Abstract

Chronic pain and migraine are leading contributors to disability worldwide, yet their underlying pathophysiological mechanisms remain incompletely understood. Perineuronal nets (PNNs) are specialized extracellular matrix structures which surround specific neurons in the brain. PNNs affect neuronal physiology by modulating synaptic plasticity, protecting the neuron from oxidative stress, and regulating neuronal firing. In addition, formation of PNNs signal the closure of the critical period and transition to mature neuronal stability. Alterations in PNNs have been observed in several neurological and psychiatric disorders, including addiction, Alzheimer’s disease, and epilepsy. A few preclinical studies have implicated PNNs in chronic pain states, although the clinical relevance of these changes is unclear. To date, studies have focused on alterations in PNNs in the cortex, nucleus accumbens, hippocampus, and spinal regions that are associated with the development of neuropathic or inflammatory pain. Notably, experimental reversal of PNN alterations alleviates pain-like behaviors, suggesting that PNN dynamics play an active role in initiating or maintaining chronic pain. Despite this emerging evidence, PNNs have not been examined in migraine - a highly prevalent pain disorder - or in pain associated with withdrawal from substances of abuse, like alcohol. Furthermore, PNNs are located in many regions throughout the brain, including midbrain structures that project to pain-processing regions. The goal of this thesis was to characterize the role of midbrain PNNs in migraine and alcohol withdrawal induced hyperalgesia, to better understand their underlying mechanisms and identify novel therapeutic targets. In this thesis, I identify a population of PNN engulfed parvalbumin (PV) neurons in the mesencephalic reticular formation (MRF), and demonstrate their involvement in nociception, migraine-related cephalic allodynia, and alcohol withdrawal-induced hyperalgesia. In Chapter 2, I show that enzymatic degradation of MRF PNNs with chondroitinase ABC (ChABC) produced mechanical allodynia and thermal hyperalgesia. Since ChABC-induced degradation of PNNs is transient, with their reemergence occurring within several weeks, I demonstrated that reformation of PNNs correlated with the alleviation of pain-like behaviors. I further show that selectively knocking down aggrecan, a major structural component of PNNs, on MRF PNNs resulted in mechanical allodynia, thermal hyperalgesia, and cold hyperalgesia. Together, these data indicate that MRF PNNs regulate nociceptive processing. Using nitroglycerin (NTG), a well-established migraine trigger, I examined whether MRF PNNs are modulated in preclinical models of episodic and chronic migraine. I show that a single administration of NTG produced transient cephalic allodynia without altering MRF PNNs. In contrast, chronic NTG administration led to reductions of PNNs and PV intensities which correlated with the development of chronic cephalic allodynia. I next demonstrated that following cessation of NTG administration, cephalic allodynia resolved within two weeks which coincided with the reformation of MRF PNNs. I next investigated whether migraine treatments could prevent PNN degradation following chronic NTG administration. Sumatriptan and a calcitonin gene-related peptide monoclonal antibody (eptinezumab), which are used clinically for abortive and preventive treatment of migraine respectively, alleviated the cephalic allodynia induced by chronic NTG, and restored PNN levels to that of control mice. Mechanistically, chronic NTG exposure increased the expression of matrix metalloproteinase-2 (Mmp2), an enzyme known to degrade PNNs. Prophylactic administration of marimastat, a pan-MMP inhibitor, attenuated the development of chronic NTG-induced allodynia. Together, these findings suggest that MRF PNN degradation is associated with migraine chronification, potentially mediated by MMP2, and that pharmacological alleviation of migraine-associated pain corresponds with restoration of MRF PNNs integrity. To determine whether similar alterations in MRF PNNs occur across pain states, I developed and validated a mouse model of alcohol withdrawal induced hyperalgesia in Chapter 3 using the Lieber DeCarli ethanol liquid diet. I demonstrated that withdrawal from chronic ethanol administration produced robust withdrawal-associated hyperalgesia. I further validated the model by showing that withdrawal-induced hyperalgesia was attenuated by administration of suberoylanilide hydroxamic acid (SAHA), a histone deacetylase inhibitor previously used to reduce alcohol withdrawal-related symptoms, including AWH in rats. In chapter 4, I showed that AWH is associated with a reduction in MRF PNNs, suggesting that MRF PNN degradation extends beyond migraine to other pain conditions. Overall, this thesis identifies a previously understudied population of PNN engulfed neurons in the midbrain that regulate pain-processing and highlights their potential as therapeutic targets in migraine and AWH.

Committee Chair

Amynah Pradhan

Committee Members

Amy Lasek; Jordan McCall; Robert Gereau; Vijay Samineni

Degree

Doctor of Philosophy (PhD)

Author's Department

Biology & Biomedical Sciences (Neurosciences)

Author's School

Graduate School of Arts and Sciences

Document Type

Dissertation

Date of Award

4-22-2026

Language

English (en)

Author's ORCID

https://orcid.org/0000-0002-0022-2207

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Available for download on Wednesday, April 21, 2027

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