title: Identification of basolateral amygdala projection cells and interneurons using extracellular recordings.
abstract: This study tested whether firing rate and spike shape could be used to distinguish projection cells from interneurons in extracellular recordings of basolateral amygdala (BLA) neurons. To this end, we recorded BLA neurons in isoflurane-anesthetized animals with tungsten microelectrodes. Projection cells were identified by antidromic activation from cortical projection sites of the BLA. Although most projection cells fired spontaneously at low rates (<1 Hz), an important subset fired at higher rates (up to 6.8 Hz). In fact, the distribution of firing rates in projection cells and unidentified BLA neurons overlapped extensively, even though the latter cell group presumably contains a higher proportion of interneurons. The only difference between the two distributions was a small subset (5.1%) of unidentified neurons with unusually high firing rates (9-16 Hz). Similarly, distributions of spike durations in both cell groups were indistinguishable, although most of the fast-firing neurons had spike durations at the low end of the distribution. However, we observed that spike durations depended on the exact position of the electrode with respect to the recorded cell, varying by as much as 0.7 ms. Thus neither firing rate nor spike waveform allowed for unequivocal separation of projection cells from interneurons. Nevertheless, we propose the use of two firing rate cutoffs to obtain relatively pure samples of projection cells and interneurons: < or =1 Hz for projection cells and > or =7 Hz for fast-spiking interneurons. Supplemented with spike-duration cutoffs of > or =0.7 ms for projection cells and < or =0.5 ms for interneurons, this approach should keep instances of misclassifications to a minimum.
authors.affiliation: Center for Molecular and Behavioral Neuroscience, Aidekman Research Center, Rutgers, The State University of New Jersey, 197 University Avenue, Newark, NJ 07102, USA.
authors.forename: Ekaterina
authors.initials: E
authors.lastname: Likhtik
authors.forename: Joe Guillaume
authors.initials: JG
authors.lastname: Pelletier
authors.forename: Andrei T
authors.initials: AT
authors.lastname: Popescu
authors.forename: Denis
authors.initials: D
authors.lastname: Paré
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000679:Amygdala / Q000166:cytology / Q000502:physiology*; D000818:Animals; D002415:Cats; D002540:Cerebral Cortex / Q000166:cytology / Q000502:physiology; D004558:Electric Stimulation; D004594:Electrophysiology; D005110:Extracellular Space / Q000502:physiology; D007395:Interneurons / Q000502:physiology*; D008297:Male; D008839:Microelectrodes; D009434:Neural Pathways / Q000166:cytology / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D018408:Patch-Clamp Techniques; D017966:Pyramidal Cells / Q000502:physiology