The effect of injury on the properties of afferent fibres in the lingual nerve

The receptor properties of mechanosensitive afferent fibres in the lingual nerve have been studied using electrophysiological techniques in cats. In normal animals some fibres responded only to mechanical stimulation of filiform or fungiform papillae but others also responded when a cold stimulus was applied to the receptive field. Twelve weeks after crushing the lingual nerve, the regenerated fibres had slower conduction velocities but the receptor properties were not significantly different from normal. Twelve weeks after sectioning the lingual nerve, there was a greater reduction in conduction velocities and in addition the mechanoreceptive fields were smaller, force thresholds were higher, adaptation times longer and a smaller proportion of fibres responded to a cold stimulus. These results suggest that section injuries are more likely to result in persistent sensory abnormalities than crush injuries.

Spinal distribution of ascending lamina I axons anterogradely labeled with Phaseolus vulgaris leucoagglutinin (PHA-L) in the cat

The location of the ascending axons of spinal lamina I cells was studied in cats that received injections of Phaseolus vulgaris leucoagglutinin (PHA-L) in the superficial dorsal horn of the cervical or lumbosacral enlargement. Lamina I axons that could be ascribed to the spinothalamic tract (STT) were of particular interest. The cases were divided into three sets: in seven optimal cases the injections were restricted to lamina I; in ten nominal cases the injections involved laminae I-II or laminae I-III and occasionally lamina IV; and in eight mixed cases laminae I-V were injected. Since ipsilateral propriospinal and bilateral supraspinal axons originate from laminae I and V, but only ipsilateral propriospinal axons from laminae II-IV, this categorization facilitated a comparative analysis. Ascending axons labeled immunohistochemically with avidin/Texas Red were observed in oblique transverse sections from the C1, C3/4, T6, T12, and L3/4 levels. Incidental axonal labeling occurred in the ipsilateral dorsal columns because of passing primary afferent fiber uptake and, in nominal and mixed cases with involvement of laminae III-IV, in the superficial dorsolateral funiculus at the location of the spinocervical tract. Ipsilateral ascending lamina I axons in optimal cases were located in Lissauer's tract and in the white matter adjacent to the dorsal horn. Since these appeared to terminate in lamina I, and few remained at C1, they were ascribed to propriospinal projections. Contralateral ascending lamina I axons in optimal and nominal cases were distributed throughout the dorsal and ventral portions of the lateral funiculus (LF), but, despite considerable variability between animals in their location and dispersion, they were consistently concentrated in the middle of the LF (i.e., at the level of the central canal). This concentration was observed in a slightly more ventral location at C1, and a similar but weaker concentration of lamina I axons was located slightly more dorsally in C1 on the ipsilateral side. These supraspinal lamina I projections were ascribed to the spinomesencephalic tract (SMT) and to the STT. In mixed cases, additional ascending axons ascribed to lamina V cells were labeled in the ventrolateral and ventral funiculi. Many labeled axons were found in this region following a large injection of biocytin into lumbosacral laminae V-VIII in a supplementary case. These results thus together support previous descriptions of a dorsoventral distribution of STT axons according to laminar origin, but they contradict recent reports that lamina I axons ascend in the dorsolateral funiculus.(ABSTRACT TRUNCATED AT 400 WORDS)

Estimation of regional cutaneous cold sensitivity by analysis of the gasping response

Regional cutaneous sensitivity to cooling was assessed in males by separately immersing four discrete skin regions in cold water (15 degrees C) during head-out immersion. The response measured was gasping at the onset of immersion; the gasping response appears to be the result of a nonthermoregulatory neurogenic drive from cutaneous cold receptors. Subjects of similar body proportions wore a neoprene "dry" suit modified to allow exposure to the water of either the arms, upper torso, lower torso, or legs, while keeping the unexposed skin regions thermoneutral. Each subject was immersed to the sternal notch in all four conditions of partial exposure plus one condition of whole body exposure. The five cold water conditions were matched by control immersions in lukewarm (34 degrees C) water, and trials were randomized. The magnitude of the gasping response was determined by mouth occlusion pressure (P0.1). For each subject, P0.1 values for the 1st min of immersion were integrated, and control trial values, although minimal, were subtracted from their cold water counterpart to account for any gasping due to the experimental design. Results were averaged and showed that the highest P0.1 values were elicited from whole body exposure, followed in descending order by exposures of the upper torso, legs, lower torso, and arms. Correction of the P0.1 response for differences in exposed surface area (A) and cooling stimulus (delta T) between regions gave a cold sensitivity index [CSI, P0.1/(A.delta T)] for each region and showed that the index for the upper torso was significantly higher than that for the arms or legs; no significant difference was observed between the indexes for the upper and lower torso.(ABSTRACT TRUNCATED AT 250 WORDS)

Thermal stress modulates temporal patterns of responding on a multiple DRL-FR schedule

To investigate temporal changes in behavior induced by moderate cold temperatures, rats performing on a multiple differential-reinforcement-of-low-rate (DRL) fixed-ratio (FR) schedule were exposed to ambient temperatures of 2, 8, 16, and 24 degrees C. DRL response rates markedly increased with decreasing cold temperatures, while FR response rates remained unchanged. In addition, as ambient temperatures decreased, the interresponse time (IRT) distribution of DRL responses shifted toward shorter times and short IRT bursts increased. Compared with cold effects, exposure to 38 degrees C heat induced decreases in both DRL and FR response rates which were associated with increases in long IRTs. Decreases in reinforcement frequency was associated only with the DRL schedule in cold, and with both DRL and FR schedules during heat exposures. The distinct effects of cold and heat on both DRL and FR responding suggest that the increases in DRL response rates and shifts in IRT distribution are unique to cold, and are not due to general effects of nonspecific thermal change in the ambient environment.

Brood patch innervation and its role in the onset of incubation in the turkey hen

The source of innervation to the brood patch in turkey hens was determined by recording the electrophysiological activity of cutaneous nerves while manually stimulating various regions of the skin. The entire area of the brood patch was innervated by eight nerves, arising from thoracic vertebra 3 to synsacrothoracic vertebra 1. To determine whether afferent input from the brood patch influenced egg production or incubation behavior, hens were bilaterally denervated prior to photoinduced egg production. Denervated hens visited nests the same number of times, but stayed on the nest for less total time than controls by the fourth week of photostimulation. Serum prolactin levels rose in control hens but not in denervated hens. Egg production was maintained in the denervated hens but not in controls. None of the denervated hens displayed incubation behavior. This experiment supports the view that peripheral nervous input plays a role in the onset of incubation behavior.

Interactions between chemical and thermal cutaneous stimuli: inhibition (counterirritation) and integration

Methyl salicylate, a commonly used chemical counterirritant, was applied topically to the forearm to determine whether a nonpainful chemical irritation could inhibit the perception of another (weaker) chemical irritation. In the first experiment, sensations of irritation (burning and stinging) produced by a 10% solution of methyl salicylate were significantly attenuated when a 15% solution of the same chemical was applied to the opposite forearm. In the second experiment, neither the perception of warmth nor the heat pain threshold was affected by application of 10% or 15% methyl salicylate to a site 10 cm from the thermal stimulus. Inhibition did, however, occur in the opposite direction: Chemical irritation was reduced after the thermal stimulus reached a painful level. In the third experiment, a 15% solution of methyl salicylate was applied immediately adjacent to the thermal stimulus, with the result that ratings of warmth intensity increased rather than decreased, and perceived irritation was again attenuated following a painful heat stimulus. Overall, the results indicate that (1) chemical counterirritation can occur at nonpainful levels; (2) the resulting inhibition is confined to the nociceptive system; and (3) when the nociceptive and warmth system are activated together, the tendency is toward integration rather than inhibition.

Effect of menthol on the bladder cooling reflex in the cat

The effect of menthol on the urinary bladder cooling reflex was studied in alpha-chloralose-anaesthetized cats. The cooling reflex was elicited by bladder or urethral instillations of cold saline and monitored by multiunit recordings from efferent and afferent pelvic nerve filaments. The bladder cooling reflex was greatly exaggerated by intraluminal exposure of the bladder or the urethra to a 0.6 mM solution of menthol. The effect occurred without a sensitizing effect on bladder mechanoreceptors. It could be described as a shift of the temperature-response curve for the cooling reflex towards higher temperatures. This change resembles the effect of menthol on cutaneous cold receptors. It is proposed that the bladder cooling reflex originates from cold receptors in the bladder and urethral walls.

Effect of inspired air temperature on genioglossus activity during nose breathing in awake humans

Experimental data suggest the presence of sensory receptors specific to the nasopharynx that may reflexly influence respiratory activity. To investigate the effects of inspired air temperature on upper airway dilator muscle activity during nose breathing, we compared phasic genioglossus electromyograms (EMGgg) in eight normal awake adults breathing cold dry or warm humidified air through the nose. EMGgg was measured with peroral bipolar electrodes during successive trials of cold air (less than or equal to 15 degrees C) and warm air (greater than or equal to 34 degrees C) nasal breathing and quantified for each condition as percent activity at baseline (room temperature). In four of the subjects, the protocol was repeated after topical nasal anesthesia. For all eight subjects, mean EMGgg was greater during cold air breathing than during baseline (P less than 0.005) or warm air breathing (P less than 0.01); mean EMGgg during warm air breathing was not significantly changed from baseline. Nasal anesthesia significantly decreased the mean EMGgg response to cold air breathing. Nasal airway inspiratory resistance, measured by posterior rhinomanometry in six subjects under similar conditions, was no different for cold or warm air nose breathing [cold 1.4 +/- 0.7 vs. warm 1.4 +/- 1.1 (SD) cmH2O.l-1.s at 0.4 l/s flow]. These data suggest the presence of superficially located nasal cold receptors that may reflexly influence upper airway dilating muscle activity independently of pressure changes in awake normal humans.

The influence of bicycle exercise, with or without hand immersion in cold water, on forearm sweating in young and middle-aged women

Forearm sweat production rate (SPR) and external auditory meatal temperature (TEAM) were examined in five young and five middle-aged women in response to intermittent exercise, on three separate occasions. The first experiment was a control study, while in the second study the left hand was immersed in cold water at the onset of sweating during each exercise bout, and in the third study this immersion was accompanied by venous occlusion of the upper left arm. TEAM increased by 0.5 degrees C during exercise with no significant differences between the groups on any occasion. The young women displayed a greater peak SPR during exercise in the control than the middle-aged women (52.5 +/- 23.9 vs. 16.7 +/- 6.5 mg cm2 h-1, P less than 0.001). With hand immersion, peak SPR was depressed to 14.0 +/- 4.6 mg cm2 h-1 (P less than 0.001) in the young women and to 13.1 +/- 4.5 mg cm2 h-1 in the middle-aged (P less than 0.05). With hand immersion and venous occlusion the peak SPR in young women increased (43.0 +/- 9.2 mg cm2 h-1). In the older women SPR was 14.9 +/- 6.1 mg cm2 h-1, which was not different from either control or cold-immersed values. Thus, forearm SPR during low-intensity intermittent exercise is greater in young compared with middle-aged women, despite similar changes in TEAM. The response to hand immersion in cold water was more marked in the young subjects.

[The frequency and sequence of the biopotentials of the cold thermoreceptors at different skin temperatures]

Electrical activity of the skin cold thermoreceptors was studied in the rabbit nasolabial area at a gradually decreasing temperature of the skin from 39.0 to 7.7 degrees C. The range of firing rate, the temperature of the maximal discharge, and the character of the discharge sequence at different skin temperature, were recorded for every thermoreceptor. The majority of the thermoreceptors were characterized by bursts of discharges (2-10 and more) at a certain skin temperature. The analysis of the data obtained revealed a wide variety of responses of the cold thermoreceptors to continuous drop of the skin temperature.

Effects of menthol on peripheral nerve and cortical unit responses to thermal stimulation of the oral cavity in the rat

Neurophysiological responses were recorded in individual fibers of the lingual and chorda tympani nerves and in single cortical neurons in the rat in response to a battery of tactile, thermal and chemical stimuli applied to the oral cavity. Two categories of thermally sensitive units were identified. Chorda tympani fibers and one type of cortical unit ('Type I') were activated by cold water stimulation but were unaffected by warm water or menthol. In contrast, lingual fibers and a different category of cortical units ('Type II') were extremely sensitive to menthol exposure. These units were cold water sensitive, however, this sensitivity was suppressed following menthol presentation.

[Difference in responses of free nerve endings and Ruffini-type endings innervating the cat mandibular periosteum to square wave pressure stimuli, ramp mechanical stimuli and triangular vibrations]

The free nerve endings and Ruffini type endings in the cat mandibular molar buccal periosteum (posterior periosteum) were selectively stimulated with specific displacements of various velocities and frequencies and the afferent impulses generated by the nerve endings were recorded.

RESULTS

1. There were two types of fast-adapting free nerve endings, discharging on effects and off-effects in response to square wave pressure stimuli and ramp mechanical stimuli and on-effects only. 2. Unencapsulated endings were distributed near the mentale foramen and again there were two types of fast adapting endings, discharging on effects and off effects in response to square wave pressure stimuli and ramp mechanical stimuli, and on-effects only. 3. Slow-adapting free nerve endings were also observed through response to square wave pressure stimuli and ramp shaped pressure stimuli. These were difficult to differentiate from the slow adapting Ruffini-type endings. 4. Ruffini type endings were slow adapting types, exhibiting impulse frequency displacement velocity curves of F = 39.627V0.743 (F = impulse frequency, V = displacement velocity, r = 0.999, n = 12 and p less than 0.001). The number of impulse displacement curves was proportional to the displacement, with F = 1.024S0.767 (F = impulse frequency, S = displacement, r = 0.981, n = 6 and p less than 0.001). 5. Free nerve endings followed Stevens' power function law, dropping in order from fast-adapting units (10 units) to intermediate type sensory units (21 units) and slow-adapting sensory units (20 units), with 0.894 +/- 0.103, 0.684 +/- 0.022 and 0.650 +/- 0.023, respectively. Values for slow adapting Ruffini type endings followed the previous order. 6. Slow adapting free nerve endings responded to triangular vibration stimuli at 0.1 Hz to 240 Hz and the lower frequency limit of 0.1 Hz (actually it was below 0.1 Hz but this value was adopted in order to facilitate the recording of the difference to fast adapting free nerve endings) was considerably lower than the 0.6 Hz to 1 Hz range for fast-adapting free nerve endings. The structure and functions of the nerve endings in the cat posterior periosteum were investigated and it was found that the relationship between the impulse frequency and displacement velocities and displacement amplitude for slow-adapting Ruffini-type endings followed Stevens' power factor law. In conclusion, it was demonstrated that the slope constant follows the order of fast-adapting free nerve endings, intermediate type free nerve endings and slow-adapting free nerve endings.

Water-responsive laryngeal receptors in the dog are not specialized endings

The primary purpose of this study was to ascertain whether laryngeal receptors activated by water are specialized endings or whether they also respond to other stimuli, such as pressure, temperature and laryngeal motion as they occur during the breathing cycle. In 35 anesthetized mongrel dogs, breathing spontaneously through a lower cervical tracheostomy, water and other test solutions at approximately 37 degrees C were injected into the functionally isolated larynx with a small catheter. Of the 130 receptors studied, none of the cold receptors (N = 13) responded to water, whereas approximately 60% of all laryngeal mechanoreceptors (72 of 117) responded with either a short delay, short duration or a long delay, long duration response. In general the former pattern of response was exhibited by nonrespiratory-modulated receptors, whereas the latter was typical of respiratory-modulated receptors. The specific nature of the stimulus (hypotonicity or lack of chloride ion) of the water response was further studied in 53 receptors with isoosmotic solutions of dextrose and sodium gluconate. The long delay, long duration response was dependent on a decreased osmolality, while the short delay, short duration response was dependent on the lack of chloride ion of the test solutions. All water-responsive receptors tested (N = 17) were blocked within 50 sec by topically applied 2% lidocaine and thus presumed to be superficial. However, 10 receptors which did not respond to water were also blocked within 50 sec, suggesting that not all superficial receptors are stimulated by water. Based on these observations, we propose that changes in osmolality or ionic composition of the laryngeal surface liquid could play an important role in modifying reflexes involved in the maintenance of upper airway patency.

Spatial summation of heat-induced pain: influence of stimulus area and spatial separation of stimuli on perceived pain sensation intensity and unpleasantness

1. Psychophysical experiments were initiated to determine the possible influence of increasing stimulus size on perceived pain intensity. Six trained human subjects (5 male, 1 female) made visual analogue scale (VAS) ratings for pain-sensation intensity and unpleasantness in response to nociceptive thermal stimuli. Test stimuli consisted of 5-s duration heat pulses (45-50 degrees C in 1 degrees increments) delivered by one, two, or three contact thermal probes (1 cm2 each) applied to the medial aspect of the anterior forearm. 2. The area of skin receiving noxious thermal stimuli was changed by randomly varying the number of thermodes activated. The effects of varying the distance between the thermal probes also were evaluated. In the first series of experiments, thermal-probe separation was kept close to 0; in subsequent experimental series, the thermodes were separated by either 5 or 10 cm. 3. In each experimental series, considerable spatial summation occurred in both pain-sensation intensity and unpleasantness dimensions of pain. This summation occurred throughout the nociceptive thermal range of 45-50 degrees C and was larger at suprathreshold temperatures (greater than or equal to 47 degrees C) than those near threshold (less than or equal to 46 degrees C). Unlike spatial summation of perceived warmth, that of pain was not characterized by systematic changes in power-function exponents but as approximately upward parallel displacements in double-logarithmic coordinates. 4. Thermal-probe separation over a range of 0-10 cm had no effects on spatial summation of pain-sensation intensity or pain unpleasantness. In contrast, increasing thermal-probe separation increased the subjects' ability to discriminate differences in stimulus size and their ability to detect correctly the number of thermal probes activated. 5. Because affective VAS ratings of unpleasantness were linearly related to, but distinctly and systematically less than, VAS ratings of pain-sensation intensity, it was clear that subjects responded quite differently to these two pain dimensions. Affective judgements were not additionally influenced by thermal probe separation and hence by the ability to perceive stimulus size or number of thermal probes activated. 6. The results indicate that powerful spatial-summation mechanisms exist for heat-induced pain. Spatial summation of pain is likely to be subserved both by local integration mechanisms at the level of single spinothalamic-tract neurons and by recruitment of central nociceptive neurons, because spatial summation of pain occurred to approximately equal extents under conditions of thermode separations over a distance of at least 20 cm.

Behavioural thermosensitivity after bilateral lesions of the lateral funiculi in the cervical spinal cord of the cat

The behavioural thermosensitivity of six cats was measured before and after single stage, symmetrical, bilateral, surgical lesions of the cervical spinal cord. The lesions were aimed at an area in the most ventral parts of the dorsal halves of the lateral funiculi. Unilateral lesions of that area have previously been found to cause reproducible, although subtotal, contralateral thermosensory defects, which were attributed to interruption of the thermosensory spinothalamic pathway. The lesions of three of the present cats were found to be incomplete, and those animals showed no postoperative thermosensory deficiency. Two of the cats with complete lesions showed marked post-operative defects, especially immediately after the operations, but the third cat with a complete lesion showed no postoperative thermosensory defect at all. The differences between the last three animals have been compared to the irregularity of previous reports about thermosensitivity after spinal cord lesions in man and animals, and may depend on the testing technique, rather than differences of thermosensitivity per se.

Behavioural thermosensitivity after unilateral, partial lesions of the lateral funiculus in the cervical spinal cord of the cat

Adult cats were tested for unilateral, behavioural thermosensitivity, before and after unilateral, surgical lesions involving part of the lateral funiculus of the cervical spinal cord. Contralateral thermosensory deficiencies were found after lesions, which involved the middle parts of the lateral funiculus. No such deficiencies were observed after lesions which were restricted to either the dorsal third, or the ventral half of the lateral funiculus. It was concluded that behaviourally important, thermosensory information is transmitted via an ascending pathway which is located ventrally in the dorsal half of the lateral funiculus.

[The temperature analyzer, thermoregulation and the problems of thermotherapy]

The paper presents data and conceptions on physiological mechanisms of thermoregulation by temperature analyzer at various levels, the relationships between the mechanisms, interaction, influence on systemic trophic function. In view of the knowledge the effects of some novel techniques different in principle from the standard ones applied in thermotherapy are specified.

A comparison of two methods for measuring thermal thresholds in diabetic neuropathy

Thermal thresholds can be measured psychophysically using either the method of limits or a forced-choice method. We have compared the two methods in 367 diabetic patients, 128 with symptomatic neuropathy. The Sensortek method was chosen for the forced-choice device, the Somedic modification of the Marstock method for a method of limits. Cooling and heat pain thresholds were also measured using the Marstock method. Somedic thermal thresholds increase with age in normal subjects, but not to a clinically significant degree. In diabetics Marstock warm threshold increased by 0.8 degrees C/decade, Sensortek by 0.1 degrees C/decade. Both methods had a high coefficient of variation in normal subjects (Sensortek 29%, Marstock warm 14%, cool 42%). The prevalence of abnormal thresholds was similar for both methods (28-32%), though Marstock heat pain thresholds were less frequently abnormal (18%). Only 15-18% of patients had abnormal results in both tests. Sensortek thresholds were significantly lower on repeat testing, and all thresholds were higher in symptomatic patients. Both methods are suitable for clinical thermal testing, though the method of limits is quicker. In screening studies the choice of a suitable apparatus need not be determined by the psychophysical basis of the test.

Arousal state vs. temperature effects on neuronal activity in subcoeruleus area

It is believed that thermoafferent neurons synapse in the subcoeruleus area (SC). To assess the effect of arousal state on thermoafferent information processing, we recorded SC unit activity in unanesthetized rats. No responses to changes in ambient temperature were observed within an arousal state, but 85% of the units dramatically altered their firing rates as the arousal state changed. We replicated previous experiments on anesthetized animals which were the basis for ascribing thermoafferent function to the SC. Additionally, we monitored electroencephalographic (EEG) activity. In lightly anesthetized rats, five distinct EEG states could be defined, and the temperature profile of the animal was a primary determinant of the EEG state. No thermoresponses were observed within an EEG state, but 78% of the units dramatically altered their firing rates in synchrony with EEG pattern changes. Transient responses to noxious stimuli were also reflected in both the EEG patterns and single-unit activity. We conclude that SC single-unit activity is not specific for processing of thermal information but is correlated with EEG activity, which in turn is determined by a variety of factors including thermal stimuli.

Non-cutaneous peripheral thermosensitivity in the goat (Capra hircus)

1. A 0.2 m2 area of the trunk skin was denervated and its center was externally cooled or warmed, when central body temperature was lowered. 2. When the denervated skin was cooled, the central body temperature, at which shivering occurred, was significantly higher than with warming of the denervated skin. 3. It is concluded that the difference was caused by temperature signals originating from thermoreceptors in tissue layers underneath the denervated skin.

Temperature and the two-point threshold

Studies dating back to 1834 have shown that the temperature of objects contacting the skin can substantially intensify their apparent pressure on the skin. Later research demonstrated qualitatively that object temperature can also sharpen the spatial acuity of the skin as revealed by gap perception (two-point and two-edge thresholds). Pressure intensification and sharpening probably relate intimately. The present experiments sought to provide several more accurate and parametric extensions of thermal sharpening: (1) sharpening can improve tactile spatial acuity by as much as 60%, but the degree of sharpening is graded as a function of deviation of stimulator temperature from normal (neutral) skin temperature; (2) thermal sharpening seems to characterize the body surface since it takes place freely in forearm, forehead, and palm; local differences do, however, become apparent; (3) large thermal sharpening can even occur when one tip of the stimulator is warm, the other cold; and (4) thermal sharpening is easily captured by experiment and is basically the same in magnitude whether assessed by modern forced-choice procedure (controlled criterion) or by the more traditional procedures (uncontrolled criterion) used for more than a century before the advent of signal detection theory. Various arguments are put forth here and elsewhere to suggest that both thermal intensification of pressure sensation and thermal sharpening of gap perception result from direct thermal stimulation of mechanoreceptors and/or polymodal nociceptor networks; neither phenomenon yeilds readily to a "cognitive" interpretation.

Nasal 'flow' receptors of the rat

This study was performed to identify trigeminal nasal 'flow' receptors and to investigate their firing characteristics. For this purpose, single unit afferent activity was recorded from the anterior ethmoidal nerve in anesthetized rats breathing through the nose or a tracheostomy. In fourteen rats breathing through the nose, 40 of 73 endings tested were identified as 'flow' receptors for the following characteristics: their spontaneous activity had an inspiratory modulation that disappeared during nasal occlusions, they were markedly stimulated by exposure to cold air and inhibited by warm air. In eleven rats breathing through a tracheostomy, 85 endings were identified as 'flow' receptors being stimulated by a constant nasal airflow (100-300 ml/min) with room air (22-26 degrees C) or cold air (0-15 degrees C), but inhibited with warm air (30-45 degrees C). Fifty-five 'flow' receptors (Type R1 and R2) exhibited a dynamic response to the constant airflow, while the other 30 receptors (Type S) showed a static response. A large proportion of 'flow' receptors (more than 52%) were responsive to tactile stimuli. For all the flow receptors, a decrease in intranasal temperature was the primary factor to excite them. These results suggest that the trigeminal nerve has a number of 'flow' receptors which operate as thermoreceptors.

The metabolic response to skin temperature

Experiments were done to assess that fraction of the metabolic response to external cold exposure, which is attributable to skin temperature. In 5 conscious and closely clipped goats the metabolic rate was determined at various stable levels of skin temperature in the range from 13 to 41 degrees C, while core temperature was kept constant at 38.8 degrees C. Skin temperature was manipulated by a rapidly circulating shower bath, while core temperature was controlled by means of heat exchangers acting on arterial blood temperature in a chronic arteriovenous shunt. The metabolic response to skin temperature fell into two clearly discernible sections: a first zone with skin temperatures above 25-30 degrees C, within which the metabolic rate rose at a rate of -0.34 +/- 0.07 W/kg.degrees C with decreasing skin temperature, and a second zone with skin temperatures below 25-30 degrees C, within which the metabolic rate either plateaued or even grew smaller with further decreasing skin temperature. It is concluded that the relationship between skin temperature and metabolic rate does not directly reproduce the temperature-response curve of cutaneous cold receptors but also reflects a complex interaction of several factors, including an unspecific temperature effect on muscle metabolism.

Substance P mediates a gastrointestinal thermoreflex in rats

We have characterized a viscerocirculatory thermoreflex, quantified its responses, and identified the major neurotransmitter. Application of fluid at 45 degrees C to mucosas or serosas of the stomach, jejunum, or ileum of anesthetized rats promptly evoked consistent cardiovascular responses, namely arterial hypotension, tachycardia, and a diminished intestinal blood flow (latency less than or equal to 5 s with a duration of 2-4 min). Thus, for example, warming of the stomach caused blood pressure to decrease 40%, heart rate to increase 15%, and mesenteric blood flow to decline 50%. These responses were inhibited totally or mostly by capsaicin, administered neonatally, topically, or perineurally, by topical lidocaine, and by parenteral administration of substance P antiserum, somatostatin, or hexamethonium. Epidural anesthesia also inhibited the cardiovascular responses to visceral warming. Pretreatment with reserpine or splanchnic ganglionectomy converted the thermally induced decline in mesenteric blood flow into a vasodilator response, which could then be blocked by an antiserum to substance P. Visceral warming also stimulated afferent, preganglionic sympathetic neural activity. Our conclusions are (a) application of fluid at 45 degrees C to gastrointestinal organs of anesthetized rats initiates a viscerocirculatory reflex that involves primary sensory, afferent C fibers; (b) the major neurotransmitter of this reflex appears to be substance P; and (c) visceral afferent C fibers have central and peripheral vasomotor functions.

Cardiorespiratory reflex responses to static contraction of vascularly isolated hindleg muscles of the rat

One hindleg of an anasthetized rat (n = 15) was isolated from systemic blood circulation. The preparation was connected to the body only by nerve and bone. A. and V. femorales were cannulated and perfused with normoxic (PO2 = 530 mm Hg) or hypoxic (PO2 = 60 mm Hg) Tyrode solutions. Static contractions of the muscle were elicited by electrical stimulation on the sciatic nerve (2 x motor threshold, 400-800 mV, 50 s-1). A 1 s stimulus was followed by a 2 s rest period. Total test time amounted to 40 min. It was proceeded and succeeded by 20 min periods of control perfusions without stimulation. Heart rate (HR) and respiratory rate (f) were measured and cross correlated with the following outflow parameters from V. femoralis of the experimental muscle: [K+], [Na+], PO2, PCO2, pH and [lactate]. During the test period HR and f increased significantly within 20 min of the start of stimulation: HR 5.8% (p less than 0.005) and f 24.3% (p less than 0.005) for hypoxic perfusion (n = 6) and HR 3.2% (p less than 0.005) and f (p less than 0.001, ANOVA) for normoxic perfusion (n = 3). The dynamic changes of several outflow parameters were nearly simultaneous with the cardiorespiratory responses. Cross correlation analyses revealed an excellent temporal relationship between HR and PO2 or [lactate] and between f and PO2 or [lactate]. In addition PCO2 and pH correlated well with HR as well as with f. Comparison of the threshold of the cardiorespiratory response revealed an optimal relationship to pH, a good one to PCO2 and lactate concentration but no correlation to PO2.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of cold and warm receptor activity in vampire bats and mice

The response characteristics of facial thermoreceptors of the common vampire bat and of the mouse have been quantitatively studied. Cold receptors were identified in bat and mouse; warm receptors were only established in the bat. Cold and warm receptor populations of the two species share most of their properties with facial thermoreceptor populations of various mammalian species investigated so far. The temporal pattern of activity of cold receptors of the mouse corresponded to that observed in cats, dogs and monkeys: impulse groups at lower, and beating activity at higher temperatures. At maintained temperature, no impulse groups were initiated in cold receptors of the bat. However, cooling steps from various initial temperatures induced a transient grouped discharge in both cold receptor populations. A discharge in regular groups of impulses was occasionally generated in warm receptors of the bat at maintained temperatures and following warming steps. The data indicate that the temperature dependence of periodic activity in warm receptors is not as uniform as it is in cold receptors. It is concluded that cyclic processes are involved in sensory transduction of both warm and cold receptors, and that this cyclic behavior seems to be a general property of thermoreceptors of presumably all vertebrate species.

SI nociceptive neurons participate in the encoding process by which monkeys perceive the intensity of noxious thermal stimulation

The activity of primary somatosensory (SI) cortical nociceptive neurons was recorded while the monkeys performed a psychophysical task in which they detected small increases in skin temperature superimposed on noxious levels of thermal stimulation. The detection latency to these stimuli, expressed as detection speed, was used as a measure of the perceived intensity of sensation. Two-thirds of the neurons that responded to noxious thermal stimulation increased their discharge in response to graded increases in stimulus intensity. The remaining neurons responded to noxious thermal stimulation, but did not grade their response with the intensity of the stimulus. The response of SI nociceptive neurons that encode the intensity of noxious thermal stimulation was significantly correlated with the monkey's detection speed. We conclude that SI nociceptive neurons are involved in the encoding process by which monkeys perceive the intensity of noxious thermal stimulation.

Effects of interferon-alpha on the activity of preoptic thermosensitive neurons in tissue slices

Effects of recombinant interferon-alpha (IFN-alpha) on the single activity of thermosensitive and thermally insensitive neurons in the preoptic and anterior hypothalamus (PO/AH) were investigated in rat's brain tissue slices. IFN-alpha, in doses of less than 5 x 10(3) U/ml, decreased the activity in 34 of 52 warm-sensitive neurons and increased the activity in 3 of 5 cold-sensitive neurons, but had no effect on the majority (12 of 17) of thermally insensitive neurons. The neuronal responses to local IFN-alpha could be observed in a Ca2+-free/high Mg2+ solution, suggesting the direct action of IFN-alpha. The actions of IFN-alpha on thermosensitive neurons were blocked by concurrent application of naloxone, but not by sodium salicylate in doses which effectively blocked the neuronal responses to endotoxin and leukocytic pyrogen in the previous studies. The fever induced by IFN-alpha may be explained, at least partly, by the direct actions of IFN-alpha on the PO/AH thermosensitive neurons, which involve the opiate receptor mechanisms.

Thermal sensitivity of neurons in a rostral part of the rat solitary tract nucleus

While stimulating the entire oral cavity of anesthetized rats, we recorded 3 types of neurons in the solitary tract nucleus; taste, mechanoreceptive and cold neurons. Most of the taste neurons were sensitive to thermal as well as to mechanical stimulations. Taste neurons predominantly sensitive to sucrose responded to warming and those most excited by NaCl or HCl were sensitive to cooling, and significant correlations were found between sucrose and warming and between NaCl and cooling. Most of the cold-sensitive taste neurons had receptive fields (RFs) at the anterior tongue and warm-sensitive taste neurons had whole or part of the RFs at the nasoincisor duct. About half the number of mechanoreceptive neurons were sensitive to cooling, producing phasic responses. RFs of some thermosensitive mechanoreceptive neurons and cold neurons were located. Warm-sensitive mechanoreceptive neurons or warm neurons were not evident. Therefore, interaction between thermal and taste sensations in the oral cavity probably takes place in the solitary tract nucleus, as well as in the chorda tympani.

Thermosensitivity of the goat's brain

1. Experiments were done in conscious goats to estimate the gain of brain temperature sensors and to evaluate that fraction of the thermosensitivity of the entire brain which can be determined by a thermode located in the hypothalamus. 2. The animals were implanted with local thermodes, carotid loops and intravascular heat exchangers permitting independent control of hypothalamic temperature, extrahypothalamic brain temperature and trunk core temperature. 3. Small and slow ramp-like displacements of hypothalamic temperature generated continuously increasing thermoregulatory responses without any dead band, if a negative feed-back from extrahypothalamic sources was suppressed. 4. The hypothalamic sensitivity determined by the metabolic response to slow ramp-like cooling of the thermode amounted to -1.4 W/(kg degrees C) and equalled approximately 30% of what had been found for total body core sensitivity in another series of experiments. 5. Total brain thermosensitivity was -1.6 W/(kg degrees C), which implies that a large thermode centred in the hypothalamus can detect approximately 85% of the thermosensitivity of the entire brain.

Thermal, osmotic and chemical modulation of neural activity in the paraventricular nucleus: in vitro studies

To investigate the functions of the paraventricular nucleus (PVN) which plays an important role as an integration site for the neuroendocrine and autonomic nervous systems, the firing activity of PVN neurons was recorded from hypothalamic slice preparations during thermal, osmotic and chemical stimulation. Neurons responded to environmental factors such as temperature and osmolarity and both warm-responsive and cold-responsive neurons were observed in the PVN. Some PVN neurons were also osmoresponsive and unlike neurons in the supraoptic nucleus, most osmoresponsive PVN neurons decreased their firing rate during hyperosmotic stimulation. One of the classical transmitters, noradrenaline, exerted excitatory effects on PVN neurons through alpha 1- and beta-receptors and inhibitory responses through alpha 2-receptors. Atrial natriuretic polypeptide exerted inhibitory effects on putative parvocellular PVN neurons but it had no effect on putative magnocellular PVN neurons. An endogenous sugar derivative, 2-deoxytetronic acid, thought to be an endogenous satiety factor, elicited inhibitory effects, supporting the possibility that the PVN also may be related to feeding behaviour. Arginine-vasopressin and oxytocin which are synthesised in the magnocellular neurosecretory cells excited PVN neurons, suggesting that the PVN may have short circuits modulating neural activity within the nucleus itself. We conclude that neurons in the PVN may receive multiple information and act as one of the important integrative sites in the brain.

In vitro electrophysiologic studies on nasal airway receptors of the rabbit

Rabbit nasal airway receptors were investigated electrophysiologically in vitro. Cold receptors, warm receptors, and mechanoreceptors were found in the nasal membrane. The cold receptors showed a maximum static discharge at 28 degrees C, and the warm receptors at 38 degrees C. These thermoreceptors were activated constantly at temperatures between 18 degrees C and 40 degrees C. The mechanoreceptors were seen to adapt rapidly to gentle mechanical stimulation and were activated easily by repeated stimuli. Air blown directly at the nasal membrane did not activate the mechanoreceptors. It was concluded that nasal airflow sensation is due mainly to the activation of cold or warm receptors in the nasal airway, rather than the stimulation of mechanoreceptors.

Limits of thermal sensation

The sensitivity of thermal receptors and responses is compared with thermal noise in receptor cells and with thermal signals in the environment. It is demonstrated that the most sensitive responses known are far less sensitive than is physically possible but sufficiently sensitive to detect the smallest signals likely to be present in the environment. Expressions for the minimal thermal gradients detectable by organisms moving through them are derived. Thermal fluctuations in a receptor over physiologically relevant times and distances are almost certainly less than 10(-6) degrees C. The most sensitive responses reported in any organism are about a thousand times larger. The thermal gradient present in soil is nearly always greater than 10(-3) degrees C/cm and it is probably higher in other environments. The suggestion that nematodes locate plant roots based on heat production is shown to be unlikely because the gradients produced are smaller than those from other causes. Bacteria, a slime mold, rattlesnakes, and mammals are discussed in addition to nematodes.

A diencephalic slice preparation and chamber for studying neuronal thermosensitivity

An in vitro slice preparation and electrophysiological recording chamber for studying neuronal thermosensitivity throughout the hypothalamus are described. A series of eight, 300 microns thick, horizontal tissue slices encompassing most of the hypothalamus are prepared from male Sprague-Dawley rats. Horizontal slice maps showing the major nuclei and fiber tracts are provided. Horizontal tissue slices contain many hypothalamic nuclei as well as the medial forebrain bundle, a large fiber tract interconnecting these nuclei. Three water-perfused thermodes directly beneath the tissue slices are used to produce discrete thermal stimulations of rostral, middle, and caudal nuclear regions. Fine thermocouples monitor slice temperature over each thermode. Limiting microelectrode explorations to regions directly over a thermode eliminates the problems of temperature gradients and permits more accurate manipulation of temperature at the recording site. While this preparation is ideal for characterizing hypothalamic neuronal thermosensitivity, it is also appropriate for electrophysiological studies of other hypothalamic functional systems.

Effects of progesterone on thermosensitive neurons in preoptic slice preparations

Single neuronal activities in preoptic (PO) slice preparations from both male and female rats were recorded and examined for their responses to 3 ng/ml or 30 ng/ml progesterone (P). Of 31 warm-sensitive neurons, 19 (61.3%) were inhibited by P, 5 (16.1%) were excited, and 7 (22.6%) did not respond to P. Of 26 thermally insensitive neurons, 4 (15.4%) were inhibited by P, 3 (11.5%) were excited, and 19 (73.1%) did not respond to P. Of 4 cold-sensitive neurons, 3 were inhibited and one was excited. These results demonstrate that P inhibits most warm-sensitive neurons directly or indirectly via local neuronal circuits in the slice.

Characteristics of laryngeal cold receptors

This study was designed to further characterize the properties of previously described laryngeal cold receptors (Respir. Physiol. 59:35, 1985). Single unit action potentials were recorded from the internal branch of the superior laryngeal nerve (SLN) in anesthetized, spontaneously breathing dogs. The nervous conduction of fibers originating from 12 laryngeal cold receptors was blocked at a mean (+/- SE) temperature of 18.8 +/- 0.7 degrees C. Twelve receptors were localized on the edge of the vocal folds in correspondence of the vocal process of the arytenoid cartilage. Topical anesthesia (2% lidocaine) blocked their activity within 4-18 sec, suggesting a superficial location. Paralysis of the vocal folds during spontaneous breathing through the upper airway did not alter the activity of 9 of 13 cold receptors. On the other hand, 7 of 12 cold receptors tested with constant flow showed respiratory modulation and laryngeal paralysis abolished the modulation of 3 of these tested with a constant flow of air. During progressive cooling in a stepwise fashion, as in frigid air breathing, laryngeal cold receptors maintained a phasic discharge. Our results indicate that these endings are particularly suited for detecting changes in temperature.

Surface cooling rapidly induces coordinated activity in the upper and lower airway muscles of the fetal lamb in utero

Stimulation of cutaneous thermoreceptors may be an important factor in the initiation of continuous breathing at birth. Maintenance of a patent airway is also important in the continuation of effective ventilation after birth, but whereas in the adult the principal pharyngeal dilator is the genioglossus muscle, in the fetus genioglossus phasic activity is not synchronous with that of the fetal diaphragm. To ascertain whether a cold stimulus that initiates continuous breathing would also induce synchronized inspiratory activity in the upper airway muscles of the fetus, we have cooled fetal lambs in utero and examined the response of the genioglossus and alae nasi muscles in relation to diaphragm activity. Deep regular breathing as recorded by diaphragmatic activity and tracheal pressure started within 1-102 s after cooling commenced and coordinated inspiratory activity was seen in the alae nasi within 2-356 s. Genioglossus activity became synchronized with that of the diaphragm within 11-356 s. Cooling was continued for 4 h but although in one fetus continuous breathing with associated inspiratory activity in the genioglossus and alae nasi muscles lasted throughout the 4-h period, in the others continuous breathing was not sustained and adaptation to the cold stimulus occurred after periods ranging from 27-218 min. The relationship between breathing, upper airway muscle activity, and sleep state passed through one or more different phases, including breathing through high voltage electrocortical activity, before the normal fetal pattern of episodic breathing restricted to the low voltage electrocortical state resumed.(ABSTRACT TRUNCATED AT 250 WORDS)

Thermally-induced activities of the mesencephalic reticulospinal and rubrospinal neurons in the rat

Unit activities of 226 midbrain reticulospinal (mRfS) and non-mRfS neurons and 238 rubrospinal (RbS) and non-RbS neurons were investigated during changes in temperatures of midbrain (Tmb), preoptic and anterior hypothalamus (Thyp) and skin (Ts) in the urethane-anesthetized rat. Responsiveness to Tmb, Thyp and Ts were found in 43.5%, 41.6% and 51.5% of neurons of midbrain reticular formation (mRf), and in 35.2%, 32.7% and 17.6% of neurons of red nucleus (Rb). Higher incidence of responsiveness to remote temperatures was found among Tmb responsive neurons than Tmb unresponsive neurons in both mRf and Rb. The mRf contains significantly greater numbers of neurons having such multiple thermal responsiveness and also of neurons which were activated by falls in temperatures (cold-responsive neurons) than the Rb. These characteristics were more conspicuously seen among mRfS neurons, showing a high degree of convergence of cold signals from different sites of body. On the other hand, RbS neurons did not differ from non-RbS neurons regarding thermal characteristics and showed no particular combinations of responsiveness to temperatures of different sites. Microinjection of procaine and glutamate into the mRf just dorsolateral to the Rb, but not into the Rb, decreased and increased cold-induced increase in EMG activity and shivering without changes in cardiovascular and respiratory parameters and pilomotor activity. The results suggest that mRfS neurons are involved in the control of thermoregulatory muscle tone and shivering.

Effects of nasal cold receptors on pattern of breathing

To investigate the effect on the pattern of breathing of cooling receptors in the nose, eight normal male volunteers underwent a steady-state CO2 stimulation by nasal inhalation. The inhaled gas temperature was randomly switched between "warm" (32 degrees C) and "cold" (2 degrees C) at each of three levels of inspired CO2 fraction (FICO2). Breathing cold air through the nose reduced the mean slope of the ventilatory response to CO2 by 27% (P less than 0.05) and the mean intercept at PCO2 of 45 Torr by 6.6 l/min (P less than 0.01). This was due mainly to a reduction in tidal volume (VT). Analysis of the breathing pattern recorded at a high level of minute ventilation (VE) (end-tidal partial pressure of CO2 approximately 52 Torr) showed a reduction of VE that was due almost entirely to a reduction in VT (P less than 0.05) associated with a reduction in inspiratory time (TI) as a fraction of total respiratory cycle time (P less than 0.05) but little change in VT/TI. In a separate experiment conducted with five subjects, there was no significant difference in inspired nasal resistance between warm and cold runs during CO2-stimulated breathing. The results confirm the previous observation that cold air breathed through the nose inhibits ventilation in normal subjects and show that this is not related to an increase in flow resistance. The reduction in ventilation is due to reduction in VT associated with shortening of the duty cycle.

Intrathecal galanin at low doses increases spinal reflex excitability in rats more to thermal than mechanical stimuli

The neuropeptide galanin (GAL) was injected intrathecally (i.t.) in decerebrate, spinalized, unanesthetized rats and its effect on the nocifensive flexor reflex was examined. The reflex, which was evoked by intense mechanical or thermal stimulation of the foot, was recorded from the ipsilateral hamstring muscles. I.t. GAL increased reflex excitability significantly more to thermal than to mechanical stimuli. It is suggested that GAL, which is present in sensory fibers that innervate the skin, is released by the central terminals of cutaneous afferents that are much more sensitive to thermal than to mechanical stimuli.

Receptive field organisation and electrophysiological responses of spinal cord thermoreactive neurones in the rat

Receptive fields and electrophysiological responses of seventy-three thermoreactive neurones were studied. The receptive fields were 1 to 10 mm wide and 1 to 15 mm long, for the warm thermoreactive neurones and 5 to 15 mm wide and 2 to 31 mm long for cold thermoreactive neurones. The receptive fields of 5 units excited by warming and heating were 5 to 11 mm wide and 3 to 16 mm long. Six units excited by warming and light mechanical stimulation had receptive fields about 1 to 7 mm wide and 1 to 10 mm long. Those of 3 units excited by cooling and light mechanical stimulation were 3 to 10 mm wide and 3 to 15 mm long. Seven bimodal units had receptive fields that were 2 to 30 mm wide and long. The receptive fields were on the ipsilateral scrotal and or inguinal and perineal skin. Only 1 unit had a bilateral receptive field. Seven dorsal horn neurones showed convergence of warm sensitive and nociceptive afferents. Also, 2 units had convergent inputs from cold sensitive and nociceptive afferents. The noxious mechanical excitatory receptive fields were separate and located on the ipsilateral and contralateral toes, the penis or ipsilateral testicle. The thermal excitatory receptive fields of these units were 15 to 17 mm wide and 20 to 21 mm long. The warm and cold-reactive neurones discharged more with the rise and fall in skin temperature, respectively. Five warm-reactive neurones showed bursting activity. The locations of the thermoreactive neurones studied were similar to those reported earlier. It is concluded that dorsal horn thermoreactive neurones, have mainly ipsilateral receptive fields. Secondly, convergence of temperature sensitive and nociceptive afferents occur in the dorsal horn of the rat.

A portable system for measuring cutaneous thresholds for warming and cooling

Measurement of cutaneous thermal thresholds is a valuable technique for detecting small fibre neuropathy. A robust and portable microcomputer controlled system, which separately measures thresholds for warming and cooling, is described. Thresholds at three sites have been measured; the cheek, the dorsum of the hand and the sole of the foot. Regional variability and a correlation with age have been found, indicating the sensitivity of this system.

Convergence of hepatoportal osmotic and cardiovascular signals on preoptic thermosensitive neurons

Effects of hepatoportal osmotic stimuli and changes in arterial blood pressure were studied on the neuronal activity of 24 thermosensitive and 47 thermally insensitive neurons of the preoptic and anterior hypothalamus (PO/AH) in the urethane-anesthetized rat. Infusion of hypertonic (3% NaCl, 9% mannitol) or hypotonic (water) solutions into the hepatic portal vein changes the activity in 59% of thermosensitive neurons and 13% of thermally insensitive neurons but the injection into the femoral vein did not. Changes in blood pressure induced by intravenous injection of vasoactive drugs altered the activity of thermosensitive neurons (75%) and thermally insensitive neurons (32%). Neurons having dual sensitivity to both osmotic and blood pressure were more frequently found among thermosensitive neurons (10/24) than among thermally insensitive neurons (4/47), chi 2(1) = 11.03, p less than 0.001. The convergence of osmotic and baro/volaemic information on thermosensitive neurons may provide explanations for thermoregulatory changes observed during dehydration and acute hypotension.

Comparison between hypothalamic thermoresponsive neurons from duck and rat slices

Neuronal thermoresponsiveness in the preoptic and anterior hypothalamic (PO/AH) region of a bird and a mammal were compared in vitro by recording the activity of 48 units from ducks and 37 units from rats in tissue slices subjected to temperature changes. Warm-responsive units were found in similar proportions in duck and rat PO/AH slices. The average degrees of thermoresponsiveness did not differ between the two species. Neurons exhibiting thresholds of warm responsiveness had higher threshold temperatures (2P less than 0.01) in duck (38.8 +/- 0.2 degrees C) than in rat (37.4 +/- 0.4 degrees C) slices (means +/- standard errors). Firing rates at threshold temperatures and thermoresponsiveness below and above thresholds did not differ between ducks and rats. During synaptic blockade in a Ca2+-free/high-Mg2+ medium, warm-responsiveness was retained in 9 out of 13 units in duck slices and in 8 out of 13 units in rat slices. In two instances in ducks and in one case in rats positive temperature coefficients were converted into negative temperature coefficients. Among two cold-responsive units tested in duck slices one retained its cold-responsiveness. It is concluded that in vitro evaluation of PO/AH neuronal thermoresponsiveness in a bird and a mammal has not revealed differences at the single unit level which might explain the diverging contributions of the avian and mammalian hypothalamus to deep body temperature perception.