Asymmetric metabolism of hypothalamic catecholamines alternates with side of ovulation in a lizard (Anolis carolinensis)

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Abstract
We determined levels of monoamines and their metabolites in 2 hypothalami dissected from the right and left hemibrains of 15 females during the right‐left alternating ovulatory cycle of Anolis carolinensis. Tissue contents of the following were measured using HPLC and electrochemical (coulometric) detection: dopamine (DA) and its metabolite 2,4‐dihydroxyphenylacetic acid (DOPAC), norepinephrine (NE) and its metabolites 3‐methoxy‐4‐hydroxyphenylglycol (MHPG) and 3,4‐dihydroxyphenylglycol (DHPG), and serotonin (5‐HT) and its metabolite 5‐hydroxyindoleacetic acid (5‐HIAA). An asymmetry ratio (AR) was determined by subtracting hypothalamic content (pM/mg) on the larger ovary (LO) side from that on the smaller ovary (SO) side, divided by the sum of the 2 sides (AR = SO − LO/SO + LO). The AR of MHPG and DHPG both decreased as the largest follicle in the LO grew during the cycle, from >0 (content higher on the SO side) at the beginning of the cycle to <0 (content higher on the LO side). The average content of MHPG in the 2 sides significantly increased during the cycle. There were no significant asymmetric changes in hypothalamic DA or DOPAC. The average content of DA increased during the cycle, whereas the content of DOPAC, as well as DOPAC/DA, did not change. The average content of 5‐HT increased, and the average metabolite ratio of 5‐HIAA/5‐HT decreased during the cycle without significant asymmetries. The metabolite ratios of NE and DA, but not 5‐HT, were asymmetric on the same side in a given female. These results suggest, that catecholamine metabolism shifts from being greater on the SO side of the hypothalamus to being greater on the LO side of the hypothalamus. This shift occurs when a follicle has reached 4.7–5.2 mm in diameter, with ovulation occurring at 8 mm. The asymmetric changes in catecholamine metabolism in synchrony with asymmetric ovarian growth indicate the presence of neural communication, in one direction or the other or both, between the ovaries and hypothalamus.