Serotonin receptor binding in the human brainstem peaks before birth, then declines sharply by infancy, especially in regions controlling cardiovascular function, respiration, and pain. Using [3H]LSD autoradiography on brainstem tissue from 5 fetuses (19-25.5 weeks postconception), 5 infants (42-55.5 weeks postconception), and 3 mature individuals (4, 20, and 52 years), the highest binding occurred prenatally throughout the brainstem, with the rostral raphe showing the highest relative binding at all ages. This fetal peak suggests serotonin plays a trophic role in developing human brainstem, and the subsequent decrease indicates reduced serotonergic modulation of vegetative functions after birth.
Lysergic acid diethylamide (LSD) primarily targets the lysosomal system within neurons. In organotypic cultures of mouse cerebellum exposed to LSD for up to 53 hours, coarse granules developed in the cytoplasm of mature neurons and outgrowth cells. Electron microscopy revealed these granules were dense bodies, specifically lysosomes, which became heterogeneous dense bodies over time. Synaptic junctions and other organelles remained unchanged. The findings suggest LSD enters cells and interacts with lysosomes, potentially altering neuronal excitability through increased endocytosis or shifts in internal metabolism, which may underlie behavioral changes.