Exhibit
4.1




FIRST
SUPPLEMENTAL INDENTURE




Dated as
of May 19, 2008




THIS
FIRST SUPPLEMENTAL INDENTURE to the Indenture referred to below is dated as of
May 19, 2008 (this “First Supplemental Indenture”) among AMEREN CORPORATION, a
Missouri corporation (the “Company”), THE BANK OF NEW YORK, a New York banking
corporation (the “Resigning Trustee”) and THE BANK OF NEW YORK TRUST
COMPANY, N.A., a national banking association, as successor trustee to The Bank
of New York (the “Successor Trustee”).




The
Company and the Resigning Trustee are parties to an Indenture, dated as of
December 1, 2001 (the “Indenture”).




Pursuant
to Section 13.01(a)(2) of the Indenture, the Company, when authorized by Board
Resolution, and the Resigning Trustee may enter into an indenture supplemental
to the Indenture to change or eliminate any of the provisions of this Indenture,
provided that any such change or elimination shall become effective only when
there is no Note outstanding created prior to the execution of such supplemental
indenture which is entitled to the benefit of such provision or such change or
elimination is applicable only to Notes issued after the effective date of such
change or elimination.




No Notes
are Outstanding as of the date hereof.




The
Company has directed the Resigning Trustee to execute and deliver this First
Supplemental Indenture in accordance with the terms of the
Indenture.




In
consideration of the foregoing premises, the parties mutually agree as
follows:




ARTICLE
I




DEFINITIONS




Section
1.1  Definitions .  Except
as otherwise defined herein, capitalized terms defined in the Indenture are used
herein as therein defined.




ARTICLE
II




AMENDMENT TO
INDENTURE




Section
2.1  Amendment to
Indenture .  On
the date hereof, Section 9.09 of the Indenture is hereby amended in its entirety
to read as follows:




“There
shall at all times be a Trustee hereunder which Trustee shall at all times be a
corporation organized and doing business under the laws of the United States or
any State thereof or of the District of Columbia having a combined capital and
surplus of at least $50,000,000 and which is authorized under such laws to
exercise corporate trust powers and is subject to supervision or examination by
Federal or State authorities.  If such corporation publishes reports
of condition at least annually, pursuant to law or to the requirements of the
aforesaid authority, then for the purposes of this Section 9.09, the combined
capital and surplus shall be deemed to be as set forth in its most recent report
of condition so published.  No obligor upon the Notes or Person
directly or indirectly controlling, controlled by, or under common control with
such obligor shall serve as Trustee.  If at any time the Trustee shall
cease to be eligible in











accordance
with this Section 9.09, the Trustee shall resign immediately in the manner and
with the effect specified in Section 9.10 hereof.”




Section
2.2  Receipt by
Trustee .  In
accordance with Section 13.05 of the Indenture, the parties acknowledge that the
Resigning Trustee has received an Officers’ Certificate and an Opinion of
Counsel as conclusive evidence that this First Supplemental Indenture complies
with the requirements of Article XIII of the Indenture.




ARTICLE
III




RESIGNATION OF RESIGNING
TRUSTEE AND APPOINTMENT OF SUCCESSOR TRUSTEE




Section
3.1  Resignation of Resigning
Trustee .  In
accordance with Section 9.10(a) of the Indenture, by executing this First
Supplemental Indenture, (i) Resigning Trustee provides written notice of its
resignation, (ii) Company acknowledges receipt of such notice and (iii)
Company accepts the resignation of Resigning Trustee, effective May 20,
2008.




Section
3.2  Resigning Trustee’s
Assignment to Successor Trustee .  Resigning
Trustee hereby assigns, transfers, delivers and confirms to Successor Trustee
all right, title and interest of Resigning Trustee in and to the trust under the
Indenture and all the rights, powers, duties, protections, benefits, immunities,
indemnities and obligations of the Trustee under the
Indenture.  Resigning Trustee shall execute and deliver such further
instruments and shall do such other things as Successor Trustee may reasonably
require so as to more fully and certainly vest and confirm in Successor Trustee
all the rights, powers, duties, protections, benefits, immunities, indemnities
and obligations hereby assigned, transferred, delivered and confirmed to
Successor Trustee.




Section
3.3  Appointment of Successor
Trustee .  In
accordance with Section 9.11(a) of the Indenture, the Company appoints Successor
Trustee as Trustee, effective May 20, 2008, pursuant to a Board Resolution, and
hereby vests Successor Trustee with, all the rights, powers, duties,
protections, benefits, immunities, indemnities and obligations of Resigning
Trustee under the Indenture with like effect as if originally named as
Trustee.




Section
3.4  Acceptance by Successor
Trustee .  In
accordance with Section 9.12(a) of the Indenture, by executing this First
Supplemental Indenture, Successor Trustee executes, acknowledges and delivers to
the Company and the Resigning Trustee its acceptance of (i) its appointment as
Trustee pursuant to Section 3.3 of this First Supplemental Indenture and (ii)
the rights, powers, duties, protections, benefits, immunities, indemnities and
obligations of Resigning Trustee as Trustee, upon the terms and conditions set
forth therein, with like effect as if originally named as Trustee under the
Indenture.




Section
3.5  Corporate Trust Office of
Successor Trustee .  References
in the Indenture to the “Corporate Trust Office of the Trustee,” or other
similar terms, shall be deemed to refer to a principal office of the Successor
Trustee, which is presently located at 911 Washington Avenue, St. Louis,
Missouri 63101.




ARTICLE
IV




REPRESENTATIONS




Section
4.1  Representations of the
Resigning Trustee .  Resigning
Trustee hereby represents and warrants to Successor Trustee that:




(a)
            Each
      person who authenticated the Notes was duly elected, qualified and acting
      as an officer of Resigning Trustee and empowered to authenticate the Notes
      at the respective times of such authentication and the signature of such
      person or persons appearing on such Notes is each such person’s genuine
      signature;






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(b)
            This
      First Supplemental Indenture has been duly authorized, executed and
      delivered on behalf of Resigning Trustee and constitutes its legal, valid
      and binding obligation, enforceable in accordance with its terms;
      and




(c)
            To
      the best knowledge of responsible officers of the Resigning Trustee’s
      corporate trust department, no event has occurred and is continuing which
      is, or after notice or lapse of time would become, an Event of Default
      under Section 8.01 of the
Indenture.




Section
4.2  Representations of the
Company .  Company
hereby represents and warrants to the Successor Trustee and to the Resigning
Trustee that:




(a)
            There
      is no action, suit or proceeding pending or, to the best of the Company’s
      knowledge, threatened against the Company before any court or any
      governmental authority arising out of any act or omission of the Company
      under the Indenture;




(b)
            This
      First Supplemental Indenture has been duly authorized, executed and
      delivered on behalf of the Company and constitutes its legal, valid and
      binding obligation, enforceable in accordance with its terms;
      and




(c)
            All
      conditions precedent relating to the appointment of Successor Trustee as
      successor Trustee under the Indenture have been complied with by the
      Company.




Section
4.3  Representations of the
Successor Trustee .  Successor
Trustee hereby represents and warrants to the Resigning Trustee and to the
Company that:




(a)
            Successor
      Trustee is eligible under the provisions of Section 9.09 of the Indenture
      to act as Trustee under the Indenture;
and




(b)
            This
      First Supplemental Indenture has been duly authorized, executed and
      delivered on behalf of Successor Trustee and constitutes its legal, valid
      and binding obligation, enforceable in accordance with its
      terms.




ARTICLE
V




MISCELLANEOUS




Section
5.1  Parties .  Nothing
expressed or mentioned herein is intended or shall be construed to give any
Person, other than the Company, the Resigning Trustee and the Successor Trustee,
any legal or equitable right, remedy or claim under or in respect of this First
Supplemental Indenture or the Indenture or any provision herein or therein
contained.




Section
5.2  Governing
Law .  This
First Supplemental Indenture shall be governed by and deemed to be a contract
under, and construed in accordance with, the laws of the State of New York, and
for all purposes shall be construed in accordance with the laws of said State
without regard to conflicts of law principles thereof.




Section
5.3  Ratification of Indenture;
First Supplemental Indenture Part of Indenture .  Except
as expressly supplemented hereby, the Indenture is in all respects ratified and
confirmed and all the terms, conditions, and provisions thereof shall remain in
full force and effect.  This First Supplemental Indenture shall form a
part of the Indenture for all purposes, and every Holder of Notes heretofore or
hereafter authenticated and delivered shall be bound hereby.  The
Trustee makes no representation or warranty as to the validity or sufficiency of
this First Supplemental Indenture.




Section
5.4  Resigning Trustee
Acknowledgment .  Resigning
Trustee hereby acknowledges payment or provision for payment in full by the
Company of compensation for all services rendered by Resigning Trustee






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under
Section 9.06 of the Indenture and reimbursement in full by the Company of the
expenses, disbursements and advances incurred or made by Resigning Trustee in
accordance with the provisions of the Indenture.  Resigning Trustee
acknowledges that it relinquishes any lien it may have upon all property or
funds held or collected by it to secure any amounts due it pursuant to the
provisions of Section 9.06 of the Indenture.  The Company acknowledges
its obligation set forth in Section 9.06 of the Indenture to indemnify Resigning
Trustee for, and to hold Resigning Trustee harmless against, any loss, liability
and expense incurred without negligence or bad faith on the part of the
Resigning Trustee and arising out of or in connection with the acceptance or
administration of the trust evidenced by the Indenture (which obligation shall
survive the execution hereof).




Section
5.5  Multiple
Originals .  The
parties may sign any number of copies of this First Supplemental
Indenture.  Each signed copy shall be an original, but all of them
shall represent the same agreement.




Section
5.6  Headings .  The
headings of the Articles and Sections of this First Supplemental Indenture have
been inserted for convenience of reference only, are not intended to be
considered a part hereof and shall not modify or restrict any of the terms or
provisions hereof.






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IN
WITNESS WHEREOF, the parties hereto have caused this First Supplemental
Indenture to be duly executed as of the date first written above.




Ameren
      CorporationBy:
            /s/
      Warner L.
      BaxterName:  Warner
      L. BaxterTitle:     Executive
      Vice President and
              Chief
      Financial OfficerThe
      Bank of New York,as
      Resigning TrusteeBy:
            /s/
      Pat
      SantivasciName:  Pat
      SantivasciTitle:    Vice
      PresidentThe
      Bank of New York Trust Company, N.A.,as
      Successor TrusteeBy:
            /s/
      Kent
      SchroederName:  Kent
      SchroederTitle:    Vice
      President