title: Isovaline, a rare amino acid, has anticonvulsant properties in two in vitro hippocampal seizure models by increasing interneuronal activity.
abstract: OBJECTIVE
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors: Center for Neuropharmacology & Neuroscience, Albany Medical College, Albany, New York 12208, USA. shind@mail.amc.edu
authors: Damian S
authors: DS
authors: Shin
authors: Wilson
authors: W
authors: Yu
authors: Alex
authors: A
authors: Sutton
authors: Megan
authors: M
authors: Calos
authors: Ernest
authors: E
authors: Puil
authors: Peter L
authors: PL
authors: Carlen
mesh_terms: D015761:4-Aminopyridine / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D000927:Anticonvulsants / Q000627:therapeutic use*; D003292:Convulsants / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006624:Hippocampus / Q000187:drug effects*; D066298:In Vitro Techniques; D007395:Interneurons / Q000187:drug effects* / Q000502:physiology; D018408:Patch-Clamp Techniques; D017966:Pyramidal Cells / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012640:Seizures / Q000188:drug therapy*; D014633:Valine / Q000627:therapeutic use*
chemical_list: D000927:Anticonvulsants; D003292:Convulsants; C032737:isovaline; D015761:4-Aminopyridine; D014633:Valine