Problems whit slideToggle and is(':visible')

Problems whit slideToggle and is(':visible')

I want to change a value tag (div class='seeMore') ("+ if hidden" & "- if show") depending on the result of the slideToggle jQuery, but I can't even make the slide work. I know that the problem lies in the way of how I call the tag to be Toggle
  1. $(this).parents('.seeMoreContainer').next().slideToggle(1000)
But can not find another way to do it because there will be multiple tags with class 'seeMore', so I have to deal with the keyword '(this)' to make the action of slideToggle to that particular div-class='seeMore'

Example HTML:
  1. <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "">
    <html xmlns="">
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
    <title>COMPANY NAME</title>
    <link href="cssFinal.css" rel="stylesheet" type="text/css" />
    <link href="productListFinal.css" rel="stylesheet" type="text/css" />
    <script src="jquery-1.5.1.min.js" type="text/javascript" charset="utf-8"></script>
    <script src="javaScriptTest.js" type="text/javascript" charset="utf-8"></script>

    <!--inicio de parentbox-->
    <div class="parentbox">
    <!--inicio de content-->
      <div class="content">
    <!--inicio de categoria01-->
          <div class="productListContainer">
          <div class="test" id="ventiladoresRespiradores">
             <h2>PRINCIPAL CATEGORY <span class="plusCategory">(+)</span></h2></div>
          <div class="categoryListContainer">
    <!--inicio de producto01-->
            <div class="productItemContainer">       
            <h3>VENTILATOR A</h3>
            <p>COMPANY A<br />
            <a href="#">WWW.COMPANYA.COM</a></p>
            <div class="seeMoreContainer">
                <div class="seeMore">+
            <div class="productToHide">
            <div class="productImg">
                   <img src="imgProductNew/0001.jpg" width="200" height="164" class="align-left">
            <div class="productDescription">
                <li>some text</li>

Here is my jQuery code:
  1. $(document).ready(function(){
  2. $('.productToHide').hide();
  3.     $('.seeMore').click(function(){
  4.         $(this).parents('.seeMoreContainer').next().slideToggle(1000,function(){
  5.             if($(this).parents('.seeMoreContainer').next().is(':visible')){
  6.             $('.seeMore').html('-');
  7.             } else {
  8.                 $('.seeMore').html('+');
  9.             }           
  10.             });           
  11.         });
  12. });