DA / NE / 5-HT & Endorphins — Structured Summary

Triad of Dopamine (DA), Norepinephrine (NE), Serotonin (5-HT) — with Endorphins

Scope. Simplified, non-clinical summary; a conceptual aid, not medical advice.

1. Roles (Core)

• Dopamine (DA): Sensitive to reward prediction error; updates “go/continue/shift” policies.
• Norepinephrine (NE): Arousal and rapid re-allocation of attention; boosts sensitivity under novelty/urgency.
• Serotonin (5-HT): Inhibition, stability, patience; tames impulses and noise to sustain effort.

2. Major Interactions (direction & typical receptors)

• 5-HT inhibits DA (mainly 5-HT2C): brakes excessive thrust/impulse.
• NE excites DA (α1 → VTA): arousal supports reward learning.
• DA inhibits 5-HT (D2-like): prioritizes motivation over restraint.
• NE ↔ 5-HT: in raphe, α1 tends to promote; α2 tends to suppress—context dependent.

3. Stabilization Mechanisms (Feedback)

• Autoinhibition: 5-HT1A/1B, D2, α2 curb “overshoot” immediately after release.
• Reuptake: SERT/DAT/NET clear extras; chronic shifts adapt transporter expression.
• Top-down control: PFC via GABA dampens VTA/LC/raphe to prune context-mismatched reactions.
• Stress axis (HPA): acutely biases toward NE/DA; chronically reshapes receptors, sleep, and motivation.

4. Time Course (Intuitive State Transitions)

Novelty raises NE → as estimates form, DA phasic bursts to write learning → in sustained work, 5-HT rises to suppress noise/impulse and hold focus → pain/fatigue recruit endorphins to soften cost → after finishing, 5-HT predominates for recovery, review, and planning.

5. Where Endorphins Fit (Endogenous Opioids)

• Not a monoamine. Endorphins (μ/κ/δ actions) modulate the gain of mood and learning.
• μ-opioid: disinhibits VTA GABA → DA ↑; suppresses LC → NE ↓; reduces nociception.
• κ-opioid: tends toward dysphoria and DA ↓.
• δ-opioid: implicated in affective stability and plasticity.
• External opioids carry serious risks (dependence, respiratory depression); clinical domain.

6. Simple Equations (Discrete-time Toy Model)

Normalize variables to [0,1]: d=DA, n=NE, s=5-HT, k=endorphin tone. Let phi(x)=1/(1+e^(-x)). Coefficients fix signs; magnitudes are tunable.

// Core dynamics (t → t+1)
d' = (1 - λ_d) d + phi( β_d + w_nd·n - w_sd·s + w_kd·k )
n' = (1 - λ_n) n + phi( β_n + u_t - w_kn·k )
s' = (1 - λ_s) s + phi( β_s - w_ds·d + (1 - σ_t)·w_ns⁺·n - σ_t·w_ns⁻·n )
k' = (1 - λ_k) k + phi( β_k + g1·exercise + g2·achievement - g3·chronic_stress )

// Sign guide (examples)
w_nd > 0   // NE → DA (facilitation)
w_sd > 0   // 5-HT ┤ DA (inhibition)
w_ds > 0   // DA ┤ 5-HT (inhibition)
w_kd > 0   // μ-opioid raises DA
w_kn > 0   // μ-opioid lowers NE
w_ns⁺, w_ns⁻ > 0  // NE↔5-HT: promote under safety, suppress under threat

// Inputs and parameters
u_t   : novelty/urgency input (external)
σ_t   : threat context in [0,1] (0=safe, 1=threat)
λ_*   : natural decay (autoinhibition + reuptake lumped)

Mode indicators (optional visualization)

Explore = d · n · (1 - s)
Focus   = n · s
Recover = s · (1 - n) · (1 - d)

7. Practical Application (Low-intrusion Levers)

• Boost 5-HT: walking, breathing, daylight, tidy routines (quiets impulse/noise).
• Tune NE: cut notifications + short deadlines (raise u_t while keeping σ_t low).
• Spark DA: small immediate rewards, visible progress, clear sub-goals.
• Endorphins (healthy): exercise, music, repeated achievement (lift k without κ-tilt).

Reminder. This is a heuristic framework for self-observation and planning, not a diagnostic or treatment guide.