Proposal of a new analgesia test based on the observation of nociceptive behavior induced by electric stimulation of dental pulp in the rat

Dental pulp was electrically stimulated in the awake rat. When the stimulus intensity was progressively increased the following four nociceptive reactions successively appeared: jaw opening reflex, scratching, head rotation, vocalization. The threshold of these four reactions was observed before and after administration of three antalgic drugs. No action of the three drugs was observed for the jaw opening reflex. However each drug showed different actions on the other three reactions.     

Vocal reactions of chickens to midbrain stimulation with different electrical current parameters]

Vocal reactions of hens are realized via nucleus intercollicularis, nucleus mesencephalicus, nucleus isthmi (pars principalis magnocellularis), nucleus isthmi (pars principalis parvocellularis), formatio reticularis and other midbrain structures. These findings indicate a widespread representation of vocal centre in the midbrain of hens. Functional properties of these structures are different. Intercollicular and dorsal mesencephalic nuclei exhibit higher excitability as compared to isthmic nuclei and the reticular formation. Vocal reactions depend on the parameters of the electrical stimuli. The increase in the amplitude and frequency of stimulation facilitates vocal reaction and changes its pattern.     

Thalamic inhibition of locomotion evoked by stimulation of the midbrain]

In the lightly anesthetized cat with an intact brain stimulation of the thalamic region with Horsley-Clarke cooordinates of its center A7 L2 H2 could suppress the locomotion elicited by stimulation of the subthalamic or midbrain "locomotor region".     

Effect of electro-acupuncture on the response of the trigeminal nucleus evoked by electric stimulation of dental pulp in the cat]

The potential in the spinal trigeminal nucleus evoked by electrical tooth pulp stimulation is depressed by electro-acupuncture given to the acupuncture point in the course of the nerve innervating the stimulated tooth.     

Effect of the spinal pain syndrome on pain reactions caused by nociceptive thermal stimuli

It has been shown that the reaction of both limbs to thermal pain stimulation was suppressed during spinal pain syndrome development caused by generators of pathologically enhanced excitation (GPEE) formed in the dorsal horns of the spinal cord lumbosacral segments on one side. The analgetic effect on physiological pain was retained long after pain syndrome disappearance (48 hours), the effect was bilateral and was independent of the type of agent producing GPEE. It was shown that neuronal activity in the antinociceptive system key structure (nucleus raphe dorsal) increases. It is assumed that physiological pain relief is caused by enhanced activity in antinociceptive system structures in pain syndrome.     

Fluoride-resistant acid phosphatase (FRAP) activity of nociceptive nerve terminals in the dental pulp

Nerve fibers in the dental pulp of the lower molar teeth of the rat exert fluoride resistant acid phosphatase (FRAP) activity. FRAP-positive axons establish a three-dimensional nerve plexus within the pulp; the individual axons are very fine (calibre less than 1 micrometer) and only their varicosities measure 1...2 micrometer in diameter. Electron microscopically, FRAP-positive amyelinate axons containing lysosomes are partly embedded in Schwann cells. Removal of the cervical superior ganglion does not induce any alteration of FRAP-positive axons, while destruction of the Gasserian ganglion results in Wallerian degeneration. No FRAP-positive nerve fibers were found in rat incisors. Since, in the rat, only molar teeth are equipped with nociceptive terminals while continuously growing incisors lack pain fibers, it is concluded that FRAP-positive varicose axons in the dental pulp represent nerve endings of trigeminal primary nociceptive neurons.     

Reactions of neurons in the dental projection area of the rabbit sensomotor cortex to photic, acoustic and painful stimulation of the dental pulp]

In experiments on unrestrained rabbits interactions of sound (tone, click), light and pain excitation occurring during stimulation of the dental pulp in the neurons of the cortical sensomotor zone, in the area of representation of the dental afferents were studied by the microelectrode method. It was shown that bi- and polysensor convergence of excitation is realized in the cells of this area. It is suggested that convergence of excitation underlies the mechanisms of formation of the integral systemic pain reaction during stimulation of the dental receptors.     

Influence of neurotransmitters on the antinociceptive effect of midbrain stimulation]

In experiments on rats with implanted electrode-cannules there were studied the effects of L-tryptophane (25 mg/kg intraperitoneally) and microinjections of serotonin (20 micrograms), dopamine (10 micrograms) and proserine (5 micrograms) into the area of periaqueductal central gray on the antinociceptive effect caused by stimulation of the same "points" of the midbrain. L-tryptophane, serotonine and proserine (in the presence of methylatropine) potentiated the effect of subthreshold antinociceptive stimulation which could be tested from the modifications of thresholds of the development of some complex pain reaction components under electrical stimulation of the rat tail. Dopamine did not have such an effect. The potentiating effect of serotonine is not eliminated by naloxone.     

Role of dental pulp in the histogenesis of the enamel organ]

The histological study of in vitro cultured associations between dental pulps and outer dental epithelium showed that the predontoblasts initiated the histogenesis of the enamel organ and particularly the differentiation of the inner dental epithelium.     

Electric stimulation of the dental pulp in the evaluation of the central effect of analgesics

We conducted a double-blind cross-over study in ten volunteers aged from 19 to 30 years, to compare the pain control effects of a single oral dose of two analgesic compounds (drug A: propyphenazone mg 250, ethylmorphine mg 5, caffeine mg 5; drug B: dipyrone mg 500, diphenhydramine mg 12.5, adiphenine mg 5, ethyl aminobenzoate mg 2.5) in an experimental pain model using stimulation of dental pulp. Constant voltage stimuli were delivered through silver chloride electrodes placed in contact with the vestibular surface of the upper medial incisor. At the beginning of the session, the pain input was graded by asking the subject to identify the weakest stimulus perceived (threshold level) and the strongest stimulus endurable (tolerance level). The range between threshold and tolerance level was divided in nine steps plus a subliminal step. The ten steps were delivered randomly, and each series of steps was repeated eight times. The subjects were instructed to rate the pain sensation in an arbitrary scale of 5 degrees. The procedure was repeated at 60 min and 180 min after drug administration. Each subject received two tablets of drug A or drug B in two different sessions at weekly intervals. Statistical analysis of the procedures showed that neither drug A nor drug B significantly affected the pain threshold. Drug A significantly reduced the total pain score (P less than 0.01) and its action peaked 60 min after administration.(ABSTRACT TRUNCATED AT 250 WORDS)