Limits...
Using light to tell the time of day: sensory coding in the mammalian circadian visual network.

Brown TM - J. Exp. Biol. (2016)

Bottom Line: In mammals, these changes are exclusively detected in the retina and are relayed by direct and indirect neural pathways to the master circadian clock in the hypothalamic suprachiasmatic nuclei.Recent work reveals a surprising level of complexity in this sensory control of the circadian system, including the participation of multiple photoreceptive pathways conveying distinct aspects of visual and/or time-of-day information.In this Review, I summarise these important recent advances, present hypotheses as to the functions and neural origins of these sensory signals, highlight key challenges for future research and discuss the implications of our current knowledge for animals and humans in the modern world.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, UK timothy.brown@manchester.ac.uk.

No MeSH data available.


Related in: MedlinePlus

SCN network organisation and possible implications of sensory processing. (A) A proposed model of SCN organisation comprising reciprocally (and locally) coupled vasoactive intestinal polypeptide (VIP)- and arginine-vasopressin (AVP)-rich regions (red and blue, respectively). The VIP-cell region receives dense retinal input (thick light blue arrow) and contains weak oscillators (represented by shallow waves) that are easily reset by external stimuli. The AVP-cell region receives less retinal innervation (thin light blue arrow), but contains more robust oscillators (deeper waves) and provides more extensive innervation of downstream brain regions (compare thick dark blue arrow versus thin red arrow). Retinal input to the two regions derives from genetically distinct mRGC subtypes, which are either Brn3b positive or negative (Brn3b+ve or −ve, respectively), proposed here to reflect cells providing chromatic versus achromatic input, respectively. (B) The normalised (relative to maximal firing) activity of blue-ON cells (top) and achromatic cells (bottom) to light steps replicating the colour and brightness of natural daylight (solar elevation=+3 deg) on clear (left panels) or cloudy days (right panels). Red and blue triangles represent the approximate strength of proposed excitatory (+) and inhibitory (−) contributions to phase resetting. Middle panels in B represent the difference between achromatic and blue-ON cell activity (weighted according to the twofold greater density of achromatic cells). Note that, because blue-ON cell activity is much more strongly suppressed under cloudy days than that of achromatic cells, the difference in activity of the two populations for a fixed solar elevation is broadly similar regardless of weather conditions. Periods of light are represented by white backgrounds and periods of darkness are represented by grey backgrounds. Data in B are derived from Walmsley et al. (2015).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4920240&req=5

JEB132167F5: SCN network organisation and possible implications of sensory processing. (A) A proposed model of SCN organisation comprising reciprocally (and locally) coupled vasoactive intestinal polypeptide (VIP)- and arginine-vasopressin (AVP)-rich regions (red and blue, respectively). The VIP-cell region receives dense retinal input (thick light blue arrow) and contains weak oscillators (represented by shallow waves) that are easily reset by external stimuli. The AVP-cell region receives less retinal innervation (thin light blue arrow), but contains more robust oscillators (deeper waves) and provides more extensive innervation of downstream brain regions (compare thick dark blue arrow versus thin red arrow). Retinal input to the two regions derives from genetically distinct mRGC subtypes, which are either Brn3b positive or negative (Brn3b+ve or −ve, respectively), proposed here to reflect cells providing chromatic versus achromatic input, respectively. (B) The normalised (relative to maximal firing) activity of blue-ON cells (top) and achromatic cells (bottom) to light steps replicating the colour and brightness of natural daylight (solar elevation=+3 deg) on clear (left panels) or cloudy days (right panels). Red and blue triangles represent the approximate strength of proposed excitatory (+) and inhibitory (−) contributions to phase resetting. Middle panels in B represent the difference between achromatic and blue-ON cell activity (weighted according to the twofold greater density of achromatic cells). Note that, because blue-ON cell activity is much more strongly suppressed under cloudy days than that of achromatic cells, the difference in activity of the two populations for a fixed solar elevation is broadly similar regardless of weather conditions. Periods of light are represented by white backgrounds and periods of darkness are represented by grey backgrounds. Data in B are derived from Walmsley et al. (2015).

Mentions: The basic anatomical organisation of the SCN is highly conserved across mammals, with a common set of inputs and several neurochemically identifiable cell types (Cassone et al., 1988; Moore, 1993; Morin and Allen, 2006), most notably, those producing vasoactive intestinal polypeptide (VIP) or arginine-vasopressin (AVP). The generally accepted model of how these elements interact (Fig. 5A) suggests that the SCN comprises two reciprocally coupled populations: a weakly rhythmic retinorecipient population that is highly responsive to external signals (primarily VIP cells) and a strongly rhythmic population (primarily AVP cells) that provides the major source of clock output and is more resistant to external perturbation (Evans and Gorman, 2016; Meijer et al., 2010). Although a full account of the evidence for and against this model is beyond the scope of this Review, there are a few aspects of SCN organisation worth discussing that are relevant to how sensory signals may be processed within the SCN.Fig. 5.


Using light to tell the time of day: sensory coding in the mammalian circadian visual network.

Brown TM - J. Exp. Biol. (2016)

SCN network organisation and possible implications of sensory processing. (A) A proposed model of SCN organisation comprising reciprocally (and locally) coupled vasoactive intestinal polypeptide (VIP)- and arginine-vasopressin (AVP)-rich regions (red and blue, respectively). The VIP-cell region receives dense retinal input (thick light blue arrow) and contains weak oscillators (represented by shallow waves) that are easily reset by external stimuli. The AVP-cell region receives less retinal innervation (thin light blue arrow), but contains more robust oscillators (deeper waves) and provides more extensive innervation of downstream brain regions (compare thick dark blue arrow versus thin red arrow). Retinal input to the two regions derives from genetically distinct mRGC subtypes, which are either Brn3b positive or negative (Brn3b+ve or −ve, respectively), proposed here to reflect cells providing chromatic versus achromatic input, respectively. (B) The normalised (relative to maximal firing) activity of blue-ON cells (top) and achromatic cells (bottom) to light steps replicating the colour and brightness of natural daylight (solar elevation=+3 deg) on clear (left panels) or cloudy days (right panels). Red and blue triangles represent the approximate strength of proposed excitatory (+) and inhibitory (−) contributions to phase resetting. Middle panels in B represent the difference between achromatic and blue-ON cell activity (weighted according to the twofold greater density of achromatic cells). Note that, because blue-ON cell activity is much more strongly suppressed under cloudy days than that of achromatic cells, the difference in activity of the two populations for a fixed solar elevation is broadly similar regardless of weather conditions. Periods of light are represented by white backgrounds and periods of darkness are represented by grey backgrounds. Data in B are derived from Walmsley et al. (2015).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4920240&req=5

JEB132167F5: SCN network organisation and possible implications of sensory processing. (A) A proposed model of SCN organisation comprising reciprocally (and locally) coupled vasoactive intestinal polypeptide (VIP)- and arginine-vasopressin (AVP)-rich regions (red and blue, respectively). The VIP-cell region receives dense retinal input (thick light blue arrow) and contains weak oscillators (represented by shallow waves) that are easily reset by external stimuli. The AVP-cell region receives less retinal innervation (thin light blue arrow), but contains more robust oscillators (deeper waves) and provides more extensive innervation of downstream brain regions (compare thick dark blue arrow versus thin red arrow). Retinal input to the two regions derives from genetically distinct mRGC subtypes, which are either Brn3b positive or negative (Brn3b+ve or −ve, respectively), proposed here to reflect cells providing chromatic versus achromatic input, respectively. (B) The normalised (relative to maximal firing) activity of blue-ON cells (top) and achromatic cells (bottom) to light steps replicating the colour and brightness of natural daylight (solar elevation=+3 deg) on clear (left panels) or cloudy days (right panels). Red and blue triangles represent the approximate strength of proposed excitatory (+) and inhibitory (−) contributions to phase resetting. Middle panels in B represent the difference between achromatic and blue-ON cell activity (weighted according to the twofold greater density of achromatic cells). Note that, because blue-ON cell activity is much more strongly suppressed under cloudy days than that of achromatic cells, the difference in activity of the two populations for a fixed solar elevation is broadly similar regardless of weather conditions. Periods of light are represented by white backgrounds and periods of darkness are represented by grey backgrounds. Data in B are derived from Walmsley et al. (2015).
Mentions: The basic anatomical organisation of the SCN is highly conserved across mammals, with a common set of inputs and several neurochemically identifiable cell types (Cassone et al., 1988; Moore, 1993; Morin and Allen, 2006), most notably, those producing vasoactive intestinal polypeptide (VIP) or arginine-vasopressin (AVP). The generally accepted model of how these elements interact (Fig. 5A) suggests that the SCN comprises two reciprocally coupled populations: a weakly rhythmic retinorecipient population that is highly responsive to external signals (primarily VIP cells) and a strongly rhythmic population (primarily AVP cells) that provides the major source of clock output and is more resistant to external perturbation (Evans and Gorman, 2016; Meijer et al., 2010). Although a full account of the evidence for and against this model is beyond the scope of this Review, there are a few aspects of SCN organisation worth discussing that are relevant to how sensory signals may be processed within the SCN.Fig. 5.

Bottom Line: In mammals, these changes are exclusively detected in the retina and are relayed by direct and indirect neural pathways to the master circadian clock in the hypothalamic suprachiasmatic nuclei.Recent work reveals a surprising level of complexity in this sensory control of the circadian system, including the participation of multiple photoreceptive pathways conveying distinct aspects of visual and/or time-of-day information.In this Review, I summarise these important recent advances, present hypotheses as to the functions and neural origins of these sensory signals, highlight key challenges for future research and discuss the implications of our current knowledge for animals and humans in the modern world.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, UK timothy.brown@manchester.ac.uk.

No MeSH data available.


Related in: MedlinePlus