Fomento del tejido cultural y social de la ciudad 151

Cytoarchitecture and Cellular Neurochemistry

The preoptic area is divided into a cell-dense medial nucleus and a cell-poor lateral zone. The medial nucleus may further be divided into dorsal and ventral portions, with cell body size increasing ventrally (151). Neuron bodies of the medial nucleus express androgen, estrogen & progesterone receptors as well as arginine vasotocin, nitric oxide,

neuropeptide-FF, aromatase, 5α-reductase, calcitonin gene-related peptide, tyrosine

hydroxylase and gonadotropin releasing hormone (22, 39, 56, 57, 90, 91, 96, 108, 155, 164, 174, 231, 238, 239, 246). Testosterone receptor-expressing cells were detected in

only males in Sceloporus undulatus (55). 5α-reductase activity is low in the preoptic

area and throughout the hypothalamus (247). Nitric oxide may be preferentially expressed in the dorsal portion of the medial preoptic nucleus (97). Gonadotropin-

releasing hormone is expressed in Thamnophis, Eumeces and Sceloporus, but not in

Anolis (22, 239).

Connectivity and Fibrous Neurochemistry

The preoptic area receives projections from the dorsal cortex, ventromedial and ventral anterior amygdaloid nuclei, septum, and accumbens nucleus (52). Innervating fibres express androgen receptors, neuropeptide-Y, orexin, neuropeptide-FF, gonadotropin releasing hormone, calcitonin gene-related peptide, vasopressin, oxytocin and galanin (22, 37, 45, 54, 96, 108, 185). The preoptic area projects to the septum, external amygdala, dorsomedial and dorsolateral thalamic nuclei, ventromedial hypothalamus, lateral hypothalamic area, lateral posterior hypothalamic nucleus and hypoglossal nucleus (98, 128, 166, 167, 180). The preoptic area projects fibres expressing aromatase to the spherical nucleus (39).

Functional Correlations

The preoptic area is associated with several functions, including body temperature regulation and hydration (178, 180, 248). As the temperature drops, neuronal firing rate in the preoptic area increases (249). However, the preoptic area is most strongly associated with male sexual behaviour and motivation. Lesions of the preoptic area have consistently abolished male sexual behaviour across multiple squamate species, and testosterone or estrogen implants into the lesioned area restore courtship behaviour (39, 157, 159, 233, 250, 251). Furthermore, the preoptic area may have an inhibitory role in female reproductive behaviour. This has made the preoptic area one of the key regions of interest in many investigations into the links between behaviour, endocrine function, and brain function in reptiles.

Overall volume and cell body size in the preoptic area are greater in the breeding season

than in the non-breeding season (145, 153, 160). In Anolis carolinensis, Urosaurus

ornatus and Cnemidophorus inornatus overall volume is also greater in males than

females both at hatching and during the breeding season, but not during the non- breeding season (95, 145, 160, 240, 252). However, the preoptic area is not sexually

dimorphic in Eublepharis macularius and Thamnophis sirtalis (163, 248, 252). In male

an aromatase inhibitor during development, the preoptic area is female-sized, not male- sized (253).

Aromatase activity in males is greater during the non-breeding season (123). Volume decreases with age and metabolic capacity increases with age (in males) and sexual experience (in females) (139, 197). Metabolic activity is higher in females after they have mated and are unreceptive than while they are still receptive (254). In males, metabolic capacity is higher in those housed with females than in isolation (147). Males express more androgen receptors, aromatase, and arginine vasotocin than females (144, 154, 157, 233). Females express more progesterone and estrogen receptors than males, and expression is increased when they are previtellogenic compared to when they are post vitellogenic (91, 157). Females also have higher noradrenergic activity (162). Though males and females do not differ in dopaminergic activity, injection of a dopamine agonist into the preoptic area facilitates courtship and reproduction (255). Furthermore, tyrosine hydroxylase expressing cells are larger in more sexually vigorous males (200). In females, androgen receptors are upregulated post vitellogenesis and testosterone increases the expression of arginine vasotocin, while in males testosterone upregulates nitric oxide and reduces activity (146, 165, 168).

Gonadectomization decreases the volume and metabolic capacity of the preoptic area, while testosterone rescues these effects and upregulates progesterone receptor expression (141, 163, 246). In contrast, gonadectomization increases androgen receptor expression (in males) and estrogen receptor expression (in both sexes) (233). Testosterone rescues both these effects as well (163, 233). Gonadectomized females implanted with testosterone show male courtship behaviour, and metabolic capacity in the preoptic area increases with the frequency of male courtship displays in these females (163, 238, 248).

In a sexually dimorphic species, males have more cells that express androgen receptors than females. However, in a closely related monomorphic species, there is no difference in androgen receptor expression between males and females (203). In another sexually dimorphic species, overall volume is greater and cell bodies are larger and more dense in males disguising themselves as females, compared to normal males (178, 256). Males from a lizard species that engages in elaborate courtship and territorial behaviours has

reduced androgen receptor expression compared to a species without elaborate courtship and territorial behaviours (257).

In a species with temperature-dependent sex determination, lizards incubated at a ‘masculinizing’ temperature have larger preoptic areas than lizards incubated at a ‘feminizing’ temperature (163). Metabolic capacity is lower in males from the ‘masculinizing’ temperature than the ‘feminizing’ temperature, and the latter more frequently engage in courtship displays (140, 201). Females incubated at the ‘masculinizing’ temperature are more likely to show male courtship behaviour and have a higher metabolic capacity than females incubated at ‘feminizing’ temperatures (163). In a parthenogenic, all-female species, lesioning the preoptic area or implanting serotonin into the preoptic area both abolish pseudo-male copulatory behaviour while androgen implants into the preoptic area and serotonergic antagonists restore this behaviour in the respective treatments (233, 258, 259). Furthermore, serotonegenic hormones downregulate serotonergic activity in this region (259). The preoptic area in parthenogenic females is the same volume as that of females of the ancestral sexual species, despite the parthenogenic species displaying male-typical copulatory behaviour (233, 252). However, metabolic activity in the preoptic area is greater in parthenogenic females displaying male pseudo-copulatory behaviour than female pseudo-copulatory behaviour (252). Compared to the ancestral sexual species females, parthenogenic females have fewer cells that express tyrosine hydroxylase and progesterone receptors, but they have a greater expression of estrogen and progesterone receptor mRNA (91, 193, 246, 252). Estrogen upregulates estrogen and progesterone receptor expression only in the parthenogenic species (236). Testosterone upregulates nitric oxide expression in parthenogenic females, and presence of another female increases nitric oxide activity (238). Post vitellogenic parthenogenic females, which take on the male pseudocopulatory role, show increased metabolic activity and aromatase expression in the medial preoptic area compared to previtellogenic females, which perform the female pseudocopulatory role (38, 246). Postvitellogenic females also have lower serotonin levels than previtellogenic females (258).

The preoptic area may also be involved in aggressive behaviour. Metabolic activity increases after viewing aggressive behaviour, and this region is part of Yang’s

together will develop a dominant-subordinate hierarchy as the result of aggressive interactions. Subordinate males have fewer cells that express arginine vasotocin compared to dominant males (260).