<i>Tph2</i>^{<i>null/null</i>} mice are depleted of brain serotonin.

<p>Representative confocal images of P0 wild-type (<b>a</b>, <b>d</b>), <i>Tph2</i>^{<i>flox/flox</i>} (<b>b</b>, <b>e</b>) and <i>Tph2</i>^{<i>null/null</i>} (<b>c</b>, <b>f</b>) brain coronal sections, showing the distribution of 5-HT immunoreactive neurons within B7 (<b>a</b>-<b>c</b>) and B1-B3 (<b>d</b>-<b>f</b>) <i>raphe</i> nuclei. While no differences are visible in the distribution of serotonin immunoractive neurons between wild-type and <i>Tph2</i>^{<i>flox/flox</i>} pups (<b>a</b>-<b>b, d</b>-<b>e</b>), the brain of <i>Tph2</i>^{<i>null/null</i>} pups appear to be devoid of 5-HT throughout its anterior-posterior axis (<b>c</b>, <b>f</b>). Scale bar: 400 μm.