This wouldn't work in the same way at all. Catecholamine and monoamine receptors are far more readily regulated to compensate for variations in activity and ligand saturation, they have to be since catecholamines are both neuromodulators and hormones, and they are the primary facilitators of sympathetic nervous system functionality including physiological indicators of physical activity. While monoamines are heavily involved in gastrointestinal functionality, reproductive capability and in fibrogenesis.
This is aside from their direct activity at the synaptic cleft, in neuronal action potential transduction. Thus having a huge effect on behaviour and perception.
Opioids on the other hand are primarily indicated in analgesia (as everyone knows) , mood and systemic secondary sedation. Physiologically their role is far less immediate, and endogeneously the levels of opioid tend to fluctuate over time, as opposed to spontaneously, so there is less demand for immediate regulatory response. They do not function directly as neurotransmitters, but are neuromodulators, especially influencing the GABA dynamic. In theory you could survive without endorphins entirely, but you wouldn't be very functional.
Too much dopamine; Hypertensive crisis. Too much serotonin; Serotonin syndrome. Too much opioid activity; respiratory depression. In terms of molar concentrations, opioid levels have to be far higher then the other two ligands in order to trigger a potentially terminal physiological response.
Basically what I'm saying is that DA and 5-HT behave in completely different ways to opioids, and it is a gross oversimplification to believe that they can be manipulated in the same way that opioids can.
Saying that, receptor up-regulation is still a tertiary response to a moderate decrease in DA or 5-HT ardency, and increased sensitivity can be enabled though a somewhat similar mechanism with a different dynamic.
Neuroleptics are DA antagonists, but their MOA tends to increase the activity of tyrosine hydroxylase, rather then receptor density, and so they will typically not facilitate the response you want, at least not at typical dosing levels. With prolonged low dose exposure however they can act in a way that would be enabling to an increase in dopamine sensitivity.
Sulbutiamine induces an increase in the density of D1 dopamine receptors in the prefrontal cortex due to a reduction in the release of dopamine. But because it has a positively charged thiazole moiety it can only be transported across the plasma membrane of dopaminergic neurons by high affinity carriers, what this means, especially in the brain because of it's anion activity, is that the rate of transport tends to fluctuate. So that you get an oscillation of dopamine release in the cortex, over a prolonged period (a few weeks) this oscillation will be compensated for through reactionary changes in endogenous dopamine production. The net result being the sulbutiamine's effectiveness will become negligible, and you'll be left with a dystonic dopaminergic system.
With regards to dopamine, agonists (particularly D1) are your best bet, but they are difficult to procure.
Serotonin on the other hand already has a novel sensitization agent in the form of Tianeptine (Stablon), a beautiful molecule which not only facilitates an increase in the density of serotonin receptors, it also increases activity of dopamine in the striatum, thus increasing the explicit activity of spiny GABA-ergic projection neurons, giving rise to anxiolysis and mood enhancement (through the increase in GABA-B). Tianeptine also enhances the affinity of the D2 and D3 dopamine receptors for their ligand through minor conformational changes, once again improving your feelings of well-being markedly.
So options are:
Dopamine - Sub theraputic doses of a neuroleptic (I recommend sulpride)
OR weekly cycling of sulbutiamine with a dopamine precursor such as L-Tyrosine.
Serotonin - Tianeptine!!! There are others, but what's the point when you already have the perfect substance.
Edited by Animal, 26 April 2010 - 10:49 PM.