Brain serotonin dysfunction accounts for aggression in male mice lacking neuronal nitric oxide synthase - PubMed (original) (raw)

Brain serotonin dysfunction accounts for aggression in male mice lacking neuronal nitric oxide synthase

S Chiavegatto et al. Proc Natl Acad Sci U S A. 2001.

Abstract

Genetically engineered mice with targeted disruption of the neuronal nitric oxide synthase (nNOS) gene established the inhibitory role of nitric oxide (NO) in male impulsive aggressive behavior. This was later confirmed by using selective nNOS inhibitors in male wild-type mice. The molecular mechanisms accounting for the aggressive behavior caused by the lack of neuronally derived NO is not known. Recent studies suggest that central serotonergic neuronal circuits and particularly 5-HT(1A) and 5-HT(1B) receptors play a prominent role in the regulation of aggression. Accordingly, we investigated whether the aggressiveness caused by the lack of nNOS might be because of alterations in serotonergic function. We now demonstrate that the excessive aggressiveness and impulsiveness of nNOS knockout mice is caused by selective decrements in serotonin (5-HT) turnover and deficient 5-HT(1A) and 5-HT(1B) receptor function in brain regions regulating emotion. These results indicate an important role for NO in normal brain 5-HT function and may have significant implications for the treatment of psychiatric disorders characterized by aggressiveness and impulsivity.

PubMed Disclaimer

Figures

Figure 1

5-HT, 5-HIAA, and 5-HT turnover (5-HIAA/5-HT ratio) determinations by HPLC in cerebral cortex (Cor), hypothalamus (Hyp), hippocampus (Hipp), amygdala (Amy), midbrain (Mid), and cerebellum (Cer) of nNOS−/− mice as compared with WT. The levels of 5-HT, 5-HIAA (ng/mg tissue), and 5-HT turnover in WT mice are as follows (±SEM): Cor = 0.349 ± 0.012, 0.134 ± 0.005, 0.386 ± 0.018 (n = 6); Hyp = 1.200 ± 0.038, 0.683 ± 0.043, 0.569 ± 0.032 (n = 6); hipp = 0.614 ± 0.019, 0.351 ± 0.027, 0.571 ± 0.038 (n = 6); Amy = 0.807 ± 0.056, 0.364 ± 0.023, 0.470 ± 0.060 (n = 6); Mid = 0.949 ± 0.023, 0.557 ± 0.035, 0.586 ± 0.031 (n = 5); Cer = 0.093 ± 0.005, 0.100 ± 0.005, 1.094 ± 0.086 (n = 6), respectively. In nNOS−/− mice, n = 6 for Hyp, Hipp, Mid, and Cer; n = 5 for Cor and Amy. Data are percent change in relation to WT mice ± SEM; *,P < 0.05 by Student's t test.

Figure 2

Reduction in aggressive behavior and increase in 5-HT metabolism by the precursor 5-HTP. (A and B) Aggressive behavior as measured by the resident–intruder test 30 min after 0.9% saline solution, 50 mg/kg or 100 mg/kg 5-HTP i.p. injections in WT and nNOS−/− mice (n = 6 each group). (C) Locomotor activity in an open field 30 min after i.p. injections in different animals (saline and 5-HTP 100 mg/kg,n = 6 in each genotype; and 5-HTP 50 mg/kg,n = 5 in each genotype). *,P < 0.05; and †, P < 0.01 in relation to the saline group in the same genotype; and #,P < 0.05; and ##, P < 0.01 in relation to WT same treatment. Data are means ± SEM and were analyzed by using two-way ANOVA (genotype × treatment) with post hoc Tukey test. (D) HPLC determinations of 5-HT (S) and its metabolite 5-HIAA (M) in the cerebral cortex (Cor), hypothalamus (Hyp), hippocampus (Hipp), amygdala (Amy), midbrain (Mid), and cerebellum (Cer) of WT and nNOS−/− mice (n = 5 each genotype) 45 min after 100 mg/kg 5-HTP. Data are percent increase above saline groups in each genotype (n = 6 each; means ± SEM). The percent of turnover increase (5-HIAA/5-HT) ranged from 346% to 646% in these brain areas. All data in D are P < 0.01 in relation to saline controls (two-way ANOVA with post hoc Tukey test).

Figure 3

Increase in aggressive behavior and 5-HT reduction by the 5-HT synthesis inhibitor pCPA. (A and B) Aggressive behavior as measured by the resident–intruder test 72 h after 0.9% saline solution (single injection, n = 5 for each genotype; three daily injections, n = 4 each genotype; group collectively named as saline because no differences are detected), single dose of 300 mg/kg pCPA (1 × 300, n = 10 each genotype) or three doses of 300 mg/kg pCPA (72, 48, and 24 h before tests, 3 × 300,n = 7 each genotype) i.p. injections in WT and nNOS−/− mice. (C) Locomotor activity in an open field 74 h after first i.p. injection (n = 6–10 in each group). *, P < 0.05; †,P < 0.01 in relation to saline in the same genotype; and #, P < 0.05; and ##,P < 0.01 in relation to WT same treatment. Data are means ± SEM and were analyzed by using two-way ANOVA (genotype × treatment) with post hoc Tukey test. (D and E) HPLC determinations of 5-HT (S) and its metabolite 5-HIAA (M) in the cerebral cortex (Cor), hypothalamus (Hyp), hippocampus (Hipp), amygdala (Amy), midbrain (Mid), and cerebellum (Cer) of WT and nNOS−/− mice 75 h after single i.p. injection of 300 mg/kg pCPA (D) and 3 × 300 mg/kg pCPA (E). Data are percent decrease from saline group in each genotype (means ± SEM,n = 5–6 mice each group). *,P < 0.05; and †, P < 0.01 in relation to saline in the same genotype. In E, all data are P < 0.05 or P < 0.01 in relation to saline controls (two-way ANOVA with post hoc Tukey test).

Figure 4

Serotonergic innervations in the cerebral cortex of WT and nNOS−/− mice. Dark-field photomicrographs of 5-HT-immunoreactive axons in sagittal sections. (5× objective.) No differences are visualized in any brain area in sagittal or coronal sections of five nNOS−/− and four WT mice.

Figure 5

(A and B) Aggressive behavior after increasing doses of the 5-HT1A agonist 8-OH-DPAT in WT and nNOS−/− mice (n = 8 each). Data are presented as percent change from saline groups in each genotype (means ± SEM) and a regression line. *,P < 0.05, and †, P < 0.01 in relation to saline control, two-way ANOVA (genotype × treatment) with post hoc Tukey test. The ED50 in the reduction of number of attacks, calculated for each animal, is 0.019 ± 0.011 mg/kg for WT mice and 0.081 ± 0.007 mg/kg for nNOS−/− mice (P < 0.01, Student's_t_ test). (C and D) Aggressive behavior after increasing doses of the 5-HT1B agonist CP-94,253 in WT and nNOS−/− mice (n = 8 WT and 9 nNOS−/− mice). Data are presented as percent change from vehicle groups in each genotype (means ± SEM) and a regression line. *,P < 0.05 in relation to vehicle in each genotype (two-way ANOVA with post hoc Tukey test). The ED50 in the number of attacks, calculated for each animal, is 3.70 ± 1.21 mg/kg for WT mice and 6.76 ± 0.61 mg/kg for nNOS−/− mice (P < 0.05, Student's_t_ test).

References

1. Huang P L, Dawson T M, Bredt D S, Snyder S H, Fishman M C. Cell. 1993;75:1273–1286. - PubMed
1. Burnett A L, Calvin D C, Chamness S L, Liu J X, Nelson R J, Klein S L, Dawson V L, Dawson T M, Snyder S H. Nat Med. 1997;3:571–574. - PubMed
1. Jumrussirikul P, Dinerman J, Dawson T M, Dawson V L, Ekelund U, Georgakopoulos D, Schramm L P, Calkins H, Snyder S H, Hare J M, et al. J Clin Invest. 1998;102:1279–1285. - PMC - PubMed
1. Kriegsfeld L J, Eliasson M J, Demas G E, Blackshaw S, Dawson T M, Nelson R J, Snyder S H. Neuroscience. 1999;89:311–315. - PubMed
1. Nelson R J, Demas G E, Huang P L, Fishman M C, Dawson V L, Dawson T M, Snyder S H. Nature (London) 1995;378:383–386. - PubMed

Brain serotonin dysfunction accounts for aggression in male mice lacking neuronal nitric oxide synthase - PubMed (original) (raw)