The midcycle E2 surge induces a synaptic reorganization
in the mediobasal hypothalamus (MBH), thus increasing
the ratio of stimulatory/inhibitory synapses. This synaptic
reorganization disinhibits GnRH neurons and leads to an LH
surge. Synaptic functions are energy dependent and require
mitochondrial ATP production. Ectonucleoside triphosphate
diphosphohydrolase 3 (NTPDase3) may play a crucial role
in the regulation of mitochondrial ATP levels in stimulatory
MBH neurons. The positive gonadophin feedback involves
the generation and function of large numbers of hypothalamic
stimulatory synapses, thus, it might be associated with increased
mitochondrial ATP production and increased mitochondrial
respiration (mr). Anatomically, there are paired brain areas
in the two hemispheres and unpaired structures along the
anatomical midline. Distinct sides of paired brain areas
usually regulate distinct physiological processes, rather than
sharing roles to regulate the exact same functions. However,
there are certain brain regions with no known functional
differences between the two sides. One such brain area is the
MBH, which has always been investigated as an unpaired
midline structure despite its clearly symmetric anatomical
characteristics. Investigation of mr in MBH synaptosomal
fractions in our laboratory has indicated that besides ipsylateral
intrahypothalamic differences (i.e., differences between the
lateral and medial regions of the MBH on the same side) a
functional laterality may exist between homologous areas
of symmetric hypothalamic structures. Therefore, we have
investigated mr rates, with special regard to ADP-dependent
state 3 mr, in the MBH with isolated left and right sides. Our
initial results imply that the MBH regulation of the E2-induced
gonadotrophin surge is unilateral, and that there is an urging
need for a technical solution to identify in vivo the dominant
hypothalamic side that enters into the positive gonadotrophin
phase of the estrous cycle