Microtubule Disruption Without Learning Impairment in the Unicellular Organism, Paramecium: Implications for Information Processing in Microtubules

Abstract

Introduction: Information processing in microtubules is an open question that has not been adequately addressed. It was suggested that microtubules could store and process information in the nervous system or even support consciousness. The unicellular organism, Paramecium caudatum, has a microtubular structure but lacks a neuron or neural network. However, it shows intelligent behaviors such as associative learning. This property may suggest that the microtubules are involved in intelligent behavior, information storage, or information processing in this organism.

Methods: To test this hypothesis and study the role of microtubules in P. caudatum learning, we utilized a learning task in which the organism associates brightness in its swimming medium with attractive cathodal shocks. To see if microtubules are an integral part of information storage and processing in P. caudatum, we disrupted the microtubular dynamics in the organism using an antimicrotubular agent (parbendazole).

Results: We observed that while a partial allosteric modulator of GABA (midazolam) could disrupt the learning process in P. caudatum, the antimicrotubular agent could not interfere with the learning.

Conclusion: Microtubules are probably not vital for the learning behavior in P. caudatum. Consequently, our results call for further investigation of the microtubular information processing hypothesis.

Highlights: Importance of Information processing in microtubules;Microtubules could store and process information in the nervous system;Unicellular organism, Paramecium caudatum, has a microtubular structure but lacks a neuron or neural network.

Plain language summary: Information processing in microtubules is an open question that has not been adequately addressed. It was suggested that microtubules could store and process information in the nervous system or even support consciousness. The unicellular organism, Paramecium caudatum, has a microtubular structure but lacks a neuron or neural network. However, it shows intelligent behaviors such as associative learning. This property may suggest that the microtubules are involved in intelligent behavior, information storage, or information processing in this organism. To test this hypothesis and study the role of microtubules in P. caudatum learning, we utilized a learning task in which the organism associates brightness in its swimming medium with attractive cathodal shocks. To see if microtubules are an integral part of information storage and processing in P. caudatum, we disrupted the microtubular dynamics in the organism using an antimicrotubular agent (parbendazole). We observed that while a partial allosteric modulator of GABA (midazolam) could disrupt the learning process in P. caudatum, the antimicrotubular agent could not interfere with the learning. Microtubules are probably not vital for the learning behavior in P. caudatum. Consequently, our results call for further investigation of the microtubular information processing hypothesis.

Keywords: Electrical stimulation; GABA; Learning and memory; Microtubules; Paramecium caudatum; Phototaxis.

Figure 1.

A schematic representation of the experimental setup

Figure 2.

Time difference between groups: control (n=30), trained without any drug (n=23), trained with parbendazole (n=26), and trained with midazolam (n=26)

Figure 3.

The population density of P. Caudatum before and 24 h after the administration of parbendazole (dash-dotted line) compared to the control group (dotted line)

Figure 4.

The population density of paramecium

Figure 5.

Swimming speed of paramecia without drug treatment (control) and 24 h after parbendazole administration not showing a significant change () Independent t-test, P>0.05, n=10; Error bars are ±SEM.

Figure 6.

A schematic representation of the proposed model for learning in Paramecium