Vasopressin and the retina

All living beings are synchronized to the rhythmic light-dark changes that occur daily. These daily (circadian) rhythms are generated by internal biological 'clocks', and these clocks are co-ordinated by specialized neurons in one special region of the brain - the suprachiasmatic nucleus (SCN). The activity of the SCN is synchronized daily by environmental signals - mainly by information on light received by the retina, which is communicated by nerve fibers to the SCN.

Exactly how the retinal input entrains the rhythm of the SCN is unclear. Several mechanisms, including gene activation and local neuropeptide release, have been linked to the regulation of this 'clock'. Signaling of the neuropeptide vasopressin in the SCN plays a particularly important role - vasopressin is critical for re-setting of the clock after a change in the light-dark cycle, for example during transcontinental travelling or shift work.

The SCN contains a large population of vasopressin neurons, but we recently found that the retina also contains many vasopressin-expressing cells, and that, strikingly, these communicate exclusively with the SCN - they are involved only with regulating circadian rhythms, and not with normal vision.

Thus, these newly discovered vasopressin cells in the retina are a major, light-activated pathway that has a key role in regulating important circadian rhythms. The proposed research will define exactly how these cells influence the SCN, and will establish how modulation of the retina-SCN pathway contributes to changes in circadian rhythm regulation.

The experimental studies will all be on laboratory rats - and will include studying the effects of selectively destroying or activating these cells using very sophisticated genetic approaches. These approaches will involve inserting a gene into these retinal vasopressin cells to enable their activity to be controlled precisely in experiments that will be carried out in deeply anesthetized rats. The SCN is part of the hypothalamus of the brain; in evolutionary terms, this is an ancient structure that is present in all vertebrates. The SCN is organised in a very similar way in all mammalian species that have been studied, so findings from studies in the rat are likely to be "translatable" into understanding of how rhythms are regulated in people.

Identifying a specific population of cells in the retina that has a key and selective role in regulating body rhythms will open up new therapeutic possibilities for helping to restore altered circadian rhythms during jet lag or rotating shift work. Epidemiology shows that rotational shift work is accompanied by major health risks, including increased propensity for cancer, depression, sleep disturbances, gastrointestinal, metabolic and cardiovascular disorders, decreased immune responses and even life span.

Circadian rhythms in physiology and behavior are orchestrated by the hypothalamic suprachiasmatic nucleus (SCN), the "master" clock of the body's circadian systems. The primary determinant of the output of the SCN is the 24-h environmental light/dark cycle, reflecting a direct retinal innervation of the SCN, but exactly how the retinal input entrains the rhythm of the SCN is unclear. Several neuropeptides, including vasopressin, have been linked to the regulation of the circadian clock. The SCN contains a large population of vasopressin neurons, but we recently found that the retina also contains many vasopressin-expressing retinal ganglion cells (RGCs), and that, strikingly, these project exclusively to the SCN. Vasopressin signaling in the SCN determines the speed of re-entrainment the environmental clock after a phase advance in the light-dark cycle. Generally it has been assumed that the time-dependent ability of a light pulse to re-entrain circadian rhythms reflects the circadian state of the target neurons in the SCN. We hypothesize that the vasopressin-expressing RGCs are a major, light-activated excitatory pathway that has a key role in regulating circadian rhythms. The research will use contemporary molecular physiology approaches (including optogenetics, transgenic rats, and adenoviral transfection systems) to define the cellular targets of this projection in the rat SCN, and establish whether this input is essential for the photic induction of immediate early gene expression that is associated with circadian entrainment. These final experiments will indicate if modulation of the retina-SCN pathway might be considered as a therapeutic approach to mitigate the adverse effects of disrupted circadian regulation.

The proposal fits into the MRC remit of the Neurosciences and Mental Health board to encourage research "addressing factors throughout life that influence health and wellbeing in older age" as set in the MRC strategy "Research Changes Life". With an aging population, interventions that can help to maintain independence and quality of life into old age are a priority.
Shift work that includes a nighttime rotation and long distance travel has become an unavoidable attribute of today's 24-h society. The related disruption of the human circadian time organization leads in the short-term to an array of jet-lag-like symptoms, and in the long-run it contributes to weight gain and obesity, metabolic syndrome, type II diabetes, and cardiovascular disease. Studies also suggest increased cancer risk, symptoms of insomnia, depression, elevated cortisol levels, cognitive impairment, and premature mortality.
The mechanisms leading to circadian dysfunction are largely unknown. Understanding the mechanisms of retina-SCN pathway may result in therapeutic approaches to mitigate the adverse effects of disrupted circadian regulation

We thus expect this project
1) to contribute to our fundamental understanding of circardian regulation
Our previous work has led to high impact publications and this has given us a high profile in the academic community. Disseminating outcomes will be a priority for this project. In the last 4 years, ML gave invited presentations at several national and international conferences, including Experimental Biology (USA), ICN (France), BES (UK), ECE (Netherlands) and SBN (USA). In the same period, GL gave plenary lectures at the Japan Endocrine Society Meeting in Nagoya and at the FEPs meeting in Istanbul, and gave invited talks at conferences in Gothenburg, Lutteren, Amsterdam, Bristol and Orleans. Accordingly we expect that there will be ample opportunities for effective dissemination through invited as well as volunteered contributions to major conferences.

2) to generate significant public interest
We will accompany published papers with targeted press releases, using the University Press Office, and also will target science journalists with whom ML and GL have established a good relationship. It is important that the outcomes of this project are effectively disseminated not only to scientific peers, but also to the general public to help explain how public investment in basic science can bring important benefits to public health. ML and GL have been extremely active in a wide range of outreach activities, including public lectures, popular articles, and on-line briefings and education. ML is the editor of "Neuroendocrine Briefings", a series of articles for the lay reader and widely disseminated in print and online and through scientific societies, and we expect to contribute a Briefing on this topic.


3) to give rise to translational opportunities.
The project may has potentially important translational implications, and these will be managed with the support of Edinburgh Research and Innovation (ERI; http://www.research-innovation.ed.ac.uk/), which has extensive expertise in the protection of intellectual property arising from grant-funded research, and in fostering translational outcomes. We have good links with pharmaceutical industry if partnership seems appropriate: GL has collaborated with Merck & Co for many years.