Intrinsic choroidal neurons in the human eye: projections, targets, and basic electrophysiological data.
OBJECTIVE
The chemical coding of intrinsic choroidal neurons (ICNs) has features in common with extrinsic fibers (e.g., from the pterygopalatine ganglion) making it impossible to assess whether a neuronal nitric oxide synthase (nNOS)/vasoactive intestinal polypeptide (VIP)-immunoreactive nerve fiber is of intrinsic or extrinsic origin. Neurobiotin injections into single neurons allow the visualization of projections of these cells and the determination of the origin of target innervation. Thus, this technique was used in the present study to help characterize the organization of the ICN in the human eye.


METHODS
ICNs were visualized with the fluorescent vital dye 4-Di-2-ASP. Electrophysiological properties were determined by means of intracellular recordings. The impaled neurons were iontophoretically filled with neurobiotin. After fixation, immunohistochemistry for neuronal nitric oxide synthase (nNOS), alpha-smooth muscle actin, and calcitonin gene-related peptide (CGRP) was conducted.


RESULTS
ICN processes were traced over distances of up to 2.612 micro m. They were found in the immediate vicinity of other nNOS-positive or -negative ICNs and were also found apposed to smooth muscle fibers (vascular and stromal nonvascular). CGRP-positive fibers forming boutons were observed closely associated with ICNs. Electrophysiological recording showed phasic firing without slow afterhyperpolarization, no spontaneous activity, an input resistance of 136 +/-73 MOmega, and a membrane time constant of 7 +/- 1 ms.


CONCLUSIONS
Apart from the first functional characterization of ICNs, this study provided more precise evidence of reciprocal ICN-to-ICN contacts and innervation of both choroidal nonvascular and vascular smooth muscle. The presented technique offers promising perspectives to further investigate the function of ICNs in ocular homeostasis.
Schrödl
Falk
F
Anatomy Institute I, Erlangen, Germany. falk.schroedl@anatomie1.med.uni-erlangen.de
De Laet
Ann
A
Tassignon
Marie-Jose
MJ
Van Bogaert
Pierre-Paul
PP
Brehmer
Axel
A
Neuhuber
Winfried L
WL
Timmermans
Jean-Pierre
JP
D000199:Actins / Q000378:metabolism; D000368:Aged; D000369:Aged, 80 and over; D001710:Biotin / Q000031:analogs & derivatives*; D015740:Calcitonin Gene-Related Peptide / Q000378:metabolism; D002829:Choroid / Q000294:innervation*; D004594:Electrophysiology; D005260:Female; D019084:Fluorescent Antibody Technique, Indirect; D005456:Fluorescent Dyes; D006801:Humans; D008297:Male; D008856:Microscopy, Fluorescence; D009434:Neural Pathways / Q000502:physiology; D009474:Neurons / Q000166:cytology* / Q000502:physiology*; D019001:Nitric Oxide Synthase / Q000378:metabolism; D052248:Nitric Oxide Synthase Type I; D011726:Pyridinium Compounds; D017779:Sympathetic Fibers, Postganglionic / Q000033:anatomy & histology / Q000502:physiology
D000199:Actins; D005456:Fluorescent Dyes; D011726:Pyridinium Compounds; C070614:neurobiotin; C052247:4-(4-diethylaminostyryl)-N-methylpyridinium; D001710:Biotin; C496320:NOS1 protein, human; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; D015740:Calcitonin Gene-Related Peptide