**Acknowledgements**

The following people are acknowledged for their support and supervision rendered to me during my study period:

Professor Emmanuel Udo Etuk (Department of Pharmacology, Usmanu Danfodio University, Sokoto, Nigeria); Professor Shaibu Oricha Bello (Department of Pharmacology, Usmanu Danfodio University, Sokoto, Nigeria); and Professor Sanusi Wara Hassan (Department of Biochemistry, Usmanu Danfodio University, Sokoto, Nigeria).
