Glutamatergic Neurons in the Piriform Cortex Influence the Activity of D1- and D2-Type Receptor-Expressing Olfactory Tubercle Neurons.

Sensory cortices process stimuli in manners essential for perception. Very little is known regarding interactions between olfactory cortices. The piriform "primary" olfactory cortex, especially its anterior division (aPCX), extends dense association fibers into the ventral striatum's olfactory tubercle (OT), yet whether this corticostriatal pathway is capable of shaping OT activity, including odor-evoked activity, is unknown. Further unresolved is the synaptic circuitry and the spatial localization of OT-innervating PCX neurons. Here we build upon standing literature to provide some answers to these questions through studies in mice of both sexes. First, we recorded the activity of OT neurons in awake mice while optically stimulating principal neurons in the aPCX and/or their association fibers in the OT while the mice were delivered odors. This uncovered evidence that PCX input indeed influences OT unit activity. We then used patch-clamp recordings and viral tracing to determine the connectivity of aPCX neurons upon OT neurons expressing dopamine receptor types D1 or D2, two prominent cell populations in the OT. These investigations uncovered that both populations of neurons receive monosynaptic inputs from aPCX glutamatergic neurons. Interestingly, this input originates largely from the ventrocaudal aPCX. These results shed light on some of the basic physiological properties of this pathway and the cell-types involved and provide a foundation for future studies to identify, among other things, whether this pathway has implications for perception.SIGNIFICANCE STATEMENT Sensory cortices interact to process stimuli in manners considered essential for perception. Very little is known regarding interactions between olfactory cortices. The present study sheds light on some of the basic physiological properties of a particular intercortical pathway in the olfactory system and provides a foundation for future studies to identify, among other things, whether this pathway has implications for perception.

Perturbation of in vivo Neural Activity Following α-Synuclein Seeding in the Olfactory Bulb.

BACKGROUND: Parkinson's disease (PD) neuropathology is characterized by intraneuronal protein aggregates composed of misfolded α-Synuclein (α-Syn), as well as degeneration of substantia nigra dopamine neurons. Deficits in olfactory perception and aggregation of α-Syn in the olfactory bulb (OB) are observed during early stages of PD, and have been associated with the PD prodrome, before onset of the classic motor deficits. α-Syn fibrils injected into the OB of mice cause progressive propagation of α-Syn pathology throughout the olfactory system and are coupled to olfactory perceptual deficits. OBJECTIVE: We hypothesized that accumulation of pathogenic α-Syn in the OB impairs neural activity in the olfactory system. METHODS: To address this, we monitored spontaneous and odor-evoked local field potential dynamics in awake wild type mice simultaneously in the OB and piriform cortex (PCX) one, two, and three months following injection of pathogenic preformed α-Syn fibrils in the OB. RESULTS: We detected α-Syn pathology in both the OB and PCX. We also observed that α-Syn fibril injections influenced odor-evoked activity in the OB. In particular, α-Syn fibril-injected mice displayed aberrantly high odor-evoked power in the beta spectral range. A similar change in activity was not detected in the PCX, despite high levels of α-Syn pathology. CONCLUSION: Together, this work provides evidence that synucleinopathy impacts in vivo neural activity in the olfactory system at the network-level.

Abstinence from Cocaine-Induced Conditioned Place Preference Produces Discrete Changes in Glutamatergic Synapses onto Deep Layer 5/6 Neurons from Prelimbic and Infralimbic Cortices.

Glutamatergic signaling in the medial prefrontal cortex (mPFC) plays a critical role in drug addiction and relapse. The mPFC is functionally subdivided into dorsal (prelimbic, PL) and ventral (infralimbic, IL) regions, and evidence suggests a differential role of these two divisions in the control of drug seeking and taking; however, there is a dearth of information on the cocaine-induced adaptations in PL- and IL-mPFC synaptic glutamate transmission and their regulation of behavioral responses to cocaine-associated stimuli. We tested male rats in a cocaine-induced conditioned place preference (CPP) paradigm. In vitro whole-cell recordings were performed at different abstinence intervals to investigate the neuroadaptations in synaptic glutamate transmission in PL- and IL-mPFC deep layer (5/6) pyramidal neurons. Our results show that in naïve animals, PL-mPFC neurons expressed higher frequency of spontaneous events (sEPSCs) than IL-mPFC neurons. Following cocaine-CPP and a short abstinence (SA) period (8 d), we observed decreases in the amplitude of sEPSCs in both mPFC regions. Longer abstinence periods (30 d), resulted in a sustained decrease in the frequency of sEPSCs and an increase in AMPA receptor rectification only in PL-mPFC neurons. In addition, PL-mPFC neurons expressed a decrease in the area under the curve of sEPSCs, suggesting altered receptor activation dynamics. Synaptic glutamate transmission was not significantly different between retested and naïve rats. These results suggest that retention of cocaine-CPP requires differential modulation of glutamate transmission between PL- and IL-mPFC neurons and that these adaptations are dependent on the abstinence interval and reexposure to the cocaine context.