Reinhold Necker

Thermoregulatory responses of the pigeon to changes of the brain and the spinal cord temperatures

Summary1.The thermoregulatory responses of pigeons were tested by selective and combined cooling and heating of thermodes implanted chronically into the brain stem and vertebral canal.2.Under thermoneutral conditions lowering the brain temperature to 36°C did not elicit shivering. Similar stimulations of the spinal cord evoked shivering in each case. Simultaneous temperature changes in same direction (cooling the brain and spinal cord) or in opposite direction (heating the brain and cooling the spinal cord) could not influence the intensity of shivering due to cooling the spinal cord alone. Thermal stimulation of the brain stem did not affect shivering due to environmental cold, whereas this response was intensified by cooling and diminished by heating the spinal cord.3.Selective heating of the brain to 44°C rarely induced panting, whereas heating the spinal cord to 42–43°C resulted generally in polypnea under thermoneutral conditions. Opposite changes at both sites (heating the spinal cord and cooling the brain) inhibited panting due to heating the spinal cord in 3 of 12 cases. Under conditions of environmental heat, persisting thermal panting was often inhibited by cooling the spinal cord, but hardly affected by cooling the brain stem.4.Cooling the brain as well as the spinal cord raised the feathers (piloerection) and lowered the skin temperature of the naked feet (vasoconstriction). Both reactions were affected to about the same extent by stimuli in each of the two parts of CNS.5.The results suggest that the temperature signals generated in the brain stem of the pigeon especially effect piloerection and vasomotor reactions. These responses enable the animals to maintain a constant deep body temperature under mild thermal load. Changes of the spinal cord temperature chiefly drive shivering and panting which avoid hypo- and hyperthermia of birds under stronger thermal stress.

Electrophysiological mapping of body representation in the cortex of the blind mole rat.

The cortex of the blind mole rat (Spalax ehrenbergi) was explored for somatosensory responses with special reference to an extension into the occipital cortex which serves vision in sighted mammals. Head and body representation was similar as in other rodents or mammals. However, the somatosensory area extended far into the occipital cortex. No responses to auditory or visual stimulation were found caudal to the somatosensory area. However, auditory responses were recorded in an area lateral to and slightly caudal to the head representation. It is concluded that in this naturally blind animal the area normally occupied by the visual cortex serves somatosensory function.

Temperature sensitivity of thermoreceptors and mechanoreceptors on the beak of pigeons

Summary1.The temperature sensitivity of thermoreceptors and slowly adapting mechanoreceptors in the trigeminal area of pigeons were tested while recording from all three main branches of the trigeminal nerve.2.Warm receptors were excited by warming and totally inhibited by cooling. During rewarming no overshooting excitation occurred. The impulse frequency increased with increasing temperature; at low temperature the receptors fired in bursts.3.A special “warm-sensitive” receptor with a regular discharge rate at high skin temperature was totally inhibited by cooling and restored its initial frequency after rewarming without any overshoot. The impulse frequency did not increase with increasing temperature but was constant above a critical skin temperature.4.Most of the slowly adapting mechanoreceptors had a very regular, rather high impulse frequency (20–50 imp./sec) at constant mechanical stimulus. The impulse frequency decreased during cooling without an excitatory overshoot and increased during warming without an inhibition.5.Only few slowly adapting mechanoreceptors were excited by cooling and inhibited by warming, a behaviour which is reported for all temperature-sensitive mammalian mechanoreceptors.

Temperature-sensitive mechanoreceptors, thermoreceptors and heat nociceptors in the feathered skin of pigeons

Summary1.Single unit recordings from afferent fibres of a cutaneous branch of the radial nerve were done during thermal stimulation of the skin of the wing with a thermode or with radiant heat or cold. The response of all cutaneous receptors to this thermal stimulation was studied.2.Rapidly-adapting mechanoreceptors were never excited by thermal stimulation.3.Slowly-adapting mechanoreceptors had characteristics similar to the type I slowly-adapting mechanoreceptor in mammals. There was an excitatory overshoot during rapid cooling and a transient inhibition during warming when activated by a thermode. The phasic response depended on the rate of temperature change and on the temperature range. Radiant heating or cooling was ineffective in eliciting a response in most cases. The static curves showed a broad maximum between about 36 and 43 °C. At temperatures above about 45 °C there was always a reduced activity.4.Two receptors with thermoreceptor characteristics were found. One cold receptor showed increased activity at low skin temperature and one warm receptor was excited by moderate heating in the temperature range 35–40 °C.5.Heat nociceptors were excited both by radiant heating and thermode stimulation. During staircase-like increases in skin temperature the mean threshold of the response of eight heat nociceptors was 47.1 ± 1.4 °C. There was a steep increase in firing rate up to at least 52 °C. Some of the heat nociceptors were also excited by noxious mechanical stimulation.

Response of trigeminal ganglion neurons to thermal stimulation of the beak in pigeons

SummaryThe activity of neurons from the trigeminal ganglion of pigeons have been recorded while cooling or warming the beak. Thermosensitive neurons were seldom compared with mechanosensitive units. From a total of 16 thermosensitive neurons, 13 were excited by cooling and 3 by warming. The impulse frequency strongly depended on temperature. At constant temperatures, constant firing rates were established. The static curves of cold-sensitive units showed, that with decreasing temperature a nearly linear rise in firing rate occurred between about 36 °C and 20 °C. One quantified, warm-sensitive neuron showed, with increasing temperature, a nearly linear rise between about 35 °C and 44 °C. Sudden cooling or warming caused no pronounced overshoot as in mammals. Six cold-sensitive neurons were totally inhibited by rewarming as were 2 warm-sensitive units by cooling. No comparable influence of temperature on the discharge rate of some slowly-adapting mechanoreceptors (pressure stimulus) was exhibited.

Thermal sensitivity of different skin areas in pigeons

SummaryPigeons lightly anaesthetized with urethane regulate their body temperature at a hypothermic level. During recovery from anaesthesia there is a continuous shivering at an ambient temperature of about 22 °C. The effect of thermal stimulation (radiant heat) of different skin areas on this ongoing shivering (EMG of the breast muscle) was taken as a measure of the thermal sensitivity of the skin area under study. Feathered skin areas, which were plucked before stimulation, turned out to be very sensitive with regard to the thermoregulatory effector mechanism of shivering. Moderate heating of the most sensitive skin of the back often resulted in cessation of shivering. Similar feathered skin areas on back, wing, and breast showed that there was a decreasing sensitivity in that order they are mentioned. Graded stimulation was followed by a graded response and there was an interaction between different skin areas. Heating the beak caused only a small reduction of shivering. There was no effect at all during heating or cooling naked parts of the feet even during painful thermal stimulation which was often followed by retraction of the whole leg.

Temperature-sensitive ascending neurons in the spinal cord of pigeons

Summary1.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 warmsensitive 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°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±1.3imp./sec·°C (mean value and s. d.) and that of three cold-sensitive ones −2.3±0.3imp./sec·°C in the range 35°C–45°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.

Head-bobbing of walking birds

Many birds show a rhythmic forward and backward movement of their heads when they walk on the ground. This so-called “head-bobbing” is characterized by a rapid forward movement (thrust phase) which is followed by a phase where the head keeps its position with regard to the environment but moves backward with regard to the body (hold phase). These head movements are synchronized with the leg movements. The functional interpretations of head-bobbing are reviewed. Furthermore, it is discussed why some birds do bob their head and others do not.

Zur Entstehung der Cochleapotentiale von Vögeln: Verhalten bei O2-Mangel, Cyanidvergiftung und Unterkühlung sowie Beobachtungen über die räumliche Verteilung

1. Ableitmethoden fur die verschiedenen in der Cochlea von Vogeln (Taube, Star, Sperling, Amsel) vorhandenen oder auf Schallreiz entstehenden Potentiale [Mikrophonpotential (CM); Summationspotential (SP); endocochleares Potential (EP); Aktionspotential (AP)] werden beschrieben, und es werden Verfahren zum O2-Entzug, zur Cyanidvergiftung des Innenohres und zur Unterkuhlung angegeben. 2. Die CM werden in eine positive (CM+) und eine negative Teilkomponente (CM-) aufgeteilt (Polaritat bezogen auf Scala tympani) und diese getrennt untersucht. Hinsichtlich der Abhangigkeit von der Reizintensitat verhalten sich beide Teilkomponenten etwa gleich, sie unterscheiden sich jedoch in ihrer Empfindlichkeit gegenuber Stoffwechseleinflussen. 3. CM- erweist sich gegenuber O2-Mangel und lokaler Cyanidvergiftung als sehr empfindlich; es verschwindet bei Anoxie innerhalb 30–40 sec. Bei Hypothermie ergibt sich eine einfache Abhangigkeit von der Temperatur mit einem Q10 von 2,0. Aus diesen Ergebnissen wird geschlossen, das CM- eine Hyperpolarisation darstellt, der ein unmittelbarer aktiver Ionen-Transport zugrundeliegt. 4. CM+ zeigt bei kurzzeitiger Anoxie erhebliche interindividuelle Variabilitat; es schwankt aber insgesamt nur geringfugig um den Ausgangswert. Postmortal und nach lokaler Cyanidvergiftung sinkt es langsam auf Null ab (etwa 1/2 Std). Durch die andersartige Empfindlichkeit von CM+ (im Vergleich zu CM-) kommt es zu einer Gleichrichtung der CM. Auch bei Hypothermie verhalt sich CM+ anders als CM- indem es meist erst unterhalb 30° C absinkt; unterhalb 30° C ergibt sich ein Q10 von 1.54. Aus dem Verhalten von CM+ wird geschlossen, das ihm eine Depolarisation zugrundeliegt. 5. Die CM der Vogel konnen somit als normale Erregungsvorgange an sensiblen Strukturen (Haarzellmembran) angesehen werden. Die Theorie von Davis, wonach die CM dadurch entstehen, das durch Anderung des Membranwiderstandes ein standig durch die Membran fliesender Strom moduliert wird, mus dahingehend erweitert werden, das die Hyperpolarisation durch aktiven Transport geleistet wird und nur die Depolarisation auf passivem Ionenstrom beruht. Der postmortale Anteil der CM besteht nur aus CM+ und ist danach ein Depolarisationspotential, das von der Hohe des Ruhepotentials abhangt. 6. SP hat das Vorzeichen und weitgehend auch das Verhalten gegenuber Stoffwechseleinflussen mit CM+ gemeinsam. Im Gegensatz zu den Verhaltnissen bei Saugern wird wahrend Anoxie kein Vorzeichenwechsel durchlaufen. Postmortal sinkt SP wie CM+ langsam auf Null ab. Bei Hypothermie sinkt es meist erst unterhalb 30° C, und dann relativ steil ab. Aus diesen Ergebnissen wird geschlossen, das SP als Dauerdepolarisation anzusehen ist. 7. Unregelmasigkeiten im Verlauf der Anderungen von SP und CM + stehen in Beziehung zur Herzfrequenz und konnen somit auf sekundare Folgen der Stoffwechselbelastung zuruckgefuhrt werden. 8. Neben mechanischer Nichtlinearitat bei der Reiztransformation wird die Entstehung von SP auf die unterscheidbaren Entstehungsbedingungen von CM+ und CM-, d. h. auf nichtlineare Vorgange bei der Potentialbildung an den Haarzellen, zuruckgefuhrt. 9. Der Polaritatswechsel von SP, CM+ und CM- wird im apikalen Bereich der Haarzellen lokalisiert: ein weiterer Hinweis dafur, das diese Potentiale an den Haarzellen entstehen. 10. EP hat bei den hier untersuchten Singvogeln einen mittleren Wert von +15 mV. Bei Anoxie sinkt EP rasch auf negative Werte ab, deren Maximum bei 20–30 mV liegt. Postmortal geht dieses negative Potential langsam gegen Null. 11. Der Verlauf der Anderungen von EP wahrend Anoxie gleicht demjenigen von CM-, doch besteht eine zeitliche Verschiebung: EP reagiert fruher. Dies wird darauf zuruckgefuhrt, das das Tegmentum vasculosum (Entstehungsort von EP) direkt aus dem Blutstrom, die Papilla basilaris (Entstehungsort von CM) dagegen durch Diffusion aus dem Tegmentum mit O2 versorgt wird. 12. AP steigt zu Beginn der Anoxie und Hypothermie oftmals zunachst an und sinkt dann rasch ab (Hypothermie) oder verschwindet (Anoxie). Die Latenzzeit von AP nimmt mit abnehmender Temperatur zu, wahrend diejenige von CM+ und CM- nahezu konstant bleibt.

Spinal distribution and brainstem projection of lamina I neurons in the pigeon

Lamina I neurons of the spinal dorsal horn serve nociception both in mammals and in birds. The projection of these neurons to the brain is largely unknown in birds. Injections of retrogradely transported fluorescent tracers into various brainstem nuclei showed that these neurons, which are distributed throughout the spinal cord, heavily project to the nucleus of the solitary tract and the parabrachial area but not to the hypothalamus. Injections into the nucleus of the solitary tract revealed a group of neurons located in Lissauers tract of thoracic segments. These results point to a functional role of spinal lamina I neurons in avian visceronociception.