Solve textarea editing with jQuery

Question

I am making an event registration, with PHP and jQuery, to register it all happens well, but when I change, it causes an error:

Example:
We all know that when we enter a page to edit, we have to have the fields already filled with the database data, this is a fact.

Only when I change the text of textarea, and click on Submit, my database does not change the field, and even trying to show on the console, the new content does not show on the console, shows the database text.

My HTML field:

<textarea name="post_content" id="post_content" class="form-control tinymce"><?=$result->post_content;?></textarea>

This is the variable:

var descricao_edit = j("textarea[name='post_content']").val();

Javascript Script:

<script type="text/javascript">
    var j = jQuery.noConflict();
    j(document).ready(function () {
        var base_url = window.location.origin;
        var btn_enviar = j('#cadastro-dados');

        btn_enviar.on('click', function (event) {
            var base_url = window.location.origin;
            event.preventDefault();

            var categoria = j("input[type=radio][name=post_category]").val();
            var subcategoria = j("#post_category_parent").val();
            var titulo = j("#post_title").val();
            var descricao = j("#post_content").val();
            var id = j("#post_author").val();

            j.ajax({
                url: "<?= INCLUDE_PATH; ?>/modulos/cadastro_evento.php",
                type: 'POST',
                data: 'acao=dados&id=' + id + '&categoria=' + categoria + '&sub=' + subcategoria + '&titulo=' + titulo + '&descricao=' + descricao,
                beforeSend: function () {
                    btn_enviar.attr("disabled", true);
                },
                success: function (data) {
                    j.gritter.add({
                        title: '<i class="fa fa-check"></i> Sucesso!',
                        text: 'Dados registrados com sucesso.',
                        sticky: false,
                        time: ''
                    });

                    btn_enviar.attr("disabled", false);
                    window.location.href = base_url + "/editar/" + data;                    
                },
                error: function (data) {
                    if (data == 'erro') {
                        btn_enviar.attr("disabled", false);
                        alert('Erro ao tentar registrar');
                    }                   
                }
            });
        });
    });
</script>