CGP 36216 hydrochloride

CGP 36216 hydrochloride is a potent and selective antagonist of GABAB receptors with IC50 value of 43 µM.

GABAB receptors (GABABR) are metabotropic transmembrane receptors for gamma-aminobutyric acid (GABA) and are linked through G-proteins to potassium channels. Expression of GABAB receptors are found in the central as well as in the autonomic division of the peripheral nervous system. GABAB receptors play a key role in regulating membrane excitability and synaptic transmission in the brain.

In rat neocortical preparations maintained in Mg2+-free Krebs medium, CGP 36216 acts as antagonism of baclofen-induced suppression of spontaneous discharges in a concentration-dependent manner. However, CGP 36216, up to 1 mM, was ineffective in antagonising baclofen-induced hyperpolarisations, mediated through gamma-aminobutyric acid (B) GABAB postsynaptic receptors 1.

In electrically stimulated brain slices preloaded with [3H] GABA, CGP 36216 increased the release of [3H] GABA, that was reversed by baclofen. While CGP 36216 is ineffective at GABAB postsynaptic receptors, it is appreciably more active at presynaptic receptors1.

Reference:
1.   Ong J, Bexis S, Marino V, et al. CGP 36216 is a selective antagonist at GABA(B) presynaptic receptors in rat brain. European journal of pharmacology. 2001;415(2-3):191-195.

CGP 36216 is a selective antagonist at GABA(B) presynaptic receptors in rat brain.[Pubmed:11274998]

Eur J Pharmacol. 2001 Mar;415(2-3):191-5.

In rat neocortical preparations maintained in Mg(2+)-free Krebs medium, baclofen depressed the frequency of spontaneous discharges in a concentration-dependent manner (EC(50) = 6 microM), sensitive to (3-aminopropyl)ethylphosphinic acid (CGP 36216) (100, 300 and 500 microM) (pA(2) = 3.9 +/- 0.1). By contrast, CGP 36216, up to 1 mM, was ineffective in antagonising baclofen-induced hyperpolarisations, mediated through gamma-aminobutyric acid(B) (GABA(B)) postsynaptic receptors. In electrically stimulated brain slices preloaded with [3H]GABA, CGP 36216 increased [3H]GABA release (IC(50) = 43 microM), which was reversed by baclofen (20 microM). While CGP 36216 is ineffective at GABA(B) postsynaptic receptors, it is appreciably more active at presynaptic receptors.

Phosphinic acid analogues of GABA. 2. Selective, orally active GABAB antagonists.[Pubmed:7650685]

J Med Chem. 1995 Aug 18;38(17):3313-31.

In 1987, 25 years after the synthesis of the potent and selective GABAB agonist baclofen (1), Kerr et al. described the first GABAB antagonist phaclofen 2. However, phaclofen and structurally similar derivatives 3-5 did not cross the blood-brain barrier and hence were inactive in vivo as central nervous system agents. As a consequence, the therapeutic potential of GABAB antagonists remained unclear. In exploring GABA and baclofen derivatives by replacing the carboxylic acid residue with various phosphinic acid groups, we discovered more potent and water soluble GABAB antagonists. Electrophysiological experiments in vivo demonstrated that some of the new compounds were capable of penetrating the blood-brain barrier after oral administration. Neurotransmitter release experiments showed that they interacted with several presynaptic GABAB receptor subtypes, enhancing the release of GABA, glutamate, aspartate, and somatostatin. The new GABAB antagonists interacted also with postsynaptic GABAB receptors, as they blocked late inhibitory postsynaptic potentials. They facilitated the induction of long-term potentiation in vitro and in vivo, suggesting potential cognition enhancing effects. Fifteen compounds were investigated in various memory and learning paradigms in rodents. Although several compounds were found to be active, only 10 reversed the age-related deficits of old rats in a multiple-trial one-way active avoidance test after chronic treatment. The cognition facilitating effects of 10 were confirmed in learning experiments in Rhesus monkeys. The novel GABAB antagonists showed also protective effects in various animal models of absence epilepsy.