Zamin Ladha

Date of Award


Degree Type


Degree Name

Master of Science


Anatomy and Cell Biology


Dr. Michael Lehman


The neural circuitry underlying seasonal reproduction in sheep involves A15 dopamine neurons that undergo annual changes in synaptic inputs and dendritic complexity. Thyroidectomy (TH×) in late breeding season blocks both seasonal plasticity and the transition to anestrous.

To determine if neurotrophins regulate these morphological changes, we first examined the effects of TH× on the mRNA expression of neurotrophins, and their receptors, during the late breeding season. THX ewes had elevated TrkA expression in

the A15, and elevated NGF expression in the arcuate nucleus (ARC). The effects of TH× on seasonal alterations in glutamatergic inputs onto A15 neurons

were also examined. Anestrous ewes had significantly more vGlutl- and vGlut2-positive appositions than breeding season ewes; THX completely blocked this seasonal increase.

These results point to alterations in NGF∕TrkA signaling between the ARC and A15 in mediating thyroid-dependent processes underlying neural plasticity, and seasonal changes in A15 glutamatergic inputs responsible for the annual transition to anestrous.



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