Light-Induced Fos Expression in Intrinsically Photosensitive Retinal Ganglion Cells in Melanopsin Knockout (Opn4−/−) Mice

Retinal ganglion cells that express the photopigment melanopsin are intrinsically photosensitive (ipRGCs) and exhibit robust synaptically driven ON-responses to light, yet they will continue to depolarize in response to light when all synaptic input from rod and cone photoreceptors is removed. The light-evoked increase in firing of classical ganglion cells is determined by synaptic input from ON-bipolar cells in the proximal sublamina of the inner plexiform layer. OFF-bipolar cells synapse with ganglion cell dendrites in the distal sublamina of the inner plexiform layer. Of the several types of ipRGC that have been described, M1 ipRGCs send dendrites exclusively into the OFF region of the inner plexiform layer where they stratify near the border of the inner nuclear layer. We tested whether M1 ipRGCs with dendrites restricted to the OFF sublamina of the inner plexiform layer receive synaptic ON-bipolar input by examining light-induced gene expression in vivo using melanopsin knockout mice. Mice in which both copies of the melanopsin gene (opn4) have been replaced with the tau-lacZ gene (homozygous tau-lacZ+/+ knockin mice) are melanopsin knockouts (opn4−/−) but M1 ipRGCs are specifically identified by their expression of β-galactosidase. Approximately 60% of M1 ipRGCs in Opn4−/− mice exposed to 3 hrs of light expressed c-Fos; no β-galactosidase-positive RGCs expressed c-Fos in the dark. Intraocular application of L-AP4, a compound which blocks transmission of visual signals between photoreceptors and ON-bipolar cells significantly reduced light-evoked c-Fos expression in M1 ipRGCs compared to saline injected eyes (66% saline vs 27% L-AP4). The results are the first description of a light-evoked response in an ipRGC lacking melanopsin and provide in vivo confirmation of previous in vitro observations illustrating an unusual circuit in the retina in which ganglion cells sending dendrites to the OFF sublamina of the inner plexiform layer receive excitatory synaptic input from ON-bipolar cells

Novel Visual Lures for the Management of Brushtail Possums

The successful management of vertebrate wildlife populations can be dependent on the availability of reliable monitoring methods, and, depending on the status of the species in question, effective methods of conservation or control. The brushtail possum, introduced to New Zealand from Australia, is considered New Zealand’s number one vertebrate pest. We assessed possum preferences for 3 types of visual lures and the potential use of this information for enhancing existing possum control technologies. Significantly more lures were interfered with by possums when the lures were associated with a luminescent strip, compared to lures that were plain white or UV-enhanced (P < 0.01 in both cases). In addition, more possums were killed when luminescent lures were attached to kill traps and bags of bait than when these devices were deployed without lures. This study has highlighted new information showing that luminescent lures could be a valuable new tool in the management of nocturnal marsupials, be they species considered pests (such as the brushtail possum in New Zealand), or species of conservation concern, such as many of Australia’s marsupial species

Novel Visual Lures for the Management of Brushtail Possums

The successful management of vertebrate wildlife populations can be dependent on the availability of reliable monitoring methods, and, depending on the status of the species in question, effective methods of conservation or control. The brushtail possum, introduced to New Zealand from Australia, is considered New Zealand’s number one vertebrate pest. We assessed possum preferences for 3 types of visual lures and the potential use of this information for enhancing existing possum control technologies. Significantly more lures were interfered with by possums when the lures were associated with a luminescent strip, compared to lures that were plain white or UV-enhanced (P < 0.01 in both cases). In addition, more possums were killed when luminescent lures were attached to kill traps and bags of bait than when these devices were deployed without lures. This study has highlighted new information showing that luminescent lures could be a valuable new tool in the management of nocturnal marsupials, be they species considered pests (such as the brushtail possum in New Zealand), or species of conservation concern, such as many of Australia’s marsupial species

Light-induced c-Fos expression in an ipRGC lacking melanopsin.

<p>(upper panel) An M1 ipRGC in the retina of a <i>tau-lacZ^+/+</i> mouse identified by β-galactosidase immunostaining. Note the dendrite emanating from this ipRGC extends to the outer aspect of the IPL, bifurcates and stratifies along the border of the INL, contributing to the definition of this ganglion cell as an M1 ipRGC. (middle panel) Same section as in upper panel illustrating light-induced Fos expression in the nuclei of neurons in the ganglion cell layer and INL. (bottom panel) Merged image illustrating light-induced Fos expression in an M1 ipRGC lacking melanopsin.</p

Intraocular application of L-AP4 inhibits light-induced Fos expression in M1 ipRGCs lacking melanopsin.

<p>The number of Fos-positive β-galactosidase cells is presented as a percentage of the number of β-galactosidase cells observed for each eye of each animal (#1–#3) after intravitreal injection of 1 µl saline (sal) or 1 µl L-AP4 (1 mM) followed by 3 h of light stimulation or 3 h of darkness.</p

Altered Entrainment to the Day/Night Cycle Attenuates the Daily Rise in Circulating Corticosterone in the Mouse

The suprachiasmatic nucleus (SCN) is a circadian oscillator entrained to the day/night cycle via input from the retina. Serotonin (5-HT) afferents to the SCN modulate retinal signals via activation of 5-HT1B receptors, decreasing responsiveness to light. Consequently, 5-HT1B receptor knockout (KO) mice entrain to the day/night cycle with delayed activity onsets. Since circulating corticosterone levels exhibit a robust daily rhythm peaking around activity onset, we asked whether delayed entrainment of activity onsets affects rhythmic corticosterone secretion. Wheel-running activity and plasma corticosterone were monitored in mice housed under several different lighting regimens. Both duration of the light:dark cycle (T cycle) and the duration of light within that cycle was altered. 5-HT1B KO mice that entrained to a 9.5L:13.5D (short day in a T = 23 h) cycle with activity onsets delayed more than 4 h after light offset exhibited a corticosterone rhythm in phase with activity rhythms but reduced 50% in amplitude compared to animals that initiated daily activity ,4 h after light offset. Wild type mice in 8L:14D (short day in a T = 22 h) conditions with highly delayed activity onsets also exhibited a 50% reduction in peak plasma corticosterone levels. Exogenous adrenocorticotropin (ACTH) stimulation in animals exhibiting highly delayed entrainment suggested that the endogenous rhythm of adrenal responsiveness to ACTH remained aligned with SCN-driven behavioral activity. Circadian clock gene expression in the adrenal cortex of these same animals suggested that the adrenal circadian clock was also aligned with SCN-driven behavior. Under T cycles ,24 h, altered circadian entrainment to short day (winter-like) conditions, manifest as long delays in activity onset after light offset, severely reduces the amplitude of the diurnal rhythm of plasma corticosterone. Such a pronounced reduction in the glucocorticoid rhythm may alter rhythmic gene expression in the central nervous system and in peripheral organs contributing to an array of potential pathophysiologies