Afferent nerve information underlying the effects of electroacupuncture in rat

Evidence of Long-range nerve pathways connecting and coordinating activity in secondary lymph organs

Background

Peripheral nerve reflexes enable organ systems to maintain long-term physiological homeostasis while responding to rapidly changing environmental conditions. Electrical nerve stimulation is commonly used to activate these reflexes and modulate organ function, giving rise to an emerging class of therapeutics called bioelectronic medicines. Dogma maintains that immune cell migration to and from organs is mediated by inflammatory signals (i.e. cytokines or pathogen associated signaling molecules). However, nerve reflexes that regulate immune function have only recently been elucidated, and stimulation of these reflexes for therapeutic effect has not been fully investigated.

Methods

We utilized both electrical and ultrasound-based nerve stimulation to activate nerve pathways projecting to specific lymph nodes. Tissue and cell analysis of the stimulated lymph node, distal lymph nodes and immune organs is then utilized to measure the stimulation-induced changes in neurotransmitter/neuropeptide concentrations and immune cellularity in each of these sites.

Results and conclusions

In this report, we demonstrate that activation of nerves and stimulated release of neurotransmitters within a local lymph node results in transient retention of immune cells (e.g. lymphocytes and neutrophils) at that location. Furthermore, such stimulation results in transient changes in neurotransmitter concentrations at distal organs of the immune system, spleen and liver, and mobilization of immune cells into the circulation. This report will enable future studies in which stimulation of these long-range nerve connections between lymphatic and immune organs can be applied for clinical purpose, including therapeutic modulation of cellularity during vaccination, active allergic response, or active auto-immune disease.

Rat hypothalamic arcuate neuron response in electroacupuncture-induced analgesia

Electroacupuncture (EA) effects on activity of arcuate neurons of the hypothalamus (ARH) and on magnitude of the digastric electromyogram (dEMG) in the jaw opening reflex were investigated, in both p-chlorophenylalanine pretreated and normal Wistar rats. EA stimulation (300-500 microA, 5 msec pulses, for 15 min) was delivered unilaterally to a meridian Ho-Ku point of anesthetized rats at 3, 45 and 100 Hz. In control animals, EA stimulation at 3, 45 or 100 Hz induced long-lasting suppression of the magnitude of the dEMG activity and changed the spontaneous firing rate of most of the ARH neurons: the rate either increased (type I) or decreased (type II). After low-frequency stimulation, there were significantly more type I neurons than type II; after high-frequency stimulation, there were significantly more type II neurons than type I. In serotonin-depleted rats, however, high-frequency stimulation suppressed dEMG activity only slightly and induced a smaller proportion of type II neurons.

Effects of electroacupuncture on the neuronal activity of the arcuate nucleus of the rat hypothalamus

Electroacupuncture (EA) effects on the spontaneous unit activities of 143 neurons in the hypothalamic arcuate nucleus (ARH) which were electrophysiologically identified to project to the median eminence were investigated using anesthetized rats weighing about 300 g. Stimuli were delivered unilaterally to a meridian point of Ho-Ku in the forepaw as rectangular pulses of 5 ms duration, intensity 300 to 500 microA, for 15 min at 3 and 45 Hz. Unit activities of ARH cells were extracellularly recorded and the mean firing rates were compared before and after EA stimulation. Stimulation at 3 or 45 Hz induced a long-lasting and naloxone-reversible suppression of the magnitude of the digastric electromyogram (dEMG) in the jaw opening reflex to 48 to 56% of the control value. Based upon the EA effects on the spontaneous firing rate, the ARH cells were classified into three types: the rate either increased (type I), decreased (type II), or did not change (type III). Type I, II, and III neurons composed 56, 40, and 4% of the recorded neurons (N = 45) when EA stimulation was applied at 3 Hz, and 27, 70, and 3% (N = 37) at 45 Hz, respectively. The distribution of the three types of ARH neurons after EA stimulation at 3 Hz was significantly different (P less than 0.05, chi-square test) from that at 45 Hz.

Quantitative relation between the intensity of tooth pulp stimulation and the magnitude of jaw opening reflex in the rat

The stimulus-response relation in the jaw opening reflex evoked by tooth pulp stimulation, which is considered as a "pain index", follows the power function with an exponent of about six over a range of lower stimulus intensities.