Selective D1 agonism but not D2 antagonism is reflected in cAMP and cGMP levels in rat CSF.

Cyclic adenosine 3'5'-monophosphate (cAMP) and cyclic guanosine 3'5'-monophosphate (cGMP) serve as second messengers in several cellular pathways within the central nervous system. In various neurological and psychiatric disorders with known deficits in neurotransmission function, CSF levels of cAMP and/or cGMP in patients were studied. Very little information is currently available on cAMP and cGMP levels in CSF of animals. Moreover, this is the first study on the effects of pharmacological treatment on cAMP and cGMP levels in rat CSF. Effect of systemic treatment with a D1 receptor agonist SKF82958 and a D2 receptor antagonist haloperidol on cAMP and cGMP levels, as well as baseline cAMP and cGMP levels in CSF of rats was determined. A significantly increased cAMP and cGMP level in cisternal CSF of rats systemically treated with the D1 receptor agonist SKF82958 was observed, while when treated with the D2 antagonist haloperidol, no effect on cAMP and only a slight decrease of cGMP was observed after treatment with the highest dose. Determining cAMP and/or cGMP in CSF of experimental animals can serve as a useful tool to study neural processes affected by disease and treatment.

Investigating association between behavior, corticosterone, heart rate, and blood pressure in rats using surrogate marker evaluation methodology.

The drug development process involves identifying a compound and assessing its merit through rigorous pre-clinical and clinical trials. The pre-clinical stage is designed to assess the chemical properties of the new drug, as well as to determine the steps for synthesis and purification. In this stage of drug development, circumstances might dictate the use of alternative endpoints than the originally anticipated clinically relevant endpoint. In this regard, identification and evaluation of surrogate endpoints is of paramount importance. The validation methods make it possible to quantify degrees of association between the clinically relevant endpoint, also termed the true endpoint, and the alternative, surrogate endpoint. In this paper, we adapt the surrogate marker evaluation methodology of Alonso et al. (2003); (2006), developed for the case of two longitudinal outcomes, to the situation where either a longitudinal surrogate and cross sectional true endpoint is recorded, or vice versa. The work is motivated by a preclinical experiment conducted to assess association between corticosterone (CORT), heart rate, and blood pressure in rats, the data from which are then subjected to analysis. It was found that there is a weak relationship between CORT and behavior, and between CORT on the one hand and heart rate and blood pressure on the other hand, but a reasonably high degree of association was registered between heart rate and behavior.