Inhibitory Interneurons in the Piriform Cortex

Abstract

1. The piriform cortex (PC) is the largest subdivision of the olfactory cortex and the first cortical destination of olfactory information. Despite the relatively simple anatomy of the PC and its obvious appeal as a model system for the study of cortical sensory processing, there are many outstanding questions about its basic cell physiology. In the present article, we review what is known about GABAergic inhibitory interneurons in the PC. 2. The GABA-containing neurons in the PC are morphologically diverse, ranging from small neurogliaform cells to large multipolar forms. Some of these classes are distributed across all three main layers of the PC, whereas others have a more restricted laminar expression. 3. Distinct and overlapping populations of GABAergic basket cells in Layers II and III of the PC express different combinations of calcium-binding proteins and neuropeptides. Few Layer I interneurons express any of the molecular markers so far examined. 4. The intrinsic firing properties of one or two types of putative PC interneurons have been measured and inhibitory post-synaptic responses have been recorded in PC pyramidal cells following extracellular stimulation. However, little is known about the physiology of the subtypes of interneurons identified. 5. In view of the likely importance of PC interneurons in olfactory learning, olfactory coding and epileptogenesis, further investigation of their properties is likely to be highly informative.

Generalized vs. stimulus-specific learned fear differentially modifies stimulus encoding in primary sensory cortex of awake rats

“…Furthermore, inhibitory interneurons are a target of some descending inputs to the piriform cortex (Luna 2011;Mouly and Di Scala 2006), which help contribute to experiencedependent shaping of cortical odor responses. Thus a contribution from either changes in local inhibitory circuitry (Poo and Isaacson 2009;Suzuki and Bekkers 2007;Zhang et al 2006) or higher order centers such as the amygdala (Luna 2011), orbitofrontal cortex (Cohen et al 2008), or entorhinal cortex (Ferry et al 1996) may contribute to the constellation of learning induced changes observed here. Manipulation of the described learned changes in aPCX sensory physiology will be required to determine their necessary and/or sufficient contribution to the behavioral changes.…”

Differential dynamics of amino acid release in the amygdala and olfactory cortex during odor fear acquisition as revealed with simultaneous high temporal resolution microdialysis

“…In addition, both the BLA and pPCx contain glutamatergic pyramidal cells that send axon collaterals to neighboring cells, thus providing an intrinsic source of glutamate (Luskin and Price 1983b;Sah et al 2003). Concerning GABA origin, in both BLA and pPCx, GABA is released by local inhibitory interneurons (Sah et al 2003;Suzuki and Bekkers 2007). The cellular sources of glutamate and GABA measured using microdialysis likely include neurons and glia surrounding the dialysis probe (Watson et al 2006).…”

Learning-induced modulation of the GABAB-mediated inhibitory synaptic transmission: mechanisms and functional significance

“…Inhibitory synaptic transmission is morphologically segregated; feed-forward inhibition is terminated on the distal portion of the apical dendrite, while FB inhibition is terminated on the proximal dendrites (Suzuki and Bekkers 2007). Consequently, DC current passed via the sharp recording electrode would be much more efficient in modifying the neuron's membrane potential (V m ) at the locations where FB inhibition is generated.…”

“…Intracellular recordings were performed from cell bodies in layer II. Feed-forward inhibition (FF) inputs are terminated on the distal apical dendrite, while feed-back inhibition (FB) is terminated on cell bodies and proximal dendrites of the cell (Suzuki and Bekkers 2007). For activation of inhibitory synaptic inputs, electrical stimuli were applied to the border between layers II and III, in the presence of the glutamatergic ␣-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptor blockers.…”