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R Necker

Publications and source records attributed to R Necker.

44 records · Page 3Linked to original sources
PubMed1978

Noxious thermal input from the rat tail: modulation by descending inhibitory influences.

In anaesthetized rats, single fibres have been dissected from the tail nerves. Fibres were found which became excited when the temperature of water surrounding the tail was raised above 40 degrees C. Firing rate increased with stepwise increases in temperature, showing first a transient outburst followed by adaptation to a static level. Corresponding neurones were also found in the dorsal horn at the entry zone of the roots coming from the tail. The cord neurones had a higher threshold temperature of 42.5--45 degrees C. When the spinal cord was reversibly blocked by cooling in the thoracic region, then the threshold of the dorsal horn neurones was reduced to that of the afferent fibres. In addition, at suprathreshold temperatures dorsal horn activity was greater during cord blockade. We conclude that dorsal horn neurones responding to noxious heating are subject to a tonic descending inhibitory control.

Action Potentials↗
PubMed1975

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.

Animals↗
PubMed1975

Temperature-sensitive ascending neurons in the spinal cord of pigeons.

Ascending neuronal activity in the lateral funiculus of the spinal cord of pigeons (spinalized at about C4, recordings at about C6) has been studied with regard to effects of temperature changes with a thermode in the vertebral canal between Th4 and C8. 2. Both warm-sensitive (35) and cold-sensitive (14) neurons were found. According to the change in impulse frequency during steplike thermal stimuli, different reaction types could be distinguished. Twenty-four warm-sensitive and seven cold-sensitive units showed a proportional frequency change without any dynamic reaction. Three other warm-sensitive neurons had an additional dynamic reaction (excitatory overshoot during warming, inhibition during cooling). Five warm-sensitive and three cold-sensitive units showed no static sensitivity but responded with outstanding dynamic frequency changes during rising or falling temperature. The activity of some neurons stopped suddenly above (4) or below (3) a critical temperature, which was always near the normal spinal temperature (about 41 degrees C). Altogether the reaction to rapid temperature changes was consistently greatest near the normal body temperature. 3. The mean static sensitivity of 17 warm-sensitive units was + 4.2 plus or minus 1.3 imp./sec. degrees C (mean value and s. d.) and that of three cold-sensitive ones minus 2.3 plus or minus 0.3 imp./sec. degrees C in the range 35 degrees minus 45 degrees C (vertebral canal temperature). The temperature coefficient (Q10) which was calculated for the same neurons showed great variations with mean values of about 5 for both warm- and cold-sensitive units.

Animals↗