Glaucoma is a progressive, irreversible, blinding condition of the eye that affects millions worldwide, and
intraocular pressure (IOP) remains the only modifiable risk factor for glaucoma progression. However, we still
do not understand how IOP fluctuations are controlled centrally. Our interest is in identifying central nervous
system (CNS) nuclei responsible for controlling circadian IOP fluctuation with the hope that this knowledge
may identify novel targets for glaucoma therapy. Our previous studies have shown that chemical stimulation of
the dorsomedial hypothalamus and surrounding perifornical region (DMH/PeF) transiently, but dramatically,
elevates IOP. Further, orexins are highly localized to the DMH/PeF, and orexin neurotransmitters are
implicated in control of circadian rhythms. We have extensive data extending the role of the orexin
neurotransmitter system in the regulation of IOP. Additionally, our studies have shown that the brainstem raphe
pallidus (RP) receives projections from the DMH/PeF neurons. Further, when injected into the RP, orexins
stimulated a sustained rise in IOP directly implicating the orexins and the RP in IOP regulation. While a CNS
orexinergic pathway that eventually stimulates autonomic ganglia may be the most obvious pathway regulating
IOP fluctuation after DMH/PeF stimulation, an alternative orexinergic pathway controlling IOP may exist. Data
suggests that orexin receptors are located on the ciliary body and ciliary muscle of the eye's anterior segment.
Thus, we will investigate both. We will examine the role of the RP on DMH/PeF induced IOP elevations by
measuring the degree to which local orexin receptor antagonists in the RP attenuate the IOP response (Aim 1).
We will further assess the degree to which orexin receptor antagonists administered directly within the anterior
chamber attenuate the CNS-mediated IOP stimulation (Aim 2). We will also address mechanism of action and
examine the effect of CNS-mediated IOP stimulation on the flow dynamics of the aqueous humor (Aim 2). With
unique data demonstrating a role for the orexin system in attenuating CNS-mediated IOP stimulation, further
exploration of the association between allelic variations of the orexin neurotransmitter and its receptors with the
IOP trait is justified and appropriate. Thus, we will use a candidate gene approach and Mendelian
randomization analysis to investigate the three genes encoding the orexin signaling system using the NIH All of
Us database and the UK Biobank which offers genomic sequence data for over 100,000 participants with
matching IOP and medical data (Aim 3). Finally, IOP and IOP dynamics in transgenic mice lacking a functional
orexin peptide allele or lacking functioning alleles of either of the orexin receptors will be tested for circadian
IOP rhythm disruption, as well as for significant differences in IOP elevation, in our validated CNS stimulation
methodologies (Aim 4). Together, these aims establish a comprehensive approach to identify potential
mechanisms of action for the orexin system in mediating IOP increases caused by stimulation of the DMH/PeF
region and may provide additional insights into CNS control of IOP and its circadian dynamics.