Biology subjects

Hegarty, D. M.

Publications and source records attributed to Hegarty, D. M..

5 recordsLinked to original sources

bioRxiv2024

Perineuronal nets in the rat medial prefrontal cortex alter hippocampal-prefrontal oscillations and reshape cocaine self-administration memories

The medial prefrontal cortex (mPFC) is a major contributor to relapse to cocaine in humans and to reinstatement behavior in rodent models of cocaine use disorder. Output from the mPFC is modulated by parvalbumin (PV)-containing fast-spiking interneurons, the majority of which are surrounded by perineuronal nets (PNNs). Here we tested whether chondroitinase ABC (ABC)- mediated removal of PNNs prevented the acquisition or reconsolidation of a cocaine self-administration memory. ABC injections into the dorsal mPFC prior to training attenuated the acquisition of cocaine self-administration. Also, ABC given 3 days prior to but not 1 hr after memory reactivation blocked cue-induced reinstatement. However, reduced reinstatement was present only in rats given a novel reactivation contingency, suggesting that PNNs are required for the updating of a familiar memory. In naive rats, ABC injections into mPFC did not alter excitatory or inhibitory puncta on PV cells but reduced PV intensity. Whole-cell recordings revealed a greater inter-spike interval 1 hr after ABC, but not 3 days later. In vivo recordings from the mPFC and dorsal hippocampus (dHIP) during novel memory reactivation revealed that ABC in the mPFC prevented reward-associated increases in beta and gamma activity as well as phase-amplitude coupling between the dHIP and mPFC. Together, our findings show that PNN removal attenuates the acquisition of cocaine self-administration memories and disrupts reconsolidation of the original memory when combined with a novel reactivation session. Further, reduced dHIP/mPFC coupling after PNN removal may serve as a key biomarker for how to disrupt reconsolidation of cocaine memories and reduce relapse.

neuroscience↗

bioRxiv2022

Resveratrol increases tear production and spontaneous ocular pain after corneal abrasion in male, but not female, rats using a preclinical model of photorefractive keratectomy (PRK)

Photorefractive keratectomy (PRK) is an alternative to LASIK and can cause intense acute pain that is often not relieved by standard treatments. To assess potential therapeutics for this type of acute pain, appropriate preclinical models are needed. Herein we describe a rodent preclinical model of PRK and a multi-faceted approach to determine the therapeutic potential of resveratrol, a natural phytoestrogen, on pain, tear production, and the corneal epithelium. Studies were conducted in male and female Sprague-Dawley rats. Heptanol was applied to one eye and the superficial corneal epithelium was removed, mimicking the abrasion seen in PRK. Spontaneous pain was assessed with orbital tightening (OT) scores for 7 days. Corneal abrasion increased OT scores in both male and female rats with peak responses at 24 - 48 hours. Topical application of resveratrol had a sex-specific effect on OT scores and tear production. Resveratrol increased OT scores in abraded males, but not females, at 72 hours and 1 week after abrasion. Resveratrol dose-dependently increased tear production in abraded males, but had no effect in abraded females. While there was no correlation between OT score at 1 week and tear production, CGRP content of corneal nerves was positively correlated with 1 week OT score. There was also a significant increase in CD68-labeled macrophages in resveratrol-treated abraded corneas as compared to naive corneas. These findings demonstrate the usefulness of our preclinical PRK model for the assessment of ocular pain therapeutics and indicate that topical resveratrol may not be useful for managing PRK-induced pain.

neuroscience↗

bioRxiv2020

Diurnal changes in perineuronal nets and parvalbumin neurons in the rat medial prefrontal cortex

Perineuronal nets (PNNs) surrounding fast-spiking, parvalbumin (PV) inhibitory interneurons are vital for providing excitatory:inhibitory balance within cortical circuits, and this balance is impaired in disorders such as schizophrenia, autism spectrum disorder, and substance use disorders. These disorders are also associated with altered diurnal rhythms, yet few studies have examined the diurnal rhythms of PNNs or PV cells. We measured the intensity and number of PV cells and PNNs labeled with Wisteria floribunda agglutinin (WFA) in the rat prelimbic medial prefrontal cortex (mPFC) at Zeitgeber times (ZT) ZT0, 6, 12, and 18. We also measured the oxidative stress marker 8-oxo-deoxyguanosine (8-oxo-dG). Relative to ZT0, the intensities of PNN and PV staining were increased in the dark (active) phase compared with the light (inactive) phase. The intensity of 8-oxo-dG was decreased from ZT0 at all time points (ZT6,12,18), in both PV cells and non-PV cells. To examine corresponding changes in inhibitory and excitatory inputs, we measured GAD 65/67 and vGlut1 puncta apposed to PV cells with and without PNNs. Relative to ZT6, there were more excitatory puncta on PV cells surrounded by PNNs at ZT18, but no changes in PV cells devoid of PNNs. No changes in inhibitory puncta were observed. Whole-cell slice recordings in fast-spiking (PV) cells with PNNs showed an increased ratio of -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor:N-methyl-D-aspartate receptor (AMPA:NMDA) at ZT18 vs. ZT6. The number of PV cells and co-labeled PV/PNN cells containing the transcription factor orthodenticle homeobox 2 (OTX2), which maintains PNNs, showed a strong trend toward an increase from ZT6 to ZT18. These diurnal fluctuations in PNNs and PV cells are expected to alter cortical excitatory:inhibitory balance and provide new insights into treatment approaches for diseases impacted by imbalances in sleep and circadian rhythms.

neuroscience↗

bioRxiv2019

Cocaine memory reactivation induces functional adaptations of fast-spiking interneurons in the rat medial prefrontal cortex

Perineuronal nets (PNNs) are specialized extracellular matrix structures that ensheathe parvalbumin-containing fast-spiking interneurons (PV FSIs) and play a key role in neuroplasticity. We previously showed that PNNs within the prelimbic prefrontal cortex (PL PFC) are required for the maintenance of cocaine-associated memories following cocaine memory reactivation. However, how cocaine memory reactivation affects PNNs, PV, and corresponding changes in PV FSI function are unknown. In this study, we characterized the electrophysiological properties of PV FSIs and corresponding changes in PNN and PV intensity within the PL PFC prior to and after cocaine memory reactivation. Adult male Sprague-Dawley rats were trained to acquire cocaine-conditioned place preference (CPP) and, following cocaine-CPP memory reactivation (30 m, 2 h, and 24 h post-reactivation), we measured PNN intensity (determined by Wisteria floribunda agglutinin [WFA] staining) as well as PV intensity using immunohistochemistry. The intensity of PV staining was reduced at all time points following memory reactivation with no changes in WFA intensity. Using whole-cell electrophysiology we found a reduction in the number of action potentials at 30 m and 2 h that returned to control levels by 24 h. The attenuation in firing was accompanied by a presumed compensatory increase in excitatory synaptic transmission, which was corroborated by an increase in VGluT1 puncta apposing PV/PNN neurons. Collectively, our results indicate that cocaine memory reactivation decreases PV intensity, which may play a role in decreasing excitation of PV FSIs. Thus, the inhibitory tone onto pyramidal neurons may be decreased following memory reactivation, resulting in an increase in PFC output to promote cocaine-seeking behaviors.

neuroscience↗

bioRxiv2018

Acute Hyperalgesia and Delayed Dry Eye After Corneal Abrasion Injury

Corneal nerves mediate pain from the ocular surface, lacrimation, and blinking, all of which protect corneal surface homeostasis and help preserve vision. Corneal nerve density correlates with neuropathic pain states and is used as an assessment of small fiber neuropathies. Because pain, lacrimation and blinking are rarely assessed at the same time, it is not known if their regulatory mechanisms have similar temporal dynamics after acute corneal injury. We examined changes in corneal nerve density, evoked and spontaneous pain, and ocular homeostasis in Sprague-Dawley male rats after a superficial epithelial injury with heptanol that acutely abolished nerve endings within the central cornea. Despite a profound loss of epithelial nerve endings, pain was transiently enhanced after abrasion injury, while basal tear production was normal. We found no relationship between epithelial nerve density and pain or homeostatic responses. Axotomy following corneal abrasion increased expression of both ATF3 (a nerve injury marker) and CGRP (a nociceptive peptide) in trigeminal ganglia 24 hours after injury. These molecular changes were absent on the contralateral side, despite reductions in corneal epithelial nerve density in the uninjured eye. ATF3 and CGRP levels in trigeminal ganglion were normal at one week post-injury when pain responses were normal. In contrast, CGRP was upregulated in peripheral corneal endings one week after injury, when dry eye symptoms emerged. Our results demonstrate dynamic trafficking of CGRP within trigeminal sensory nerves, with elevations in the ganglion correlated with pain behaviors and elevations in peripheral endings correlated with dry eye symptoms.

neuroscience↗