Isovaline, a rare amino acid, has anticonvulsant properties in two in vitro hippocampal seizure models by increasing interneuronal activity

Damian S. Shin, Wilson Yu, Alex Sutton, Megan Calos, Ernest Puil, Peter L. Carlen

Research output: Contribution to journalArticlepeer-review

13 Scopus citations


Purpose: We investigated whether RS-isovaline, a unique amino acid found in carbonaceous meteorites and presumed extraterrestrial, has anticonvulsant properties in rat hippocampal slices in vitro. Methods: Extracellular recordings were obtained in the rat hippocampal CA1 pyramidal layer in two in vitro seizure models: perfusion of low (0.25 mm) Mg 2+ and high (5 mm) K + (LM/HK), or 100 μm 4-aminopyridine (4-AP). To investigate the underlying mechanisms of isovaline action, whole-cell recordings were obtained from CA1 pyramidal neurons and stratum oriens interneurons during 4-AP blockade of K + channels. Key Findings: Perfusion of LM/HK produced seizure-like events (SLEs) or stimulus-evoked primary afterdischarges (PADs) with amplitudes of 0.9 ± 0.1 mV lasting 80 ± 14 s. Application of isovaline (250 μm) for 20-30 min abolished SLEs and PADs or attenuated seizure amplitude and duration by 57.0 ± 9.0% and 57.0 ± 12.0%, respectively. Similar effects were seen with isovaline in the 4-AP seizure model. Isovaline alone increased interneuronal spontaneous spiking from 0.9 ± 0.3 to 3.2 ± 0.9 Hz, increased input resistance by 21.6 ± 8.1%, and depolarized the resting membrane potential by 8.0 ± 1.5 mV; no changes in the firing or electrical properties of pyramidal neurons were observed. Coapplication of 4-AP and isovaline increased interneuronal spontaneous spiking from 1.0 ± 0.6 to 2.6 ± 0.8 Hz, whereas pyramidal neuronal spiking activity decreased from 0.6 ± 0.4 to 0.2 ± 0.1 Hz. Significance: Isovaline exhibited anticonvulsant properties in two hippocampal seizure models. This may lead to the development of a new class of anticonvulsants based on an unusual mechanism of action of this presumed extraterrestrial amino acid.

Original languageEnglish (US)
Pages (from-to)2084-2093
Number of pages10
Issue number11
StatePublished - Nov 2011


  • Anticonvulsant
  • CA1 interneurons
  • CA1 pyramidal cells
  • Isovaline
  • Whole-cell patch-clamp recordings


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