PHARMACOLOGICAL AND ANATOMICAL EVIDENCE FOR AN EDINGER-WESTPHAL PREGANGLIONIC (EWPG) CELL GROUP IN THE NORTHERN LEOPARD FROG RANA PIPIENS
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1
Texas Tech University, Biological Sciences, United States
The Edinger-Westphal nucleus is best known as a midbrain cholinergic cell group (EWpg) that innervates the ciliary ganglion controlling iris muscle contraction. Recent studies have suggested a new subdivision of the EW populated by urocortin-1 (UCN-1) expressing neurons that project to other CNS sites involved in homeostasis (EW central projecting, EWcp, neurons, Kozciz et al. 2010). While functional EWpg and EWcp subdivisions in mammalian brain are supported by numerous studies, little is known about the role of the EW in amphibians. In fact, early work suggested that pupil constriction in anurans is not controlled by the parasympathetic nervous system, but instead depends entirely on the photosensitive nature of the iris muscle cells. Here we report evidence of a functional cholinergic component of the EW in the frog Rana pipiens. Peripheral administration of oxotremorine, a muscarinic receptor agonist, produced statistically significant pupil constriction. Transmission electron microscopy revealed numerous smaller unmyelinated axons in the oculomotor nerve, consistent with parasympathetic nerve fibers. Examination of choline acetyltransferase (ChAT) positive cells within the oculomotor nucleus revealed a subdivision of smaller neurons. Unilateral eye ablation caused cell death in both the somatic motor ChAT neurons and the smaller ChAT neurons in the oculomotor nucleus ipsilateral to the ablated side. These smaller ChAT neurons were segregated from UCN-1 immunoreactive neurons that were scattered more dorsally and medially to the oculomotor nucleus. Collectively, our data are consistent with a functional EWpg cell group in the brain of anurans, although the precise location of these cells awaits tracing studies. Our observation of UCN-1 neurons in the vicinity of the oculomotor nucleus is consistent with work from other labs suggesting that a EWcp component of the EW is present in anurans. (JK and ND supported by the TTU Clark's Scholars Program).
Keywords:
amphibian,
Autonomic,
choline acetyl-transferase,
cholinergic,
Parasympathetic Nervous System,
Sympathetic Nervous System,
urocortin
Conference:
ISAREN 2011: 7th International Symposium on Amphibian and Reptilian Endocrinology and Neurobiology, Ann Arbor, United States, 11 Jul - 13 Jul, 2011.
Presentation Type:
Poster
Topic:
Abstracts
Citation:
Cromie
MM,
Kang
J,
Desai
N,
Patel
S and
Carr
JA
(2011). PHARMACOLOGICAL AND ANATOMICAL EVIDENCE FOR AN EDINGER-WESTPHAL PREGANGLIONIC (EWPG) CELL GROUP IN THE NORTHERN LEOPARD FROG RANA PIPIENS.
Front. Endocrinol.
Conference Abstract:
ISAREN 2011: 7th International Symposium on Amphibian and Reptilian Endocrinology and Neurobiology.
doi: 10.3389/conf.fendo.2011.03.00007
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Received:
19 Jul 2011;
Published Online:
09 Aug 2011.
*
Correspondence:
Dr. James A Carr, Texas Tech University, Biological Sciences, Lubbock, Texas, 79409-3131, United States, James.Carr@ttu.edu