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  • Title: Testosterone increases the number of substance P-like immunoreactive neurons in a specific sub-division of the lateral hypothalamus of the weakly electric, brown ghost knifefish, Apteronotus leptorhynchus.
    Author: Dulka JG, Ebling SL.
    Journal: Brain Res; 1999 Apr 24; 826(1):1-9. PubMed ID: 10216191.
    Abstract:
    During spawning, male and female brown ghost knife fish modulate their electric organ discharge to produce discrete courtship signals known as chirps. However, non-spawning fish show clear sex differences in chirp responsiveness to electrosensory stimuli; males consistently chirp, whereas females do not. This behavioral dimorphism is paralleled by sex differences in substance P-like immunoreactivity (SPl-ir) in the prepacemaker nucleus (PPn) which regulates chirping. The PPn is densely innervated by SPl-ir fibers in males, but not in females. However, we have shown that both female chirping behavior and the expression of SPl-ir in the PPn are enhanced following adult testosterone treatment [J.G. Dulka, L. Maler, W. Ellis, Androgen-induced changes in electrocommunicatory behavior are correlated with changes in substance P-like immunoreactivity in the brain of the electric fish, Apteronotus leptorhynchus, J. Neurosci. 15 (1995) 1879-1890]. Thus, testosterone-induced changes in SPl-ir input to the PPn may modulate female chirping during spawning. Recent evidence suggests that SPl-ir projections to the PPn may originate from SPl-ir neurons in the lateral hypothalamus (Hl). If so, one might expect to see a greater number of SPl-ir neurons in the Hl of testosterone-implanted females compared to Blank-implanted controls. In making this comparison, we found that both groups of females had similar numbers of SPl-ir neurons in the anterior Hl, but that testosterone-implanted females had significantly (p<0.01) more SPl-ir neurons in a distinct part of the posterior Hl. This sub-population of testosterone-sensitive, SPl-ir neurons may contribute to the regulation of chirping, since an increase in their number is positively correlated with the appearance of SPl-ir fibers in the PPn [J.G. Dulka, L. Maler, W. Ellis, Androgen-induced changes in electrocommunicatory behavior are correlated with changes in substance P-like immunoreactivity in the brain of the electric fish, Apteronotus leptorhynchus, J. Neurosci. 15 (1995) 1879-1890].
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