2. Possible! This would work fine , however, no such system exists at present (December 2006).
3. Possible. Protein will be expressed in insect cells prior to cell death induced by viral budding. However, glycosylation forms typical of insect cells might not be sufficient for mammalian receptor function. Also, Insect cells might not be the most appropriate system, since some of the components involved in the happiness cascade may not be present in insect cells.
4. Possible. This will be the system of choice for screening the most effective compounds binding the receptor. However if you are interested in regulation, MDCK cells may not be ideal, since some of the regulatory components of the happiness cascade may not be normally expressed in kidney cells.
5. Possible. Neuronal cultures may be tedious to manipulate, but are most appropriate if you wish to study the regulation of the happiness cascade.
6. Wrong. Mammalian cells will express large quantities of the receptor, which is good for purification of proteins. However, expression of a toxic protein should be moderate, to prevent rapid and excessive cell death.