Table 1.
Selected neuroanatomical sex differences in the rat.
| Structure/Region | Known roles | Sex difference | Basis of difference |
|---|---|---|---|
| Sexually dimorphic nucleus of the Preoptic Area (SDN-POA) | The POA is implicated in the regulation of male copulatory behavior [14]. Lesions of the SDN alone slow acquisition of this behavior. Potential human equivalent is INAH-3 [18]. | 2.6 times larger in males [19]. | Perinatal aromatized androgen decreases neuronal apoptotic rates in males [20]. |
| Anteroventral Periventricular Nucleus (AVPV) | Involved in regulating the luteinizing hormone surge in females [20] and male copulatory behavior [21]. | 2.2 times larger in females with a higher cell density [22]. | Degeneration of cells in this region is greater in males [23] due to prenatal action of androgen |
| Bed Nucleus of Stria Terminalis (BNST) | Plays a role in the control of male sexual behavior [24], release of gonadotropin [25], and modulation of stress [26; 27]. | The principal nucleus (BNSTp) is larger in volume in males [28]. | The larger volume in males is due to sexually different apoptotic rates caused by testosterone [29]. |
| Corpus Callosum | Conducts information between the two halves of the cortex [30]. | Larger in neonatal males [31]. | Organizational effects of testosterone lead to masculinization while feminization appears to be dependent on estrogens [32; 33]. |
| Arcuate Nucleus (ARC) | Helps regulate the estrus cycle [34], appetite and body weight [35]. | Neurokin-B neurons innervate capillary vessels in the ventromedial ARC in post-pubertal males only [6]. | Dihydrotestosterone is responsible for the masculine projection pattern [36]. |
| Amygdala | Strongly associated with emotion, decision-making and Pavlovian conditioning [37]. | Adult males have a larger medial nucleus than adult females [38]. | Treatment of females with estradiol masculinizes this nucleus [38]. |
| The posterodorsal aspect of the medial amydala is 65% larger in males [39]. | Activational effects of circulating androgens accounts for the larger region in males [40]. | ||
| Cerebral cortex | Connected to a wide range of processes from memory [41] to language [42] to emotional processing [43]. | Right posterior cortex is thicker than left but only in males [44]. | Gonadal hormones play a role in maintaining the sex difference (ovariectomy masculinizes the cortex of females) [44]. |
| Ventromedial Hypothalamic Nucleus (VMN) | Involved in the control of lordosis, mounting, and norepinephrine release [45]. High concentrations of steroid receptor mRNA have been observed in the ventrolateral VMN [46]. |
Females have less synapses in the ventrolateral VMN compared to males [8]. | Organizational effects of aromatized testosterone appear to be crucial in establishing the masculine trait [47]. |
| Substantia nigra pars compacta | Made up almost entirely of dopaminergic neurons. Dopamine is involved in control of motor activity [48]. |
Females have 20% fewer dopaminergic neurons [49]. | A genetic component has been demonstrated in mice [50]. |
*Note: This table highlights some prominent sex differences in the rat brain but it is by no means exhaustive. Conflicting evidence concerning the examples reported here (particularly in the SDN-POA) exist, and the interpretation of the data is often more complicated than this summary implies.