Increased c-fos immunoreactivity in the spinal cord and brain following spinal cord stimulation is frequency-dependent

Cannabidiol in the dorsal hippocampus attenuates emotional and cognitive impairments related to neuropathic pain: The role of prelimbic neocortex-hippocampal connections

BACKGROUND AND PURPOSE

Chronic neuropathic pain (NP) is commonly associated with cognitive and emotional impairments. Cannabidiol (CBD) presents a broad spectrum of action with a potential analgesic effect. This work investigates the CBD effect on comorbidity between chronic NP, depression, and memory impairment.

EXPERIMENTAL APPROACH

The connection between the neocortex and the hippocampus was investigated with biotinylated dextran amine (BDA) deposits in the prelimbic cortex (PrL). Wistar rats were submitted to chronic constriction injury (CCI) of the sciatic nerve and CA1 treatment with CBD (15, 30, 60 nmol).

KEY RESULTS

BDA-labeled perikarya and terminal buttons were found in CA1 and dentate gyrus. CCI-induced mechanical and cold allodynia increased c-Fos protein expression in the PrL and CA1. The number of astrocytes in PrL and CA1 increased, and the number of neuroblasts decreased in CA1. Animals submitted to CCI procedure showed increasing depressive-like behaviors, such as memory impairment. CBD (60 nmol) treatment decreased mechanical and cold allodynia, attenuated depressive-associated behaviors, and improved memory performance. Cobalt chloride (CoCl2: 1 nM), WAY-100635 (0.37 nmol), and AM251 (100 nmol) intra-PrL reversed the effect of CA1 treatment with CBD (60 nmol) on nociceptive, cognitive, and depressive behaviors.

CONCLUSION

CBD represents a promising therapeutic perspective in the pharmacological treatment of chronic NP and associated comorbidities such as depression and memory impairments. The CBD effects possibly recruit the CA1-PrL pathway, inducing neuroplasticity. CBD acute treatment into the CA1 produces functional and molecular morphological improvements.

Partially brain effects of injection of human umbilical cord mesenchymal stem cells at injury sites in a mouse model of thoracic spinal cord contusion

Purpose

The pain caused by spinal cord injury (SCI) poses a major burden on patients, and pain management is becoming a focus of treatment. Few reports have described changes in the brain after SCI. Particularly, the exact mechanism through which brain regions affect post-injury pain remains unclear. In this study, we aimed to determine the potential therapeutic mechanisms of pain. A mouse model of spinal cord contusion was established, and molecular expression in the anterior cingulate cortex (ACC) and periaqueductal gray (PAG) in the brain and animal behavior was observed after local injection of human umbilical cord mesenchymal stem cells (HU-MSCs) at the site of SCI.

Method

Sixty-three female C57BL/6J mice were divided into four groups: a sham operation group (n = 15); a spinal injury group (SCI, n = 16); an SCI + HU-MSCs group (n = 16) and an SCI + PBS group (n = 16), in which the SCI site was injected with HU-MSCs/phosphate buffer. The BMS score was determined, and the von Frey test and Hargreaves test were used to assess behavior every week after surgery. Mice were sacrificed in the fourth week after operation, and samples were collected. The expression of CGRP, Substance P, C-Fos and KCC2 in the ACC and PAG were observed with immunohistochemistry. Chromic cyanine staining was used to observe transverse sections of the injured spinal cord.

Result

In the ACC and PAG after SCI, the expression of CGRP, SP and C-Fos increased, and the expression of KCC2 decreased, whereas after HU-MSC injection, the expression of CGRP, SP and C-Fos decreased, and the expression of KCC2 increased. The SCI + HU-MSC group showed better exercise ability from 2 to 4 weeks after surgery than the SCI/SCI + PBS groups (P < 0.001). Local injection of HU-MSCs significantly improved the mechanical hyperalgesia caused by SCI in the fourth week after surgery (P < 0.0001), and sensation was significantly recovered 2 weeks after surgery (P < 0.0001); no improvement in thermal hypersensitivity was observed (P > 0.05). The HU-MSC group retained more white matter than the SCI/SCI + PBS groups (P < 0.0001).

Conclusion

Local transplantation of HU-MSCs at the site of SCI partially relieves the neuropathic pain and promotes recovery of motor function. These findings suggest a feasible direction for the future treatment of SCI.

In Vivo Measurements reveal that both low- and high-frequency spinal cord stimulation heterogeneously modulate superficial dorsal horn neurons

Current sub-perception spinal cord stimulation (SCS) is characterized by the use of high-frequency pulses to achieve paresthesia-free analgesic effects. High-frequency SCS demonstrates distinctive properties from paresthesia-based SCS, such as a longer time course to response, implying the existence of alternative mechanism(s) of action beyond gate control theory. We quantified the responses to SCS of single neurons within the superficial dorsal horn (SDH), a structure in close proximity to SCS electrodes, to investigate the mechanisms underlying high-frequency SCS in 62 urethane-anesthetized male rats. Sciatic nerve stimulation was delivered to isolate lumbar SDH neurons with evoked C-fiber activity. The evoked C-fiber activity before and after the application of SCS was compared to quantify the effects of SCS across stimulation intensity and stimulation duration at three different stimulation frequencies. We observed heterogeneous responses of SDH neurons which depended primarily on the type of unit. Low-threshold units with spontaneous activity, putatively inhibitory interneurons, tended to be facilitated by SCS while the other unit types were suppressed. The effects of SCS were more prominent with increased stimulation duration from 30 s to 30 m across frequencies. Our results highlight the importance of inhibitory interneurons in modulating local circuits of the SDH and the importance of local circuit contributions to the analgesic mechanisms of SCS.

Emerging functions of neuronostatin in physiology, pathology, and potential therapeutics

Neuronostatin, a bioactive peptide hormone, was encoded by pro-somatostatin and discovered using a bioinformatic method in 2008. Neuronostatin is widely expressed in the central nervous system (CNS) and peripheral tissues, it is also highly conserved among humans, rodents, and even goldfish. The 13 and 19 amino acids and the C-terminal amidation type play important roles in physiological and pathological functions. The present study reviews the roles of neuronostatin in food intake and drinking of water, as well as in the neuroendocrine processes, pain regulation, cardiovascular and circulation function, memory and studies, depression-like effect, and energy metabolism in animals. However, the information on the physiology and pathology of neuronostatin, especially the molecular mechanism, remains scarce. Considering the broad functions of neuronostatin, this endogenous neuropeptide could be a promising therapeutic target for future research and drug design if the exact receptor could be found in humans.

Dorsal Column and Root Stimulation at Aβ-fiber Intensity Activate Superficial Dorsal Horn Glutamatergic and GABAergic Populations

Neurostimulation therapies are frequently used in patients with chronic pain conditions. They emerged from Gate Control Theory (GCT), which posits that Aβ-fiber activation recruits superficial dorsal horn (SDH) inhibitory networks to “close the gate” on nociceptive transmission, resulting in pain relief. However, the efficacy of current therapies is limited, and the underlying circuits remain poorly understood. For example, it remains unknown whether ongoing stimulation of Aβ-fibers is sufficient to drive activity in SDH neurons. We used multiphoton microscopy in spinal cords extracted from mice expressing the genetically encoded calcium indicator GCaMP6s in glutamatergic and GABAergic populations; activity levels were inferred from deconvolved calcium signals using CaImAn software. Sustained Aβ-fiber stimulation at the dorsal columns or dorsal roots drove robust yet transient activation of both SDH populations. Following the initial increase, activity levels decreased below baseline in glutamatergic neurons and were depressed after stimulation ceased in both populations. Surprisingly, only about half of GABAergic neurons responded to Aβ-fiber stimulation. This subset showed elevated activity for the entire duration of stimulation, while non-responders decreased with time. Our findings suggest that Aβ-fiber stimulation initially recruits both excitatory and inhibitory populations but has divergent effects on their activity, providing a foundation for understanding the analgesic effects of neurostimulation devices.

Perspective: This article used microscopy to characterize the responses of mouse spinal cord cells to stimulation of non-painful nerve fibers. These findings deepen our understanding of how the spinal cord processes information and provide a foundation for improving pain-relieving therapies.

Parametric Assessment of Spinal Cord Stimulation on Bladder Pain-Like Responses in Rats

OBJECTIVES

Spinal cord stimulation (SCS) for the treatment of pelvic visceral pains has been understudied and underused. The goal of the current study was to examine multiple stimulation parameters of SCS to determine optimal settings for the inhibition of responses to urinary bladder distension (UBD) in animal models of bladder pain as a guide for human studies.

MATERIALS AND METHODS

Adult, female isoflurane/urethane-anesthetized rats underwent a T13/L1 mini-laminectomy sufficient to implant an SCS paddle lead for neuromodulation. Silver wire electrodes were inserted into the external oblique musculature. A 22-gauge angiocatheter was placed transurethrally into the bladder and used to deliver phasic, air UBDs at pressures of 10 to 60 mm Hg and visceromotor (abdominal contractile) electromyographic responses to UBD measured in the presence and absence of SCS. Electromyographic activity was quantified using standard differential amplification and rectification. Parameter settings for SCS included both conventional (10, 50, 100 Hz) and high frequency (1,000, 5,000, and 10,000 Hz) biphasic square wave pulses with 50 to 200 μs durations. To create states of hypersensitivity, pretreatment of adult rats included an intravesical zymosan infusion 24 hours before testing with and without a preceding episode of neonatal bladder inflammation.

RESULTS

Low frequency (10, 50, and 100 Hz) 200 μs biphasic pulses at submotor thresholds demonstrated inhibition of visceromotor responses (VMRs) to UBD in rats made hypersensitive to UBD by a protocol that included neonatal cystitis. Onset of inhibitory effects occurred within 20 minutes of beginning SCS. Otherwise, SCS at all other parameters studied and in other tested rat models produced either no significant effect or augmentation of VMRs.

CONCLUSIONS

Demonstration of inhibitory effects of SCS in a clinically relevant model of bladder pain suggests the potential utility of this therapy in patients with painful bladder disorders.

Effects of Noninvasive Low-Intensity Focus Ultrasound Neuromodulation on Spinal Cord Neurocircuits In Vivo

Although neurocircuits can be activated by focused ultrasound stimulation, it is unclear whether this is also true for spinal cord neurocircuits. In this study, we used low-intensity focused ultrasound (LIFU) to stimulate lumbar 4–lumbar 5 (L4–L5) segments of the spinal cord of normal Sprague Dawley rats with a clapper. The activation of the spinal cord neurocircuits enhanced soleus muscle contraction as measured by electromyography (EMG). Neuronal activation and injury were assessed by EMG, western blotting (WB), immunofluorescence, hematoxylin and eosin (H&E) staining, Nissl staining, enzyme-linked immunosorbent assay (ELISA), immunohistochemistry (IHC), somatosensory evoked potentials (SEPs), motor evoked potentials (MEPs), and the Basso–Beattie–Bresnahan locomotor rating scale. When the LIFU intensity was more than 0.5 MPa, LIFU stimulation induced soleus muscle contraction and increased the EMG amplitudes (P < 0.05) and the number of c-fos- and GAD65-positive cells (P < 0.05). When the LIFU intensity was 3.0 MPa, the LIFU stimulation led to spinal cord damage and decreased SEP amplitudes for electrophysiological assessment (P < 0.05); this resulted in coagulation necrosis, structural destruction, neuronal loss in the dorsal horn by H&E and Nissl staining, and increased expression of GFAP, IL-1β, TNF-α, and caspase-3 by IHC, ELISA, and WB (P < 0.05). These results show that LIFU can activate spinal cord neurocircuits and that LIFU stimulation with an irradiation intensity ≤1.5 MPa is a safe neurostimulation method for the spinal cord.

Tissue Temperature Increases by a 10 kHz Spinal Cord Stimulation System: Phantom and Bioheat Model

OBJECTIVE

A recently introduced Spinal Cord Stimulation (SCS) system operates at 10 kHz, faster than conventional SCS systems, resulting in significantly more power delivered to tissues. Using a SCS heat phantom and bioheat multi-physics model, we characterized tissue temperature increases by this 10 kHz system. We also evaluated its Implanted Pulse Generator (IPG) output compliance and the role of impedance in temperature increases.

MATERIALS AND METHODS

The 10 kHz SCS system output was characterized under resistive loads (1-10 KΩ). Separately, fiber optic temperature probes quantified temperature increases (ΔTs) around the SCS lead in specially developed heat phantoms. The role of stimulation Level (1-7; ideal pulse peak-to-peak of 1-7mA) was considered, specifically in the context of stimulation current Root Mean Square (RMS). Data from the heat phantom were verified with the SCS heat-transfer models. A custom high-bandwidth stimulator provided 10 kHz pulses and sinusoidal stimulation for control experiments.

RESULTS

The 10 kHz SCS system delivers 10 kHz biphasic pulses (30-20-30 μs). Voltage compliance was 15.6V. Even below voltage compliance, IPG bandwidth attenuated pulse waveform, limiting applied RMS. Temperature increased supralinearly with stimulation Level in a manner predicted by applied RMS. ΔT increases with Level and impedance until stimulator compliance was reached. Therefore, IPG bandwidth and compliance dampen peak heating. Nonetheless, temperature increases predicted by bioheat multi-physic models (ΔT = 0.64°C and 1.42°C respectively at Level 4 and 7 at the cervical segment; ΔT = 0.68°C and 1.72°C respectively at Level 4 and 7 at the thoracic spinal cord)-within ranges previously reported to effect neurophysiology.

CONCLUSIONS

Heating of spinal tissues by this 10 kHz SCS system theoretically increases quickly with stimulation level and load impedance, while dampened by IPG pulse bandwidth and voltage compliance limitations. If validated in vivo as a mechanism of kHz SCS, bioheat models informed by IPG limitations allow prediction and optimization of temperature changes.

Spinal Cord Stimulation and Treatment of Peripheral or Central Neuropathic Pain: Mechanisms and Clinical Application

Spinal cord stimulation (SCS) as an evidence-based interventional treatment has been used and approved for clinical use in a variety of pathological states including peripheral neuropathic pain; however, until now, it has not been used for the treatment of spinal cord injury- (SCI-) induced central neuropathic pain. This paper reviews the underlying mechanisms of SCS-induced analgesia and its clinical application in the management of peripheral and central neuropathic pain. Evidence from recent research publications indicates that nociceptive processing at peripheral and central sensory systems is thought to be modulated by SCS through (i) inhibition of the ascending nociceptive transmission by the release of analgesic neurotransmitters such as GABA and endocannabinoids at the spinal dorsal horn; (ii) facilitation of the descending inhibition by release of noradrenalin, dopamine, and serotonin acting on their receptors in the spinal cord; and (iii) activation of a variety of supraspinal brain areas related to pain perception and emotion. These insights into the mechanisms have resulted in the clinically approved use of SCS in peripheral neuropathic pain states like Complex Regional Pain Syndrome (CRPS) and Failed Back Surgery Syndrome (FBSS). However, the mechanisms underlying SCS-induced pain relief in central neuropathic pain are only partly understood, and more research is needed before this therapy can be implemented in SCI patients with central neuropathic pain.

Exploration of the Supraspinal Hypotheses about Spinal Cord Stimulation and Dorsal Root Ganglion Stimulation: A Systematic Review

Despite the established efficacy and effectiveness of Spinal Cord Stimulation (SCS), there is still no consensus on the supraspinal mechanisms of action of this therapy. The purpose of this study was to systematically review previously raised hypotheses concerning supraspinal mechanisms of action of SCS based on human, animal and computational studies. Searches were conducted using four electronic databases (PubMed, EMBASE, SCOPUS and Web of Science), backward reference searching and consultation with experts. The study protocol was registered prior to initiation of the review process (PROSPERO CRD42020161531). A total of 54 publications were included, 21 of which were animal studies, and 33 were human studies. The supraspinal hypotheses (n = 69) identified from the included studies could be categorized into six groups concerning the proposed supraspinal hypothesis, namely descending pathways (n = 24); ascending medial pathway (n = 13); ascending lateral pathway (n = 10); affective/motivational influences (n = 8); spinal–cerebral (thalamic)-loop (n = 3) and miscellaneous (n = 11). Scientific support is provided for the hypotheses identified. Modulation of the descending nociceptive inhibitory pathways, medial and lateral pathways were the most frequently reported hypotheses about the supraspinal mechanisms of action of SCS. These hypotheses were mainly supported by studies with a high or moderate confidence in the body of evidence.

High-frequency spinal cord stimulation treatment attenuates the increase in spinal glutamate release and spinal miniature excitatory postsynaptic currents in rats with spared nerve injury-induced neuropathic pain

High-frequency spinal cord stimulation (HFSCS) at 10 kHz provides paresthesia-free treatment for chronic pain. However, the underlying mechanisms of its action have not been fully elucidated. The aim of the present study was to investigate the effect of HFSCS treatment on spinal glutamate release and uptake in spared nerve injury (SNI) rats. HFSCS was applied to the T10/T11 spinal cord 3 days after SNI. The concentration of spinal glutamate, glutamate transporter activity and miniature excitatory postsynaptic currents (mEPSCs) from neurons in lamina II were evaluated. HFSCS treatment alleviated SNI pain induced by mechanical and cold allodynia. HFSCS treatment also partially restored altered spinal glutamate uptake activity, the levels of spinal glutamate, and the frequency of mEPSCs following SNI. In conclusion, HFSCS treatment attenuated SNI-induced neuropathic pain and partially restored the altered glutamate uptake after SNI.

Early high-frequency spinal cord stimulation treatment inhibited the activation of spinal mitogen-activated protein kinases and ameliorated spared nerve injury-induced neuropathic pain in rats

BACKGROUND

Neuromodulation therapies offer a treatment option that has minimal side effects and is relatively safe and potentially reversible. Spinal cord stimulation (SCS) has been used to treat various pain conditions for many decades. High-frequency SCS (HFSCS) involves the application of a single waveform at 10,000 Hz at a subthreshold level, therefore providing pain relief without any paresthesia.

METHODS

We tested whether early HFSCS treatment attenuated spared nerve injury (SNI)-induced neuropathic pain. The phosphorylation profile of mitogen-activated protein kinases (MAPKs), i.e., extracellular signal-regulated kinases (ERKs), c-Jun N-terminal kinases (JNKs), and p38, was evaluated to elucidate the potential underlying mechanism.

RESULTS

SNI of rat unilateral sciatic nerves induced mechanical hyperalgesia in the ipsilateral hind paws. Rats were assigned to SCS sessions with HFSCS (frequency 10 kHz; pulse width 30 μs; pulse shape of charge-balanced, current controlled; delivered continuously for 72 h), or sham stimulation immediately after SNI. Tissue samples were examined at 1, 3, 7, and 14 days after SNI. Behavioral studies showed that HFSCS applied to the T10/T11 spinal cord significantly attenuated SNI-induced mechanical hyperalgesia compared with the sham stimulation group. Moreover, western blotting revealed a significant attenuation of the activation of ERK1, ERK2, JNK1, and p38 in the dorsal root ganglia and the spinal dorsal horn.

CONCLUSION

Application of HFSCS provides an effective treatment for SNI-induced persistent mechanical hyperalgesia by attenuating ERK, JNK, and p38 activation in the dorsal root ganglia and the spinal dorsal horn.

Epidural Spinal Cord Stimulation Promotes Motor Functional Recovery by Enhancing Oligodendrocyte Survival and Differentiation and by Protecting Myelin after Spinal Cord Injury in Rats

Epidural spinal cord stimulation (ESCS) markedly improves motor and sensory function after spinal cord injury (SCI), but the underlying mechanisms are unclear. Here, we investigated whether ESCS affects oligodendrocyte differentiation and its cellular and molecular mechanisms in rats with SCI. ESCS improved hindlimb motor function at 7 days, 14 days, 21 days, and 28 days after SCI. ESCS also significantly increased the myelinated area at 28 days, and reduced the number of apoptotic cells in the spinal white matter at 7 days. SCI decreased the expression of 2',3'-cyclic-nucleotide 3'-phosphodiesterase (CNPase, an oligodendrocyte marker) at 7 days and that of myelin basic protein at 28 days. ESCS significantly upregulated these markers and increased the percentage of Sox2/CNPase/DAPI-positive cells (newly differentiated oligodendrocytes) at 7 days. Recombinant human bone morphogenetic protein 4 (rhBMP4) markedly downregulated these factors after ESCS. Furthermore, ESCS significantly decreased BMP4 and p-Smad1/5/9 expression after SCI, and rhBMP4 reduced this effect of ESCS. These findings indicate that ESCS enhances the survival and differentiation of oligodendrocytes, protects myelin, and promotes motor functional recovery by inhibiting the BMP4-Smad1/5/9 signaling pathway after SCI.

Spinal cord stimulation in chronic pain: evidence and theory for mechanisms of action

Well-established in the field of bioelectronic medicine, Spinal Cord Stimulation (SCS) offers an implantable, non-pharmacologic treatment for patients with intractable chronic pain conditions. Chronic pain is a widely heterogenous syndrome with regard to both pathophysiology and the resultant phenotype. Despite advances in our understanding of SCS-mediated antinociception, there still exists limited evidence clarifying the pathways recruited when patterned electric pulses are applied to the epidural space. The rapid clinical implementation of novel SCS methods including burst, high frequency and dorsal root ganglion SCS has provided the clinician with multiple options to treat refractory chronic pain. While compelling evidence for safety and efficacy exists in support of these novel paradigms, our understanding of their mechanisms of action (MOA) dramatically lags behind clinical data. In this review, we reconstruct the available basic science and clinical literature that offers support for mechanisms of both paresthesia spinal cord stimulation (P-SCS) and paresthesia-free spinal cord stimulation (PF-SCS). While P-SCS has been heavily examined since its inception, PF-SCS paradigms have recently been clinically approved with the support of limited preclinical research. Thus, wide knowledge gaps exist between their clinical efficacy and MOA. To close this gap, many rich investigative avenues for both P-SCS and PF-SCS are underway, which will further open the door for paradigm optimization, adjunctive therapies and new indications for SCS. As our understanding of these mechanisms evolves, clinicians will be empowered with the possibility of improving patient care using SCS to selectively target specific pathophysiological processes in chronic pain.

Supraspinal Mechanisms of Spinal Cord Stimulation for Modulation of Pain: Five Decades of Research and Prospects for the Future

The field of spinal cord stimulation is expanding rapidly, with new waveform paradigms asserting supraspinal sites of action. The scope of treatment applications is also broadening from chronic pain to include cerebral ischemia, dystonia, tremor, multiple sclerosis, Parkinson disease, neuropsychiatric disorders, memory, addiction, cognitive function, and other neurologic diseases. The role of neurostimulation as an alternative strategy to opioids for chronic pain treatment is under robust discussion in both scientific and public forums. An understanding of the supraspinal mechanisms underlying the beneficial effects of spinal cord stimulation will aid in the appropriate application and development of optimal stimulation strategies for modulating pain signaling pathways. In this review, the authors focus on clinical and preclinical studies that indicate the role of supraspinal mechanisms in spinal cord stimulation-induced pain inhibition, and explore directions for future investigations.

Dependence of c-fos Expression on Amplitude of High-Frequency Spinal Cord Stimulation in a Rodent Model

OBJECTIVES

Clinical high-frequency spinal cord stimulation (hfSCS) (>250 Hz) applied at subperception amplitudes reduces leg and low back pain. This study investigates, via labeling for c-fos-a marker of neural activation, whether 500 Hz hfSCS applied at amplitudes above and below the dorsal column (DC) compound action potential (CAP) threshold excites dorsal horn neurons.

MATERIALS AND METHODS

DC CAP thresholds in rats were determined by applying single biphasic pulses of SCS to T₁₂ -T₁₃ segments using pulse widths of 40 or 200 μsec via a ball electrode placed over the left DC and increasing amplitude until a short latency CAP was observed on the L₅ DC and sciatic nerve. The result of this comparison allowed us to substitute sciatic nerve CAP for DC CAP. SCS at T₁₂ -T₁₃ was applied continuously for two hours using: sham or hfSCS at 500 Hz SCS, 40 μsec pulse width, and 50, 70, 90, or 140% CAP threshold. Spinal cord slices from T₁₁ -L₁ were immunolabeled for c-fos, and the number of c-fos-positive cells was quantified.

RESULTS

500 Hz hfSCS applied at 90 and 140% CAP threshold produced substantial (≥6 c-fos + neurons on average per slice per segment) c-fos expression in more segments between T₁₁ and L₁ than did sham stimulation (p < 0.025, 90% CAP; p < 0.001, 140% CAP, Fisher's Exact Tests) and resulted in more c-fos-positive neurons on average per slice per segment ipsilateral to than contralateral to the SCS electrode at 70, 90, and 140% CAP threshold (p < 0.01, Wilcoxon Signed Rank Tests).

CONCLUSIONS

The finding of enhanced c-fos expression in the ipsilateral superficial dorsal horn provides evidence for activation/modulation of neuronal circuitry associated with subperception hfSCS.

Spinal Cord Stimulation: Clinical Efficacy and Potential Mechanisms

Spinal cord stimulation (SCS) is a minimally invasive therapy used for the treatment of chronic neuropathic pain. SCS is a safe and effective alternative to medications such as opioids, and multiple randomized controlled studies have demonstrated efficacy for difficult-to-treat neuropathic conditions such as failed back surgery syndrome. Conventional SCS is believed mediate pain relief via activation of dorsal column Aβ fibers, resulting in variable effects on sensory and pain thresholds, and measurable alterations in higher order cortical processing. Although potentiation of inhibition, as suggested by Wall and Melzack's gate control theory, continues to be the leading explanatory model, other segmental and supraspinal mechanisms have been described. Novel, non-standard, stimulation waveforms such as high-frequency and burst have been shown in some studies to be clinically superior to conventional SCS, however their mechanisms of action remain to be determined. Additional studies are needed, both mechanistic and clinical, to better understand optimal stimulation strategies for different neuropathic conditions, improve patient selection and optimize efficacy.

Spinal Cord Stimulation for Treating Chronic Pain: Reviewing Preclinical and Clinical Data on Paresthesia-Free High-Frequency Therapy

BACKGROUND

Traditional spinal cord stimulation (SCS) requires that paresthesia overlaps chronic painful areas. However, the new paradigm high-frequency SCS (HF-SCS) does not rely on paresthesia.

STUDY DESIGN

A review of preclinical and clinical studies regarding the use of paresthesia-free HF-SCS for various chronic pain states.

METHODS

We reviewed available literatures on HF-SCS, including Nevro's paresthesia-free ultra high-frequency 10 kHz therapy (HF10-SCS). Data sources included relevant literature identified through searches of PubMed, MEDLINE/OVID, and SCOPUS, and manual searches of the bibliographies of known primary and review articles.

OUTCOME MEASURES

The primary goal is to describe the present developing conceptions of preclinical mechanisms of HF-SCS and to review clinical efficacy on paresthesia-free HF10-SCS for various chronic pain states.

RESULTS

HF10-SCS offers a novel pain reduction tool without paresthesia for failed back surgery syndrome and chronic axial back pain. Preclinical findings indicate that potential mechanisms of action for paresthesia-free HF-SCS differ from those of traditional SCS.

CONCLUSIONS

To fully understand and utilize paresthesia-free HF-SCS, mechanistic study and translational research will be very important, with increasing collaboration between basic science and clinical communities to design better trials and optimize the therapy based on mechanistic findings from effective preclinical models and approaches. Future research in these vital areas may include preclinical and clinical components conducted in parallel to optimize the potential of this technology.

Electrical stimulation of the dorsal columns of the spinal cord for Parkinson's disease

Spinal cord stimulation has been used for the treatment of chronic pain for decades. In 2009, our laboratory proposed, based on studies in rodents, that electrical stimulation of the dorsal columns of the spinal cord could become an effective treatment for motor symptoms associated with Parkinson's disease (PD). Since our initial report in rodents and a more recent study in primates, several clinical studies have now described beneficial effects of dorsal column stimulation in parkinsonian patients. In primates, we have shown that dorsal column stimulation activates multiple structures along the somatosensory pathway and desynchronizes the pathological cortico-striatal oscillations responsible for the manifestation of PD symptoms. Based on recent evidence, we argue that neurological disorders such as PD can be broadly classified as diseases emerging from abnormal neuronal timing, leading to pathological brain states, and that the spinal cord could be used as a "channel" to transmit therapeutic electrical signals to disrupt these abnormalities. © 2017 International Parkinson and Movement Disorder Society.

Lack of Analgesic Synergy of the Cholecystokinin Receptor Antagonist Proglumide and Spinal Cord Stimulation for the Treatment of Neuropathic Pain in Rats

OBJECTIVE

Neuropathic pain is difficult to manage and treat. Spinal cord stimulation (SCS) has become an established procedure for treating chronic neuropathic pain that is refractory to pharmacological therapy. In order to achieve better analgesia, a number of studies have evaluated the effectiveness of combining drug therapy with SCS. Cholecystokinin antagonists, such as proglumide, enhance the analgesic efficacy of endogenous opioids in animal models of pain. We previously reported that both systemic and spinal administration of proglumide enhances analgesia produced by both low- and high-frequency transcutaneous electrical nerve stimulation (TENS). Since SCS produces analgesia through endogenous opioids, we hypothesized that the analgesic effect of SCS would be enhanced through co-administration with proglumide in animals with neuropathic pain.

MATERIALS AND METHODS

Male Sprague-Dawley rats (n = 40) with spared nerve injury were given proglumide (20 mg/kg, i.p.) or saline prior to treatment with SCS (sham, 4 Hz, and 60 Hz). Mechanical withdrawal thresholds of the paw were measured before and after induction of nerve injury, and after SCS. Physical activity levels were measured after SCS.

RESULTS

Both proglumide and SCS when given independently significantly increased withdrawal thresholds two weeks after nerve injury. However, there was no additional effect of combining proglumide and SCS on mechanical withdrawal thresholds or activity levels in animals with nerve injury.

DISCUSSION AND CONCLUSIONS

Proglumide may be a candidate for achieving analgesia for patients with refractory neuropathic pain conditions, but does not enhance analgesia produced by SCS.

Spinal cord stimulation in experimental chronic painful diabetic polyneuropathy: Delayed effect of High-frequency stimulation

Background

Spinal cord stimulation (SCS) has been shown to provide pain relief in painful diabetic polyneuropathy (PDPN). As the vasculature system plays a great role in the pathophysiology of PDPN, a potential beneficial side‐effect of SCS is peripheral vasodilation, with high frequency (HF) SCS in particular. We hypothesize that HF‐SCS (500 Hz), compared with conventional (CON) or low frequency (LF)‐SCS will result in increased alleviation of mechanical hypersensitivity in chronic experimental PDPN.

Methods

Diabetes was induced in 8‐week‐old female Sprague–Dawley rats with an intraperitoneal injection of 65 mg/kg of streptozotocin (n = 44). Rats with a significant decrease in mechanical withdrawal response to von Frey filaments over a period of 20 weeks were implanted with SCS electrodes (n = 18). Rats were assigned to a cross‐over design with a random order of LF‐, CON‐, HF‐ and sham SCS and mechanical withdrawal thresholds were assessed with von Frey testing.

Results

Compared with sham treatment, the average 50% WT score for 5 Hz was 4.88 g higher during stimulation (p = 0.156), and 1.77 g higher post‐stimulation (p = 0.008). CON‐SCS resulted in 50% WT scores 5.7 g, and 2.51 g higher during (p = 0.064) and after stimulation (p < 0.004), respectively. HF‐SCS started out with an average difference in 50% WT score compared with sham of 1.87 g during stimulation (p = 0.279), and subsequently the steepest rise to a difference of 5.47 g post‐stimulation (p < 0.001).

Conclusions

We demonstrated a delayed effect of HF‐SCS on mechanical hypersensitivity in chronic PDPN animals compared with LF‐, or CON‐SCS.

Significance

This study evaluates the effect of SCS frequency (5–500 Hz) on mechanical hypersensitivity in the chronic phase of experimental PDPN. High frequency (500 Hz) – SCS resulted in a delayed effect‐ on pain‐related behavioural outcome in chronic PDPN.

Effects of Spinal Cord Stimulation on Pain Thresholds and Sensory Perceptions in Chronic Pain Patients

OBJECTIVE

Spinal cord stimulation (SCS) has been in clinical use for nearly four decades. In earliest observations, researchers found a significant increase in pain threshold during SCS therapy without changes associated with touch, position, and vibration sensation. Subsequent studies yielded diverse results regarding how SCS impacts pain and other sensory thresholds. This pilot study uses quantitative sensory testing (QST) to objectively quantify the impact of SCS on warm sensation, heat pain threshold, and heat pain tolerance.

MATERIALS AND METHODS

Nineteen subjects with an indwelling SCS device for chronic pain were subjected to QST with heat stimuli. QST was performed on an area of pain covered with SCS-induced paresthesia and an area without pain and without paresthesia, while the SCS was turned off and on. The temperature at which the patient detected warm sensation, heat pain, and maximal tolerable heat pain was used to define the thresholds.

RESULTS

We found that all three parameters, the detection of warm sensation, heat pain threshold, and heat pain tolerance, were increased during the period when SCS was on compared with when it was off. This increase was observed in both painful and non-painful sites.

CONCLUSION

The observed pain relief during SCS therapy seems to be related to its impact on increased sensory threshold as detected in this study. The increased sensory threshold on areas without pain and without the presence of SCS coverage may indicate a central (spinal and/or supra-spinal) influence from SCS.

Electrical stimulation of dorsal root entry zone attenuates wide-dynamic-range neuronal activity in rats

OBJECTIVES

Recent clinical studies suggest that neurostimulation at the dorsal root entry zone (DREZ) may alleviate neuropathic pain. However, the mechanisms of action for this therapeutic effect are unclear. Here, we examined whether DREZ stimulation inhibits spinal wide-dynamic-range (WDR) neuronal activity in nerve-injured rats.

MATERIALS AND METHODS

We conducted in vivo extracellular single-unit recordings of WDR neurons in rats after an L5 spinal nerve ligation (SNL) or sham surgery. We set bipolar electrical stimulation (50 Hz, 0.2 msec, 5 min) of the DREZ at the intensity that activated only Aα/β-fibers by measuring the lowest current at which DREZ stimulation evoked a peak antidromic sciatic Aα/β-compound action potential without inducing an Aδ/C-compound action potential (i.e., Ab1).

RESULTS

The elevated spontaneous activity rate of WDR neurons in SNL rats (n = 25; data combined from post-SNL groups at days 14-16 [n = 15] and days 45-75 [n = 10]) was significantly decreased from the prestimulation level (p < 0.01) at 0-15 min and 30-45 min post-stimulation. In both sham-operated (n = 8) and nerve-injured rats, DREZ stimulation attenuated the C-component, but not the A-component, of the WDR neuronal response to graded intracutaneous electrical stimuli (0.1-10 mA, 2 msec) applied to the skin receptive field. Further, DREZ stimulation blocked windup (a form of brief neuronal sensitization) to repetitive noxious stimuli (0.5 Hz) at 0-15 min in all groups (p < 0.05).

CONCLUSIONS

Attenuation of WDR neuronal activity may contribute to DREZ stimulation-induced analgesia. This finding supports the notion that DREZ may be a useful target for neuromodulatory control of pain.

Spinal autofluorescent flavoprotein imaging in a rat model of nerve injury-induced pain and the effect of spinal cord stimulation

Nerve injury may cause neuropathic pain, which involves hyperexcitability of spinal dorsal horn neurons. The mechanisms of action of spinal cord stimulation (SCS), an established treatment for intractable neuropathic pain, are only partially understood. We used Autofluorescent Flavoprotein Imaging (AFI) to study changes in spinal dorsal horn metabolic activity. In the Seltzer model of nerve-injury induced pain, hypersensitivity was confirmed using the von Frey and hotplate test. 14 Days after nerve-injury, rats were anesthetized, a bipolar electrode was placed around the affected sciatic nerve and the spinal cord was exposed by a laminectomy at T13. AFI recordings were obtained in neuropathic rats and a control group of naïve rats following 10 seconds of electrical stimulation of the sciatic nerve at C-fiber strength, or following non-noxious palpation. Neuropathic rats were then treated with 30 minutes of SCS or sham stimulation and AFI recordings were obtained for up to 60 minutes after cessation of SCS/sham. Although AFI responses to noxious electrical stimulation were similar in neuropathic and naïve rats, only neuropathic rats demonstrated an AFI-response to palpation. Secondly, an immediate, short-lasting, but strong reduction in AFI intensity and area of excitation occurred following SCS, but not following sham stimulation. Our data confirm that AFI can be used to directly visualize changes in spinal metabolic activity following nerve injury and they imply that SCS acts through rapid modulation of nociceptive processing at the spinal level.

Chronic spinal cord electrical stimulation protects against 6-hydroxydopamine lesions

Although L-dopa continues to be the gold standard for treating motor symptoms of Parkinson's disease (PD), it presents long-term complications. Deep brain stimulation is effective, but only a small percentage of idiopathic PD patients are eligible. Based on results in animal models and a handful of patients, dorsal column stimulation (DCS) has been proposed as a potential therapy for PD. To date, the long-term effects of DCS in animal models have not been quantified. Here, we report that DCS applied twice a week in rats treated with bilateral 6-OHDA striatal infusions led to a significant improvement in symptoms. DCS-treated rats exhibited a higher density of dopaminergic innervation in the striatum and higher neuronal cell count in the substantia nigra pars compacta compared to a control group. These results suggest that DCS has a chronic therapeutical and neuroprotective effect, increasing its potential as a new clinical option for treating PD patients.

Conventional and kilohertz-frequency spinal cord stimulation produces intensity- and frequency-dependent inhibition of mechanical hypersensitivity in a rat model of neuropathic pain

BACKGROUND

Spinal cord stimulation (SCS) is a useful neuromodulatory technique for treatment of certain neuropathic pain conditions. However, the optimal stimulation parameters remain unclear.

METHODS

In rats after L5 spinal nerve ligation, the authors compared the inhibitory effects on mechanical hypersensitivity from bipolar SCS of different intensities (20, 40, and 80% motor threshold) and frequencies (50, 1 kHz, and 10 kHz). The authors then compared the effects of 1 and 50 Hz dorsal column stimulation at high- and low-stimulus intensities on conduction properties of afferent Aα/β-fibers and spinal wide-dynamic-range neuronal excitability.

RESULTS

Three consecutive daily SCS at different frequencies progressively inhibited mechanical hypersensitivity in an intensity-dependent manner. At 80% motor threshold, the ipsilateral paw withdrawal threshold (% preinjury) increased significantly from pre-SCS measures, beginning with the first day of SCS at the frequencies of 1 kHz (50.2 ± 5.7% from 23.9 ± 2.6%, n = 19, mean ± SEM) and 10 kHz (50.8 ± 4.4% from 27.9 ± 2.3%, n = 17), whereas it was significantly increased beginning on the second day in the 50 Hz group (38.9 ± 4.6% from 23.8 ± 2.1%, n = 17). At high intensity, both 1 and 50 Hz dorsal column stimulation reduced Aα/β-compound action potential size recorded at the sciatic nerve, but only 1 kHz stimulation was partially effective at the lower intensity. The number of actions potentials in C-fiber component of wide-dynamic-range neuronal response to windup-inducing stimulation was significantly decreased after 50 Hz (147.4 ± 23.6 from 228.1 ± 39.0, n = 13), but not 1 kHz (n = 15), dorsal column stimulation.

CONCLUSIONS

Kilohertz SCS attenuated mechanical hypersensitivity in a time course and amplitude that differed from conventional 50 Hz SCS, and may involve different peripheral and spinal segmental mechanisms.

The rostroventromedial medulla is engaged in the effects of spinal cord stimulation in a rodent model of neuropathic pain

The neurobiological mechanisms underlying the suppression of neuropathic pain by spinal cord stimulation (SCS) are still incompletely known. The present study aims at exploring whether the descending pain control system in the rostroventromedial medulla (RVM) exerts a role in the attenuation of neuropathic pain by SCS. Experiments were performed in the rat spared nerve injury (SNI) pain model. The effects of SCS on neuronal activity of pronociceptive ON-like, antinociceptive OFF-like, and neutral cells, including 5-HT-like cells, in the RVM were analyzed in SCS responding and SCS non-responding SNI animals as well as in naïve controls. Decreased spontaneous activities in OFF-like cells and increased spontaneous activities in ON-like cells were observed in SNI animals, whereas the spontaneous activities of 5-HT-like and neutral cells were unchanged. SCS produced a prominent increase in the discharge of OFF- and 5-HT-like cells in SCS responding, but not in non-responding SNI animals or controls. Discharge rates of ON-like and neutral cell were not affected by SCS. In awake SNI animals, microinjection of a GABAA receptor agonist, muscimol, into the RVM significantly attenuated the antihypersensitivity effect induced by SCS while a non-selective opioid receptor antagonist, naltrexone, was ineffective. It is concluded that SCS may shift the reciprocal inhibitory and facilitatory pain modulation balance controlled by the RVM in favor of inhibition. This increase in the descending antinociceptive effect operates in concert with segmental spinal mechanisms in producing pain relief.

The effect of spinal cord stimulation frequency in experimental painful diabetic polyneuropathy

BACKGROUND

Spinal cord stimulation (SCS) has been shown to be an effective treatment for painful diabetic polyneuropathy (PDP). An increase of efficacy is needed since only 67% of patients benefit from SCS. This study aimed to develop an animal model for SCS in PDP and study the effect of various stimulation frequencies on the functional outcome. As the pathophysiology of PDP is complex, including vasoconstriction and nerve injury, the frequency of SCS may result in different outcomes.

METHODS

Diabetes mellitus was induced by an intraperitoneal injection of streptozotocin in 8-week-old female Sprague-Dawley rats (n=76; glucose >15 mmol/L; n=51). A SCS device was implanted at level Th13 4 weeks later. SCS of the dorsal columns was applied for 30 min and the effect on mechanical hypersensitivity was evaluated.

RESULTS

Mechanical hypersensitivity developed in 26 rats, which were included (low-frequency, n=6; mid-frequency, n=8; high frequency, n=9; and sham, n=3). SCS of the dorsal columns was applied for 40 min, and the effect on mechanical hypersensitivity was evaluated. In all treatment groups, SCS resulted in reversal of mechanical hypersensitivity and a clinically relevant reduction was achieved in 70% of animals. No differences in efficacy were found between the different treatment groups.

CONCLUSIONS

The pain-relieving effect of SCS in PDP was studied in an experimental model. Our study shows that SCS on mechanical hypersensitivity in PDP rats is equally effective when applied at low, mid and high frequency.

Mapping brain regions in which deep brain stimulation affects schizophrenia-like behavior in two rat models of schizophrenia

BACKGROUND AND OBJECTIVES

The development of more efficient treatment remains a major unmet need in the realm of schizophrenia disease. Using the maternal immune stimulation and the pubertal cannabinoid administration rat model of schizophrenia, the present study aimed at testing the hypothesis that deep brain stimulation (DBS) serves as a novel therapeutic technique for this disorder.

METHODS

Adult offspring of dams, treated with the immune activating agent poly I:C (4 mg/kg, n = 50) or saline (n = 50), underwent bilateral stereotactic electrode implantation into one of the following brain regions: subthalamic nucleus (STN, n = 12/10), entopeduncularis nucleus (EP, n = 10/11), globus pallidus (GP, n = 10/10), medial prefrontal cortex (mPFC, n = 8/8), or dorsomedial thalamus (DM, n = 10/11). Adult rats treated with the CB1 receptor agonist WIN 55,212-2 (WIN, n = 16) or saline (n = 12) during puberty were bilaterally implanted with electrodes into either the mPFC (n = 8/6) or the DM (n = 8/6). After a post-operative recovery period of one week, all rats were tested on a well-established cross-species phenomenon that is disrupted in schizophrenia, the pre-pulse inhibition (PPI) of the acoustic startle reflex (ASR) under different DBS conditions.

RESULTS

Poly I:C induced deficits in PPI of the ASR were normalized upon DBS. DBS effects depended on both stimulation target and stimulation parameters. Most prominent effects were found under DBS at high frequencies in the mPFC and DM. These effects were replicated in the pubertal WIN administration rat model of schizophrenia.

CONCLUSIONS

Brain regions, in which DBS normalized PPI deficits, might be of therapeutic relevance to the treatment of schizophrenia. Results imply that DBS could be considered a plausible therapeutic technique in the realm of schizophrenia disease.

Spinal cord stimulation: neurophysiological and neurochemical mechanisms of action

Chronic neuropathic pain can significantly reduce quality of life and place an economic burden on individuals and society. Spinal cord stimulation (SCS) is an alternative approach to the treatment of neuropathic pain when standard pharmacological agents have failed. However, an improved understanding of the mechanisms by which SCS inhibits pain is needed to enhance its clinical utility. This review summarizes important findings from recent studies of SCS in animal models of neuropathic pain, highlights current understanding of the spinal neurophysiological and neurochemical mechanisms by which SCS produces an analgesic effect, and discusses the potential clinical applicability of these findings and future directions for research.

Decreased intracellular GABA levels contribute to spinal cord stimulation-induced analgesia in rats suffering from painful peripheral neuropathy: the role of KCC2 and GABA(A) receptor-mediated inhibition

Elevated spinal extracellular γ-aminobutyric acid (GABA) levels have been described during spinal cord stimulation (SCS)-induced analgesia in experimental chronic peripheral neuropathy. Interestingly, these increased GABA levels strongly exceeded the time frame of SCS-induced analgesia. In line with the former, pharmacologically-enhanced extracellular GABA levels by GABA(B) receptor agonists in combination with SCS in non-responders to SCS solely could convert these non-responders into responders. However, similar treatment with GABA(A) receptor agonists and SCS is known to be less efficient. Since K⁺ Cl⁻ cotransporter 2 (KCC2) functionality strongly determines proper GABA(A) receptor-mediated inhibition, both decreased numbers of GABA(A) receptors as well as reduced KCC2 protein expression might play a pivotal role in this loss of GABA(A) receptor-mediated inhibition in non-responders. Here, we explored the mechanisms underlying both changes in extracellular GABA levels and impaired GABA(A) receptor-mediated inhibition after 30 min of SCS in rats suffering from partial sciatic nerve ligation (PSNL). Immediately after cessation of SCS, a decreased spinal intracellular dorsal horn GABA-immunoreactivity was observed in responders when compared to non-responders or sham SCS rats. One hour later however, GABA-immunoreactivity was already increased to similar levels as those observed in non-responder or sham SCS rats. These changes did not coincide with alterations in the number of GABA-immunoreactive cells. C-Fos/GABA double-fluorescence clearly confirmed a SCS-induced activation of GABA-immunoreactive cells in responders immediately after SCS. Differences in spinal dorsal horn GABA(A) receptor-immunoreactivity and KCC2 protein levels were absent between all SCS groups. However, KCC2 protein levels were significantly decreased compared to sham PSNL animals. In conclusion, reduced intracellular GABA levels are only present during the time frame of SCS in responders and strongly point to a SCS-mediated on/off GABAergic release mechanism. Furthermore, a KCC2-dependent impaired GABA(A) receptor-mediated inhibition seems to be present both in responders and non-responders to SCS due to similar KCC2 and GABA(A) receptor levels.

Central administration of neuronostatin induces antinociception in mice

Neuronostatin, a recently discovered endogenous bioactive peptide, was encoded by pro-mRNA of somatostatin that contributes to modulation of nociception. However, nociceptive effect of neuronostatin is still not fully known. The aim of this study was to evaluate effect of neuronostatin on nociception and elucidate its possible mechanism of action. Intracerebroventricular (i.c.v.) administration of neuronostatin (0.3, 3, 6, 12nmol/mouse) produced a dose- and time-related antinociceptive effect in the tail immersion assay in mice, an acute pain model. The antinociceptive effect of neuronostatin was significantly antagonized by naloxone, and was strongly inhibited by co-injection with β-funaltrexamine or nor-binaltorphimine, but not by naltrindole. Also, melanocortin 3/4 receptor antagonist, SHU9119, completely blocked the effect of neuronostatin. These data indicated the involvement of both μ- and κ-opioid receptors and central melanocortin system in the analgesic response induced by neuronostatin. In addition, neuronostatin (6nmol, i.c.v.) increased c-Fos protein expression in the periaqueductal gray (PAG) and the nucleus raphe magnus (NRM) that have a pivotal role in regulating descending pain pathways. Taken together, this study is the first to reveal that neuronostatin produces antinociceptive effect via opioid and central melanocortin systems, which is associated with an increase in neuronal activity the PAG and NRM.

Deep brain stimulation in clinical trials and animal models of depression

Deep brain stimulation (DBS) is currently being investigated as a therapy for the treatment of depression. Despite promising results of recent clinical trials, neural and chemical mechanisms responsible for the effects of stimulation are still unclear. In this article, we review clinical and laboratory findings on DBS for depression. Particular emphasis will be given to aspects involved in the translation of data from animal models to humans and in our findings on the potential substrates involved in the antidepressant effects of DBS in rats.

Effects of different stimulation parameters on the antidepressant-like response of medial prefrontal cortex deep brain stimulation in rats

Subcallosal cingulate gyrus (SCG) deep brain stimulation (DBS) is currently being investigated as a treatment for major depression. Despite the encouraging findings of the initial clinical series, several questions remain unanswered, including the most effective stimulation parameters (i.e., current intensity and frequency) and whether unilateral stimulation is also beneficial. We have recently found that some of the effects of SCG DBS could be modeled by stimulating the ventromedial prefrontal cortex (vmPFC) of rats undergoing the forced swim test (FST). Here we investigate whether changes in a number of DBS parameters, including electrode placement, influence outcome in this paradigm. Overall, we found that the antidepressant-like effects of DBS varied as a function of stimulation settings and target. The strongest response was observed with a current intensity of 200 microA, followed by 100 microA, and 300 microA. In contrast, 400 microA produced no effect. Using 200 microA, a frequency of 130 Hz was more effective than 20 Hz. An intriguing finding was that left unilateral stimulation was as effective as bilateral DBS. When different targets within the vmPFC were considered, a significant antidepressant-like response was observed after PL DBS, whereas IL stimulation was associated with a non-significant reduction in immobility scores. In summary, vmPFC DBS at high frequency and moderate intensity led to a maximal response in the FST.