Males (right) show denser AVP fiber development than females (left) in the lateral septum (LS).

Sexual differences in AVP fiber density

However, as fiber development is observed as early as P14 in the LS and LH in rat models where puberty generally kicks in at P30-42, it is safe to assume that the gonadal steroid levels may not have an impact on the AVP- fiber development.

AVP development is puberty-independent

The development of the Bed Nucleus Stria Terminalis (BNST) and Medial Amygdala (MeA) associated social behavior pathway might be triggered by increased gonadal steroid hormone levels during puberty.

AVP development is puberty-dependent

1. Studies indicate that the development of AVP pathways occurs in the lateral septum (LS) and lateral habenula (LH)
2. Males show a higher density of AVP fiber development
3. AVP Fiber development generally begins around P12 & P14.

State University of New York at Buffalo

Also known as Antidiuretic Hormone (ADH) or Arginine Vasopressin (AVP), it is a neuroendocrine hormone/ neuropeptide which is produced in the hypothalamus and upon release, travels to the pituitary, post which it is released in the anterior pituitary for general circulation.

It has various functions, mainly water reabsorption in the kidneys and regulation of social behavior. 

Vasopressin

De Vries GJ, Panzica GC. Sexual differentiation of central vasopressin and vasotocin systems in vertebrates: different mechanisms, similar endpoints. Neuroscience. 2006;138(3):947-55. doi: 10.1016/j.neuroscience.2005.07.050. Epub 2005 Nov 28. PMID: 16310321; PMCID: PMC1457099.


Sexual differentiation of central vasopressin and vasotocin systems in vertebrates

de Vries, G. J., Buijs, R. M., & Swaab, D. F. (1981). Ontogeny of the vasopressinergic neurons of the suprachiasmatic nucleus and their extrahypothalamic projections in the rat brain--presence of a sex difference in the lateral septum. Brain Res, 218(1-2), 67-78. doi:10.1016/0006-8993(81)90989-6

Ontogeny of the vasopressinergic neurons of the suprachiasmatic nucleus and their extrahypothalamic projections in the rat brain

1. In the CNS, magnocellular cells, primarily, the Supraoptic Nucleus (SON) and the Paraventricular Nucleus (PVN), synthesize a majority of the AVP. 
2. In normal animals, an inactive precursor consisting of a signal peptide (SP), AVP, neurophysin carrier protein (NPY) and a Carboxy-terminal glycopeptide (CP), is encoded by the AVP gene, which post-translation, results in the synaptic release of AVP from the neurohypophyseal axons. 
3. Brattleboro rats serve as animal models in studies involving social behaviors induced by AVP deficiency. Due to a single-bp deletion in the exon 2 of the AVP gene in Brattleboro rats, a mutated AVP prohormone is trapped in the ER, thus preventing its systemic circulation. 

Vasopressin affects Social Behavior

1. AVP production occurs at supraoptic nucleus (SON), paraventricular nucleus (PVN), medial amygdala (MeA) and the bed nucleus stria terminalis (BNST)
2. AVP projections have an influence on Circadian Rhythms, Social Behavior and Thirst-associated behaviors. 
3. The water balance circuit consists of magnocellular neurons of the PVN and SON projecting their VP fibers towards the neurohypophysis. (VRIES, CRENSHAW, & AL-SHAMMA, 1992) 
4. AVP projections involved in regulation of circadian rhythms trace a route from the SCN, travelling rostrodorsally toward the LS, rostrally toward OVLT and dorsocaudally through the PVN, terminating at the LHb. (de Vries & Miller, 1998) 
5. The sexually dimorphic parvocellular VP projections from the BNST and the MeA, projecting towards the LC, LH, LS and VSA, are involved in depicting social behaviors.(de Vries, Buijs, & Swaab, 1981) 

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