Ultrastructural changes in the neural lobe of the hypophysis of the rat during lactation and suckling

Abstract

Ultrastructural changes in the neural lobe related to lactation and release of oxytocin in response to suckling were observed. Neural lobes of nonlactating controls showed abundant stores of osmiophilic neurosecretion contained in vesicles in the axons. In contrast, the glands of lactating rats sacrificed during suckling by the young displayed extensive depletion as evidenced by decreased numbers of vesicles containing osmiophilic neurosecretion and increased numbers of optically clear neurosecretory vesicles. When a lapse of 15 minutes was allowed between removal of the suckling young and sacrifice of the mother, a high degree of restoration of neurosecretion had taken place, with approximately 50% of the axons filled with neurosecretion. After 1 hour the restoration of neurosecretion was virtually complete. Observations on synaptic vesicles were also made. Relations of these changes to hormonal events and mechanisms of release and restoration of neurosecretion are discussed.