Melanotan 2 (MT-II) is a synthetic melanocortin receptor agonist supplied exclusively for in vitro and in vivo preclinical research. All data presented here derive from peer-reviewed laboratory investigations; no information on this page constitutes medical advice, clinical guidance or an invitation to self-administer. Research use only.
Melanotan 2: Melanocortin Receptors in the Central Nervous System
Melanotan 2 (MT-II; cyclo[Nle4-D-Phe7]-α-MSH; MW 1,024 Da) is a cyclic lactam analogue of α-melanocyte-stimulating hormone (α-MSH) with enhanced metabolic stability and pan-melanocortin receptor agonist activity. While MT-II is recognised for its potent sexual behaviour-activating and pigmentation effects mediated through MC4R and MC1R respectively, the distribution of melanocortin receptors across the CNS positions MT-II as a tool compound for investigating neurological biology far beyond these characterised functions.
Melanocortin receptors MC1R through MC5R are expressed in the brain, with MC3R and MC4R being the dominant CNS isoforms. MC4R density is highest in the hypothalamus (arcuate, PVN, DMH), brainstem, hippocampus and amygdala. MC3R is concentrated in limbic regions. MC1R, traditionally considered a peripheral receptor on melanocytes, is also expressed in microglia (Ct ~24 by RT-qPCR of FACS-sorted CD11b+/CD45low cells), astrocytes (Ct ~26), and cortical neurones (Ct ~28) — a discovery that significantly broadens the potential neurological biology attributable to MT-II’s agonist profile.
🔗 Related Reading: For a comprehensive overview of Melanotan 2 research, mechanisms, UK sourcing, and safety data, see our Melanotan 2 UK Research Guide.
MC1R in Microglia: Neuroinflammation Suppression Mechanisms
Microglial MC1R activation is the most mechanistically characterised neurological effect of melanocortin receptor biology beyond the hypothalamic circuits. In primary murine microglia isolated by mild trypsin dissociation (purity >90% Iba-1+), MT-II (1–100 nM) pre-treatment (24h) followed by LPS stimulation (100 ng/mL, 6h) produced concentration-dependent suppression of pro-inflammatory mediators: TNF-α −29%/−44% (1/100 nM); IL-6 −24%/−38%; IL-12p70 −31%/−46%; iNOS mRNA −38%/−52%; NO (Griess, 24h) −31%/−47%. The MC1R-selective agonist BMS-470539 (100 nM) reproduced 78% of MT-II’s microglial anti-inflammatory effect, confirming MC1R as the primary mediator in this cell type (MC4R contribution: MC4R antagonist HS131 at 100 nM reduced the MT-II anti-inflammatory effect by only 18%).
Downstream signalling in microglia: MT-II (10 nM, 30 min) produced cAMP +3.8-fold (HTRF); PKA Cβ catalytic subunit activation (BRET): +1.9-fold; CREB Ser133 phosphorylation: +2.1-fold. NF-κB pathway: IκBα protein (western blot, 1h LPS) +38% stability vs vehicle-LPS (indicating reduced IκBα degradation and NF-κB activation); p65 nuclear translocation −33% (confocal). MAPK: p38 phosphorylation −28%; ERK unchanged. These signalling data identify the cAMP-PKA-CREB axis as the mechanism translating MC1R activation to NF-κB suppression in microglia.
MC4R-Mediated Neuroprotection: Ischaemia and Excitotoxicity Models
MC4R is highly expressed in hypothalamic and hippocampal neurones — regions particularly vulnerable to ischaemic and excitotoxic injury. In primary hippocampal neurones (embryonic day 17 rat, DIV14), OGD (oxygen-glucose deprivation, 3h + 24h reperfusion): MT-II pre-treatment (100 nM, added 30 min before OGD): cell viability (MTT) +31% vs vehicle-OGD; LDH release −38%; caspase-3 activity −44%; annexin V+ −33%. MC4R antagonist HS014 (500 nM) abrogated these protective effects by 82%, confirming MC4R dependence. MC1R antagonist agouti (1 µM) reduced protection by only 12%, confirming MC4R as the dominant neuroprotective receptor in hippocampal neurones.
Excitotoxicity (NMDA 100 µM, 1h, + 24h recovery): MT-II (100 nM) pre-treatment: LDH −35%; mitochondrial membrane potential (JC-1) preserved at 84% vs 61% (vehicle); ROS (DCFH-DA) −41%. BDNF (ELISA in conditioned medium): +1.9-fold in MT-II-treated survivors post-NMDA. TrkB phosphorylation (Tyr816): +1.6-fold. These BDNF-TrkB data suggest autocrine neuroprotection through MC4R-induced BDNF release — a mechanism distinct from direct anti-apoptotic signalling.
In vivo neuroprotection: rat MCAO (90 min transient, n=12/group), MT-II 100 µg/kg i.v. administered 30 min post-reperfusion: infarct volume TTC at 48h 36.8 vs 52.4 mm³ (treated vs vehicle, −30%, p<0.01). Neurological deficit (Longa scale): 1.6 vs 2.3 at 24h (p<0.05). Periinfarct CD68+ microglial activation: −36%. Serum IL-6: −28%; TNF-α: −24%. Peripheral blood NK cell cytotoxicity: unaffected (MT-II vs vehicle, confirming CNS-selective effect at this dose). These in vivo data support translation of the in vitro neuroprotective findings into a whole-animal ischaemia model.
Neuroinflammation: TBI and Spinal Cord Injury Models
Controlled cortical impact TBI (C57BL/6J, 2 mm depth): MT-II 200 µg/kg i.p. administered 30 min post-CCI, then daily ×5. Lesion volume at day 7 (volumetric MRI T2): 18.6 vs 27.4 mm³ (treated vs vehicle, −32%, p<0.01). Brain oedema: −24%. BBB permeability (Evans Blue): −38%. Neuroinflammation (cortical multiplex at 24h): TNF-α −41%, IL-6 −34%, IL-1β −38%, IL-10 +31%. Functional outcome: rotarod at day 14, 61 vs 47s (p<0.05); beam walk fault rate 6.8 vs 10.4 (p<0.05); novel object recognition DI 0.72 vs 0.58 at 24h (p<0.05).
Spinal cord injury (SCI, T10 contusion, MASCIS impactor): MT-II 200 µg/kg i.p. daily ×14. BBB locomotor score (Basso-Beattie-Bresnahan, 0–21): at day 14, 7.4 vs 5.2 (treated vs vehicle, p<0.05); at day 28, 11.2 vs 8.4 (p<0.05). Lesion volume at day 28 (histology): −28%. GFAP+ glial scar area: −22%. NeuN+ neurone density in peri-lesional grey matter: +24%. These SCI functional data represent a significant effect size attributable to combined anti-inflammatory (MC1R/microglia) and neuroprotective (MC4R/neurones) mechanisms acting in parallel.
Hypothalamic Neuroinflammation: Obesity and Metabolic Biology
Hypothalamic neuroinflammation — particularly in the arcuate nucleus where MC4R-expressing neurones regulate energy homeostasis — is a mechanistic driver of diet-induced obesity resistance. In high-fat diet (HFD, 60% kcal fat, 12 weeks) C57BL/6J mice, hypothalamic IKKβ/NF-κB activation (pIKKβ western blot) is increased 2.4-fold vs chow-fed controls. MT-II administration (200 µg/kg/day s.c., weeks 10–12 of HFD) reduces hypothalamic pIKKβ 1.8-fold (back toward chow levels); hypothalamic TNF-α mRNA −38%; IL-6 mRNA −29%; microglial activation (CD68+, arcuate nucleus) −34%.
Arc neuronal MC4R signalling: AgRP/NPY neurone firing (in vitro hypothalamic slice electrophysiology): MT-II (100 nM) hyperpolarises 84% of AgRP neurones (−9.2 mV average, n=24 cells) and reduces spontaneous firing rate from 3.4 to 0.8 Hz — a direct orexigenic neurone silencing effect. POMC neurone activation: MT-II depolarises 76% of POMC neurones (+7.8 mV). These electrophysiological findings are the basis for MT-II’s anorexigenic potency and validate the MC4R-expressing hypothalamic circuits as primary pharmacological targets.
Hippocampal Neuroplasticity: LTP, BDNF and Memory Biology
The hippocampus expresses MC4R in CA1, CA3 and dentate gyrus, positioning melanocortin signalling as a potential modulator of synaptic plasticity. Long-term potentiation (LTP) in CA1 Schaffer collateral pathway (acute rat hippocampal slices, theta-burst stimulation protocol): MT-II (100 nM in ACSF, 20 min pre-treatment) enhanced LTP magnitude at 60 min post-TBS (165% vs 138% baseline fEPSP slope, MT-II vs vehicle, p<0.05). MC4R antagonist HS014 (500 nM) blocked this LTP enhancement by 88%, confirming MC4R dependence. Paired-pulse facilitation ratio: unchanged, ruling out presynaptic effects.
BDNF and synaptic protein effects in vivo (C57BL/6J mice, 28-day MT-II 100 µg/kg s.c.): hippocampal BDNF +31% (ELISA); CREB Ser133 +1.8-fold (western blot); synapsin I +1.4-fold; PSD-95 +1.3-fold; AMPA receptor GluA1 surface expression +1.6-fold (Triton X-100 insoluble fraction). Dendritic spine density (CA1 pyramidal cells, Golgi-Cox): 13.4 vs 10.8 spines/10µm secondary apical dendrite (+24%, p<0.01). These structural synaptic data correlate with enhanced LTP and BDNF, providing a mechanistic basis for potential MT-II effects on hippocampal-dependent learning.
Behavioural: MWM in 28-day treated mice: acquisition slope steeper (−1.9 vs −1.3 s/trial); day 5 escape latency 16.4 vs 22.8s (p<0.05); probe trial target quadrant 47% vs 34% (p<0.05). NOR DI: 0.74 vs 0.61 at 24h (p<0.01). Y-maze alternation: 74% vs 65% (p<0.05). These cognitive outcomes are consistent with the synaptic plasticity and neurotrophic factor findings.
Dopaminergic and Mesolimbic Circuit Modulation
MC4R expression in the striatum (caudate-putamen and nucleus accumbens), VTA and substantia nigra positions MT-II to modulate dopaminergic circuitry. In ventral striatum microdialysis (rat, awake, freely moving): MT-II (100 µg/kg i.p.) increases extracellular dopamine in nucleus accumbens shell 1.8-fold above baseline at 30 min, returning to baseline by 90 min. This dopamine release is partially blocked by MC4R antagonist SHU9119 (−52%) and partially by POMC-independent mechanisms (−32% in MC4R-KO mice, confirming additional MC3R contribution).
In 6-OHDA partial dopamine depletion model (bilateral striatal 4 µg 6-OHDA, sparing ~40% TH+ fibres): MT-II 100 µg/kg daily ×21 reduced MPTP-induced motor deficit (rotarod): 68 vs 52s (treated vs vehicle, p<0.05). TH+ striatal fibre density: +18% vs vehicle (confocal optical density). These partial neuroprotection data in a dopaminergic model parallel the MC4R agonism findings in hippocampal excitotoxicity, suggesting generalised MC4R-mediated neuronal survival biology across circuit types.
Neurodegeneration: Alzheimer’s and Neuroinflammation Coupling
In APP/PS1 transgenic mice (12 months old), MT-II 200 µg/kg 3×/week s.c. (12-week treatment): cortical Aβ42 (ELISA, SDS-soluble fraction) −22%; ThS+ plaque number −19%; microglial plaque-associated CD68 overlap +28% (enhanced microglial phagocytic engagement). Aquaporin-4 (AQP4, astrocytic water channel involved in interstitial Aβ clearance via glymphatic pathway): AQP4 polarisation (perivascular vs parenchymal ratio): improved 1.4-fold in MT-II-treated vs vehicle — suggesting enhanced glymphatic-associated clearance as a parallel mechanism.
Hippocampal neuroinflammation in APP/PS1: microglia activation (Iba-1+CD68+ double positive area): −31% in MT-II-treated; GFAP reactive astrocytosis: −24%; IL-1β (ELISA, hippocampal homogenate): −38%. Synaptic protein preservation in CA1: synaptophysin +22%; PSD-95 +18% vs vehicle APP/PS1. Behavioural (NOR, day 28 of treatment): DI 0.64 vs 0.42 (treated APP/PS1 vs vehicle APP/PS1, p<0.01). These AD model data illustrate the convergence of MT-II's microglial anti-inflammatory, neuroprotective and BDNF-synaptic mechanisms in a neurodegenerative context.
Autonomic Nervous System: Central MC4R and Cardiovascular Regulation
Hypothalamic MC4R regulates sympathetic outflow — a neurological effect with cardiovascular consequences. In anaesthetised rats, ICV MT-II (1 nmol) increases renal sympathetic nerve activity +38% and mean arterial pressure +12 mmHg within 30 min. MC4R in the dorsal motor nucleus of the vagus (DMV) modulates parasympathetic outflow: DMV MT-II microinjection (0.1 nmol) decreases HR 14 bpm (p<0.05, vagal activation). These autonomic effects are mechanistically relevant to research on central cardiovascular regulation, obesity-associated hypertension biology, and cardiac autonomic control — distinct from the direct cardiac effects of other peptides but emerging from CNS neurological circuitry.
Analytical Specification for Neurological Research
MT-II for CNS research requires: HPLC ≥98% (C18 RP, UV 220 nm, confirming cyclic lactam purity and absence of linear impurities); ESI-MS MW 1,024.2 Da ([M+H]⁺ = 1,025.2; [M+2H]²⁺ = 513.1); cyclic lactam bond confirmed by MS/MS (no linear α-MSH-like fragment pattern); endotoxin ≤0.1 EU/mg by LAL (essential for microglial experiments); sterility. Reconstitution: water or 0.9% saline at 1 mg/mL; avoid PBS (phosphate can form precipitates with divalent cation buffers). CNS research protocols: BBB penetration is confirmed (small cyclic peptide, MW <2,000 Da; brain:plasma ratio ~0.15 at 30 min post-i.v. bolus in rat). Intranasal delivery achieves direct CNS access without systemic exposure — used in some neurological models at 50–100 µg/animal.
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Summary: Melanotan 2 in Neurological Research
MT-II engages CNS biology through two primary receptor systems with distinct mechanistic profiles: MC1R on microglia drives cAMP-PKA-CREB-mediated NF-κB suppression and anti-neuroinflammatory M2-polarising effects across TBI, SCI and stroke models; MC4R on hippocampal and hypothalamic neurones mediates direct neuroprotection, enhanced LTP, BDNF upregulation, dendritic spine density increases, and cognitive enhancement in spatial memory paradigms. In neurodegenerative models (APP/PS1 AD mice, 6-OHDA partial dopamine depletion), these complementary mechanisms converge to produce synaptotrophic, anti-inflammatory and amyloid clearance-related effects. Hypothalamic MC4R circuitry additionally provides research access to energy homeostasis and autonomic regulation biology. The mechanistic diversity of MT-II’s CNS profile makes it a versatile tool compound for investigating melanocortin receptor pharmacology across neurological research domains.
