Temperature dependency of the chemical responses of the polymodal receptor units in vitro

Thermal effects on chemical responses of polymodal receptors were studied using in vitro testis-superior spermatic nerve preparations excised from anesthetized dogs. Unitary discharge rates of the polymodal receptors responding to bradykinin and hypertonic NaCl solutions were found to be dependent on the temperature: the higher the temperature, the greater the discharge rate induced, although the temperature itself was mostly subthreshold to activate the receptor.

Post-stimulus facilitatory and inhibitory effects on respiration induced by chemical and electrical stimulation of thin-fiber muscular afferents in dogs

In anesthetized, vagotomized, paralyzed, and artificially ventilated dogs, respiratory responses to both electrical stimulation of the muscle nerve and chemical stimulation of muscular (polymodal) receptors by means of intra-arterial injection of NaCl solution were studied by recording phrenic nervous discharges. During the period of stimulation both types of stimulation caused intensity-dependent facilitation of neural respiratory outputs. After cessation of stimulation, facilitation persisted for a long time (more than 5 min) with a lower intensity stimulation; however, suppression was observed with a higher intensity stimulation. The present results suggest that afferent inputs from the muscular polymodal receptors activate long-acting central mechanisms for enhancement or suppression of respiration.

Responses of neurons in VPL and VPL-VL region of the cat to algesic stimulation of muscle and tendon

1. The responses evoked by electrical stimulation of cutaneous and muscle nerves, by noxious and innocuous mechanical stimulation of muscle, tendon, and cutaneous tissues, and by intra-arterial (ia) injection of algesic substances (potassium, bradykinin) into arteries supplying the gastrocnemius-soleus muscle (GS) were studied in single neurons located in the ventroposterolateral nucleus (VPL) and in the transitional zone between VPL and the ventrolateral nucleus (VL) of cats lightly anesthetized with thiopenthal. Such chemical stimulation of the muscles has been shown to activate muscular groups III and IV axons specifically (43, 44) and presumably is nociceptive in character (14, 17, 31). 2. One hundred eight neurons were tested. Eighty-three of the units responded only to various types of cutaneous stimulation of the hindlimb. The other 25 responded to algesic stimulation of muscle and/or tendon. Of these latter 25, 7 had no apparent cutaneous receptive field although 4 of them responded to electrical stimulation of the common peroneal and/or sural nerve. Thus, only three neurons responded exclusively to algesic chemical and noxious mechanical stimulation of the muscle. Of the other 18 neurons, 14 had cutaneous receptive fields restricted to the hindlimb and often responded to non-noxious repetitive light stroking and to noxious pinching with a high-frequency discharge. Four cells (two of which had cutaneous input only from low-threshold mechanoreceptors) had complex and large receptive fields extending to more than one limb. 3. Potassium was a more potent muscle receptor stimulant than bradykinin, the latter only weakly exciting 3 neurons of 24 tested with both substances. The responses to potassium were rapid (approximately 4.0 s in latency) and tended to be greater (have higher response rates) for the units that responded to cutaneous as well as muscle/tendon stimulation. 4. Most neurons that responded to noxious deep stimulation had a threshold for the GS nerve volley in the group III fiber range. The few neurons with thresholds slightly below the group III range did not respond to activation of group I or II muscle spindle afferents by intra-arterial application of succinylcholine or by stretching the muscle. 5. Neurons with responses to any of the muscle, tendon, or cutaneous nociceptive stimuli were located at the ventral and dorsal periphery of VPL and in the VPL-VL transitional zone. 6. These results strongly suggest that there exist regions within the lateral diencephalon of cats that are capable of processing nociceptive information and that these regions are located at the periphery of VPL.

Hemihidrosis due to skin pressure with particular remarks on the intensity and area of the pressure stimuli

Sweating of symmetrical areas of the torso was measured by means of both the filter paper method and electrohygrometric method. Spontaneous sweating rates of the left and right side of the upper and lower chest and the back were statistically highly correlated. Reduction of sweating by pressure application to the unilateral subaxillary region ("pressure hemihidrosis") was studied quantitatively with 12 combination of pressure stimuli, i.e., 1, 2, 3 and 4 kg weights applied to disks with a surface area of 2, 6 and 16.6 cm/, respectively. The amount of reduction in sweating rate was proportional to both the intensity and the surface area to pressure applied. It was revealed that hemihidrotic effects induced from the unit area of pressure stimulation was statistically highly correlated to the pressure intensity.

Mechanical and thermal responses of polymodal receptors recorded from the superior spermatic nerve of dogs

1. One hundred and fifty-three units were recorded from the superior spermatic nerve of dogs and were tested with mechanical, chemical or heat stimulation. Among 104 units tested with all three methods of stimulation ninety-three units responded to all of them; thus 90% of the superior spermatic nerve units are considered to be polymodal receptors. Only mechanical and thermal responses are reported in this paper. 2. Conduction velocities measured at the nerve trunk in the abdominal cavity were mostly within the A-delta fibre range (average conduction velocity: 11.1 m.s-1, n = 63), but in the receptive region much delay was observed. In contrast to the cutaneous polymodal receptors, polymodal receptors in the superior spermatic nerve usually had multiple receptive sites, up to nine in number. 3. Mechanical responses of these polymodal receptors consisted of dynamic and steady-state responses and sometimes were followed by after-discharges. Maximum responses were obtained with a noxious intensity of stimulation, but thresholds scattered over a wide range including non-noxious intensities. 4. In response to heating, these polymodal units gave an irregular discharge that increased roughly in parallel to temperature rise with an average threshold and S.E. of mean, 42.6+/-0.4 degrees C (n = 73). They showed sensitization or deactivation or both on repetition of heating. Cooling the receptive site caused only transient and weak responses, if any.

Chemical responses of polymodal receptors of the scrotal contents in dogs

1. Chemical responses of polymodal receptors of the superior spermatic nerve were studied by single unit recording in dogs. The responses were similar to those found in the muscular polymodal receptors of dogs. 2. Solutions of hypertonic NaCl, KCl and bradykinin caused responses in more than 90% of these polymodal units. The responses were related to the dose of these three chemical but discharge patterns differed substantially. Responses to Na citrate were very capricious, and those to acetylcholine and histamine were weak. 3. When bradykinin was applied repeatedly the responses of the subsequent trials decreased if the repetition interval was short (less than 15 min), but an increase of response was observed if the repetition interval was long (30-60 min). 4. Indomethacin 10 micrograms.ml-1 suppressed or abolished the response to 1 microgram.ml-1 bradykinin without significant influence on the response to 60 mmol.l-1 KCl at the same receptive site. Involvement of prostaglandins in the response of the polymodal units to bradykinin is suggested.

Thin-fibre receptors responding to mechanical, chemical, and thermal stimulation in the skeletal muscle of the dog

1. Unitary activities of muscular thin fibre afferents, which were not sensitive to muscle stretching, were recorded from the nerve of the medial gastrocnemius muscle of the dog. Responses to mechanical stimulation, intra-arterial injection and local application of chemical solutions, and thermal stimulation of the surface of the muscle were studied. It was observed that polymodal receptors which responded to all types of stimulation existed in the thin fibre afferents of the muscle.2. The receptive area of these units tested by mechanical stimulation was spot-like and appeared to be located not only on the surface but in the midst of the muscle.3. The mechanical response varied among these units with respect to the threshold and the pattern of discharges.4. In these units, NaCl, KCl, and bradykinin consistently evoked responses, with differences in the latencies and discharge patterns, while solutions of histamine, acetylcholine and sodium citrate caused responses less consistently and less effectively. In the stretch receptors, chemical stimulation applied in the same way as tested in the thin fibre afferents produced quite different features in their responses.5. Heating the receptive area of the muscle surface caused responses in twenty-five out of thirty-six units, which were sensitive both to mechanical and to chemical stimulations. The threshold varied from 38.0 to 48.3 degrees C, with a mean of 43.1 degrees C for C fibre units and 41 degrees C for A-delta fibre units.6. The responses to heating were consistently obtained in the units responding to the surface application of chemical solutions. However, the above response was never obtained in the units which did not respond to surface chemical stimulation but responded to intra-arterial injection. These results suggest a large population of polymodal receptors in the muscular thin fibre afferents.