Androgens alter the organization of the spinal Androgens alter the organization of the spinal

cord and the connections between motoneurons cord and the connections between motoneurons

and target musclesand target muscles

In fact,…………. In fact,………….

• T-treated females before birth mantain T-treated females before birth mantain perineal muscles and the SNB is masculinizedperineal muscles and the SNB is masculinized

• DHT-treated females before birth maintain DHT-treated females before birth maintain perineal muscles, but the number of neurons of perineal muscles, but the number of neurons of SNB do not increase.SNB do not increase.It is hypothesized that the muscles are It is hypothesized that the muscles are innervated by other motoneurons, that normally innervated by other motoneurons, that normally do not innervate perineal regiondo not innervate perineal region

Matsumoto, Zool Sci, 1992

Synaptic plasticity of SNB is a consequence of exposure to sex steroids

Matsumoto, Zool Sci, 1992

Synaptic plasticity of SNB and sex steroids

-actin mRNA

C CX CX+T

Matsumoto, Zool Sci, 1992

Synaptic plasticity of SNB and sex steroids

Gap junction mRNA

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.

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)

Forger and Breedlove, Proc Natl Acad Sci, 1986

SNB MODEL IN DOGSNB MODEL IN DOG

T-female

T before birthT before birthNeonatal subcutaneously T-implant (1.1mg/Kg/die)Neonatal subcutaneously T-implant (1.1mg/Kg/die)Sacrifice at 3-6 yearsSacrifice at 3-6 years

Forger and Breedlove, Proc Natl Acad Sci, 1986

SNB MODEL IN DOGSNB MODEL IN DOG

4 4 5

Females had significantly fewer motoneurons and smaller nuclear volume than males.Females had significantly fewer motoneurons and smaller nuclear volume than males.Females treated with androgen early in development did not differ significantly from males.Females treated with androgen early in development did not differ significantly from males.

SNB IN HUMANSNB IN HUMAN

Forger and Breedlove, Proc Natl Acad Sci, 1986 Nissl staining

SNB IN HUMANSNB IN HUMAN

Yakovlev Collection, USA Army Pathology Institut(Forger and Breedlove, Proc Natl Acad Sci USA, 1986)

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)

89

THE PREOPTIC AREATHE PREOPTIC AREA

Hypothalamus and control of autonomic Hypothalamus and control of autonomic functionsfunctions

Preoptic area

anterior part of the hypothalamu

s

Visceral afferents

Solitary nucleus

Brainstem nuclei Preganglionic nuclei of NAS

NAS output

Hormonaloutput

Targetorgans

Preoptic regionPreoptic region

In mammals there are In mammals there are sexually dimorphic sexually dimorphic nucleinuclei– Larger volume in malesLarger volume in males– Larger number of cells Larger number of cells

in malesin males

A - Rat (A - Rat (Gorski et al., Brain Gorski et al., Brain Res, 1978)Res, 1978)

B - Gerbil (B - Gerbil (Commins and Yahr, Commins and Yahr, J Comp Neurol, 1984J Comp Neurol, 1984))

C - Ferret (C - Ferret (Tobet et al., Brain Tobet et al., Brain

Res, 1983Res, 1983))

Preoptic regionPreoptic region

Also in other Also in other vertebrates …….vertebrates …….

A - Toad (A - Toad (Takami et al., Takami et al., Zool Sci, 1984Zool Sci, 1984))

B - Lizard (B - Lizard (Crews et al., Crews et al., Brain Behav, 1990Brain Behav, 1990))

C - Quail (Viglietti-Panzica C - Quail (Viglietti-Panzica et al., Neurosci Lett, et al., Neurosci Lett, 1986)1986)

MALESFEMALES

VOLUME

INTACT GONADECTOMIZED

FEMALE MALE

SCN

OC

AC

SON

SEXUALLY DIMORPHIC NUCLEUS IN THE GUINEA PIG(Hines et al., 1985)

Preoptic regionPreoptic region

Preoptic region of RatPreoptic region of Rat

Chresyl violet stained sections show a sexually Chresyl violet stained sections show a sexually dimorphic nucleus (SDN) in the preotic area with dimorphic nucleus (SDN) in the preotic area with volume, neuronal density and diameter larger in male volume, neuronal density and diameter larger in male than in femalethan in female

(Gorski, Progr Brain Res,1984)

Cytoarchitecture of the medial preoptic nucleus (MPN)Cytoarchitecture of the medial preoptic nucleus (MPN)

Thionine stainingThionine staining

Serotonin-ir fibersSerotonin-ir fibers

C: SDN of preoptic C: SDN of preoptic area is larger in malearea is larger in male

MPNm: medial MPNm: medial component of MPNcomponent of MPN

MPNl: lateral MPNl: lateral component of MPNcomponent of MPN

V3: third ventricleV3: third ventricle

Jacobson et al, Brain Res, 1987

T-concentrating cells

E-concentrating cells

DHT-concentrating cells

SDN has a higher percentage of testosterone- concentrating cells in male than in female

EB+P: estradiol benzoate plus progesterone

The volume of SDN is not The volume of SDN is not influenced by hormonal influenced by hormonal treatment in adulttreatment in adult

NO ACTIVATIONAL EFFECTSNO ACTIVATIONAL EFFECTS(reversible changes in nervous circuits)

(Bloch and Gorski, J Comp Neurol, 1988)

Changes in the volume of the SDN-POA related to day of birthChanges in the volume of the SDN-POA related to day of birth

(Gorski, Progr Brain Res,1984)

Neurogenesis within SDN-POANeurogenesis within SDN-POA

Males: hatched barsMales: hatched barsFemales: open barsFemales: open barsOffspring were sacrificed on postnatal day 30Offspring were sacrificed on postnatal day 30

Injection of 3H-thymidine at different prenatal ages

Prolongation of neurogenesis of the neurons of the SDN-POAProlongation of neurogenesis of the neurons of the SDN-POA

Dark-field photomicrographs of coronal sectionsDark-field photomicrographs of coronal sections

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 gestationSacrificeC: 18 days plus 2hD: 22 daysE: 26 daysF: 32 days post conception

TP TP TP injections for 10 days

16 days 18 days

H3 thymidine

20 days birth

PERINATAL HORMONAL TREATMENT WITH TESTOSTERONE

VOLUME OF SDN

STEROID EFFECTS IN EMBRYOSSTEROID EFFECTS IN EMBRYOS

M F M F M F

NEURON NUMBER OF SDN

STEROID EFFECTS IN EMBRYOSSTEROID EFFECTS IN EMBRYOS

TP TP TP injections for 10 days

16 days 18 days

H3 thymidine

20 days birth

PERINATAL HORMONAL TREATMENT WITH TESTOSTERONE

LABELLED CELL NUMBEROF SDN

During development there are steroid sensitive late neurons (18 day)SDN of female can be masculinized by Testosterone in the perinatal periodTestosterone do not influence the neurogenesis(Dodson et al, J Comp Neurol, 1988)

STEROID EFFECTS IN EMBRYOSSTEROID EFFECTS IN EMBRYOS

M F M F M F

TP TP TP injections for 10 days

16 days 18 days

H3 thymidine

20 days birth

PERINATAL HORMONAL TREATMENT WITH TESTOSTERONE

Preoptic region of RatPreoptic region of Rat

A single perinatal injection of testosterone A single perinatal injection of testosterone propionate (500µg) increases the volume of female SDNpropionate (500µg) increases the volume of female SDN

(Gorski, Progr Brain Res,1984)

ORGANIZAZIONAL EFFECTSORGANIZAZIONAL EFFECTS

STEROID EFFECTS ON SDN-POA

The sexually dimophic nucleus of the preoptic area (SDN-POA) of rat is larger in maleThe sexually dimophic nucleus of the preoptic area (SDN-POA) of rat is larger in malethan in female.than in female.Perinatal treatments of females with T or DES (E2 analogue) induce an increase of thePerinatal treatments of females with T or DES (E2 analogue) induce an increase of thevolume of SDN in femalesvolume of SDN in females