bay as species faces population recovery challenges
July 17, 2025
Read More{"image":"\/Animals\/Patients\/Harbor seals\/cropped-images\/hs-group-with-hats-photo-by-bill-hunnewell-c-the-marine-mammal-center-34-0-1270-992-1750873865.jpg","alt":"Four harbor seals with small ID tags on their heads swim in a rehabilitation pool.","title":"How Our Patients are Named and Identified","link_url":"https:\/\/www.marinemammalcenter.org\/news\/how-our-patients-are-named-and-identified","label":"Patient Update","date":"2025-06-26 02:00:00"}
{"image":"\/Animals\/Wild\/Gray whale\/cropped-images\/gray-whale-oreo-by-josie-slaathaug-c-the-marine-mammal-center-108-0-1270-992-1750880575.jpg","alt":"Gray whale fluke above the water","title":"Los Angeles Times: The numbers of gray whales migrating along the California coast continue to plummet","link_url":"https:\/\/www.marinemammalcenter.org\/news\/los-angeles-times-the-numbers-of-gray-whales-migrating-along-the-california-coast-continue-to-plummet","label":"In the News","date":"2025-06-25 02:00:00"}
Los Angeles Times: The numbers of gray whales migrating along the California coast continue to plummet
June 25, 2025
Read More{"image":"\/Animals\/Wild\/Harbor seal\/cropped-images\/harbor-seal-pup-photo-by-Ruvim-Miksanskiy-251-0-1270-992-1750880392.jpg","alt":"Harbor seal pup resting on the beach","title":"ABC7 San Francisco: Animal trauma could be linked to bad human behavior, Bay Area marine mammal experts say","link_url":"https:\/\/www.marinemammalcenter.org\/news\/abc7-san-francisco-animal-trauma-could-be-linked-to-bad-human-behavior-bay-area-marine-mammal-experts-say","label":"In the News","date":"2025-06-24 02:00:00"}
ABC7 San Francisco: Animal trauma could be linked to bad human behavior, Bay Area marine mammal experts say
June 24, 2025
Read More