5-HT1C/5-HT2 Receptor

The inhibitory effects of microiontophoretically-applied serotonin (5-HT) and 6-chloro-2[1-piperazinyl]pyrazine (MK-212) were examined on spontaneously firing somatosensory cerebral cortical neurons and dorsal raphe neurons in rats anesthetized with chloral hydrate. On cortical neurons, MK-212 caused only weak and variable inhibition of extracellularly recorded neuronal activity, compared to the effects of 5-HT. However, on raphe cells, MK-212 exerted potent inhibitory effects, equivalent to those observed with 5-HT. In contrast to the inhibitory actions of D-lysergic acid diethylamide (LSD) and 5-HT at presumed 5-HT autoreceptors, MK-212 did not affect the in vitro release of [3H]5-HT from slices of rat hypothalamus stimulated by methiothepin. These findings, coupled with previously reported behavioral, biochemical and electrophysiological effects of MK-212 may indicate that this novel serotonergic agonist uniquely discriminates between subsets of serotonergic receptors in the CNS.[3]

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Both quipazine and 6-chloro-2-[1-piperazinyl]-pyrazine (MK-212) stimulated phosphoinositide hydrolysis in cerebral cortex, and these effects were blocked by ketanserin. The maximum responses to these agonists were 80% of the maximum response to 5-HT. m-Trifluoromethylphenylpiperazine (TFMPP), m-chlorophenylpiperazine (MCPP) and 1-(1-naphthyl)-piperazine (1-NP) did not stimulate phosphoinositide hydrolysis in cerebral cortex at concentrations that blocked the effect of 5-HT. In the choroid plexus, TFMPP and MCPP, as well as MK-212 and quipazine, increased phosphoinositide hydrolysis and mianserin blocked these effects. MK-212 had an efficacy which was equal to that of 5-HT, whereas quipazine, MCPP and TFMPP were partial agonists in the choroid plexus. 1-NP did not stimulate phosphoinositide hydrolysis in choroid plexus but completely blocked the effect 5-HT. On the basis of these data, we conclude that quipazine and MK-212 are partial agonists at 5-HT-2 receptors in cerebral cortex, whereas 1-NP, TFMPP and MCPP are pure antagonists of the cortical 5-HT-2 receptor. However, TFMPP and MCPP as well as quipazine and MK-212 are agonists at the 5-HT-1c receptor, while 1-NP is a pure antagonist of the 5-HT-1c receptor in choroid plexus. [2]

The effects of 6-chloro-2-(1-piperaziny)pyrazine (MK-212), a centrally acting 5-HT1C/5-HT2 agonist, on body temperature and behavior were assessed using a single-blind cross-over design in 23 schizophrenic patients and 22 normal controls. Body temperature was assessed before drug administration and at 30-min intervals for 3 hr. Each subject was administered placebo or MK-212. MK-212 significantly elevated temperature in normal controls. There was no overall MK-212-induced increase in temperature compared to placebo in the schizophrenic patients; however, 13 of 23 (56.5%) patients had a larger increase in temperature after MK-212 than placebo, 3 of 23 (13.1%) had no change, whereas the temperature change after placebo was greater than after MK-212 in 7 of 23 (30.4%) patients. MK-212 produced significant increases in nausea, feeling strange, and arousal but these effects did not differ between groups. These results are consistent with decreased 5-HT2 receptor responsivity in some patients with schizophrenia. [1]

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Prepulse inhibition (PPI) is disrupted in many neuropsychiatric diseases. Molecules such as 5-HT2C receptor agonists alleviate PPI deficits in rodents; however, the precise mechanisms and critical regions of the brain responsible for the reversal effect of these agonists remain inconclusive. The present study aimed to investigate the areas of the brain critical for the reversal effect of 5-HT2C receptor agonists on PPI deficits in mice. The results showed that systemic administration of the 5-HT2C receptor agonist MK212 did not affect normal PPI behavior, but reversed the PPI deficits induced by the N-methyl d-aspartate receptor antagonist MK801 in mice. In addition, the 5-HT2C receptor antagonist SB242084 had no effect on PPI behavior despite MK801 treatment. Moreover, local infusion of MK212 into the medial prefrontal cortex and ventral hippocampus, excluding the nucleus accumbens or ventral tegmental area, rescued the PPI deficits induced by MK801. These data suggest that the medial prefrontal cortex and ventral hippocampus are critical brain areas responsible for the reversal of 5-HT2C agonists on PPI deficits. The results will contribute to our current knowledge on the molecular and neural mechanisms underlying the antipsychotic effects of 5-HT2C receptor agonists, especially the neural circuits modulated by 5-HT2C receptor activity. [4]

MK212 and MK801 were dissolved in 0.9% saline solution. [4]
Experiment 1: Effects of systemic administration of MK212 on normal PPI[4]
To investigate whether the systemic administration of 5-HT2C receptor agonists influences normal PPI behavior, the mice were randomly assigned to one of the following treatment groups: saline, MK212 (0.5 mg/kg), or MK212 (1.0 mg/kg). Twenty minutes before the formal PPI tests, saline and two doses of MK212 were intraperitoneally administered, and then the mice were placed in the SR-LAB™ startle response system to test their PPI.

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Experiment 2: Effects of systemic administration of MK212 on PPI deficits[4]
We then examined whether the systemic administration of MK212 can reverse the PPI deficits in mice. The mice were randomly assigned to one of five treatment groups, as shown in Table 1. The doses of the test drugs were chosen based on a literature review (Suryavanshi et al., 2014) and pilot experiments. MK801, an NMDA receptor antagonist, was used to induce PPI deficits. The procedures of the administration of saline and drugs on the formal test days are shown in Table 1. After systemic administration, the mice were placed in the SR-LAB™ startle response system to test their PPI.

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Experiment 4: Investigation of the critical brain regions responsible for the reversal effect of MK212 on PPI deficits[4]
To investigate the critical brain regions responsible for the reversal effects of MK212 on PPI deficits, we infused MK212 into the nucleus accumbens (NAcc), medial prefrontal cortex (mPFC), ventral hippocampus (VH), and ventral tegmental area (VTA) before performing the PPI tests. Briefly, for each target brain region, mice were implanted with guide cannulas, and were then assigned to the saline + saline, MK801 + saline, and MK801 + MK212 treatment groups. On the formal test days, MK212 (0.25 μg/0.25 μl/side) and saline (0.25 μl/side) were locally infused into the target brain regions (NAcc, mPFC, VH, or VTA) at a rate of 0.2 μl/min. The procedures for the administration of saline and drugs are shown in Table 3. The bilateral internal cannulas were kept for an additional 2 min before removal to allow drug diffusion. The mice were returned to their cages after infusion. Afterwards, the mice were then placed in the SR-LAB™ startle response system to test for PPI.

rat LD50 oral 79600 ug/kg United States Patent Document., #4409228

[1]. Effect of the serotonin agonist, MK-212, on body temperature in schizophrenia. Biol Psychiatry. 1992 Mar 1;31(5):460-70.

[2]. Relative efficacies of piperazines at the phosphoinositide hydrolysis-linked serotonergic (5-HT-2 and 5-HT-1c) receptors. J Pharmacol Exp Ther. 1987 Aug;242(2):552-7.

[3]. A comparative electrophysiological and biochemical assessment of serotonin (5-HT) and a novel 5-HT agonist (MK-212) on central serotonergic receptors. Neuropharmacology . 1984 Nov;23(11):1271-7.

[4]. MK212, a 5-hydroxytryptamine 2C receptor agonist, reverses prepulse inhibition deficits in the medial prefrontal cortex and ventral hippocampus. Prog Neuropsychopharmacol Biol Psychiatry . 2022 Mar 8:113:110441.

2-chloro-6-(1-piperazinyl)pyrazine is a N-arylpiperazine.
MK-212 has been used in trials studying the treatment of Alcoholism.

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The present study found that systemic administration of the 5-HT2C receptor agonist MK212 or antagonist SB242084 did not affect normal PPI behavior; however, MK212 reversed the PPI deficits induced by the non-competitive NMDA receptor antagonist MK801. In addition, local infusion of MK212 into the medial prefrontal cortex and ventral hippocampus reversed the PPI deficits induced by MK801. These results contribute to our current knowledge regarding the accurate molecular and neural mechanisms underlying the antipsychotic effects of 5-HT2C receptor agonists.[4]

C8H11CLN4

198.654

103.063

C, 48.37; H, 5.58; Cl, 17.85; N, 28.20

64022-27-1

MK-212 monohydrochloride;61655-58-1

107992

Typically exists as solid at room temperature

1.1±0.1 g/cm3

215.2±23.0 °C at 760 mmHg

83.9±22.6 °C

0.1±0.9 mmHg at 25°C

1.462

-0.15

1

4

1

13

160

0

C1CN(CCN1)C2=CN=CC(=N2)Cl

CJAWPFJGFFNXQI-UHFFFAOYSA-N

InChI=1S/C8H11ClN4/c9-7-5-11-6-8(12-7)13-3-1-10-2-4-13/h5-6,10H,1-4H2

2-chloro-6-piperazin-1-ylpyrazine

MK-212; MK 212; 64022-27-1; 2-Chloro-6-(1-piperazinyl)pyrazine; MK-212; 2-chloro-6-(piperazin-1-yl)pyrazine; 2-chloro-6-piperazin-1-ylpyrazine; MK 212; 6-Chloro-2-(1-piperazinyl)pyrazine; Pyrazine, 2-chloro-6-(1-piperazinyl)-; MK212

2934.99.9001

Powder      -20°C    3 years

4°C     2 years

In solvent   -80°C    6 months

-20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

May dissolve in DMSO (in most cases), if not, try other solvents such as H2O, Ethanol, or DMF with a minute amount of products to avoid loss of samples

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

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Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

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Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

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Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

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Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

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Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

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 (Please use freshly prepared in vivo formulations for optimal results.)