I am trying to grab the current value of a drop down list with Prototype and passing it along using :with like this

<%= link_to_remote "today", :update => "choices",
    :url => { :action => "check_availability" } , 
    :with => "'practitioner='+$F('practitioner')&'clinic='+$F('clinic')&'when=today'",
    :loading => "spinner.show(); $('submit').disable();",
    :complete   => "spinner.hide(); $('submit').enable();" %>

However, this is not working as expected. I am unable to access parameters in the controller as the link_to_remote helper is sending parameters like this:

Parameters: {"succ"=>"function () {\n    return this + 1;\n}", "action"=>"check_availability", "round"=>"function () {\n    return __method.apply(null, [this].concat($A(arguments)));\n}", "ceil"=>"function () {\n    return __method.apply(null, [this].concat($A(arguments)));\n}", "floor"=>"function () {\n    return __method.apply(null, [this].concat($A(arguments)));\n}", "times"=>"function (iterator, context) {\n    $R(0, this, true).each(iterator, context);\n    return this;\n}", "toPaddedString"=>"function (length, radix) {\n    var string = this.toString(radix || 10);\n    return \"0\".times(length - string.length) + string;\n}", "toColorPart"=>"function () {\n    return this.toPaddedString(2, 16);\n}", "abs"=>"function () {\n    return __method.apply(null, [this].concat($A(arguments)));\n}", "controller"=>"main"}

Where am I going wrong? Is there a better way to do this?