1) dopamine => motivation, action 2) norepinephrine => excitatory 3) melatonin => sleep 4) serotonin => confidence Tremors, lack of balance, and lack of response caused by lack of 1). Lack of sleep caused by lack of receptors for 3). Depression maybe caused by lack of 4) or its receptors. Constipation and excess saliva can be caused by an excess of 2), not a decrease. Also anxiety should be cause by an excess of it. So somehow damage to the LC seems to appear as an increase 2) even as it is supposed to produces 2). I mean if the LC is damaged, you would think 2) is less but PD and other conditions that "affect" the LC look as if they increase 2). A 5th important neurotransmitter is oxytocin, the "trust" or "love" hormone that works with dopamine that is also sometimes thought to be a pleasure hormone. Notice each of the 5 hormones can help increase "pleasure".
"The OXT-immunoreactive cell number in the PVN of the  PD patients was 22% lower"
" Lower oxytocin neuron numbers are found in Prader-Willi syndrome, AIDS and Parkinson's disease."
"administration of rats with oxytocin significantly lessened the neuronal death. These findings suggest that injury of dopaminergic neurons triggers exaggerated neuronal oscillations in the striatum and oxytocin may have some inhibitory effects on neuronal activity in PD."
" By incubation of stable isotope-labeled oxytocin with tissue preparations, it was also confirmed that oxytocin at least partially contributed to the production of MIF-1 in the hypothalamus by action of peptidases. ...MIF-1 has potent therapeutic effects in depression and Parkinson's disease,"
"oxytocin (OT) plays a role in neuropsychiatric disorders characterized by social dysfunction" (I could fall into this category)
"sexual dysfunction (decrease in libido and erection) in PD, via altered dopamine-oxytocin pathways, which normally promote libido and erection"
"OT improves memory consolidation and extinction, but only if given at a low dose immediately after the acquisition phase.... OT plays a role in elementary forms of behavioral flexibility and adaptive responses and support its therapeutic potential in neuropsychiatric disorders characterized by cognitive inflexibility and/or impairment (autism, schizophrenia, Alzheimer's disease, Parkinson disease, stroke, posttraumatic stress disorder)."
"mice treated with [lipid-form OXT] displayed more recovery than those given OXT. The results suggest that LOXT has a functional advantage in recovery of social behavioral impairment, such as those caused by neurodegenerative diseases, autism spectrum disorders, and schizophrenia."