Reimplantable Microdrive for Long-Term Chronic Extracellular Recordings in Freely Moving Rats

Abstract

Extracellular recordings of electrical activity in freely moving rats are fundamental to understand brain function in health and disease. Such recordings require a small-size, lightweight device that includes movable electrodes (microdrive) to record either a new set of neurons every day or the same set of neurons over time. Ideally, microdrives should be easy to implant, allowing precise and smooth displacement of electrodes. The main caveat of most commercially available microdrives is their relatively short half-life span, in average ranging from weeks to a month. For most experiments, recording days–weeks is sufficient, but when the experiment depends on training animals for several months, it is crucial to develop new approaches. Here, we present a low-cost, reusable, and reimplantable device design as a solution to extend chronic recordings to long-term. This device is composed of a baseplate that is permanently fixed to the rodent’s skull, as well as a reusable and replaceable microdrive that can be attached and detached from the baseplate, allowing its implantation and reimplantation. Reimplanting this microdrive is particularly convenient when no clear neuronal signal is present, or when the signal gradually decays across days. Our microdrive incorporates a mechanism for moving a 16 tungsten-wire bundle within a small (∼15 mm 3 ) lightweight device (∼4 g). We present details of the design, manufacturing, and assembly processes. As a proof of concept, we show that recordings of the nucleus accumbens core (NAcc) in a freely behaving rat are stable over a month. Additionally, during a lever-press task, we found, as expected, that NAc single-unit activity was associated with rewarded lever presses. Furthermore, we also show that NAc shell (NAcSh) responses evoked by freely licking for sucrose, consistent with our previously published results, were conserved from a first implant to a second microdrive reimplant in the same rat, notably showing reimplantation is possible without overtly affecting the functional responses of the area of interest. In sum, here we present a novel microdrive design (low-cost, small size, and light weight) that can be used for long-term chronic recordings and reimplanted in freely behaving rats.

A 3D Printed Device for Low Cost Neural Stimulation in Mice

“…Notably, some groups have developed microdrive devices with 3D printed bodies suitable for implantation in mice (Voigts et al, 2013; Freedman et al, 2016). Other works have used 3D printing to produce a headstage (Pinnell et al, 2016), waterproof cap (Pinnell et al, 2018), and microdrive housing (Polo-Castillo et al, 2019) to protect electronic implants in rats. 3D printing has also been utilized in human applications through the fabrication of individualized headsets that can hold a stimulator in position over the scalp with better accuracy and reproducibility than traditional methods (Mansouri et al, 2018).…”

Chronic, Multi-Site Recordings Supported by Two Low-Cost, Stationary Probe Designs Optimized to Capture Either Single Unit or Local Field Potential Activity in Behaving Rats

“…Fixed devices can have up to 384 recording sites, targeting many brain areas simultaneously as is seen with the Neuropixels silicon probe (46)(47)(48). The other approach utilizes a microdrive to move electrodes along the vertical axis to advance after surgical implantation (52)(53)(54)(55)(56)(57)(58). Microdrives are advantageous for reaching neural dense areas and moving past the site of initial injury/ inflammatory response, however fabrication can be more challenging and expensive than fixed implants and are typically limited in the number of multi-site trajectories they can support (52,53,(55)(56)(57).…”

“…The other approach utilizes a microdrive to move electrodes along the vertical axis to advance after surgical implantation (52)(53)(54)(55)(56)(57)(58). Microdrives are advantageous for reaching neural dense areas and moving past the site of initial injury/ inflammatory response, however fabrication can be more challenging and expensive than fixed implants and are typically limited in the number of multi-site trajectories they can support (52,53,(55)(56)(57). Favoring a simple, cost-effective design, we built a custom stationary probe with 32-64 electrodes for multi-site single unit recordings and another probe with 32 channels optimized to record "brain-wide" field potentials.…”

A fully adapted headstage for electrophysiological experiments with custom and scalable electrode arrays to record widely distributed brain regions

“…To successfully deal with the costs and in an attempt to create more versatile electrode arrays, some authors have developed creative and custom-made solutions for recording the Local Field Potential (LFP) and the multiunit activity in freely moving animals (França et al, 2020;Polo-Castillo et al, 2019). Nevertheless, these solutions still need expensive commercial connectors, which are not easily recoverable after the experiment, present a reasonably rigid geometry that does not allow recording widely distributed brain regions and, often have mechanical problems if long-term continuous recordings are intended.…”