Neural Coding by Two Classes of Principal Cells in the Mouse Piriform Cortex

Abstract

The piriform (or primary olfactory) cortex is a trilaminar structure that is the first cortical destination of olfactory information, receiving monosynaptic input from the olfactory bulb. Here, we show that the main input layer of the piriform cortex, layer II, is dominated by two classes of principal neurons, superficial pyramidal (SP) and semilunar (SL) cells, with strikingly different properties. Action potentials in SP cells are followed by a Ni 2ϩ -sensitive afterdepolarization that promotes burst firing, whereas SL cells fire nonbursting action potentials that are followed by a powerful afterhyperpolarization. Synaptic inputs from the olfactory bulb onto SP cells exhibit prominent paired-pulse facilitation, which is attributable to residual presynaptic Ca 2ϩ and a low probability of neurotransmitter release. In contrast, the same inputs onto SL cells do not facilitate. These distinctive synaptic and firing properties cause SP and SL cells to respond differently to in vivo-like bursts of afferent stimulation: SP cells tend to fire bursts of output action potentials at a higher frequency than the input, whereas SL cells tend to fire at a lower frequency than the input. When connected together in the canonical circuit of the piriform cortex, SP and SL cells transform the pattern of synaptic inputs they receive from the olfactory bulb, dispersing the firing rate and latency of output action potentials to an extent that depends on the strength of the input. Thus, the presence of two types of principal cells in layer II of the piriform cortex may underlie coding strategies used for the representation of odors.

Dendritic Compartment and Neuronal Output Mode Determine Pathway-Specific Long-Term Potentiation in the Piriform Cortex

“…It has been demonstrated by Suzuki and Bekkers that intrinsic AP bursting during suprathreshold depolarization is a key feature of piriform cortex pyramidal cells. In the same study, short bursts with high instantaneous firing frequencies of up to 150 Hz were evoked by strong stimulation of sensory or associative pathways with typical sensory input patterns (Suzuki and Bekkers, 2006). During sniffing, short AP bursts with instantaneous firing rates above 100 Hz have also been observed in intracellular recordings in vivo (Wilson, 1998).…”

Comparison of localisation of α- and β-oestrogen receptors in posterior part of the piriform cortex in rabbit males

“…This difference was observed not only in PC but in other brain areas such as amygdale and hippocampus (11,15). The previous studies have shown that in PC, there are interneurons classified according to the expression of two types of cell markers (molecular markers) -calcium-binding proteins and neuropeptides (23).…”

“…It obtains direct signals from the olfactory bulb (5,6,17) and processes them in different way in anterior and posterior part of the piriform cortex (10,23). The piriform cortex communicates with brain structures, such as the olfactory bulb, enthorinal cortex, amygdaloid cortex, hypothalamus, basal forebrain, brainstem, olfactory tubercle, olfactory peduncle, superior colliculus thalamus, frontal cortex, and with the hippocampus through the enthorinal cortex.…”

“…Nervous fibres dominate in the superficial layer I. Layer II -the middle one, has the most densely arranged neurons, layer III -the deepest, contains neurons, which are loosely arranged. Neurons in layer II are divided into lying superficially pyramidal neurons, identified as SP (superficial pyramidal) and cells identified as SL (semilunar cells) responsible for odour (2,23). These cells differ from each other by having different sensitivity threshold.…”

“…These cells differ from each other by having different sensitivity threshold. In layer III the nerve cells defined as DP (deep pyramidal cells) are present (2,23).…”