Serotonin in a diencephalic nucleus controlling communication in an electric fish: Sexual dimorphism and relationship to indicators of dominance

Abstract

Serotonin regulates aggressive behavior. The production or release of serotonin is sexually dimorphic and related to social rank in many species. We examined serotonin expression in the central posterior/prepacemaker nucleus (CP/PPn) of the electric fish Apteronotus leptorhynchus. The CP/PPn is a thalamic nucleus that controls agonistic and reproductive electrocommunication signals known as chirps and gradual frequency rises. In parts of the CP/PPn that control chirping, females had more than twice as many serotonergic fibers and terminals as did males. Serotonin immunoreactivity in chirp-controlling areas of the CP/PPn was also negatively correlated with two indicators of dominance: electric organ discharge (EOD) frequency and body mass. Within sexes, the negative correlation between EOD frequency and serotonergic innervation of the PPn was significant in females, but not in males. Females with higher EOD frequencies had less serotonin in the CP/PPn than did females with lower EOD frequencies. Thus, the CP/PPn contained more serotonin in females than in males, and in particular, more serotonin in females with EOD frequencies typical of social subordinates than in females with EOD frequencies typical of social dominants. These results, combined with previous findings that serotonin inhibits chirping and that females chirp much less than males, suggest that serotonin may link sex, social rank, and the production of agonistic communication signals. The relative simplicity of the neural circuits that control the EOD and chirping make the electromotor system well-suited for studying the cellular, physiological, and behavioral mechanisms by which serotonin modulates agonistic communication.

Evolution and hormonal regulation of sex differences in the electrocommunication behavior of ghost knifefishes (Apteronotidae)

“…Serotonin-immunoreactive terminals are more abundant in the PPn in females than in males (Telgkamp et al, 2007). Furthermore, fish with higher EODfs, which may be an indicator of dominance (see above), have reduced expression of serotonin in the PPn than fish with lower EODfs.…”

“…Serotonin, for example, is expressed in both the PPn and the lateral segment of the ELL, which is particularly involved in processing electrocommunication signals (Johnston et al, 1990;Telgkamp et al, 2007). Serotonin both modulates chirp production and changes the way that ELL pyramidal neurons encode communication signals, specifically by enhancing their ability to encode both low-frequency beats created by same-sex interactions and the low-frequency chirps produced during such interactions (Deemyad et al, 2011).…”

Influence of long-term social interaction on chirping behavior, steroid levels and neurogenesis in weakly electric fish

“…For example, exogenous treatment of fish with arginine vasotocin (Bastian et al, 2001), noradrenaline (Maler and Ellis, 1987), androgens (Dunlap et al, 1998;Dulka et al, 1995) or cortisol (Dunlap et al, 2006) increases chirp rates, while treatment with serotonin inhibits chirping via the 5HT2 receptor (Maler and Ellis, 1987;Telgkamp et al, 2007;Smith and Combs, 2008).…”

The Effect of male-male competition and its Underlying Regulatory Mechanisms on the Electric Signal of the Gymnotiform fish <em>Brachyhypopomus gauderio</em>

“…Serotonin not only regulates overt aggressive physical behaviors but it also regulates production of aggressive communication signals , including electrocommunication signals Smith & Combs 2008;Stoddard et al 2003a;Telgkamp et al 2007). Although high chronic serotonin activity is typically related to low levels of aggressive behavior, this is not always the case Summers 2001;Veenema et al 2005).…”

“…Serotonin not only regulates overt aggressive physical behaviors but it also regulates production of aggressive communication signals , including electrocommunication signals Smith and Combs, 2008;Telgkamp et al, 2007).…”