Microdialysis reveals dynamics of coupling between noradrenaline release and melatonin secretion in conscious rats

Generation of the Melatonin Endocrine Message in Mammals: A Review of the Complex Regulation of Melatonin Synthesis by Norepinephrine, Peptides, and Other Pineal Transmitters

“…This nocturnal inhibition could result from presynaptic inhibition of NE release and/or postsynaptic inhibition of the cAMP/AA-NAT/MEL pathway. It is possible that NPY is involved in the rapid inhibition of NE release induced by acute light exposure at night (Drijfhout et al, 1996c). In support of this, various lesion experiments suggest involvement of NPY in the light-induced inhibition of MEL synthesis and release (Dafny, 1980;CipollaNeto et al, 1995;Bartol et al, 1997;see Section V.A.6).…”

“…In addition, the activity of these three structures is directly (IGL, raphe) or indirectly (PVN) modulated by light. Since short light exposure at night induces a very rapid diminution of MEL synthesis and release Illnerova et al, 1979;Drijfhout et al, 1996c), it is possible that the central pathway involved in this rapid light inhibition (Dafny, 1980) that the central IGL-pineal pathway could be involved in the rapid inhibitory effect of a light flash on the metabolic activity of the pineal gland (Cipolla-Neto et al, 1995;Bartol et al, 1997).…”

“…The pivotal role of NE in the control of rat pineal metabolic activity has been supported by several experiments: 1) intraperitoneal injections of an NAergic agonist during the day stimulate MEL synthesis with a comparable amplitude to that of the endogenous nocturnal increase (see King and Steinlechner, 1985 for review); 2) SCGx abolishes the nocturnal increase in Aanat mRNA, AA-NAT activity, and MEL synthesis (Deguchi and Axelrod, 1972b;Roseboom et al, 1996;Garidou et al, 2001); 3) electrical SCG stimulation during the day provokes an increase in MEL synthesis in the pineal gland (Bowers and Zigmond, 1980); 4) exogenous NAergic stimulation of the pineal gland in organ cultures or in perifusion (Simonneaux et al, 1989) or of pinealocytes in primary culture Simonneaux et al, 1994b) induces a large increase in AA-NAT activity and MEL release; 5) the synthetic rate and renewal of NE in the pineal gland are higher at night than during the day (Brownstein and Axelrod, 1974;Craft et al, 1984); and 6) the use of pineal microdialysis to study the in situ regulation of MEL synthesis has demonstrated the positive coupling between the nighttime release of NE and stimulation of MEL synthesis (Drijfhout et al, 1993(Drijfhout et al, , 1996c.…”

“…Acute light exposure at night induces a rapid and complete inhibition of AA-NAT activity and MEL synthesis in the rat pineal gland Illnerova et al, 1979). A 1-min light pulse is sufficient to reduce AA-NAT activity and MEL concentrations to daytime values within 20 min Drijfhout et al, 1996c). Inhibition by light can be produced by light intensity as weak as 0.5 lux (Vanecek and Illnerova, 1982).…”

“…The other component of light inhibition arises from the SCN, which drives a slower, more sustained inhibition of NE release via the SCG sympathetic fibers. Even though postsynaptic inhibitory mechanisms exist for AA-NAT activity, it is more probable that light-induced inhibition of MEL synthesis essentially results from the very rapid termination of NE release (t 1/2 Ͻ 10 min) (Drijfhout et al, 1996c). Cessation of NAergic stimulation induces a rapid decrease in the intracellular concentration of cAMP and a consequent fast (t 1/2 Ͻ 2 min) degradation of AA-NAT protein by proteasome, independent of the Aa-nat mRNA level .…”