Preoptic And Anterior Hypothalamic Research Articles

Developmental and hormonal regulation of thermosensitive neuron potential activity in rat brain.

To understand the involvement of thyroid hormone on the postnatal development of hypothalamic thermosensitive neurons, we focused on the analysis of thermosensitive neuronal activity in the preoptic and anterior hypothalamic (PO/AH) regions of developing rats with and without hypothyroidism. In euthyroid rats, the distribution of thermosensitive neurons in PO/AH showed that in 3-week-old rats (46 neurons tested), 19.5% were warm-sensitive and 80.5% were nonsensitive. In 5- to 12-week-old euthyroid rats (122 neurons), 33.6% were warm-sensitive and 66.4% were nonsensitive. In 5- to 12-week-old hypothyroid rats (108 neurons), however, 18.5% were warm-sensitive and 81.5% were nonsensitive. Temperature thresholds of warm-sensitive neurons were lower in 12-week-old euthyroid rats (36.4+/-0.2 degrees C, n = 15, p<0.01,) than in 3-week-old and in 5-week-old euthyroid rats (38.5+/-0.5 degrees C, n = 9 and 38.0+/-0.3 degrees C, n = 15, respectively). The temperature thresholds of warm-sensitive neurons in 12-week-old hypothyroid rats (39.5+/-0.3 degrees C, n = 8) were similar to that of warm-sensitive neurons of 3-week-old raats (euthyroid and hypothyroid). In contrast, there was no difference in the thresholds of warm-sensitive neurons between hypothyroid and euthyroid rats at the age of 3-5 weeks. In conclusion, monitoring the thermosensitive neuronal tissue activity demonstrated the evidence that thyroid hormone regulates the maturation of warm-sensitive hypothalamic neurons in developing rat brain by electrophysiological analysis.

Temperature sensitivity of neurones in slices of the rat spinal cord.

1. The inherent temperature sensitivity of 343 spontaneously active neurones recorded from rat spinal cord (SC) slices was investigated electrophysiologically. Recordings were made from 321 neurons from transverse and 22 neurons from longitudinal slices and their thermosensitivity was determined by relating changes in firing rate to changes in slice temperature. 2. Of the neurones from transverse slices, 53% were warm sensitive, 2% were cold sensitive and 45% were temperature insensitive. In longitudinal slices, 68% were warm sensitive and the remaining neurones were temperature insensitive. 3. When classified according to their recording sites in transverse slices, warm-sensitive neurones in laminae I and II had the same mean temperature coefficient compared with those recorded from lamina X, despite the fact that the latter had a significantly higher spontaneous activity. 4. The intrinsic temperature sensitivity of the majority of warm-sensitive neurones was confirmed by blocking their synaptic input. 5. A transient overshoot in activity, i.e. a dynamic response characteristic following rapid temperature stimuli (0.4 degree C s-1) was observed in 73% of the warm-sensitive and 59% of the temperature-insensitive neurones in laminae I and II in response to rapid warming, but only rarely (< 10%) in lamina X. 6. Temperature-sensitive SC neurones share response characteristics with temperature-sensitive neurones in the preoptic and anterior hypothalamic (PO/AH) area and with peripheral temperature receptors. Functionally, these neurones may represent the cellular basis for the temperature sensory function of the spinal cord that has been well characterized in vivo in homeothermic species.

Cardiovascular responses induced in free-moving rats by immune cytokines.

1. We investigated the effect of intraperitoneal (I.P.) injections of the immune cytokines, interleukin-1 beta (IL-1 beta) and tumour necrosis factor (TNF) on cardiovascular responses in free-moving rats, using a biotelemetry system. 2. The I.P. injection of a small dose of IL-1 beta (1 microgram/kg) induced a monophasic increase in the heart rate, and that of a large dose (10 micrograms/kg) induced biphasic increases in the blood pressure and heart rate. However, the I.P. injection of any of several doses of TNF (1, 10 and 50 micrograms/kg) had no effect on cardiovascular responses in rats. 3. Pre-treatment with I.P. injection of indomethacin (10 mg/kg), an inhibitor of cyclo-oxygenase, significantly suppressed the cardiovascular responses and the increase in the plasma noradrenaline (NA) concentration induced by I.P. injection of IL-1 beta. 4. Microinjection of IL-1 beta (1 and 10 ng) into the preoptic and anterior hypothalamic (PO-AH) region induced dose-dependent increases in the blood pressure and heart rate in rats. These responses were also suppressed by pretreatment with I.P. indomethacin (10 mg/kg). In addition, microinjection of prostaglandin E2 (20 and 100 ng) into the PO-AH region increased blood pressure and heart rate, but that of prostaglandin D2 (100 ng) had no effect. 5. The present results suggest that IL-1 beta stimulates the release of prostaglandins, presumably E series, near regions of the hypothalamus, which act on the hypothalamus to induce activation of the sympathetic nervous system. Subsequently, the blood pressure, heart rate and the plasma level of NA increase.

Response of thermoresponsive neurons of rat's hypothalamus during intracarotid infusion of prostaglandin E 2

We investigated the effect of intracarotid infusion of prostaglandin E 2 (PGE 2) on the single-unit activity of neurons in the preoptic and anterior hypothalamic (PO/AH) region. A total of 35 neurons in the PO/AH region were examined: 10 were warm-responsive neurons, 6 were cold-responsive neurons, and 19 were thermally insensitive neurons. In the warm-responsive neurons, the activities of 4 neurons were facilitated, while 3 neurons were inhibited and 3 neurons were not affected after intracarotid infusion of PGE 2. In the cold-responsive neurons, the activities of 2 neurons were facilitated and 4 neurons were not affected by PGE 2 infusion. Furthermore, 15 out of 19 thermally insensitive neurons were not affected by PGE 2 infusion. These results suggest that thermoresponsive neurons of the PO/AH region respond well to intracarotid infusion of PGE 2, compared with thermally insensitive neurons. However, the direction of neuronal response induced by intracarotid infusion of PGE 2 could not be generally categorized based on the thermoresponsiveness of individual neurons.

Thermal characterization and transmitter analysis of single units in the preoptic and anterior hypothalamus of conscious ducks.

With a multibarrel assembly combining one carbon fiber micropipette as recording electrode and 6 pipettes for microiontophoretic application of drugs, the activity of neurons in the preoptic and anterior hypothalamic (POAH) region was extracellularly recorded in situ in conscious ducks implanted chronically with a device permitting hypothalamic thermal stimulation. Among 355 neurons 17% were identified as warm-responsive (warm units) and 20% as cold-responsive (cold units). In 58 warm and 56 cold units control discharge rates at 40 degrees C local temperature (F40) and temperature coefficients (delta F/delta T) were determined and presented as means +/- SEM. The F40 values of warm units (35.2 +/- 2.3 Imp . s-1) were significantly higher than of cold units (16.3 +/- 1.8 Imp . s-1). The delta F/delta T values (+1.77 +/- 0.15 and -1.77 +/- 0.19 Imp . s-1 . degree C-1) of warm and cold units were not different in absolute terms. In pilot experiments either activation or inhibition by lowering whole-body temperature was observed in both warm and cold units. Microiontophoretic application of one or more of the amines acetylcholine (ACh), 5-hydroxytryptamine (5-HT), and noradrenaline (NA) to warm and cold units revealed differences in their responsiveness to ACh, which more consistently stimulated cold units. NA inhibited the majority of warm units; 5-HT stimulated the majority of cold units. In both warm and cold units NA and ACh differed in their actions, with the latter amine more consistently producing activation.

Effects of endogenous pyrogen and prostaglandin E2 on hypothalamic neurons in guinea pig brain slices

To investigate the direct effects of endogenous pyrogen (EP) and prostaglandin E2 (PGE2) on the activity of neurons in the preoptic and anterior hypothalamic (PO-AH) region, single-unit activity was recorded from brain tissue slices prepared from the PO-AH region of guinea pigs. When EP was applied into the perfusate 18% of warm-responsive neurons decreased their activity, and 23% of warm-responsive neurons increased their activity. Most of the thermally insensitive neurons did not respond to EP. PGE2 inhibited 29% of warm-responsive neurons and facilitated 15% of them. Moreover, when EP and PGE2 were applied to the same neurons at different times, the same directions of changes in neuronal activity were observed in 72% of total neurons examined. These results suggest that EP and PGE2 change the neuronal activity of the thermoresponsive neurons in the PO-AH region involved in fever induction. However, by these results, the direction of neuronal response induced by these substances could not be generally categorized based on the thermoresponsiveness of the individual neuron.

Effects of endogenous pyrogen and prostaglandin E2 on hypothalamic neurons in rat brain slices.

We investigated the effects of endogenous pyrogen and prostaglandin E2 (PGE2) on the preoptic and anterior hypothalamic (POAH) neurons using brain slice preparations from the rat. Partially purified endogenous pyrogen did not change the activities of most of the neurons in the POAH region when applied locally through a micropipette attached to the recording electrode in proximity to the neurons. This indicates that partially purified endogenous pyrogen does not act directly on the neuronal activity in the POAH region. The partially purified endogenous pyrogen, applied into a culture chamber containing a brain slice, facilitated the activities in 24% of the total neurons tested, regardless of the thermal specificity of the neurons. Moreover, PGE2 added to the culture chamber facilitated 48% of the warm-responsive, 33% of the cold-responsive, and 29% of the thermally insensitive neurons. The direction of change in neuronal activity induced by partially purified endogenous pyrogen appears to be almost the same as that induced by PGE2 when these substances were applied by perfusion to the same neuron in the culture chamber. These results suggest that partially purified pyrogen applied to the perfusate of the culture chamber stimulates some constituents of brain tissue to synthesize and release prostaglandin, which in turn affects the neuronal activity of the POAH region.

Activity of hypothalamic thermosensitive neurons during cortical spreading depression in the rat

Effects of single waves of cortical spreading depression (CSD) on unit activity of the ipsilateral preoptic and anterior hypothalamic (PO/AH) neurones were studied in urethane-anesthetized rats. When CSD entered the frontal cortex, the firing rate of teh majority, (85%, 22/26 units) of Po/AH warm-sensitive neurons decreased for 1.4–14.2 min and the remaining 4 neurons were unaffected. In contrast, 10 (77%) of the 13 cold-sensitive neurons increased their firing rates for 1.2–10.4 min after the CSD entrance of the frontal cortex. Of the remaining 3 neurons, two decreased their firing rates and one showed no change during CSD. Thirteen (76%) of the 17 thermally insensitive neurons were not affected by CSD, but the remaining 4 neurons decreased their firing rates slightly for about 1.4 min. The most critical cortical region responsible for the activity change of the PO/AH thermosensitive neurons during CSD was found to lie in the sulcal prefrontal cortex by observing the effect of a single CSD elicited separately from the occipital and the frontal cortex on the same PO/AH neurons (a double-CSD technique). The result, together with the previous ones on thermoregulatory responses during the frontal CSD, suggests that the sulcal prefrontal cortex exerts a tonic influence on the activity of the hypothalamic thermosensitive neurons and is involved in the central control of thermoregulation.

Midbrain neurons of rats responsive to hypothalamic temperature change and their local thermosensitivity

1. 1. A water-perfused thermode was implanted in the preoptic region of urethane-anaesthetized rats. Single-unit activities were recorded by glass microelectrodes in the limited area of the limited area of the rostal midbrain, and the response of these units to changes in preoptic temperature ( T PO ) was studied. 2. 2. Of the 170 midbrain units studied, 58 responded to changes in T PO in the range 30–42°C with a high correlation between temperature and firing rate. Of these 58, 24 units increased their firing rate by a rise in T PO , showing a positive temperature coefficient (W-type), 33 units increased their firing rate by a fall in T PO , showing a negative temperature coefficient (C-type) and 1 unit increased its firing rate in both the temperature ranges below and above normal temperature (WC-type). 3. 3. To clarify the possibility that the conductive heating and cooling might affect neuronal activity in the midbrain, the temperatures of the preoptic and midbrain regions were independently controlled. In the 32 midbrain units responsive to changes in T PO (16 W-type and 16 C-type), local thermosensitivity was examined, and the type of temperature coefficient for local temperature ( T LOC )—positive (W-type), negative (C-type) or temperature insensitive (N-type)—was determined. The above possibility was analysed based on the type of temperature coefficient and magnitude of response to changes in T PO and T LOC . It was concluded that the responses of these midbrain units (more than 93%) to preoptic thermal stimulation are attributed to the neuronal signals derived from the preoptic and anterior hypothalamic (POAH) temperature-sensitivie neurons. 4. 4. The processing of the efferent signals from the POAH temperature sensors to the midbrain level is discussed, and its significance in the descending information for shivering is suggested.

Dynamic response of preoptic and hypothalamic neurons to scrotal thermal stimulation in rats.

Activities of preoptic and anterior hypothalamic (POAH) neurons were recorded in anesthetized rats in response to scrotal thermal stimulation. Thirteen out of 54 neurons responsive to changes of scrotal temperature (Tscr) showed dynamic responses. Four of these neurons increased and 3 neurons decreased their firing rates responding dynamically to warming but not to cooling. Six other neurons were inhibited by scrotal cooling only. These dynamic responses were produced even by temperature changes as slow as 2 degrees C/min and only when the scrotum was warmed or cooled in the Tscr range above 35 degrees C. These dynamic responses are suggested to be a result of signal processing in supraspinal structures including POAH itself.

Temperature sensitivity of the preoptic and anterior hypothalamic neurons in organ culture.

Single unit activities were recorded from the preoptic and anterior hypothalamic (POAH) explants obtained from newborn mice brain to study neural temperature sensitivities in the period of 10-34 days culture. The firing rate of recorded units was less than 13 impulses per sec at 35 degrees C. Fifteen warm sensitive, 2 cold sensitive and 37 thermally insensitive units were obtained. The temperature sensitivities of the cultured POAH neurons were similar to those of in vitro neurons, i.e. the discharge frequencies changed smoothly in proportion to 1-5 degrees C changes in local temperature. The thermal responses of warm sensitive units increased after 18 days and decreased over 30 days in vitro. Two warm sensitive neurons were identified and observed under the optical microscope. The cold sensitive units were unable to be recorded until about 20 days in vitro. It became evident that the neural temperature sensitivities of POAH neurons were maintained in an absence of the extrahypothalamic afferents.