Presence of Corticotrophin‐Releasing Factor and /or Tyrosine Hydroxylase in Cells of a Neural Brain‐Testicular Pathway That are Labelled by a Transganglionic Tracer

Our laboratory has shown that male testosterone levels are not solely controlled by the release of hypothalamic gonadotrophin‐releasing hormone and pituitary luteinising hormone, but are also regulated by a multisynaptic pathway connecting the brain and the testis that interferes with the testosterone response to gonadotrophins. This pathway, which is independent of the pituitary gland, is activated by an i.c.v. injection of either the stress‐related peptide corticotrophin‐releasing factor (CRF) or of β‐adrenoceptor agonists, both of which alter androgen release and decrease levels of the peripheral‐type benzodiazepine receptor and the steroidogenic acute regulatory protein within Leydig cells. Our original studies used the retrograde transganglionic tracer pseudorabies virus (PRV) to map progression of the virus from the testes to upper brain levels. The present study aimed to extend this work by identifying the regions where CRF and catecholamine neurones represented components of the stress‐activated, brain–testicular pathway that prevents testosterone increases. To this end, anaesthetised adult male rats received an intra‐testicular injection of PRV. Using immunofluorescence, we identified co‐labelling of PRV and either CRF or tyrosine hydroxylase (TH), the enzyme responsible for biogenic amine synthesis. Co‐labelling of PRV and CRF was found in the bed nucleus of the stria terminalis, the paraventricular nucleus of the hypothalamus (PVN) and the central amygdala. Co‐labelling of PRV and TH was found in the PVN, substantia nigra, A7/Kölliker‐Fuse area, area of A5, locus coeruleus, nucleus of solitary tract, area of C3, area of C2 and the area of C1/A1. These results indicate that most cell groups of the ventral noradrenergic pathway have neurones that are a part of the brain–testicular pathway. This suggests that the stress hormones CRF and catecholamines may act as neurotransmitters that signal the pathway to inhibit increases in plasma testosterone levels.