Document:

<PAGE>

                                                                     Exhibit 4.5

                               THIRD AMENDMENT TO
                     COMMON STOCK PURCHASE WARRANT AGREEMENT

          This Third Amendment to Common Stock Purchase Warrant Agreement, dated
as of October 9, 2000, is between MURDOCK COMMUNICATIONS CORPORATION, an Iowa
corporation (the "Company") and FIRSTAR BANK, N.A., as Warrant Agent and
successor-in-interest to Firstar Trust Company (the "Warrant Agent").

                                    RECITALS

          A. The Warrant Agent and the Company are parties to a Common Stock
Purchase Warrant Agreement dated as of October 21, 1996 (the "Agreement").

          B. The Warrant Agent and the Company entered into a First Amendment to
Warrant Agreement dated as of September 30, 1999, to, among other things, extend
the "Warrant Expiration Date" to April 21, 2000 and a Second Amendment to
Warrant Agreement dated as of April 14, 2000, to extend the "Warrant Expiration
Date" to October 21, 2000.

          C. The Company and the Warrant Agent deem it desirable to amend the
Agreement to extend the "Warrant Expiration Date" to October 21, 2001.

          D. Pursuant to Section 10 of the Agreement, the Company and the
Warrant Agent may by supplemental agreement make any changes or corrections in
the Agreement that they may deem necessary or desirable and which do not
adversely affect the interests of the holders of Warrant Certificates.

                                   AGREEMENTS

          In consideration of the foregoing and the mutual covenants and
agreements contained herein and in the Agreement, and intending to be legally
bound hereby, the Warrant Agent and the Company hereby agree as follows:

          1. Amendment of Section 1(i). The definition of "Warrant Expiration
Date" in Section 1(i) of the Agreement is hereby amended to read in its entirety
as follows:

               "Warrant Expiration Date" shall mean 5 p.m. (Central Time) on
               October 21, 2001, or if such date shall in the State of Wisconsin
               be a holiday or a day on which banks are authorized to close,
               then 5 p.m. (Central Time) on the next

<PAGE>

               following day which in the State of Wisconsin is not a holiday or
               a day on which banks are authorized to close. Unless exercised
               during the Warrant Exercise Period, the Warrants will
               automatically expire. The Warrants may be called for redemption
               and the expiration date herefor accelerated, on the terms and
               conditions set forth in sections 4(b) and 4(c) of this Agreement.
               If so called for redemption, Warrant Certificate holders shall
               have a period of at least 30 days after the date of the call
               notice within which to exercise the Warrants. However, Warrant
               Certificate holders will receive the redemption price only if
               such certificates are surrendered to the Corporate Office within
               the redemption period (as defined below).

          2. Full Force and Effect. All remaining provisions of the Agreement,
as previously amended, remain unchanged and in full force and effect.

          3. Governing Law. This Amendment shall be governed by and construed in
accordance with the laws of the State of Wisconsin. Section headings in this
Amendment appear for convenience of reference only and shall not be used in any
interpretation of this Amendment.

          4. Binding Effect. This Amendment shall be binding upon and inure to
the benefit of the Company, the Warrant Agent and their respective successors
and assigns, and the Registered Holders from time to time of Warrant
Certificates or any of them. Nothing in this Amendment shall be construed to
confer any right, remedy or claim upon any other person.

          5. Counterparts. This Amendment may be executed in counterparts, which
taken together shall constitute a single document.

     IN WITNESS WHEREOF, the Warrant Agent and the Company have caused this
Amendment to be executed as of the date first written above by their respective
officers thereunto duly authorized.

                                           MURDOCK COMMUNICATIONS CORPORATION

                                           BY /s/ Paul C. Tunink
                                              ----------------------------------
                                                  Paul C. Tunink, Vice President

                                           FIRSTAR BANK, N.A.

                                           BY /s/
                                              ----------------------------------
                                                  Authorized Officer

                                       2<PAGE>

                                                                     Exhibit 4.6

                               FOURTH AMENDMENT TO
                     COMMON STOCK PURCHASE WARRANT AGREEMENT

This Fourth Amendment to Common Stock Purchase Warrant Agreement, dated as of
October X, 2001, is between MURDOCK COMMUNICATIONS CORPORATION, an Iowa
corporation, (the "Company") and FIRSTAR BANK, N.A., as Warrant Agent and
successor-in-interest to Firstar Trust Company (the "Warrant Agent").

                                    RECITALS

     A.   The Warrant Agent and the Company are parties to a Common Stock
          Purchase Warrant Agreement dated as of October 21, 1996 (the
          "Agreement").

     B.   The Warrant Agent and Company entered into a First Amendment to
          Warrant Agreement dated as of September 30, 1999, to, among other
          things, extend the "Warrant Expiration Date" to April 21, 2000, a
          Second Amendment to Warrant Agreement dated as of April 14, 2000, to
          extend the "Warrant Expiration Date" to October 21, 2000 and a Third
          Amendment to Warrant Agreement dated as of October 9, 2000, to extend
          the "Warrant Expiration Date" to October 21, 2001.

     C.   The Company and Warrant Agent deem it desirable to amend the Agreement
          to extend the "Warrant Expiration Date" to October 21, 2002.

     D.   Pursuant to Section 10 of the Agreement, the Company and the Warrant
          Agent may by supplemental agreement make any changes or corrections in
          the Agreement that they may deem necessary or desirable and which do
          not adversely affect the interests of the holders of Warrant
          Certificates.

                                   AGREEMENTS

     In consideration of the foregoing and the mutual covenants and agreements
     contained herein and in the Agreement, and intending to be legally bound
     hereby, the Warrant Agent and Company hereby agree as follows:

     1.   Amendment of Section 1 (i). The definition of "Warrant Expiration
          Date" is Section 1 (i) of the Agreement is hereby amended to read in
          its entirety as follows:

          "Warrant Expiration Date" shall mean 5 p.m. (Central Time) on October
          21, 2002, or if such date shall in the State of Wisconsin be a holiday
          or a day on which banks are authorized to closed, then 5 p.m. (Central
          Time) on the next following day which in the State of Wisconsin is not
          a holiday or a day on which banks are authorized to close. Unless
          exercised during the Warrant Exercise Period, the Warrants will
          automatically expire. The Warrants may be called for redemption and
          the expiration date herefor accelerated, on the terms and conditions
          set forth in sections 4(b) and 4(c) of this Agreement. If so called
          for redemption, Warrant Certificate holders shall have a period of at
          least 30 days after the date of the call notice within which to
          exercise the Warrants. However, Warrant Certificate holders will
          receive the redemption price only if such certificates are surrendered
          to the Corporate Office with the redemption period (as defined below).

     2.   Full Force and Effect. All remaining provisions of the Agreement, as
          previously amended, remain unchanged and in full force and effect.

     3.   Governing Law. This Amendment shall be governed by and construed in
          accordance with the laws of the State of Wisconsin. Section headings
          in this Amendment appear for convenience of reference only and shall
          not be used in any interpretation of this Amendment.

<PAGE>

     4.   Binding Effect. This Amendment shall be binding upon and insure to the
          benefit of the Company, the Warrant Agent and their respective
          successors and assigns, and the Registered Holders from time to time
          of Warrant Certificates or any of them. Nothing in this Amendment
          shall be construed to confer any right, remedy or claim upon any other
          person.

     5.   Counterparts. This Amendment may be executed in counterparts, which
          taken together shall constitute a single document.

     IN WITNESS WHEREOF, the Warrant Agent and the Company have caused this
     Amendment to be executed as of the date first written above by their
     respective officers thereunto duly authorized.

                                           MURDOCK COMMUNICATIONS CORPORATION

                                           BY /s/ Paul C. Tunink
                                              ----------------------------------
                                                  Paul C. Tunink, Vice President

                                           FIRSTAR BANK, N.A.

                                           BY /s/
                                              ----------------------------------
                                                  Authorized Officer<PAGE>

                                                                     Exhibit 4.7

                               FIFTH AMENDMENT TO
                     COMMON STOCK PURCHASE WARRANT AGREEMENT
                              AND JOINDER AGREEMENT

          This Fifth Amendment to Common Stock Purchase Warrant Agreement and
Joinder Agreement, dated as of October 18, 2002, is between MURDOCK
COMMUNICATIONS CORPORATION, an Iowa corporation (the "Company") and
COMPUTERSHARE TRUST COMPANY, INC., as Warrant Agent (the "Warrant Agent").

                                    RECITALS

          A. The Company has entered into a Common Stock Purchase Warrant
Agreement dated as of October 21, 1996, as amended (the "Agreement"), with U.S.
Bank National Association, formerly known as Firstar Trust Company, as warrant
agent (the "Former Warrant Agent"), with respect to 920,000 Common Stock
Purchase Warrants (the "Warrants") issued by the Company on October 21, 1996.

          B. Pursuant to Section 10(f) of the Agreement, the Former Warrant
Agent resigned as warrant agent effective July 9, 2002. Pursuant to Section
10(f) of the Agreement, the Company desires to appoint the Warrant Agent as the
new warrant agent to act on behalf of the Company, and the Warrant Agent is
willing to so act, in connection with the issuance, registration, transfer and
exchange of certificates representing the Warrants and the exercise of the
Warrants.

          C. The Company and the Warrant Agent deem it desirable to amend the
Agreement to extend the "Warrant Expiration Date" from October 21, 2002 to
October 21, 2003.

          D. Pursuant to Section 10 of the Agreement, the Company and the
Warrant Agent may by supplemental agreement make any changes or corrections in
the Agreement that they may deem necessary or desirable and which do not
adversely affect the interests of the holders of Warrant Certificates

                                   AGREEMENTS

          In consideration of the foregoing and the mutual covenants and
agreements contained herein and in the Agreement, and intending to be

<PAGE>

legally bound hereby, the Warrant Agent and the Company hereby agree as follows:

          1. Joinder of the Warrant Agent. The Warrant Agent hereby accepts its
appointment to act as agent for the Company as provided in the Agreement. The
Warrant Agent agrees to the terms and conditions of the Agreement and
acknowledges that, by the execution hereof by the Warrant Agent and the Company,
the Warrant Agent shall be bound by the Agreement as the "Warrant Agent"
thereunder.

          2. Amendment of Section 1(i). The definition of "Warrant Expiration
Date" in Section 1(i) of the Agreement is hereby amended to read in its entirety
as follows:

               "Warrant Expiration Date" shall mean 5 p.m. (Central Time) on
               October 21, 2003, or if such date shall in the State of Wisconsin
               be a holiday or a day on which banks are authorized to close,
               then 5 p.m. (Central Time) on the next following day which in the
               State of Wisconsin is not a holiday or a day on which banks are
               authorized to close. Unless exercised during the Warrant Exercise
               Period, the Warrants will automatically expire. The Warrants may
               be called for redemption and the expiration date herefor
               accelerated, on the terms and conditions set forth in sections
               4(b) and 4(c) of this Agreement. If so called for redemption,
               Warrant Certificate holders shall have a period of at least 30
               days after the date of the call notice within which to exercise
               the Warrants. However, Warrant Certificate holders will receive
               the redemption price only if such certificates are surrendered to
               the Corporate Office within the redemption period (as defined
               below).

          3. Full Force and Effect. All remaining provisions of the Agreement
remain unchanged and in full force and effect.

          4. Governing Law. This Amendment shall be governed by and construed in
accordance with the laws of the State of Wisconsin. Section headings in this
Amendment appear for convenience of reference only and shall not be used in any
interpretation of this Amendment.

                                       2

<PAGE>

          5. Binding Effect. This Amendment shall be binding upon and inure to
the benefit of the Company, the Warrant Agent and their respective successors
and assigns, and the Registered Holders from time to time of Warrant
Certificates or any of them. Nothing in this Amendment shall be construed to
confer any right, remedy or claim upon any other person.

          6. Counterparts. This Amendment may be executed in counterparts, which
taken together shall constitute a single document.

     IN WITNESS WHEREOF, the Warrant Agent and the Company have caused this
Amendment to be executed as of the date first written above by their respective
officers thereunto duly authorized.

                                            MURDOCK COMMUNICATIONS CORPORATION

                                            BY  /s/ Eugene I. Davis
                                               ---------------------------------
                                                    Eugene I. Davis
                                                    Chief Executive Officer

                                            COMPUTERSHARE TRUST COMPANY, INC.

                                            BY  /s/
                                               ---------------------------------
                                                    Authorized Officer

                                       3

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00047-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00047-of-00352.parquet"}], [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00047-of-00352.parquet"}]]