Pinealocyte ultrastructure in mutant mice that lack sympathetic innervation to the pineal gland

Pinealocyte synaptic ribbons (SR) and dense-cored vesicles (DCV) were quantitated in mice that have developmental deficiencies in the sympathetic innervation of the pineal gland due to a null mutation for the p75 low-affinity NGF receptor (NGFR). SR exhibited a significant increase whereas there was a significant decline in the frequency of DCV in mutant mice. These findings support the hypothesis that pinealocyte SR and DCV are regulated by neural mechanisms associated with sympathetic system. Ultrastructural characteristics of pinealocytes in mutants included degenerative changes that culminated in the breakdown of cellular components and the accumulation of flocculent-containing vesicles within the cytoplasm. Ribosomal lamellar complexes were also commonly seen in pinealocytes of mutant rats. Although the mutant pineal gland exhibited signs of metabolic imbalances, the cytoarchitecture of the gland (e.g., vascular compartment) and differentiation of the cells were generally unaffected by developmental deficiencies in the gland's innervation.