Dopamine in Male Sexual Behavior

Elaine M. Hull

The Florida State University

Psychology Department & Neuroscience Program

Neural circuits regulating sexual behaviorNeural circuits regulating sexual behavior

OB

MeA

MPOA

NAc

BST

VTA

Brain Stem

CTF

Neural circuits regulating sexual behaviorNeural circuits regulating sexual behavior

OB

MeA

MPOA

NAc

BST

VTA

Brain Stem

CTF

Neural circuits regulating sexual behaviorNeural circuits regulating sexual behavior

OB

MeA

MPOA

NAc

BST

VTA

Brain Stem

CTF

Neural circuits regulating sexual behaviorNeural circuits regulating sexual behavior

OB

MeA

MPOA

NAc

BST

VTA

Brain Stem

CTF

Neural circuits regulating sexual behaviorNeural circuits regulating sexual behavior

OB

MeA

MPOA

NAc

BST

VTA

Brain Stem

CTF

Our lab has focused on the medial preoptic area, which contains A14 periventricular DA neurons. It is the main integrative area for male sexual behavior in all vertebrate species.

Model for MPOA dopamine’s influence on male sexual behavior

Is dopamine released in the MPOA during copulation?

Gonadally intact males and T-treated castrates had increased extracellular DA during pre-exposure to a female and during copulation. Vehicle-treated 1-week castrates that copulated also showed DA increases, but those that did not copulate did not show the DA increase.

What elicits the MPOA DA release?

Large lesions of the amygdala abolished copulation, which was restored by

apomorphine in the MPOA.

Smaller lesions of the MeA impaired, but did not abolish mating.

Basal DA levels in the MPOA were normal, but

the DA response to the female was abolished.

Chemical stimulation of the MeA mimicked the MPOA DA response to a female.

Therefore, normal basal DA in the MPOA is sufficient for suboptimal copulation. The DA increase in response to a female facilitates

mating and is mediated by input from the MeA.

• But there are no DA neurons in the MeA. What elicits the DA increase?

Glutamatergic axons from the MeA and BNST to MPOA

• Juan Dominguez, my former post-doc, showed that a few axons from the MeA, and numerous axons from the BNST, ended in the MPOA and contained glutamate.

Is glutamate released in the MPOA before and during mating?

Sample

BL PRE COP EJAC PEI POST

Glu

tam

ate

% c

han

ge

0

100

200

300

400**

*

Sexual activity increases glutamate in the MPOA of male rats.

Using 2 min microdialysis samples

Samples

BL UPTKi PRE COP EJAC PEI POST

Glu

tam

ate

% c

han

ge

0

100

200

300

400ACSFUPTKi

0

100

200

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400

0

100

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600

EJACULATIONFREQUENCY

EJACULATIONLATENCY (sec) PEI (sec)

Reverse dialysis of glutamate uptake inhibitors into the MPOA increased glutamate levels and facilitated mating.

**

0

1

2

3

4

5 *** *

Therefore, glutamate is released in the MPOA during copulation, and it facilitates mating.

• Does glutamate also affect MPOA DA levels?

Sample (6 min)

DO

PA

C %

C

HA

NG

EH

VA

%

CH

AN

GE

Sample (6 min)

Exogenous glutamate in the MPOA increased DA levels, but decreased DOPAC and HVA

DA

%

CH

AN

GE

Nitric oxide has been reported to inhibit DA transport and increase DA levels in the striatum.

• Could NO explain our results?

L-NAME blocked the glutamate-evoked DA release and the decreases in

DOPAC and HVA.

DA

%

CH

AN

GE

Sample (6 min)

DO

PA

C %

C

HA

NG

EH

VA

%

CH

AN

GE

Sample (6 min)

Metabolite levels were lower for animals receiving glutamate alone compared with those receiving glutamate+ L-NAME.

Exogenous glutamate in the MPOA increased DA levels, but inhibited

metabolites: Role for NO?POSSIBLE EXPLANATIONS FOR

THIS EFFECT:

1. Glutamate induces exocytocis of DA

2. Glutamate binds NMDA receptors, which allows for Ca2+ influx and induces NO production in NOS- containing cells.

a) Increased NO may inhibit DA uptake in neighboring terminals, prolonging DA’s effects & decreasing DA catabolism.

b) Increased NO might also increase extracellular DA by inducing vesicular leakage.

MPOA dopamine release during copulationdepends on nitric oxide

L-NAME blocked mating-induced DA release in the MPOA.

Microinjection of L-NAME into the MPOA impaired copulation in sexually naïve (A) and experienced (B) males.

A B

Sexually Experienced Males

1. Show increased preference for being with a receptive female.

Sexually Experienced Males

1. Increased preference for being with a receptive female.

2. Require less time and stimulation to achieve ejaculation.

Sexually Experienced Males

1. Increased preference for being with a receptive female.

2. Require less time and stimulation to achieve ejaculation.

3. Require less time to resume copulation after ejaculating.

Sexually Experienced Males

1. Increased preference for being with a receptive female.

2. Require less time and stimulation to achieve ejaculation.

3. Require less time to resume copulation after ejaculating.

4. Are more resistant to sexual impairments due to castration, brain damage, or stress.

Sexually Experienced Males

1. Increased preference for being with a receptive female

2. Require less time and stimulation to achieve ejaculation

3. Require less time to resume copulation after ejaculating

4. Are more resistant to sexual impairments due to castration, brain damage, or stress

Is the MPOA implicated?Is the MPOA implicated?

Stronger Activation of the MPOA in Sexually Experienced Males

Sexually experienced males had more Fos-ir in the MPOA resulting from mating to one ejaculation, than did naïve males that mated for the first time.

First Experience

Repeated Experience

Does NOS in the MPOA contribute to exposure-induced enhancement of mating?

L-NAME administration before each of seven non-copulatory exposures to an estrous female blocked exposure-induced enhancements on the drug-free test day. (Preliminary data suggest that a D1 antagonist has similar effects.)

NNS NS ENS ES

% NOS w/NR1P

erce

ntag

e

0

25

50

75

100

Total NOS

# Cel

ls

NNS NS ENS ES0

20

40

60

80

* **

Sexual experience increases NOS-ir in the MPOA of male

rats

NOS

NMDAR1

Overlay

Nearly all cells containing NOS also contained NMDA receptors. Sexual experience increased the number of NOS-ir cells in MPOA.

Sexually Naïveand Mated

(NM)

SexuallyExperienced

and Not Mated(EC)

Sexually Naïveand Not Mated

(NC)

SexuallyExperiencedand Mated

(EM)M

EA

N D

EN

SIT

Y

(PIX

ELS

)

0

50

100

150

NC NM EC EM

* *

*

Sexual experience increases NOS protein concentration in the MPOA of male rats

A major means of activating NOS is via NMDA glutamate receptors. Does an NMDA antagonist in the MPOA also impair sexual sensitization?

Blocking NMDA receptors in the MPOA impaired sexual sensitization.

Microinjecting MK-801 before each noncopulatory exposures to an estrous female impaired exposure-induced enhancements of:

1. number of mounts

0

2

4

6

8

10

12

14

16

MO

UN

TS

Saline

MK801

Naive*

0

2

4

6

8

10

12

14

16

18

INT

RO

MIS

SIO

NS

Saline

MK801

Naive

Blocking NMDA receptors in the MPOA impaired sexual sensitization.

Microinjecting MK-801 prior to repeated noncopulatory exposures to an estrous female impaired experience-induced enhancements on:

1. number of mounts2. number of intromissions

*

0

0.5

1

1.5

2

2.5

EJA

CU

LA

TIO

NS

Saline

MK801

Naive

Blocking NMDA receptors in the MPOA impaired sexual sensitization.

Microinjecting MK-801 prior to repeated noncopulatory exposures to an estrous female impaired experience-induced enhancements on:

1. number of mounts2. number of intromissions3. number of ejaculations

*

• What intracellular messenger mediates NO’s effects?

Inhibition of guanylyl cyclase blocked effects of the NO donor (sodium nitroprusside).

Cyclic GMP mediates NO’s facilitation of DA release in the MPOA

Cyclic GMP mediates NO’s facilitation of DA release in the MPOA

Inhibition of NOS did not affect facilitation by cGMP analog, because cGMP is downstream of NOS.

Summary

NOS

NM

DA

r

Glutamate

Dopamine

Sexual stimulation

NO

Summary

NOS

NM

DA

r

Glutamate

Dopamine

Sexual stimulation

NO

Summary

NOS

NM

DA

r

Glutamate

Dopamine

Sexual stimulation

(Higher NOSw/ experience)

Postscript: Orexin/hypocretin increases mesolimbic DA activity and facilitates

copulation

Copulation increased Fos-ir in orexin-containing

neurons of perifornical LH.

Double-labeled cells in Non-copulating males

Double-labeled cells in copulating males

Castration decreased

orexin-containing cells; E2

restored them.

Orexin (.014 nmol) in the VTA increased firing rates

of DA neurons.

Orexin (1.4 nmol) in the VTA increased cells per track,

but not firing rates.

Orexin (140 nmol) in the VTA decreased cells per track, probably due to

depolarization block, an effect reversed by

autoreceptor stimulation by

systemic apomorphine.

Red orexin-containing axons end near green TH-containing neurons that are activated (Fos-ir, black) by

copulation.

• Estrogen receptor-containing cells in the MPOA, BNST, and LHA orexin-containing cells in the LHA. Axons from those cells depolarize DA-ergic cells in the VTA and, perhaps, the MPOA. Microinjection of orexin into the MPOA facilitates male sexual behavior (Gulia et al., 2003). 5-HT is released in the LHA at the time of ejaculation and inhibits mating. It also decreases DA release in the NAc (Lorrain et al., 1999) and hyperpolarizes orexin neurons (Li et al., 2002).

Acknowledgments Acknowledgments

K02-MH001714R01-MH040826

Former and Present Lab Members:Bradley Lown, Ph.D Linda Rosselli-Austin, Ph.D Rosemary D’Agostino, Ph.D Deborah Kleese Edelstein, Ph.D Mary Solanto, Ph.D Richard Thomas, Ph.D J. Ken Nishita, Ph.D Daniel Bitran, Ph.D Elizabeth A. Pehek, Ph.D Linda C. Band, Ph.DTerrence Bazzett, Ph.D Vincent P. Markowski, Ph.D Robert C. Eaton, Ph.D Jason Moses, Ph.DLeslie Matuszewich, Ph.D Jianfang Du, Ph.D Susan K. Putnam, Ph.D Jon V. Riolo, Ph.DKatie Grausam

Juan Dominguez, Ph.D

Mario Gil

Gwen Lagoda

Lucy Lumley, Ph.D

Daniel Lorrain, Ph.D

Satoru Sato, Ph.D

Anna Vigdorchik

John Muschamp, Ph.D

Harvey Rattus

SNP and 8-Br-cGMP increase DA levels in the MPOA of DHT-treated castrates.

However, SNP was somewhat more effective.

Only SNP increased DOPAC in DHT-Treated Castrates

Only SNP into the MPOA facilitated sexual behavior in DHT treated castrates

0.00

10.00

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Control 8-Br-cGMP SNP

Percent that Displayed Mounts

PE

RC

EN

T

*

Only SNP into the MPOA facilitates sexual behavior in DHT treated castrates

Control 8-Br-cGMP SNP

Percent that Displayed Intromissions

PE

RC

EN

T

0.00

10.00

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70.00

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*

Only SNP into the MPOA facilitates sexual behavior in DHT treated castrates

Control 8-Br-cGMP SNP

Percent that Displayed Ejaculations

PE

RC

EN

T

0.00

10.00

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*

PEI (Sec)

100 200 300 400 500 600

Glu

tam

ate

% d

ecre

ase

0

100

200

300

400

500

600

Sample

BL PRE COP EJAC PEI POST

Glu

tam

ate

% c

han

ge

0

100

200

300

400

**

*

Magnitude of decrease in glutamate after ejaculation correlates with post-ejaculatory

interval.

Blocking D1 Receptors Attenuated Activation of MPOA During Initial

Experience

Males receiving a D1 antagonist had less Fos-ir in the MPOA after their first sexual experience, than did males receiving vehicle.

Vehicle

D1 Antagonist