Chemical communication between cells within the body has been long recognized as an integral part of understanding how the human body functions, especially within the central and peripheral nervous system. Electrochemistry at microelectrodes in tissue slices extracted from the body has become a method of choice for probing the release, reuptake, and overall function of chemical messengers. Here, fast-scan cyclic voltammetry (FSCV) and constant potential amperometry at carbon-fiber microelectrodes is used in various different types of tissues such as the adrenal gland and the spinal cord in order to detect and quantify the release of various chemical messengers including epinephrine, norepinephrine, and adenosine. Pharmacological manipulation of these signals allows for further analysis of the origins of these signals as well as their overall function in integral bodily functions. Work performed on the adrenal gland gave new insight into the exocytotic release characteristics of the hormones epinephrine and norepinephrine which had never been carried out in intact tissue. Also, extensive studies on the methods used to probe the release of these hormones were performed, and allowed for the distinction of electrical stimulation of two different cell types, both the neurons which innervate the tissue, and the chromaffin cells which release the neuromodulators detected with this technology. Moving the detection of adenosine by FSCV into lamina II of the spinal cord allowed for determination of enzymatic activity of ectonucleotidases. Furthermore, it provided new proof of adenosine as an antinociceptive neurotransmitter, and gave evidence for an adenosinergic tone in these circuits with the first ever detection of adenosine transientsanywhere in the nervous system. Also, total tissue analysis of various brain regions by high performance liquid chromatography (HPLC) is used to determine fundamental difference or similarities in different strains of animals, animals which have been genetically altered, or animals which have been treated with drugs. Finally, the coating of Ag/AgCl reference electrodes with Nafion for chronic implantation is discussed. These studies use fundamental analytical tools to advance our understanding of the nervous system, and shows new methods of answering long standing biological questions.