Table 2. E_max and Log EC₅₀ Values of WIN55,212-2 and THC-stimulated [³⁵S]GTPγS Binding in Mouse Cortico-hippocampal Membranes.

	EC50	Emax
	−log, M	% of stimulation
Vehicle
WIN	−6.005±0.09	321±11
WIN+CPA	−5.654±0.16	254±13a
THC	−7.389±0.37	167±11
Chronic caffeine
WIN	−6.006±0.08	269±8a
WIN+CPA	−6.035±0.10	252±8a
THC	−7.660±0.56	135±8a

Note that the E_max, but not the EC₅₀, of WIN55,212-2 (WIN) and THC-stimulated [³⁵S]GTPγS binding was significantly decreased in the chronic caffeine group (3 mg/kg/day, for 22 days), compared with control (vehicle-treated) mice. The A₁ receptor agonist, CPA (100 nM), reduced the E_max of WIN55,212-2 in control mice, but did not further decrease the E_max of WIN55,212-2 in chronic caffeine-treated mice. The EC₅₀ of WIN in either vehicle or chronic caffeine groups was not significantly affected by CPA (p>0.05, extra sum-of-squares F test). Data represent mean values±SEM (n=4–5) obtained from nonlinear regression analyses of the data shown in Figure 8.

^ap<0.05, versus corresponding control, calculated using the extra sum-of-squares F test.