New insights into the reptilian catecholaminergic systems as revealed by antibodies against the neurotransmitters and their synthetic enzymes.

The catecholaminergic systems in the lizard Gekko gecko and the turtle Pseudemys scripta elegans have been studied with specific and sensitive antibodies against the neurotransmitters dopamine (DA) and noradrenaline (NA) and the biosynthetic enzymes tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH) and phenylethanolamine-N-methyltransferase. Our results demonstrate that: (1) the hypothalamic periventricular organ contains both DA and NA cerebrospinal fluid-contacting cells. These cells are immunonegative for TH and DBH which suggests that they accumulate rather than synthesize these amines; (2) at several places, particularly in the olfactory bulb, the hypothalamus, the nucleus of the solitary tract and the area postrema, cells are present that stain with TH-antibodies but not with any of the other antisera, suggesting that these neurons contain L-dihydroxyphenylalanine as their endproduct; (3) antibodies against TH demonstrate primarily DA fibres and varicosities, whereas the distribution of DBH-immunoreactive fibres generally corresponds to that shown by antibodies against NA. The present study underscores the importance of utilizing different approaches for a complete understanding of catecholaminergic systems.