I am wondering whether POIS can be the result of
overstimulation of muscarinic receptors. Let me explain:
The research by Prof. Komisaruk as well as recent discussions on this forum revolve around the role the vagus nerve might play for POIS. I was reading about the relationship between the vagus nerve and ejaculation.
Ejaculation and muscarinic receptorsThe vagus nerve "communicates" with smooth muscles and organs by releasing the neurotransmitter Acetylcholine (ACh). Acetylcholine binds to two kinds of receptors: nicotinic and muscarinic. What does that have to do with ejaculation? First of all, the neurological mechanism behind ejaculation is not yet fully understood - but "pharmacological evidence relating to a cholinergic mechanism for both contraction and secretion of prostate and seminal vesicle exist [70, 91, 99]. Essentially, these glands were activated by cholinomimetic compounds acting on muscarinic receptors [49]" (Giuliano and Clement, 2013).
Here is the abstract from a study on rodent models (Gil et al., 2000):
"The effects of muscarinic receptor stimulation were tested on the urethro genital reflex (UGR) in anesthetized and spinal cord-transected rats. Drugs were applied directly to the spinal cord. The electromyographic activity (EMG) of the bulbospongiosus (BS) muscle was used for recording UGR. In six animals BS as well as soleus, posterior biceps or peroneus tertius muscle EMG was recorded simultaneously. Muscarine (5, 10, 20, 50 and 100 μg) was applied in 22 animals after cutting L6?S1 dorsal roots. Some observations were made on another six animals, to which an extensive bilateral dorsal rhizotomy (L3?S2) was performed. Rhythmic bursts of similar frequency and size to those seen during UGR were found in BS muscle a few minutes after muscarine application. No rhythmic bursting was found on the hindlimb muscles, but exclusively on BS muscles. The effects of homatropine (25, 50, 100 and 200 μg), an acetylcholine muscarinic receptor antagonist, were tested in 21 rats after UGR was elicited three times at low stimulation intensity (7 mm Hg). Homatropine produced two effects: (i) A significant increase in the latency of UGR. (ii) A facilitation of UGR inhibition. In view of these results it can be speculated that muscarinic receptor stimulation is involved in the elicitation of UGR."
Symptoms of muscarinic receptor overstimulationFor now let us take as given that stimulation of muscarinic receptors plays a role in ejaculation. Why could this matter for POIS? Here are the symptoms of OVERstimulation of muscarinic receptors (see
http://www.atsdr.cdc.gov/csem/csem.asp?csem=11&po=9 , see also: (
https://en.wikipedia.org/wiki/SLUDGE_syndrome)
Respiratory tract
- bronchorrhea (thick, mucoid secretions)
- bronchospasm
- chest tightness
- dyspnea
- productive cough
- rhinorrhea
Eyes
- blurred vision (especially, difficulty focusing on near objects)
- conjunctival injection
- dimness of vision
- miosis (pupillary constriction)
Gastrointestinal tract
- cramping
- diarrhea
- incontinence
- nausea
- vomiting
Urinary tract
- incontinence
- urination
Cardiovascular system
- AV block
- bradycardia
- hypotension
- idioventricular rhythm
- ventricular dysrhythmias (torsades des points)
Exocrine glands
- hyperamylasemia
- lacrimation
- salivation
Many of these symptoms also occur in POIS. Overstimulation of muscarinic receptors is rare and usually occurs after contact with pesticides. However, POIS is rare as well, and maybe overstimulation of muscarinic receptors could be involved in its mechanism.
More evidenceThere is more evidence:
At least two users on this forum (Outsider, FloppyBanana) have eliminated or reduced their POIS symptoms by taking Mytelase (
https://en.wikipedia.org/wiki/Ambenonium_chloride). Mytelase is a cholinesterase inhibitor - the drug inhibits the breakdown of the ACh, the neurotransmitter which binds to muscarinic receptors. The concentration of ACh between neuron and receptor thus increases - and one might think that it might lead to more stimulation of the receptor. However, this does not have to be the case. From
https://en.wikipedia.org/wiki/Acetylcholinesterase :
"For a cholinergic neuron to receive another impulse, ACh must be released from the ACh receptor. This occurs only when the concentration of ACh in the synaptic cleft is very low. Inhibition of AChE leads to accumulation of ACh in the synaptic cleft and results in impeded neurotransmission."
To repeat:
A cholinesterase inhibitor can thus lead to LESS stimulation of cholinergic receptors (of which one group are muscarinic receptors). It could thus be that Metylase helps in POIS because it downregulates stimulation of muscarinic receptors.
There is yet more evidence:
Many of us suffer from premature ejaculation. (Over)stimulation of muscarinic receptors could cause this. Studies in rodents have found that treating the animals with muscarinic agonists (hence stimulation of muscarinic receptors) decreases time to ejaculation.
Gil et al. (2000) write "also, it has been suggested that acetylcholine may play a role in the phenomenon of premature ejaculation [2]." They quote Ahlenius and Larsson (1985) who write "It is possible, however, that the antimuscarinic effects
of thioridazine and chlofimipramine are responsible for the effects of these drugs on time to ejaculation. Available evidence indicates that both activation and blockade of muscarinic acetylcholine receptors may suppress male rat sexualbehavior (Soulairac 1963; Bignami 1966; Leavitt 1969)" And from (Hull et al., 1988): "The muscarinic agonist oxotremorine, injected alone into the preoptic area decreased ejaculatory threshold (i.e., decreased the number of intromissions preceding ejaculation) as previously reported. These data suggest that some cholinergic activation of the preoptic area is critical for normal copulation, since bilateral blockade of muscarinic receptors there dramatically decreased the number of animals copulating. However, increased cholinergic activity there only reduced ejaculation threshold."
Now, these studies also find that some stimulation of muscarinic receptors is required for sexual behavior. What is required is the right level.
Yet more evidence:
Some users on this forum have reported cases in which they do not experience POIS symptoms (e.g. sometimes after nocturnal emissions, myself included). This evidence seems hard to square with a theory of POIS as auto-immune condition. In contrast, if overstimulation of muscarinic receptors causes POIS, it is plausible that this overstimulation does not happen for some of us during nocturnal emissions - the vagus nerve (which regulates ACh release and thus stimulation of muscarinic receptors) might "function" better at night for these users.
How the hypothesis could be testedThe hypothesis could be tested in different ways.
First, stimulation of muscarinic receptors could be downregulated by cholinesterase inhibitors. (See
https://en.wikipedia.org/wiki/Acetylcholinesterase_inhibitor for a list)
Second, stimulation of muscarinic receptors could be downregulated by muscarinic antagonists. (See
https://en.wikipedia.org/wiki/Muscarinic_antagonist for a list)
Both should make POIS less severe - and could help with premature ejaculation.
IMPORTANT: I DO NOT SUGGEST THAT WE TEST THESE HYPOTHESES BY OURSELVES.I am looking forward to hearing your thoughts.
REFERENCES:Giuliano, Fran?ois, and Pierre Cl?ment. ?Anatomy and Physiology of Ejaculation.? In Premature Ejaculation, edited by Emmanuele A. Jannini, Chris G. McMahon, and Marcel D. Waldinger, 25?44. Springer Milan, 2013.
http://link.springer.com/chapter/10.1007/978-88-470-2646-9_3.
Gil, L, L. E G?mez, I Dur?n, and R Cueva-Rol?n. ?Muscarinic Mediation of the Urethro Genital Reflex in Spinal Cord-Transected Rats.? Pharmacology Biochemistry and Behavior 67, no. 2 (October 2000): 215?23. doi:10.1016/S0091-3057(00)00323-3.
Ahlenius, Sven, and Knut Larsson. ?Central Muscarinic Receptors and Male Rat Sexual Behavior: Facilitation by Oxotremorine but Not Arecoline or Pilocarpine in Methscopolamine Pretreated Animals.? Psychopharmacology 87, no. 2 (October 1985): 127?29. doi:10.1007/BF00431794.
Hull, Elaine M., Elizabeth A. Pehek, Daniel Bitran, Gregory M. Holmes, Robert K. Warner, Linda C. Band, Terence Bazzett, and Lynwood G. Clemens. ?Brain Localization of Cholinergic Influence on Male Sex Behavior in Rats: Antagonists.? Pharmacology Biochemistry and Behavior 31, no. 1 (September 1988): 175?78. doi:10.1016/0091-3057(88)90330-9.