Gonadotropin-Releasing Hormone and Receptor Distributions in the Visual Processing Regions of Four Coral Reef Fishes

Abstract

Gonadotropin-releasing hormone (GnRH) is widely distributed in the brain of fishes where it may function as a neuromodulator of sensory processing and behavior. Immunocytochemical and neuronal label experiments were conducted on species from four families of coral reef fishes (Chaetodontidae, butterflyfish; Pomacentridae, damselfish; Gobiidae, goby; and Labridae, wrasse) to assess conservation of GnRH targets in the visual processing retina and brain. In all species, GnRH-immunoreactive (-ir) axons from the terminal nerve project principally to the boundary between the inner plexiform (IPL) and inner nuclear (INL) layers of the retina, and are less prominent in the optic nerve, ganglion cell, IPL and INL. However, the density of GnRH innervation within the retina differed among fish species with highest concentrations in the damselfish and butterflyfish and lowest in the goby and wrasse. Experiments also show that GnRH receptors are associated with GnRH-ir axons within the fish retina primarily at the IPL-INL boundary, the region of light-dark adaptation and image processing of contrast, motion or color. GnRH-ir axons overlapped central projections of retinal ganglion cell axons primarily within the stratum album centrale and stratum griseum centrale of the tectum in all species, and were concentrated in several diencephalic visual processing centers. GnRH receptors are also localized to diencephalic visual centers and the stratum griseum periventriculare of the tectum, where motion perception and coordination of motor behavioral responses in three-dimensional space occur. This work demonstrates that the basic neural substrates for peptide-sensory convergence are conserved at multiple processing levels in the visual system of several reef fishes. Species differences in GnRH innervation to the retina and GnRH receptor distributions may be related to phylogeny, their use of vision in natural behaviors, or possibly binding properties of the antibodies. Future studies are needed to characterize the exact GnRH variants and receptor types found in these species so that possible functional consequences of GnRH influence on vision can be defined.

Neural and hormonal mechanisms of reproductive-related arousal in fishes

“…There are even fewer functional studies of the teleost POA (or other brain areas) in regards to sexually motivated behavior (but see below and discussion on vocal fishes). AVT-ir and GnRH-ir and/or their receptors are also found in peripheral sensory organs and central sensory processing areas (Dewan et al, 2008; Foran et al, 1997; Goodson and Bass, 2000b; Grens et al, 2005; Maruska, 2009; Maruska and Fernald, 2010; Maruska and Tricas, 2007; Stell et al, 1987), implicating the role of these neuropeptides in modulating levels of “sensory responsiveness”.…”

Identification and Analysis of Two Novel Sites of Rat GnRH Receptor Gene Promoter Activity: The Pineal Gland and Retina

“…Recent evidence reported that class 1 GnRHR is indeed expressed in retinal amacrine cells of the teleost Astatotilapia ( Haplochromis) burtoni whereas class 2 GnRHR is expressed in the ganglion cell layer [45]. Also, GnRHR was identified in the retina of four coral reef fishes [46]. In mammals, data are extremely scarce and result from isolated observations in a small number of species like rhesus macaque, opossum, vole, bat and rat [47,48].…”

Mechanisms of Neuromodulation by a Nonhypophysiotropic GnRH System Controlling Motivation of Reproductive Behavior in the Teleost Brain

“…But how does the GnRH peptide that is released from these neurons modulate the information processing of target neurons to control reproduction, especially reproductive behaviors? Recently, many researchers are interested in the forebrain olfactory and visual systems as target systems of GnRH neuromodulation because of the projection of TN-GnRH3 neurons [4,37,[42][43][44] and localization of GnRH receptors [16][17][18].…”

“…The axons of TN-GnRH3 neurons innervate the retina and optic tectum [42,44,51]. GnRH positively modulates the efficiency of synaptic transmission from the retinal efferent axons to the periventricular neurons of the optic tectum in the rainbow trout [52].…”