[Influence of temperature upon the afferent and efferent motor innervation of the spinal cord. I. Temperature dependence of afferent and efferent spontaneous activity]

Temperature effects on the discharge frequency of primary and secondary endings of isolated cat muscle spindles recorded under a ramp-and-hold stretch

The effects of changes in temperature on primary and secondary endings of isolated cat muscle spindles were investigated under ramp-and-hold stretches and different degrees of pre-stretch. Temperature-induced alterations of the discharge frequency were compared over a temperature range of 25-35 degrees C. Both primary and secondary endings responded to warming with increasing discharge frequencies when the spindle was pre-stretched by 5-10% of its in situ length. The following differences between the temperature effects on primary and secondary endings were observed: (1) The temperature coefficients (Q(10)) obtained from the discharge frequencies during the dynamic and static phase of a stretch were similar for endings of the same type, but they were larger in primary endings (range of Q(10): 2.3-3.3; mean: 2.9) than in secondary endings (range of Q(10): 1.6-2.2; mean: 2.0); (2) With primary endings, but not with secondary endings, the temperature sensitivity (imp s(-1) degrees C(-1)) was larger during the dynamic phase than during the static phase of a stretch; (3) In primary endings, the fast and slow adaptive components occurring in the discharge frequency during the static phase of a stretch clearly increased with warming while in secondary endings, the slow decay was less affected, and the fast decay showed no change; (4) In relaxed spindles, the excitatory effect of warming was overlaid by a strong inhibitory effect as soon as the temperature exceeded about 30 degrees C, resulting in an abrupt cessation of the background activity in most secondary endings, but not usually in primary endings. In general, warming induced an enhanced stretch sensitivity in both types of ending, and additionally an inhibitory effect that is obvious only in secondary endings of relaxed spindles. The different effects of temperature on the discharge frequency of primary and secondary afferents are assumed to be caused by different properties of their sensory membranes.

Effect of photoperiod and melatonin on cold resistance, thermoregulation and shivering/nonshivering thermogenesis in Japanese quail

The effect of photoperiod and melatonin treatment on cold resistance and thermogenesis of quails was studied. The birds were acclimated for 8 weeks to short day (8L:16D) or long day (16L:8D) conditions, and 8 of 16 quails in each group were implanted with melatonin capsules. One group of quails was maintained outside in an aviary during winter. Oxygen consumption (VO2), body temperature (Tb, recorded with temperature transmitters) and shivering (integrated pectoral EMG) were recorded continuously, and samples of heart rate and breathing rate were picked up when ambient temperature was decreased stepwise from 27 down to -75 degrees C. Heat production maximum (HPmax), cold limit, lower critical temperature, basal metabolic rate (BMR) and thermal conductance were determined. The results show that short day, cold and melatonin treatment improved cold resistance and thermal insulation of quails when compared with quails acclimated to long day conditions. An increase in HPmax was induced only by melatonin treatment. The results suggest that the acclimatization of quails is under control of the pineal gland. The linear increase of shivering intensity with VO2 at moderate cold load shows that shivering is the primary source for thermoregulatory heat production in the quail. At Ta's below -40 degrees C shivering remained constant although VO2, heart rate and breathing rate continued to increase with increasing cold load. This could indicate the existence of a nonshivering thermogenesis in birds. Unlike to mammals, this non-shivering thermogenesis in birds would serve as secondary source of heat supporting shivering thermogenesis in severe cold.

Effects of changes in preoptic temperature on stretch response of muscle spindle endings in the cat's soleus muscle

The effects of changing the temperature in the preoptic region on the stretch responses of primary and secondary endings of the muscle spindle in the soleus muscle was investigated in urethane anesthetized cats. The local temperature of the preoptic region was controlled by implanting water perfused thermodes (32-42.5 degrees C). A standard ramp and hold stretch stimulus was repeatedly applied to the soleus muscle during changes of preoptic temperature from normal to hypo- or hyperthermic values. During each stretch the instantaneous firing rate was recorded and the static firing frequency and the dynamic index were electronically determined according to Crowe and Matthews (1964). Of a total of 76 investigated muscle spindle afferents, the stretch responses of 49 (65%) were altered by changing preoptic temperature. The static stretch response was increased in all cases during cooling, whereas during preoptic heating the static stretch response increased in about half of the afferents and decreased in the rest. Increase in the static stretch response during both cooling and heating was usually combined with the appearance of spontaneous discharges at rest. With regard to the static stretch response, primary and secondary muscle spindle endings responded similarly to cooling and heating. Two types of preoptic temperature effects on the stretch responses of primary endings were observed. In the majority of afferents only the static stretch response was augmented during cooling, whereas the peak response was little changed resulting in a decrease of the dynamic index ('static' response type).(ABSTRACT TRUNCATED AT 250 WORDS)

Antagonistic changes of gastric and colonic motility during selective thermal stimulation of thoracic and lumbosacral cords in anesthetized dogs

Changes in gastric and distal colonic motility evoked by thermal stimulation of the thoracic and lumbosacral cords, either individually or simultaneously, were investigated in spinal-intact dogs and in dogs spinalized at the cervical level. Simultaneous cooling of the thoracic and lumbosacral cords increased both gastric and colonic motility before and after spinalization. The direction of the responses evoked by simultaneous heating was the opposite, but only the decrease in gastric activity in the spinal-intact dog was significant. Selective cooling of the thoracic cord increased gastric motility, but decreased colonic motility before and after spinalization. Selective heating decreased gastric motility before and after spinalization, and increased colonic motility before spinalization. Selective cooling of the lumbosacral cord decreased gastric motility and increased colonic motility in spinal-intact dogs. No significant responses could be observed during selective heating in spinal-intact dogs. However, in spinalized dogs, the selective cooling and heating increased and decreased colonic motility respectively, while no significant change was observed in gastric motility during the cooling and the heating. It is concluded from the results that thermal stimulation of the spinal cord directly affects spinal functions which control gastrointestinal motility, and that there exists a mutual inhibitory interaction between the thoracic and lumbosacral innervation of the gastrointestinal tract.

Initiation of muscle activity in spinalized pigeons during spinal cord cooling and warming

1. The effect of spinal cord temperature changes on muscle activity was investigated in unanaesthetized intact and chronically spinalized pigeons and in acutely spinalized pigeons which were artifically respirated and lightly anaesthetized with ether. 2. Spinal cord cooling regularly produced an increase in muscle activity and visible muscle tremor in intact and spinalized pigeons. This motor cold defence reaction was less intensive in spinalized animals, but was qualitatively identical in all groups with regard to spindle shaped firing patterns and grouped discharges. 3. Intravenous injection of 60-100 mg/kg L-Dopa enhanced the motor response to spinal cord cooling in acutely spinalized pigeons. It is suggested that L-Dopa may act on dopaminergic or noradrenergic neurones in the spinal cord. 4. The results demonstrate that the generation of the motor cold defence response to cooling of the spinal cord in pigeons is basically independent from supra-spinal nervous mechanisms. The decreased intensity of cold induced muscle activity in spinalized animals may be attributed to the loss of excitatory or disinhibitory descending inputs to the spinal cord. 5. Spinal cord warming above normal body temperature (41.5 degrees C) produced an increase in muscle activity and slow muscle movements. The pattern was qualitatively different from that of the cold induced tremor.

Effect of temperature on postsynaptic potentials of cat spinal motoneurones

The effect of spinal cord temperature on excitatory postsynaptic potentials (EPSP) and inhibitory postsynaptic potentials (IPSP) were measured by means of intracellular recordings from lumbar motoneurones of 43 cats. While body temperature and oil bath temperature were maintained between 37 and 38 degrees C, the temperature of the spinal segment under investigation was changed separately in the range between 30 and 42 degrees C. Cooling consistently produced an increase in amplitude and duration of both, mono- and poly-synaptic EPSPs and recurrent and direct IPSPs. Warming caused the opposite effect. The input resistance of the motoneurones was inversely related to the spinal cord temperature, while the latency of action potentials produced by intracellular injection of outward current was directly and exponentially related to spinal temperature. Although the data do not provide a quantitative differentiation of pre- versus postsynaptic temperature effects, they are consistent with the notion that temperature dependent changes on postsynaptic membrane properties contribute to the observed PSP changes. It is further suggested that similar postsynaptic temperature effects may be concerned in temperature sensitivity of proposed specific central neurones.

Effect of spinal deafferentation on temperature regulation and spinal thermosensitivity in pigeons

1. To study the effect of spinal deafferentation on temperature regulation and spinal thermosensitivity in acute experiments, the spinal cord of pigeons was transected at Th4 and the dorsal roots cut carefully on both sides from Th4 to C6 or C4 (13 or 15 segments); only afferent signals from the upper neck and the head could reach the CNS. Selective changes of the spinal cord temperature in the deafferented region were performed by a thermode in the vertebral canal. 2. At thermoneutral ambient conditions (Ta 23-30 degrees C) the deafferented pigeons were able to maintain a normal body temperature (about 41 degrees C). During ambient cooling (Ta 1-10 degrees C) the core temperature was regulated at a lower level of about 38 degrees C, strong shivering occurred, and heat production was increased. 3. If the decreased spinal cord temperature at low Ta was adjusted experimentally to normal values (about 41 degrees C) then shivering stopped and oxygen consumption decreased. This decrease in heat production was followed by a continuous fall in rectal temperature to values as low as 33-34 degrees C without any initiation of shivering or extra heat production. This means that shivering in the deafferented pigeons must be elicited by cold sensors in the spinal cord alone and that there are no important cold sensors in the non-deafferented region including the brain. 4. Selective spinal cooling of the deafferented region at thermoneutral Ta was followed by an immediate onset of shivering and an increase in heat production. Spinal heating resulted in an increase in wing temperature which served as an indication of vasodilatation, i.e., an activation of a heat loss mechanism. This is a confirmation of the assumption that the spinal temperature sensors are indeed located in the spinal cord and that the responses to experimental changes of spinal canal temperature are not mediated by extraspinal thermoreceptors. The results show clearly that the regulation of body temperature in pigeons at moderate thermal loads can be mediated by these spinal sensors alone. 5. Continued spinal cooling resulted in an increase in body temperature by about 2 degrees C and a subsequent regulation at this high level. This means that there must exist warm sensors in the non-deafferented cranial region.

Thermosensitivity of neurons in the sensorimotor cortex of the cat

Extracellular action potentials were recorded from 80 neurons in the sensorimotor cortex of the cat as brain temperature was varied by 4 degrees to 8 degrees C. The discharge rate of 37 percent of the neurons studied increased with increasing brain temperature. The discharge rate varied inversely with temperature in 11 percent of the neurons.