Direct pathways to the supraoptic nucleus from the brainstem and the main olfactory bulb are activated at parturition in the rat

• Published in: Neuroscience Vol. 101; no. 4; pp. 1013 - 1021
• Main Authors: Meddle, S.L, Leng, G, Selvarajah, J.R, Bicknell, R.J, Russell, J.A
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.01.2000; Elsevier
• Subjects: Afferent Pathways - physiology; Animals; Biological and medical sciences; Brain Stem - physiology; catecholamines; Catecholamines - metabolism; Female; Fos; Fundamental and applied biological sciences. Psychology; Hormone metabolism and regulation; Labor, Obstetric - physiology; Medulla Oblongata - physiology; nucleus tractus solitarii; Olfactory Bulb - physiology; organum vasculosum of the lamina terminalis; Pregnancy; Pregnancy. Parturition. Lactation; Proto-Oncogene Proteins c-fos - metabolism; Rats; Rats, Sprague-Dawley; retrograde tracing; Solitary Nucleus - physiology; Supraoptic Nucleus - physiology; Synaptic Transmission - physiology; Tyrosine 3-Monooxygenase - metabolism; ventrolateral medulla; Vertebrates: reproduction; catecholamines; SON, supraoptic nucleus; nucleus tractus solitarii; VLM, ventrolateral medulla; SFO, subfornical organ; Fos; DAB, 3,3′ diaminobenzidine tetrahydrochloride; OVLT, organum vasculosum of the lamina terminalis; MPOA, medial preoptic area; IR, immunoreactive; organum vasculosum of the lamina terminalis; BST, bed nucleus of the stria terminalis; MA, medial amygdala; NTS, nucleus tractus solitarii; ANOVA, analysis of variance; TH tyrosine hydroxylase; ventrolateral medulla; retrograde tracing; Parturition; Rat; Brain stem; Rodentia; Central nervous system; Terminal lamina; Projection; Hypothalamus; Catecholamine; Organum vasculosum; Solitary nucleus; Vertebrata; Mammalia; Olfactory pathway; Olfactory bulb; Medulla oblongata; Supraoptic nucleus; Brain (vertebrata)
• ISSN: 0306-4522; 1873-7544
• DOI: 10.1016/S0306-4522(00)00300-6

Sensory input from female reproductive structures is paramount for the co-ordination of neuroendocrine changes at parturition. Using a retrograde tracer (fluorescent latex microspheres) in combination with Fos (as an indicator of neuronal activation) and tyrosine hydroxylase (to identify catecholaminergic neurons) immunocytochemistry we identified cells within the brainstem and main olfactory bulb that project to the supraoptic nucleus, and which become significantly activated at parturition (compared to virgin rats and rats on the day of expected parturition). Within the A2/C2 region in the nucleus tractus solitarii, 60% of the projecting activated cells were catecholaminergic, as were 59% of such cells in the A1/C1 region of the ventrolateral medulla. This suggests that oxytocin and vasopressin neurons within the supraoptic nucleus are stimulated at parturition via afferent inputs from the brainstem, but the input is not exclusively noradrenergic. Within the mitral layer of the main olfactory bulb, cells that projected to the supraoptic nucleus were significantly activated, suggesting that the olfactory system may regulate supraoptic nucleus cell firing at parturition. The preoptic area, organum vasculosum of the lamina terminalis and medial amygdala contained cells that projected to the supraoptic nucleus but these projections were not significantly activated at parturition, although non-projecting cells in these regions were. On the expected day of parturition, but before birth, projections from the organum vasculosum of the lamina terminalis to the supraoptic nucleus became significantly activated. These findings provide evidence of direct afferent pathways to the supraoptic nucleus from the brain stem and olfactory bulbs that are activated at parturition.