SCN Lesion and Neural Transplant
Objective: To demonstrate that fetal SCN grafts can restore circadian rhythms of locomotor activity in adult hamsters made arrhythmic by SCN lesions, and to characterize the neuropeptide content and neural integration of the grafts
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Equipment1
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Materials1
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Protocol Steps
SCN Lesion Surgery
Surgical lesioning of the hypothalamic suprachiasmatic nucleus in adult hamsters to induce arrhythmia
Note: This procedure permanently disrupts overt circadian rhythms prior to graft implantation
View evidence from paper
“overt circadian rhythms are permanently disrupted following lesions of the hamster hypothalamic suprachiasmatic nucleus (SCN)”
Fetal SCN Graft Implantation
Implantation of brain grafts containing fetal SCN tissue into the lesioned adult hamster brain
Note: Timing of implantation relative to lesion not specified
View evidence from paper
“implantations of brain grafts containing the fetal SCN reestablish circadian rhythms of locomotor activity in adult hamsters”
Circadian Rhythm Assessment
Measurement of free-running locomotor activity rhythms in conditions of constant darkness to assess restoration of circadian function
Note: Conducted in constant darkness conditions
View evidence from paper
“The restoration of free-running rhythms in conditions of constant darkness is correlated with the presence in the graft”
Immunocytochemical Characterization
Immunocytochemical analysis of graft tissue to identify presence of neuropeptides including VIP, NPY, and vasopressin
Note: Neuropeptides examined are those normally present in SCN of unlesioned hamsters
View evidence from paper
“neuropeptides normally present in the SCN of unlesioned hamsters, including vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY), and vasopressin (VP)”
Assessment of Graft Neural Integration
Examination of graft tissue for evidence of retinal input and efferent projections into host brain
Note: Not all grafts showed these connections; presence correlated with functional restoration
View evidence from paper
“In several recipients, grafts were found to receive retinal input, and appeared to send efferents into the host brain”
Assessment of Gonadal Function
Evaluation of gonadal regression in response to absence of light in animals with restored locomotor rhythms
Note: This SCN function was not reinstated by the graft
View evidence from paper
“animals with restored locomotor rhythms did not show gonadal regression in the absence of light”
Assessment of Light Entrainment
Testing of graft-bearing animals' ability to synchronize (entrain) to various light intensities
Note: Graft-bearing animals failed to entrain to light intensities that SCN-intact animals responded to
View evidence from paper
“failed to synchronize (entrain) to light intensities to which SCN-intact animals responded”