Distribution and changes in ?- and ?-opiate receptors during the midlife neurodevelopmental period of coho salmon,Oncorhynchus kisutch

Abstract

Parr-smolt transformation (PST) in coho salmon is associated with a plasma thyroid hormone (PT4) surge and a critical period of neural development that includes axonal sprouting, neurogenesis, and surges of select neurotransmitters. Here we provide a description of the selectivity, distribution, and the changes in the density of mu- and kappa-opiate receptors during PST, as revealed by quantitative in vitro autoradiography of [3H]Tyr-D-Ala-Gly-NMe-Phe-Gly-ol ([3H]DAMGO) and [3H]ethylketocyclazocine ([3H]EKC), respectively. The concentration of mu-receptors increased significantly in select cell groups in the early stages of parr-smolt transformation, until a peak was reached at the time coinciding with the peak of the PT4 surge. In other cell groups, the peaks occurred 1 or 2 weeks later. With one exception, this increase was followed by a decrease in concentration. The brain areas showing the highest concentrations are the dorsal nucleus of the ventral telencephalic area, the glomerular region, the granular layer of the valvula cerebelli, the nucleus diffuses of the inferior lobe, and the nucleus diffuses of the torus lateralis. Other regions with distinctly elevated mu-receptor concentrations are the stratum griseum centrale of the optic tectum and the preoptic area. The distribution of kappa-receptors is more diffuse, and the densities are considerably lower. The overlap in distribution of mu- and kappa-receptors is considerable, but significant exceptions are noted. For example, the dorsomedial nucleus of the dorsal telencephalic area, the habenular nucleus, and the dorsomedial nucleus of the thalamus exhibit a surge in density of kappa-receptors at the time of the PT4 surge, while the density of mu-receptors in these nuclei remain very low throughout parr-smolt transformation. The kappa-receptor containing cell groups are not identifiable until 3 weeks before the PT4 surge because of low densities. The most prominently labeled kappa-receptor regions are the ventral and dorsal nuclei of the ventral telencephalic area, the medial and dorsal zones of the dorsal telencephalic area, the optic tectum (all layers), the dorsomedial nucleus of the thalamus, the torus lateralis of the ventral hypothalamus, and the preoptic area. An increase of mu- and kappa-opiate receptor densities in specific brain regions may reflect roles in the alteration of brain organization, olfactory imprinting, neuroendocrine activity or other physiological activities. The overall distribution of these receptors are relatively more extensive in salmon than in other vertebrates so far studied.

Transcriptional profiling of the parr–smolt transformation in Atlantic salmon

“…These hormones in turn may affect transcription of other genes involved in the parr-smolt transformation (Yada et al, 1992;Sakamoto et al, 1995), and are themselves controlled by hypothalamic factors. Brain and hypothalamic changes occur during smolt development, including increased numbers of corticotropin releasing factor neurons (Ebbesson et al, 2011), retinal innervation of the preoptic nucleus and altered opiate receptor distribution (Ebbesson et al, 1996). These changes may be critical to the altered photoperiod responsiveness that characterizes smolt development McCormick et al, 2007).…”

Aluminum exposure impacts brain plasticity and behavior in Atlantic salmon (Salmo salar)

“…Such an effect is likely to have a negative influence on the ability of the fish to cope with the transition from freshwater to the marine environment, a time when the fish need to perform critical behaviors such as predator avoidance, social interactions and navigation Ebbesson and Braithwaite, 2012). Furthermore, it is possible that the reduced forebrain neural plasticity and cognitive deficit at the critical smolt stage also affect imprinting, by altering the olfactory-telencephalic plasticity associated with smoltification (Ebbesson et al, 1996a;Ebbesson et al, 2003;Folgueira et al, 2004). Memories of the natal stream formed during imprinting are later used to return as adults (Hasler and Scholz, 1983;Yamamoto et al, 2010), and thus impaired imprinting could have a profound impact on return success.…”

“…These arise because of the neuroendocrine and behavioral changes associated with olfactory imprinting that are essential for migration to the ocean and return to natal streams (Ebbesson et al, 1996a;Ebbesson et al, 1996b;Ebbesson et al, 2003;Ebbesson et al, 2007;Ebbesson et al, 2011;Stefansson et al, 2008). The physiological effects of stress also have an impact on behavior, through modification or impairment of signaling pathways that control behaviors such as feeding and aggression (Barton, 2002).…”

Identification of beta-endorphins in the pituitary gland and blood plasma of the common carp (Cyprinus carpio)

“…In addition to its opioid function, -endorphin was found to be involved in a variety of physiological processes (reviewed by Dalayeun et al 1993), including regulation of the immune (Heijnen et al 1987, Shahabi et al 1991, 1996 and reproductive (e.g. Faletti et al 1999) systems.…”

“…The existence of opiate active -endorphins in teleosts is indicated by the localisation of µ-opiate receptors in the coho salmon (Oncorhynchus kisutch) brain (Ebbesson et al 1996).…”