I've always thought the higher incidence of adverse effects with more stimulating entactogens or MDMA + amphetamine combos could just have to do with more stress hormones --> more neuroplasticity, consistent with a higher likelihood of LTC-like symptoms from a bad trip rather than a pleasant one (LTC-like symptoms are reported from classical psychedelics as well)
......Ignoring that vasopressin regulates ACTH, which of course causes downstream neuroplastic changes that are known to manifest with haste, the neurons that release vasopressin are in the paraventricular nucleus of the hypothalamus that contain the oxytocin releasing neurons.
https://www.ncbi.nlm.nih.gov/pubmed/11906204 - "
Oxytocin-secreting neurons: A physiological model of morphological neuronal and glial plasticity in the adult hypothalamus."
"Oxytocin-secreting neurons of the hypothalamoneurohypophysial system undergo reversible morphological changes whenever they are strongly stimulated. In the hypothalamus, such structural plasticity is represented by modifications in the size and shape of their somata and dendrites, in the extent to which their surfaces are covered by glia, and in the density of their synapses. In the neurohypophysis, there is a parallel reduction in glial (pituicyte) coverage of their axons together, with retraction of pituicyte processes from the perivascular basal lamina and an increase in the number and size of their terminals.
These changes occur rapidly, within a few hours. On the other hand, the system returns to its prestimulated condition on arrest of stimulation at a rate
that depends on the length of time it has remained activated.
Such neuronal-glial changes have several functional consequences. In the hypothalamic nuclei, reduction in astrocytic coverage of oxytocinergic neurons and their synapses modifies extracellular ionic homeostasis and glutamate clearance and, therefore, their overall excitability. Since it results in extensive dendritic bundling, it may also lead to ephaptic interactions and may facilitate dendritic electrotonic coupling. A most important indirect effect may be to permit synaptic remodeling that occurs concomitantly and that results in significant increases in the number of excitatory and inhibitory synapses driving their activity. In the stimulated neurohypophysis, glial retraction results in increased levels of extracellular K+ which can enhance neurohormone release while an enlarged neurovascular contact zone may facilitate diffusion of neurohormone into the circulation. Ongoing work aims to unravel the cell mechanisms and factors underlying such plasticity and has revealed that
neurons and glia of the hypothalamoneurohypophysial system continue to express juvenile molecular features associated with similar neuronglial interactions and synaptic events during development and regeneration."
The supraoptic nucleus containing the vasopressin and oxytocin releasing neurons has been well studied for its adaptive capabilities.. Considering MDMA works largely via oxytocin via 5-HT1A activation, I'd say this could be relevant...