Table 1.

Examples of neuroanatomical, neurochemical and physiological sex differences in the brains of rodents

End point measured	Measurements displaying male bias	Measurements displaying female bias	Measurements displaying context-, age- or region-specific biases
Volume	mPOA117 VMN118 BNST60 Binocular area of the visual cortex119 Amygdala120	Dorsal agranular insular subarea (orbital prefrontal cortex)121 AVPV of the hypothalamus122 LC123	Differences in medial amygdala volume are dependent on circulating testosterone in adult males124
Fibre density	Lateral septum (vasopressin neurons)125 Medial preoptic nucleus (serotonergic fibres)126 BNST (vasopressin neurons)127	AVPV (kisspeptin fibres)128	None known
Synapses	Excitatory synapses in the mPOA47,48,129,130 Hippocampal CA3 primary dendrites and spines131 Axosomatic synapses in the arcuate nucleus132 Axodendritic synapses in the VMN133,134	Axodendritic synapses in the arcuate nucleus132	Hippocampus dendritic spine density (female > male, but this reverses following stress)135 CA3 dendritic atrophy (male > female, but this reverses following stress)136
Branching	Length of glial processes in the arcuate nucleus134 Dendritic branching in prefrontal cortex cingulate areas137 Dendritic branching in the VMN138	Dendritic branching in the agranular insular cortex137	Differences in dendritic branching in dentate granule cells following environmental enrichment139 Difference in dendritic branching and soma size of spinal nucleus bulbocavernosus is maintained by testosterone in males140
Neurochemical phenotype	Vasopressin cells in the BNST141 Androgen receptor-expressing cells in the mPOA and BNST142	Oestrogen receptor-α immunoreactive cells in the median preoptic nucleus and VMN143 Kisspeptin-expressing cells in the AVPV144 Dopamine neurons in the AVPV54 Whole-brain levels of serotonin and its metabolites145	Differences in aromatase activity and progesterone receptor expression are region specific146–148
Cell number	Activated microglia in neonatal mPOA43 Glia in visual cortex119 Glia in the globus pallidus and CA1 (REF. 149) Astrocytes in the posterodorsal medial amygdala150	Radial glia in the mPOA and hypothalamus151 Oligodendrocyte precursors152	Biases in brain-wide microglia counts in neonates and adult depend on age42 Sex difference in astrocyte number in the medial amygdala only occurs in the left hemisphere153
Activational state	Duration of developmental excitatory actions of GABA154	Hippocampal long-term potentiation, excitatory postsynaptic potential slope, burst depolarization2 Hypothalamic proopiomelanocortin-expressing neurons and cannabinoid receptor type 1 mediated miniature inhibitory postsynaptic current frequency155	Hormonal control of nigrostriatal dopamine system156
Cell genesis	Neurogenesis in CA1 and dentate gyrus157,158	Cell genesis in the medial amygdala159 Neurogenesis in the LC160	Addition of new cells to sexually dimorphic AVPV and medial amygdala at puberty depends on gonadal steroids161

The categorization of sex differences in the rodent brain for over 40 years makes a comprehensive list unwieldy. Here, we note some examples of the range of types of sex differences that are found throughout the brain. AVPV, anteroventral periventricular nucleus; BNST, bed nucleus of the stria terminalis; LC, locus coeruleus; mPOA, medial preoptic area; VMN, ventromedial nucleus of the hypothalamus.