In fact,………….

1. In fact,…………. • T-treated females before birth mantain perineal muscles and the SNB is masculinized • DHT-treated females before birth maintain perineal muscles, but the number of neurons of SNB do not increase. • It is hypothesized that the muscles are innervated by other motoneurons, that normally do not innervate perineal region Androgens alter the organization of the spinal cord and the connections between motoneurons and target muscles

2. Synaptic plasticity of SNB is a consequence of exposure to sex steroids Matsumoto, Zool Sci, 1992

3. Synaptic plasticity of SNB and sex steroids -actin mRNA Matsumoto, Zool Sci, 1992 C CX CX+T

4. Synaptic plasticity of SNB and sex steroids Gap junction mRNA Matsumoto, Zool Sci, 1992

5. Before birth, the SNB system is present in both male and female rats, and motor neurons have established a functional neuromuscular junction (Breedlove and Arnold, Brain Res, 1981) However, the muscles and their motor neurons die shortly after birth unless exposed to (or treated with) testosterone. In males, testosterone acts primarily to prevent the muscles from dying and this action secondarily prevents death of the motor neurons. Hypothesis: testosterone induces the muscles to produce a trophic factor that preserves the muscles and either the same factor or an additional factor preserves the motor neurons.

6. SNB MODEL IN DOG T-female T before birth Neonatal subcutaneously T-implant (1.1mg/Kg/die) Sacrifice at 3-6 years Forger and Breedlove, Proc Natl Acad Sci, 1986

7. SNB MODEL IN DOG 4 4 5 Forger and Breedlove, Proc Natl Acad Sci, 1986 Females had significantly fewer motoneurons and smaller nuclear volume than males. Females treated with androgen early in development did not differ significantly from males.

8. SNB IN HUMAN Nissl staining Forger and Breedlove, Proc Natl Acad Sci, 1986

9. SNB IN HUMAN Penis muscles and their motoneurons are involved in the control of sexual behavior. The contraction of bulbocavernosus muscle determines the discharge of last drops of urine. In women it induces the opening of the vagina. In women nuclei are smaller than in men (in rat this dimorphism is more drastic: in the adult female the muscles are absent) 9 8 Yakovlev Collection, USA Army Pathology Institut (Forger and Breedlove, Proc Natl Acad Sci USA, 1986)

10. THE PREOPTIC AREA

11. Preoptic area anterior part of the hypothalamus Visceral afferents Hormonal output Target organs Solitary nucleus NAS output Brainstem nuclei Preganglionic nuclei of NAS Hypothalamus and control of autonomic functions

12. Preoptic region • In mammals there are sexually dimorphic nuclei • Larger volume in males • Larger number of cells in males A - Rat (Gorski et al., Brain Res, 1978) B - Gerbil (Commins and Yahr, J Comp Neurol, 1984) C - Ferret (Tobet et al., Brain Res, 1983)

13. Preoptic region • Also in other vertebrates ……. A - Toad (Takami et al., Zool Sci, 1984) B - Lizard (Crews et al., Brain Behav, 1990) C - Quail (Viglietti-Panzica et al., Neurosci Lett, 1986)

14. MALES FEMALES VOLUME INTACT GONADECTOMIZED Preoptic region AC SCN SON OC FEMALE MALE SEXUALLY DIMORPHIC NUCLEUS IN THE GUINEA PIG (Hines et al., 1985)

15. Preoptic region of Rat Chresyl violet stained sections show a sexually dimorphic nucleus (SDN) in the preotic area with volume, neuronal density and diameter larger in male than in female (Gorski, Progr Brain Res,1984)

16. Cytoarchitecture of the medial preoptic nucleus (MPN) Thionine staining C: SDN of preoptic area is larger in male MPNm: medial component of MPN MPNl: lateral component of MPN V3: third ventricle Serotonin-ir fibers

17. DHT-concentrating cells T-concentrating cells E-concentrating cells Jacobson et al, Brain Res, 1987 SDN has a higher percentage of testosterone- concentrating cells in male than in female

18. The volume of SDN is not influenced by hormonal treatment in adult NO ACTIVATIONAL EFFECTS (reversible changes in nervous circuits) (Bloch and Gorski, J Comp Neurol, 1988) EB+P: estradiol benzoate plus progesterone

19. Changes in the volume of the SDN-POA related to day of birth (Gorski, Progr Brain Res,1984)

20. Neurogenesis within SDN-POA Injection of 3H-thymidine at different prenatal ages Males: hatched bars Females: open bars Offspring were sacrificed on postnatal day 30

21. Prolongation of neurogenesis of the neurons of the SDN-POA A: pregnants rats exposed to tritiated thymidine on day 15 of gestation, and offspring sacrificed on postnatal day 30 B: pregnants rats exposed to tritiated thymidine on day 18 of gestation, and offspring sacrificed on postnatal day 30 C-F: changes in position of labelled cells over time following exposure to tritiated thymidine on day 18 of gestation Sacrifice C: 18 days plus 2h D: 22 days E: 26 days F: 32 days post conception Dark-field photomicrographs of coronal sections

22. PERINATAL HORMONAL TREATMENT WITH TESTOSTERONE H3 thymidine TP TP injections for 10 days TP 16 days 18 days 20 days birth STEROID EFFECTS IN EMBRYOS VOLUME OF SDN M F M F M F

23. PERINATAL HORMONAL TREATMENT WITH TESTOSTERONE H3 thymidine TP TP injections for 10 days TP 16 days 18 days 20 days birth STEROID EFFECTS IN EMBRYOS NEURON NUMBER OF SDN

24. PERINATAL HORMONAL TREATMENT WITH TESTOSTERONE H3 thymidine TP TP injections for 10 days TP 16 days 18 days 20 days birth STEROID EFFECTS IN EMBRYOS LABELLED CELL NUMBER OF SDN M F M F M F During development there are steroid sensitive late neurons (18 day) SDN of female can be masculinized by Testosterone in the perinatal period Testosterone do not influence the neurogenesis (Dodson et al, J Comp Neurol, 1988)

25. Preoptic region of Rat ORGANIZAZIONAL EFFECTS A single perinatal injection of testosterone propionate (500µg) increases the volume of female SDN (Gorski, Progr Brain Res,1984)

26. STEROID EFFECTS ON SDN-POA The sexually dimophic nucleus of the preoptic area (SDN-POA) of rat is larger in male than in female. Perinatal treatments of females with T or DES (E2 analogue) induce an increase of the volume of SDN in females