The Two-Faced Peptide

Dynorphin — the kappa-opioid peptide. Released under stress it dampens dopamine and colors mood gray, which is the face it shows in the depression literature. But every botanical studied on it moves it the other way: mitragynine stimulates kappa-opioid, the Gosha-jinki-gan effect is abolished by a kappa-opioid blocker and diminished by anti-dynorphin antiserum, and ginsenoside Re protects dopamine neurons from stimulant damage by upregulating dynorphin-mediated kappa-opioid signaling. Three sources in three languages, all one direction.

Stress & cortisol increases it.

Bruchas 2009, PLoS One — stress (via CRF/CRF1-R) induces dynorphin release and kappa-opioid-receptor activation; swim stress raises dynorphin-mediated signaling, blocked by the KOR antagonist norBNI. PMID 20052275. Activation of the dynorphin / kappa-opioid receptor system is described as playing a major role in the pro-addictive effects of stress, with dynorphin and CRF together inducing dysphoria, potentiating drug seeking and mediating stress-induced reinstatement. this arm is characterized principally in addiction and affective-state models — it is a dysphoria/relapse pathway, not a general stress-tone marker. PMID 20052275

Reproductive trigger hormone increases it.

Kisspeptin neurons of the arcuate nucleus co-express neurokinin B and dynorphin — they are called KNDy neurons for those three peptides. KNDy cells mediate both the positive and negative feedback of estrogen onto GnRH secretion, and the arcuate is the site of the GnRH pulse generator. Dynorphin is best known as a stress and dysphoria signal; here the same peptide has a second, reproductive job in the same cells. doi 10.3389/fendo.2022.925206 · PMC2789414

Stress-relapse axis increases it.

It shows the CRF → Anxiety link runs through dynorphin rather than beside it. Blockade proves the order: using a phosphoselective antibody to identify sites of dynorphin action, CRF increased KORp-immunoreactivity in the basolateral amygdala of WILDTYPE mice but not in mice pretreated with the selective CRF1-receptor antagonist ANTALARMIN — CRF1 is upstream of dynorphin release. Two receptors, two behaviors, one peptide. PMC2795205

Motivation increases it.

Dopamine drives dynorphin expression in striatal neurons: 'This suggests that dopamine normally stimulates expression of dynorphin and substance P in striatal neurons' (Gerfen, McGinty & Young, Dopamine differentially regulates dynorphin, substance P, and enkephalin expression in striatal neurons: in situ hybridization histochemical analysis, J Neurosci 1991;11(4):1016-1031). Scope stated before anyone asks: that paper manipulated dopamine by lesion and by chronic agonist and does not identify the D1 receptor as the mediator, so no receptor subtype is claimed here. The return arrow - dynorphin restraining dopamine release - is carried separately on the Dynorphin → Dopamine arrow.

It reduces Motivation.

Dynorphin/KOR-dopamine study 2017, eLife — kappa-opioid receptors (activated by dynorphin) decrease VTA dopamine-neuron firing via GIRK channels, inhibiting mesolimbic dopamine release. PMC5389861

It reduces Mood.

Bruchas 2010, Brain Res — dynorphin activation of kappa-opioid receptors inhibits mesolimbic dopamine, producing dysphoria and negative mood (the dysphoric component of stress). PMID 19716811

It increases Calm under stress.

10.1371/journal.pone.0008528 — The control is what makes this strong — it is anatomical, not just pharmacological: local injection of the kor antagonist norBNI into the basolateral amygdala blocked the stress- or crf-induced increase in anxiety-like behavior, whereas the same antagonist injected into a nearby thalamic nucleus did not. Same drug, millimeters apart, opposite result — the effect is located, not systemic. doi 10.1371/journal.pone.0008528

It reduces Quiets overexcitation.

Dynorphin acting on presynaptic KORs inhibits glutamate release from afferent inputs to the prefrontal cortex, but selectively: with channelrhodopsin in each source region, dynorphin inhibited inputs from the paraventricular thalamus, basolateral amygdala and contralateral cortex, but not from the ventral hippocampus. One peptide, four inputs, three silenced. Presynaptic proven by exclusion: dynorphin failed to modify currents evoked by glutamate UNCAGING — bypassing the terminal abolishes the effect, so it acts on release, not on the receiving neuron. The block was reversed by norBNI without leaving plasticity behind. And the anxiety link is causal: KOR activation inhibits glutamate release from BLA inputs to the BNST and OCCLUDES the anxiolytic phenotype produced by optogenetic activation of BLA-BNST projections, while deletion of KORs from amygdala neurons produces an anxiolytic phenotype. doi 10.1038/s41380-023-02226-5

It reduces Calm.

In central amygdala slices, superfusing dynorphin or the KOR agonist U69593 decreased evoked inhibitory postsynaptic potentials in a concentration-dependent manner, an effect prevented by the antagonist norBNI. The antagonist-alone result is the applied alone, norBNI increased GABAergic transmission, revealing a tonic endogenous activity at KOR. The receptor is already occupied; blocking it releases a brake that was always on. Paired-pulse analysis places the mechanism presynaptically. And the sign can invert with drug history: in cocaine-experienced animals the effects of KOR ligands on CeA GABA synapses switch, attributed to persistently elevated dynorphin altering KOR-coupled presynaptic signaling. This edge describes a naive brain. doi 10.1038/s41386-025-02226-9 · PMID 24157490 · PMC3773286

It increases Lowers cortisol.

the human data is the strong part: stress induces dynorphin release, and activation of KORs with a synthetic agonist increases corticosterone in rats and cortisol levels in rhesus monkeys and humans. KORs are expressed in the organs of the HPA axis as well as the brain regions that regulate it. The mechanism is explicitly unsettled and that is recorded: it likely involves stimulation of CRF release in the hypothalamus as well as CRF-independent mechanisms — so this arrow does not run wholly through crf. The return path is disinhibition — KOR activation in the central amygdala presynaptically inhibits the FEEDFORWARD inhibition driven by glutamatergic parabrachial input, thereby disinhibiting CeA CRF neurons. Each peptide recruits the other, by opposite mechanisms. And they compete in the same synapse: exogenous CRF raised GABAergic mIPSC frequency by 20.2 percent, and while norBNI alone had no significant effect, it enhanced the CRF effect by 43.9 percent (P=0.02) — blocking KOR makes CRF stronger, because CRF was recruiting an opposing KOR arm all along. doi 10.1016/j.neuropharm.2021.108456 · PMC3770816

It reduces Mood (serotonin).

Acute KOR activation inhibits serotonergic neuronal excitability within the dorsal raphe by two routes at once — presynaptic inhibition of excitatory synaptic transmission and postsynaptic activation of inwardly-rectifying potassium conductance. Both the input and the cell itself are damped. Site-specific causal proof: injecting the KOR antagonist norBNI into the dorsal raphe blocked the aversive response to a systemic KOR agonist and blocked stress-induced reinstatement. The dysphoric effect of kappa activation requires the raphe — block it there and systemic drug loses its aversive quality. This is the cellular content of the classic finding that the dysphoric component of stress is encoded by activation of the dynorphin kappa-opioid system (Land 2008). And repeated stress changes the machinery, not just the signal: repeated stress dysregulates KOR signaling in the dorsal raphe through a p38-alpha MAPK-dependent mechanism — so the same peptide acts differently on a stressed brain than a naive one, the same caveat already recorded on the Dynorphin → GABA link for drug history. doi 10.1073/pnas.0910705106

It reduces Reproductive axis.

The evidence is electrophysiological and steroid-sensitive: stimulation of KNDy neurons by the NK3R agonist SENKTIDE was attenuated in intact versus castrated mice and suppression by dynorphin was enhanced. Both estradiol and DHT suppressed senktide-induced KNDy firing and enhanced the inhibition caused by dynorphin. The authors propose steroid modulation of responses to NK3R and kappa-opioid receptor activation as mechanisms for negative feedback in KNDy neurons. This is the cellular route for the other two edges: GnRH neurons carry no steroid receptors, so the feedback must land somewhere else — and it lands here, on the kisspeptin neuron, by making its dynorphin brake more effective. mouse brain-slice electrophysiology; the human arm is the aromatase-deficient men on the estrogen edge. doi 10.1210/en.2015-1741 · PMC10516609