Neuropeptide coding of sympathetic preganglionic neurons; focus on adrenally projecting populations

• Published in: Neuroscience Vol. 170; no. 3; pp. 789 - 799
• Main Authors: Kumar, N.N, Allen, K, Parker, L, Damanhuri, H, Goodchild, A.K
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Ltd 27.10.2010; Elsevier
• Subjects: Adrenal glands; Adrenal Medulla - innervation; adrenaline; Animals; Autonomic Fibers, Preganglionic - metabolism; Biological and medical sciences; dorsal root ganglia; enkephalin; Enkephalins - metabolism; Fundamental and applied biological sciences. Psychology; Ganglia, Spinal - metabolism; Male; Neurology; Neuropeptides - metabolism; noradrenaline; PACAP; Peripheral nervous system. Autonomic nervous system. Neuromuscular transmission. Ganglionic transmission. Electric organ; Pituitary Adenylate Cyclase-Activating Polypeptide - metabolism; Protein Precursors - metabolism; Rats; Rats, Sprague-Dawley; Sensory Receptor Cells - metabolism; Sympathetic Nervous System - metabolism; Vertebrates: nervous system and sense organs; immunoreactivity; Ad; PPE; vesicular acetylcholine transporter; intermediolateral column of the spinal cord; preproPACAP; preproenkephalin; NAd; SPN; enkephalin; adrenally projecting SPN; PPP; adrenaline; cholera toxin B; vAChT; noradrenaline; AP-SPN; ISH; PACAP; dorsal root ganglia; IML; ir; tyrosine hydroxylase; CTB; pituitary adenylate cyclase activating polypeptide; sympathetic preganglionic neurons; TH; DRG; in situ hybridization; Epinephrine; Preganglionic neuron; Spinal cord; Central nervous system; Enkephalin; Catecholamine; Sympathetic nervous system; Opioid peptide; Neuropeptide; Autonomic nervous system; Spinal ganglion; Norepinephrine; Pituitary adenylate cyclase activating peptide
• ISSN: 0306-4522; 1873-7544
• DOI: 10.1016/j.neuroscience.2010.07.047

Abstract Chemical coding of sympathetic preganglionic neurons (SPN) suggests that the chemical content of subpopulations of SPN can define their function. Since neuropeptides, once synthesized are transported to the axon terminal, most demonstrated chemical coding has been identified using immunoreactive terminals at the target organ. Here, we use a different approach to identify and quantify the subpopulations of SPN that contain the mRNA for pituitary adenylate cyclase activating polypeptide (PACAP) or enkephalin. Using double-labeled immunohistochemistry combined with in situ hybridization (ISH) we firstly identified the distribution of these mRNAs in the spinal cord and determined quantitatively, in Sprague–Dawley rats, that many SPN at the T4-T10 spinal level contain preproPACAP (PPP+, 80±3%, n =3), whereas a very small percentage contain preproenkephalin (PPE+, 4±2%, n =4). A similar neurochemical distribution was found at C8-T3 spinal level. These data suggest that PACAP potentially regulates a large number of functions dictated by SPN whereas enkephalins are involved in few functions. We extended the study to explore those SPN that control adrenal chromaffin cells. We found 97±5% of adrenally projecting SPN (AP-SPN) to be PPP+ ( n =4) with only 47±3% that were PPE+ ( n =5). These data indicate that adrenally projecting PACAPergic SPN regulate both adrenal adrenaline (Ad) and noradrenaline (NAd) release whereas the enkephalinergic SPN subpopulation must control a (sub) population of chromaffin cells – most likely those that release Ad. The sensory innervation of the adrenal gland was also determined. Of the few adrenally projecting dorsal root ganglia (AP-DRG) observed, 74±12% were PPP+ ( n =3), whereas 1±1% were PPE+ ( n =3). Therefore, if sensory neurons release peptides to the adrenal medulla, PACAP is most likely involved. Together, these data provide a neurochemical basis for differential control of sympathetic outflow particularly that to the adrenal medulla.