Investigation of Corticospinal Excitability Aspects of Itch and Pain

Aalborg University30 enrolled

Overview

The experiment consists of three experimental sessions conducted over a period of two weeks. In the first experimental session, we apply in your hand: either an injection of salt water (7% NaCl) or we apply small needles from the plant mucuna pruriens or histamine (1%). For 10 minutes after this, you are to assess the itch and pain you perceive. We will also apply non-invasive magnetic stimulations to your brain. During the experiment, you should fill in questionnaires. The second and third experimental sessions are conducted in the same way as the first session. The purpose of this experiment is to investigate the changes appearing in the brain during artificially applied itch and pain corticomotor adaptations.

The experiment consists of three experimental sessions conducted over a period of two weeks. The duration of each session is approx. two hours. In the first experimental session, we apply one of three experimental methods in your hand: either an injection of salt water (7% NaCl) or we apply small needles from the plant mucuna pruriens or histamine (1%) Histamine is an itch-provoking substance formed in the human body. For 10 minutes after this, you are to assess the itch and pain you perceive on a scale from 0 to 10, in which 0 is no itch/pain and 10 is worst itch/pain imaginable. We will also apply non-invasive magnetic stimulations to your brain. This is done using a magnetic coil which is held over your head. During the experiment, you should fill in questionnaires about how you experience itch/pain and about your personality. The second and third experimental sessions are conducted in the same way as the first session. However, we will apply one of the other two experimental methods than the one used in the first session (i.e., first session: histamine, second session: plant needles, third session: injection with salt water). The experimental methods will be applied in random order.

Study Type

INTERVENTIONAL

Allocation

Purpose

BASIC_SCIENCE

Masking

NONE

Interventions

Hypertonic SalineOTHER

A bolus injection of hypertonic saline (7% NaCl) will be administered to the FDI muscle using a 1 mL syringe with a disposable needle (27G), and the volume of the bolus will be 0.2 mL

HistamineOTHER

A small drop of histamine dihydrochloride will be applied to a previously determined area on the volar forearm, followed by a prick through the drop

CowhageOTHER

This insertion is conducted by forceps using a stereo-microscope, and 30-35 spicules are gently rubbed into a 1 cm diameter skin area.

Transcranial magnetic stimulation (TMS)DEVICE

Transcranial magnetic stimulation (TMS) will be used to evoke motor-evoked potentials (MEPs) in the muscle of interest and cortical responses (TMS-evoked potentials - TEPs) in the motor cortex with a figure-eight-shaped cone coil.

Eligibility

Sex: ALLMin age: 18 YearsMax age: 60 YearsHealthy volunteers:

Medical Language ↔ Plain English

Inclusion Criteria: * Healthy men and women * 18-60 years * Speak and understand English Exclusion Criteria: * Pregnancy or lactation * Drug addiction defined as any use of cannabis, opioids, or other addictive drugs * Previous or current history of neurological (e.g. neuropathy), immunological (e.g. asthma, immune deficiencies, arthritis), musculoskeletal (e.g. muscular pain in the upper extremities,), cardiac disorder (e.g., heart stroke), or psychiatric diagnoses (e.g. depression) that may affect the results * Current use of medications that may affect the trial, such as antihistamines, antipsychotics, and painkillers, as well as systemic or topical steroids * Skin diseases (e.g., atopic dermatitis, pruritus nodularis, eczema, psoriasis) * Moles, scars, or tattoos in the area to be treated or tested. * Consumption of alcohol or painkillers 24 hours before the study days and between these * Acute or chronic pain * Unable to pass the "Transcranial Magnetic Stimulation Adult Safety Screen" (subproject 1 and 2) * Contraindications to transcranial magnetic stimulation (TMS) application (history of epilepsy, metal implants in head or jaw, etc.) (subproject 1 and 2) * Presence of implanted hearing aids or metal implants on the face, including permanent makeup or tattoos (subproject 1 and 2) * Participation in other trials within one week of study entry (four weeks in the case of pharmaceutical trials) * Lack of ability to cooperate

Outcomes

Primary Outcomes

Numeric rating scales (NRS)

NRS are essentially VAS but have tick marks spaced every centimeter so as to create 11-point scale (from 0 to 10). Subject can use these tick marks as a guide when they mark their severity on the scale.

Time frame: 1 minute after every itch/pain induction

Measuring corticospinal excitability

Time frame: Baseline

Measuring corticospinal excitability

Time frame: 1 minute after every itch/pain induction for 10 minutes

Measuring corticospinal excitability

Time frame: post induction (1 minute)

Measuring corticospinal excitability

Time frame: post induction (30 minutes)

electromyography (EMG) recordings

For electromyography (EMG) recordings, two electrodes (Disposable Electrode Pack - AMBU Neuroline 720) will be placed on the muscle belly of the FDI muscle. The reference electrode will be placed on the ulnar styloid process of the left arm.

Time frame: 1 minute after every itch/pain induction

Secondary Outcomes

Pain Catastrophizing Scale (PCS).

The PCS assesses negative and exaggerated coping concerning anticipated or experienced painful stimuli. Thirteen items have to be answered on a 5-point Likert-type scale.

Time frame: Baseline

Itch Catastrophizing Scale (ICS).

he ICS assesses negative and exaggerated coping concerning anticipated or experienced itchy stimuli. Thirteen items have to be answered on a 5-point Likert-type scale.

Time frame: Baseline

Reinforcement Sensitivity Theory - Personality Questionnaire (RST-PQ).

The RST-PQ contains the following subscales: the Fight-Flight-Freeze System (FFFS, 10 items), which represents a defensive factor related to active avoidance of adverse stimuli; the Behavioral Inhibition System (BIS, 23 items), which represents a defensive factor related to anxiety and passive avoidance of adverse stimuli; and the Behavioral Approach System (BAS, 32 items), which reflects reward interest, goal-drive persistence, reward reactivity, and impulsivity. In total, 65 items have to be answered on a 4-point Likert-type scale

Time frame: Baseline

The Pittsburg Sleep Quality Index (PSQI)

The PSQI consists of 19 items generating seven component scores: subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleeping medication, and daytime dysfunction. The seven component scores can be summarized in a global score ranging from zero to 21 with higher scores reflecting a worse overall quality of sleep

Time frame: Baseline

Depression, Anxiety, Stress Scale (DASS-21)

he questionnaire measures the magnitude of depression, anxiety, and stress. Each of these three subscales consists of 7 questions answered using a 0-3 Likert scale, with 0 meaning "it did not apply to me", and 3 meaning "it applied to me very much".

Time frame: Baseline

Learned Helplessness Scale (LHS)

The questionnaire consists of 20 items, and the participant's response to each item is rated on a 4-point Likert scale ranging from strongly agree (1) to strongly disagree (4).

Investigation of Corticospinal Excitability Aspects of Itch and Pain

Overview

Conditions

Interventions

Eligibility

Locations (1)

Outcomes

Primary Outcomes

Secondary Outcomes