Neuromodulation of Color Change in Panther Chameleons: A New Animal Model of Behavior and Psychoactive Drug Action

Overview

Chameleons have captured the collective imagination for millennia due to their remarkable ability to change the color of their skin. Panther chameleons (Furcifer pardalis) produce rapid, dynamic color changes for thermoregulation, camouflage, and communication by fine-tuning guanine nanocrystals within dermal iridophores. While the physical basis for this phenomenon was recently established, the neurophysiological mechanisms and molecular signaling pathways regulating iridophore activity remain unknown. Using rodent models to study complex behaviors and psychoactive drug action is extremely challenging, due to our severely limited ability to access the internal state of the animal. Chameleons represent a uniquely advantageous model for studying the neural basis of behavior and psychopharmacology. Changes in their mood and behavioral state are reflected on their skin, providing accessible, robust, and highly quantifiable physical variables to measure. This project proposes a multidisciplinary investigation combining physiology, advanced imaging, and machine learning to decode the relationship between behavioral states, neuromodulation, and dynamic skin color changes. By establishing panther chameleons as a non-mammalian model for psychopharmacological research, we aim to explore how neuromodulators and psychoactive drugs (e.g., psychedelics) affect behaviorally relevant physiological outputs in real time.

Introduction

Panther chameleons (Furcifer pardalis) exhibit a remarkable ability to actively tune the color of their skin by modifying the lattice structure of photonic nanocrystals within dermal iridophores¹. While the physical and optical properties of this mechanism are established, the underlying neural control and molecular signaling pathways remain unexplored. Monoamine neurotransmitters such as serotonin have been detected in the chameleon brain². Iridophores also share neural-crest origin with pigmented chromatophores³. In fish and amphibians, pigmented chromatophores are modulated by hormones and various neurotransmitters such as acetylcholine, dopamine, norepinephrine and serotonin^4,5,6. These data support the hypothesis that neuromodulation controls iridophore activity in panther chameleons through neurotransmitters acting on G-protein coupled receptor pathways¹.

Numerous studies have shown that color change in chameleons represents a rich and dynamic form of communication^{7,8,9,10,11,12}. Color change rates, level of saturation and maximum brightness in courting males all have a significant impact on female panther chameleon mate selection¹³. A recent study also showed that the outcome of an agonistic interaction (fight) between male panther chameleons can be predicted based on the dynamics of color change variables¹⁴. The ability to visualize continuous and reversible physiological changes on the skin’s surface provides a unique, non-invasive physiological marker for behavioral states. Unlike typical rodent models, the chameleon offers a quantifiable readout of neuropharmacological manipulations in real time. Machine learning algorithms can eventually be employed to classify and predict neural state-dependent color patterns, providing a new methodological framework for studying neuropharmacological dynamics. This is particularly attractive in preclinical psychopharmacology research, where interpretable rodent studies of psychoactive drugs like psychedelics (with known effects in humans) have proven extremely challenging¹⁵.

We hypothesize that color dynamics in Furcifer pardalis reflect complex behavioral states that are controlled by intrinsic neuromodulation of s-iridophores, can be altered by psychoactive drugs targeting neurotransmitter receptors, and ultimately decoded through machine learning to establish a new animal model in neuropsychopharmacology.

To investigate this hypothesis, we will (1) establish validated, ethical husbandry and surgical protocols to support neurophysiological studies of Furcifer pardalis, (2) perform in vitro electrophysiology and single cell imaging for neuropharmacological characterization of iridophore activity.

Completion of the proposed experiments will lay the foundation for future studies using in vivo RGB photometry paired with machine learning-based analysis to decode color change dynamics during naturalistic behaviors under controlled pharmacological manipulations. By exploiting the unique physiology of chameleons, our future goal is to develop a real-time quantitative biomarker system for studying the biochemical basis of complex behavior and psychoactive drug action, with potential applications in drug screening and translational neuroscience.

Research Design and Methods

Aim 1: Development and validation of ethical husbandry, surgical and experimental protocols for Furcifer pardalis

Design and implement a detailed description of all ethical husbandry, surgical, and experimental procedures under a vertebrate animal protocol approved by the Institutional Animal Care and Use Committee (IACUC) to establish Furcifer pardalis as a reliable and humane model organism for the proposed studies. The protocol will emphasize species-appropriate environmental and social enrichment, justification of species use and numbers, ethical endpoints, and monitoring criteria

Construct ventilated glass terraria with proper substrates, climbing structures, plants (real or artificial), dual climate zones, misting systems, and full-spectrum (UVA/UVB) lighting that meet protocol guidelines to mimic native environments.

Automate and monitor microclimatic stability (temperature, humidity gradients, photoperiod) using real-time environmental sensors.

Monitor health and stress indicators (weight, behavior, feeding, coloration) longitudinally.

Develop and refine minimally invasive protocols for skin biopsy collection and pharmacological manipulations

Maintain all procedures in accordance with institutional standards and the guide for the care and use of laboratory animals

Aim 2: In vitro characterization of intrinsic and exogenous iridophore neuromodulation using patch clamp electrophysiology and single-cell videography

Perform enzymatic dissociation of dermal biopsies to isolate iridophores. Conduct patch-clamp recordings and single cell videography using isolated iridophore and whole-skin explant preparations.

Apply adrenergic, muscarinic, serotonergic, and dopaminergic agonists/antagonists.

Test major classes of psychoactive drugs including psychostimulants, psychedelics, deliriants, sedatives and dissociative anesthetics.

Quantify electrophysiological and single cell imaging responses in control and pharmacological conditions.

Budget

Total Budget: $50,000

Custom terrarium builds (multiple units for controlled environmental variables): $10,000

Animal procurement (chameleon colony acquisition): $5,000

Animal husbandry (feeding, habitat maintenance, routine care): $10,000

Veterinary care & surgical equipment (routine veterinary check-ups, anesthesia, surgical tools): $10,000

Electrophysiology consumables (patch-clamp microelectrodes, solutions, cell biology and acute dissociation reagents): $5,000

In vitro imaging equipment (Leica MZ16 stereomicroscope, Nikon D800 HD camera, Ludin chamber, microscope accessories): $10,000

Timeline

Months 1-4: Terrarium setup, husbandry/surgical protocols, IACUC approval, colony procurement
Months 5-8: Biopsy, dissociation, and isolated iridophore optimization
Months 9-12:In vitro characterization using electrophysiology and single cell videography

References

1. Teyssier J, Saenko SV, Van Der Marel D, Milinkovitch MC. Photonic crystals cause active colour change in chameleons. Nature communications. 2015 Mar 10;6(1):6368.

2. Bennis M, Gamrani H, Geffard M, Calas A, Kah O. The distribution of 5-HT immunoreactive systems in the brain of a saurian, the chameleon. Journal fur Hirnforschung. 1990 Jan 1;31(5):563-74.

3. Bagnara JT, Matsumoto J. Comparative anatomy and physiology of pigment cells in nonmammalian tissues. The pigmentary system: physiology and pathophysiology. 2006 Apr 25:11-59.

4. Fuji RY. The regulation of motile activity in fish chromatophores. Pigment Cell Research. 2000 Oct;13(5):300-19.

5. Nilsson Sköld H, Aspengren S, Wallin M. Rapid color change in fish and amphibians–function, regulation, and emerging applications. Pigment cell & melanoma research. 2013 Jan;26(1):29-38.

6. Ligon RA, McCartney KL. Biochemical regulation of pigment motility in vertebrate chromatophores: a review of physiological color change mechanisms. Current zoology. 2016 Jun 1;62(3):237-52.

7. Stuart-Fox D, Moussalli A. Selection for social signalling drives the evolution of chameleon colour change. PLoS biology. 2008 Jan;6(1):e25.

8. Stuart-Fox D, Moussalli A. Camouflage, communication and thermoregulation: lessons from colour changing organisms. Philosophical Transactions of the Royal Society B: Biological Sciences. 2009 Feb 27;364(1516):463-70.

9. Ligon RA, McGraw KJ. Chameleons communicate with complex colour changes during contests: different body regions convey different information. Biology letters. 2013 Dec 23;9(6):20130892.

10. Ligon RA. Defeated chameleons darken dynamically during dyadic disputes to decrease danger from dominants. Behavioral Ecology and Sociobiology. 2014 Jun;68:1007-17.

11. Ligon RA, McGraw KJ. 2018 A chorus of color: hierarchical and graded information content of rapid color change signals in chameleons. Behav. Ecol. 29, 1075–1087. (doi:10.1093/ beheco/ary076)

12. Drown RM, Liebl AL, Anderson CV. The functional basis for variable antipredatory behavioral strategies in the chameleon Chamaeleo calyptratus. Journal of Experimental Biology. 2022 May 15;225(10):jeb242955.

13. Dollion AY, Herrel A, Marquis O, Leroux-Coyau M, Meylan S. The colour of success: does female mate choice rely on male colour change in the chameleon Furcifer pardalis?. Journal of Experimental Biology. 2020 Oct 15;223(20):jeb224550.

14. Dollion AY, Meylan S, Marquis O, Leroux-Coyau M, Herrel A. Do male panther chameleons use different aspects of color change to settle disputes?. The Science of Nature. 2022 Feb;109(1):13.

15. Lu OD, White K, Raymond K, Liu C, Klein AS, Green N, Vaillancourt S, Gallagher A, Shindy L, Li A, Li R. A multi-institutional investigation of psilocybin's effects on mouse behavior. bioRxiv. 2025:2025-04.

Funding

Funding

Neuromodulation of Color Change in Panther Chameleons: A New Animal Model of Behavior and Psychoactive Drug Action

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