The pineal gland of the horse. Morphological and histochemical results. (With notes on the donkey and mule pineal).

The research paper focuses on the investigation of the horse’s pineal gland through morphological and histochemical methods, specifically analyzing cellular types, possible neurosecretory activity, and the nature of pigments. It reveals that two populations of pinealocytes can be distinguished in a horse’s pineal gland, and a considerable number of these pinealocytes respond positively to certain chemical reactions. Also, the existence of different types of pigment-carrying cells is documented, especially indicating a higher presence in older animals.

Morphological and histochemical investigation

• The researchers conducted a deep investigation on the horse’s pineal gland, utilizing morphological and histochemical methods for the study. The focus was particularly on understanding the diverse types of cells, detecting any presence of neurosecretory activity, and determining the nature of the pigments present in the gland.

Pinealocytes in the horse pineal gland

• Through their study, they found that even within the horse pineal gland, it’s possible to distinguish between two populations of pinealocytes. These are morphologically different but do not show any difference in their histochemical properties.
• A substantial number of these pinealocytes tested positive for the Masson-Hamperl reaction, Gomori-Bargmann’s chromic haematoxylin-phloxine, and Gomori’s paraldehyde-fuchsin. These chemical reactions are typically used in histology to identify specific substances in cells.

Pigmented cells in the pineal gland

• The study further highlights the presence of many brown-blackish pigmented cells along the connective septa of the pineal gland. The pigment in these cells tested positive for Lillie and the Masson-Fontana reactions, which are typically used to determine the presence of melanin pigment.
• Another type of pigmented cells was found to carry a brown-yellowish pigment, identified to be of lipofuscin nature. These cells were notably present in older animals along the connective septa, suggesting a possible link between the pineal gland’s pigmentation and the age of the animal.