vasopressin cell and fibre distribution patterns are highly conserved across species (with centrally projecting systems being sexually dimorphic), the vasopressin receptor AVPR1A distribution differs both between and within species; vasopressin production occurs in the hypothalamus, bed nucleus of the stria terminalis, and the medial amygdala (projecting to the lateral septum and ventral pallidum), while vasopressin binding sites in humans are in the lateral septum, thalamus, basal amygdaloid nucleus, and brainstem, but not cortex. Human AVPR1A is situated on chromosome 12q14-15, and the promoter region does not have repeat sequences homologous to those found in prairie voles. Three polymorphic repetitive sequences have been found in humans in the 5’ flanking region: RS3, RS1, and a (GT)25 dinucleotide repeat. A 2015 study found a correlation between AVPR1A expression and predisposition to extra-pair mating in women but not in men. Polymorphisms RS3 The AVPR1A repeat polymorphism RS3 is a complex (CT)4-TT-(CT)8-(GT)24 repeat that is 3625 bp upstream of the transcription start site. Homozygosity in allele 334 of RS3 is associated in men (but not women) with problems with pair-bonding behavior, measured by traits such as partner bonding, perceived marital problems, marital status, as well as spousal perception of marital quality. In a study of 203 male and female university students, participants with short (308–325 bp) vs. long (327–343) versions of RS3 were less generous, as measured by lower scores on both money allocations in the dictator game, as well as by self-report with the Bardi-Schwartz Universalism and Benevolence Value-expressive Behavior Scales; although the precise functional significance of longer AVPR1A RS3 repeats is not known, they are associated with higher AVPR1A postmortem hippocampal mRNA levels. Relative to all other alleles, the 334 allele of RS3 shows overactivation of left amygdala (in response to fearful face stimuli), with longer variants of RS3 additionally associated with stronger amygdala activation. RS1 The AVPR1A repeat polymorphism RS1 is a (GATA)14 tetranucleotide repeat that is 553 bp upstream from the transcription start site. Allele 320 in RS1 is associated with increased novelty seeking and decreased harm avoidance; additionally, relative to all other alleles, the 320 allele of RS1 showed significantly less activity in the left amygdala, with shorter variants showing a trend of stronger activity. Other microsatellites The AGAT polymorphism is associated with age of first intercourse in females, with those homozygous for long repeats more likely to have sex before age 15 than any other genotype. However, there