Lecture 7: Sex

Excitation

Norepinephrine

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Locus Coeruleus | Summary, Location, Structure & Function

Image with caption: Cell bodies in the locus coeruleus: projections to hypothalamic, limbic, and cortical regions; descending projections to cerebellum and spinal cord (arousal)

Recap:

For males; dopamine receptor subtypes( d1 and d2) mpOA controls timing for males (d1 activation promotes erection, d2 activation reduces latency of activation)

For females, it is more complex; two main area (VMH involved in lordosis reflex, and smt else.) D1 activation in mPOA seems to regulate the motivation to engage in sexual response, D2 activation means cessation of engagement in sexual behaviour. (solicitation vs lordosis).

Experiment; Ovarectomized females (no pregrancy, cntrol hormonal rpofile), exogenous injectionsof estrogen and progesterone. Artifical scenario in which only one hormone is experienced

Precopulatory Switch

  • In EB + P conditions:

    • D1R

    • D2R stimulation increase GLU in VMH, decreasing lordisis

Oxytocin

  • Brings about a sense of closeness or binding between two individuals

  • In some species (particulalry monogamous species), there is a release of oxytocin post ejaculation

  • Voles (vicious hell creatures), prairie vs mountain voles, genetically similar, but over the course of evolution they separated to mountain region and prairie regions

    • One region, less available mates, so finding partner = monogamy, more oxytocin release

    • Prairie ones have more available mates, so polygamous = mating with as many partners as possible, less oxytocin release

    • Similar genetically, but different behavioural response… oxytocin release keeps them in close proximity

Melanocortins

  • Thought to be involved in the desire aspect, not performative

  • POMC peptide include Beta-endorphin, ACTH, and alpha-MSH

    • All have prnounced effects on the sexual behaviour of female and male rats

  • a-MSH facilitates…

Melanocortins Receptors

  • 6 in total, only 2 inside the brain:

  • MC3R: brain (HYP and limbic system —

  • MC4R:

Bremelanotide

  • Formerly PT-141

  • Active peptide sequence of Melanotan-II

  • Binds to MC3R and MC4R in brain

  • Induces erections in healthy men and rats

  • Induces erections in men with mild-to-moderate erectile dysfunction and in men who do not respond well to PDE-5 inhibitors

  • Rapid effects in rats (within 5-20 mins)

Bremelanotide & Female SB

  • Selective increase in solitications, but no effect on pacing or lordosis

    • This occured in females primed wit EB-alone or EB+P, and in both chambers

  • In males,

Bremalanotide and Dopamine

  • Seems only to impact dopamine in the mPOA

  • Effects of systemic bremelanotide are reveresed by D1R blockade in mPOA

Inhibition

Opioids

Proopiomelanocortin…

Curious Case of Opioids

  • opioids feel good, but inhibit sexual responding

    • Why? They go hand-in-hand with satiety. They cause a sensitization of mesolimbic DA to cues associated with their own reward

  • Attention to reward-related stimuli involves acivation o mesolimbic and hypothalamic DA systems

  • …

Serotonin

SSRI-Induced Sexual Dysfunctions

  • Two types:

    • Anorgasmia/Delayed ejaculation

    • Decrease sexual desire

  • These are observed consistently with certain SSRIs compared to others (e.g., fluoexetine, paroxetine)

Fluoxetine & Male Rat SB

  • Increased SSRI dosage decrease ejaculation frequency, level changes, and desire

  • Oxytocin can reverse some of its effects to a degree, particularly the delayed ejaculation side effect

Brain Areas Involved

  • Prefrontal cortex controls executive functions, including behavioural inhibition

mPOA as an Integrator

  • Integrates both excitatory and inbhibitory signals for sexual desire