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Lesions of the Intergeniculate Leaflet Lead to a Reorganization in Circadian Regulation and a Reversal in Masking Responses to Photic Stimuli in the Nile Grass Rat.

Gall AJ, Smale L, Yan L, Nunez AA - PLoS ONE (2013)

Bottom Line: Light influences the daily patterning of behavior by entraining circadian rhythms and through its acute effects on activity levels (masking).Dark pulses had no effect on controls, but significantly increased activity in lesioned animals at ZT0.Taken together, our results suggest that the IGL plays a vital role in the maintenance of both the species-typical masking responses to light, and the circadian contribution to diurnality in grass rats.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychology and Neuroscience Program, Michigan State University, East Lansing, Michigan, United States of America.

ABSTRACT
Light influences the daily patterning of behavior by entraining circadian rhythms and through its acute effects on activity levels (masking). Mechanisms of entrainment are quite similar across species, but masking can be very different. Specifically, in diurnal species, light generally increases locomotor activity (positive masking), and in nocturnal ones, it generally suppresses it (negative masking). The intergeniculate leaflet (IGL), a subdivision of the lateral geniculate complex, receives direct retinal input and is reciprocally connected with the primary circadian clock, the suprachiasmatic nucleus (SCN). Here, we evaluated the influence of the IGL on masking and the circadian system in a diurnal rodent, the Nile grass rat (Arvicanthis niloticus), by determining the effects of bilateral IGL lesions on general activity under different lighting conditions. To examine masking responses, light or dark pulses were delivered in the dark or light phase, respectively. Light pulses at Zeitgeber time (ZT) 14 increased activity in control animals but decreased it in animals with IGL lesions. Dark pulses had no effect on controls, but significantly increased activity in lesioned animals at ZT0. Lesions also significantly increased activity, primarily during the dark phase of a 12:12 light/dark cycle, and during the subjective night when animals were kept in constant conditions. Taken together, our results suggest that the IGL plays a vital role in the maintenance of both the species-typical masking responses to light, and the circadian contribution to diurnality in grass rats.

No MeSH data available.


Related in: MedlinePlus

Smallest, medium-sized, and largest electrolytic lesions that destroyed the intergeniculate leaflet bilaterally, along with an animal that had lesions that left the IGL intact (i.e., “miss”), seen in five coronal sections.Millimeters caudal to bregma are indicated on the right. Behavioral data for the smallest IGL lesions and miss are in Figure 3 (labeled IGL Lesion #1 and DLG lesion, respectively). Abbreviations: DLG: dorsolateral geniculate nucleus; IGL: intergeniculate leaflet; VPL: ventral posterolateral nucleus; VPM: ventral posteromedial nucleus; OPT: olivary pretectal nucleus; APT: anterior pretectal nucleus; PPT: posterior pretectal nucleus.
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pone-0067387-g002: Smallest, medium-sized, and largest electrolytic lesions that destroyed the intergeniculate leaflet bilaterally, along with an animal that had lesions that left the IGL intact (i.e., “miss”), seen in five coronal sections.Millimeters caudal to bregma are indicated on the right. Behavioral data for the smallest IGL lesions and miss are in Figure 3 (labeled IGL Lesion #1 and DLG lesion, respectively). Abbreviations: DLG: dorsolateral geniculate nucleus; IGL: intergeniculate leaflet; VPL: ventral posterolateral nucleus; VPM: ventral posteromedial nucleus; OPT: olivary pretectal nucleus; APT: anterior pretectal nucleus; PPT: posterior pretectal nucleus.

Mentions: Three groups of animals were identified based on histology: those with (1) complete, bilateral IGL lesions (n = 20) (i.e., “hits”; defined as an area devoid of cells in the IGL in thionin-stained sections), (2) unilateral, partial, or no damage in the IGL (n = 4) (i.e., “misses”), and (3) shams (n = 8) (Figure 1). To confirm the lesion of IGL, brain tissue from a subset of the animals was processed for NPY immunostaining. NPY-ir was seen in both the IGL and the SCN of shams and of those with lesions deemed to be misses. In contrast, in lesioned animals in which the IGL could not be seen in thionin stained material, NPY was absent in the IGL as well as in the SCN, providing further evidence that these lesions completely destroyed the IGL. The brain regions that were damaged following these lesions are depicted in Figure 2. The smallest complete bilateral lesion of the IGL also damaged parts of the dorsolateral geniculate nucleus (DLG). The largest complete bilateral lesion of the IGL also included partial lesions of the DLG, VLG, hippocampus, olivary pretectal nucleus (OPT), and the thalamus [including the ventral posterolateral thalamus (VPL) and ventral posteromedial thalamus (VPM)]. Lesions that were deemed as misses had damage to the DLG, VLG, hippocampus, and/or parts of the IGL, but in all of these cases, at least some IGL tissue remained intact.


Lesions of the Intergeniculate Leaflet Lead to a Reorganization in Circadian Regulation and a Reversal in Masking Responses to Photic Stimuli in the Nile Grass Rat.

Gall AJ, Smale L, Yan L, Nunez AA - PLoS ONE (2013)

Smallest, medium-sized, and largest electrolytic lesions that destroyed the intergeniculate leaflet bilaterally, along with an animal that had lesions that left the IGL intact (i.e., “miss”), seen in five coronal sections.Millimeters caudal to bregma are indicated on the right. Behavioral data for the smallest IGL lesions and miss are in Figure 3 (labeled IGL Lesion #1 and DLG lesion, respectively). Abbreviations: DLG: dorsolateral geniculate nucleus; IGL: intergeniculate leaflet; VPL: ventral posterolateral nucleus; VPM: ventral posteromedial nucleus; OPT: olivary pretectal nucleus; APT: anterior pretectal nucleus; PPT: posterior pretectal nucleus.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3686741&req=5

pone-0067387-g002: Smallest, medium-sized, and largest electrolytic lesions that destroyed the intergeniculate leaflet bilaterally, along with an animal that had lesions that left the IGL intact (i.e., “miss”), seen in five coronal sections.Millimeters caudal to bregma are indicated on the right. Behavioral data for the smallest IGL lesions and miss are in Figure 3 (labeled IGL Lesion #1 and DLG lesion, respectively). Abbreviations: DLG: dorsolateral geniculate nucleus; IGL: intergeniculate leaflet; VPL: ventral posterolateral nucleus; VPM: ventral posteromedial nucleus; OPT: olivary pretectal nucleus; APT: anterior pretectal nucleus; PPT: posterior pretectal nucleus.
Mentions: Three groups of animals were identified based on histology: those with (1) complete, bilateral IGL lesions (n = 20) (i.e., “hits”; defined as an area devoid of cells in the IGL in thionin-stained sections), (2) unilateral, partial, or no damage in the IGL (n = 4) (i.e., “misses”), and (3) shams (n = 8) (Figure 1). To confirm the lesion of IGL, brain tissue from a subset of the animals was processed for NPY immunostaining. NPY-ir was seen in both the IGL and the SCN of shams and of those with lesions deemed to be misses. In contrast, in lesioned animals in which the IGL could not be seen in thionin stained material, NPY was absent in the IGL as well as in the SCN, providing further evidence that these lesions completely destroyed the IGL. The brain regions that were damaged following these lesions are depicted in Figure 2. The smallest complete bilateral lesion of the IGL also damaged parts of the dorsolateral geniculate nucleus (DLG). The largest complete bilateral lesion of the IGL also included partial lesions of the DLG, VLG, hippocampus, olivary pretectal nucleus (OPT), and the thalamus [including the ventral posterolateral thalamus (VPL) and ventral posteromedial thalamus (VPM)]. Lesions that were deemed as misses had damage to the DLG, VLG, hippocampus, and/or parts of the IGL, but in all of these cases, at least some IGL tissue remained intact.

Bottom Line: Light influences the daily patterning of behavior by entraining circadian rhythms and through its acute effects on activity levels (masking).Dark pulses had no effect on controls, but significantly increased activity in lesioned animals at ZT0.Taken together, our results suggest that the IGL plays a vital role in the maintenance of both the species-typical masking responses to light, and the circadian contribution to diurnality in grass rats.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychology and Neuroscience Program, Michigan State University, East Lansing, Michigan, United States of America.

ABSTRACT
Light influences the daily patterning of behavior by entraining circadian rhythms and through its acute effects on activity levels (masking). Mechanisms of entrainment are quite similar across species, but masking can be very different. Specifically, in diurnal species, light generally increases locomotor activity (positive masking), and in nocturnal ones, it generally suppresses it (negative masking). The intergeniculate leaflet (IGL), a subdivision of the lateral geniculate complex, receives direct retinal input and is reciprocally connected with the primary circadian clock, the suprachiasmatic nucleus (SCN). Here, we evaluated the influence of the IGL on masking and the circadian system in a diurnal rodent, the Nile grass rat (Arvicanthis niloticus), by determining the effects of bilateral IGL lesions on general activity under different lighting conditions. To examine masking responses, light or dark pulses were delivered in the dark or light phase, respectively. Light pulses at Zeitgeber time (ZT) 14 increased activity in control animals but decreased it in animals with IGL lesions. Dark pulses had no effect on controls, but significantly increased activity in lesioned animals at ZT0. Lesions also significantly increased activity, primarily during the dark phase of a 12:12 light/dark cycle, and during the subjective night when animals were kept in constant conditions. Taken together, our results suggest that the IGL plays a vital role in the maintenance of both the species-typical masking responses to light, and the circadian contribution to diurnality in grass rats.

No MeSH data available.


Related in: MedlinePlus