Transsynaptic connections between the hypothalamus and adipose tissue: relationship to reproduction.

Neurophysiological mechanisms that control energy balance are reciprocally linked to those that control reproduction. Neuromorphological studies using retrograde tracing methods revealed that nerve cells within the central (CNS) and autonomic (ANS) nervous systems in different species, including the pig, are transsynaptically connected to different fat tissue depots. In the pig, neurons localised in the paraventricular nucleus, supraoptic nucleus and arcuate nucleus were infected with pseudorabies virus (PRV) 9 days after injections into both the perirenal and subcutaneous adipose tissue depots. Infected neurons were in the ventromedial nucleus, dorsomedial nucleus and preoptic area after injection of PRV into perirenal adipose tissue, while infected cells in the lateral hypothalamic area projected only to the subcutaneous adipose tissue depot. Additionally, numerous centres of the ANS innervate adipose tissue depots in the pig. Fast blue stained (FB+) neurons, which projected to the subcutaneous adipose tissue overlaying the thoracolumbar area were located in the thoraco-lumbar region of the sympathetic chain ganglia (SChG). However, neurons supplying perirenal and mesentery adipose tissue depots were found in both the SChG and prevertebral ganglia. The vast majority of labelled neurons, in both the CNS and ANS, which innervated adipose tissue depots, expressed leptin receptor (OBR) immunoreactivity. The purpose of this brief review is to establish evidence for a multisynaptic circuit of neurons, which innervate adipose tissue in the pig and demonstrate that hypothalamic nuclei and sympathetic ganglion neurons involved in reproductive processes are transsynaptically connected to different adipose tissue depots.