Multisynaptic neuronal pathways from the submandibular and sublingual glands to the lamina terminalis in the rat: a model for the role of the lamina terminalis in the control of osmo- and thermoregulatory behavior

The median preoptic nucleus: A major regulator of fluid, temperature, sleep, and cardiovascular homeostasis

Located in the midline lamina terminalis of the anterior wall of the third ventricle, the median preoptic nucleus is a thin elongated nucleus stretching around the rostral border of the anterior commissure. Its neuronal elements, composed of various types of excitatory glutamatergic and inhibitory GABAergic neurons, receive afferent neural signals from (1) neighboring subfornical organ and organum vasculosum of the lamina terminalis related to plasma osmolality and hormone concentrations, e.g., angiotensin II; (2) from peripheral sensors such as arterial baroreceptors and cutaneous thermosensors. Different sets of these MnPO glutamatergic and GABAergic neurons relay output signals to hypothalamic, midbrain, and medullary regions that drive homeostatic effector responses. Included in the effector responses are (1) thirst, antidiuretic hormone secretion and renal sodium excretion that subserve osmoregulation and body fluid homeostasis; (2) vasoconstriction or dilatation of skin blood vessels, and shivering and brown adipose tissue thermogenesis for core temperature homeostasis; (3) inhibition of hypothalamic and midbrain nuclei that stimulate wakefulness and arousal, thereby promoting both REM and non-REM sleep; and (4) activation of sympathetic pathways that drive vasoconstriction and heart rate to maintain arterial pressure and the perfusion of vital organs. The small size of MnPO belies its massive homeostatic significance.

Orexin A and B in the rat superior salivatory nucleus

Orexin (OX), which regulates sleep and wakefulness and feeding behaviors has 2 isoforms, orexin-A and -B (OXA and OXB). In this study, the distribution of OXA and OXB was examined in the rat superior salivatory nucleus (SSN) using retrograde tracing and immunohistochemical and methods. OXA- and OXB-immunoreactive (-ir) nerve fibers were seen throughout the SSN. These nerve fibers surrounded SSN neurons retrogradely labeled with Fast blue (FB) from the corda-lingual nerve. FB-positive neurons had pericellular OXA- (47.5%) and OXB-ir (49.0%) nerve fibers. Immunohistochemistry for OX receptors also demonstrated the presence of OX1R and OX2R in FB-positive SSN neurons. The majority of FB-positive SSN neurons contained OX1R- (69.7%) or OX2R-immunoreactivity (57.8%). These neurons had small and medium-sized cell bodies. In addition, half of FB-positive SSN neurons which were immunoreactive for OX1R (47.0%) and OX2R (52.2%) had pericellular OXA- and OXB-ir nerve fibers, respectively. Co-expression of OX1R- and OX2R was common in FB-positive SSN neurons. The present study suggests a possibility that OXs regulate the activity of SSN neurons through OX receptors.

Central nervous system circuits that control body temperature

Maintenance of mammalian core body temperature within a narrow range is a fundamental homeostatic process to optimize cellular and tissue function, and to improve survival in adverse thermal environments. Body temperature is maintained during a broad range of environmental and physiological challenges by central nervous system circuits that process thermal afferent inputs from the skin and the body core to control the activity of thermoeffectors. These include thermoregulatory behaviors, cutaneous vasomotion (vasoconstriction and, in humans, active vasodilation), thermogenesis (shivering and brown adipose tissue), evaporative heat loss (salivary spreading in rodents, and human sweating). This review provides an overview of the central nervous system circuits for thermoregulatory reflex regulation of thermoeffectors.

Efferent thermoregulatory pathways regulating cutaneous blood flow and sweating

Cutaneous vasoconstrictor nerves regulate heat retention, and are activated by falls in skin or core temperature. The efferent pathways controlling this process originate within the preoptic area. A descending GABAergic pathway, activated by warm skin or core, indirectly inhibits sympathetic premotor neurons in the medullary raphé. Those premotor neurons drive cutaneous vasoconstriction via excitatory glutamatergic and serotonergic connections to spinal preganglionic neurons. Cold skin and/or cold core temperatures activate a direct preoptic-to-raphé excitatory pathway. The balance of inhibitory and excitatory influences reaching the medullary raphé determines cutaneous blood flow. During fever, prostaglandin E₂ inhibits preoptic GABAergic neurons, resulting in disinhibition of the excitatory preoptic-to-raphé pathway, and hence, cutaneous vasoconstriction. A weaker, parallel source of descending excitatory drive reaches cutaneous preganglionic neurons from the rostral ventrolateral medulla. Sweating follows local heating of the preoptic area in cats and monkeys, and heated humans show sweating-related activation of this same region in functional magnetic resonance imaging (fMRI) studies. A descending pathway that drives sweating has been traced in cats from the hypothalamus to putative premotor neurons in the parafacial region at the pontomedullary junction. The homologous parafacial region in humans also shows sweating-related activation in fMRI studies. The central pathways that drive active vasodilatation in human nonacral skin remain unknown.

The Hypothalamic Preoptic Area and Body Weight Control

The preoptic area (POA) of the hypothalamus is involved in many physiological and behavioral processes thanks to its interconnections to many brain areas and ability to respond to diverse humoral factors. One main function of the POA is to manage body temperature homeostasis, e.g. in response to ambient temperature change, which is achieved in part by controlling brown adipose tissue thermogenesis. The POA is also importantly involved in modulating food intake in response to temperature change, thus making it relevant for body weight homeostasis and obesity research. POA function in body weight control is highly unexplored, and a better understanding of POA circuits and their integration into classic hypothalamic circuits that regulate energy homeostasis is expected to provide new opportunities for the scientific basis and treatment of obesity and comorbidities.

Current understanding on the neurophysiology of behavioral thermoregulation

Temperature influence on the physiology and biochemistry of living organisms has long been recognized, which propels research in the field of thermoregulation. With the cloning and characterization of the transient receptor potential (TRP) ion channels as the principal temperature sensors of the mammalian somatosensory neurons, the understanding, at a molecular level, of thermosensory and thermoregulatory mechanisms became promising. Because thermal environment can be extremely hostile (temperature range on earth's surface is from ∼ −69°C to 58°C), living organisms developed an array of thermoregulatory strategies to guarantee survival, which include both autonomic mechanisms, which aim at increasing or decreasing heat exchange between body, and ambient and behavioral strategies. The knowledge regarding neural mechanisms involved in autonomic thermoregulatory strategies has progressed immensely compared to the knowledge on behavioral thermoregulation. This review aims at collecting the up-to-date knowledge on the neural basis for behavioral thermoregulation in mammals in order to point out perspectives and deployment of this research field.

The median preoptic nucleus: front and centre for the regulation of body fluid, sodium, temperature, sleep and cardiovascular homeostasis

Located in the midline anterior wall of the third cerebral ventricle (i.e. the lamina terminalis), the median preoptic nucleus (MnPO) receives a unique set of afferent neural inputs from fore-, mid- and hindbrain. These afferent connections enable it to receive neural signals related to several important aspects of homeostasis. Included in these afferent projections are (i) neural inputs from two adjacent circumventricular organs, the subfornical organ and organum vasculosum laminae terminalis, that respond to hypertonicity, circulating angiotensin II or other humoural factors, (ii) signals from cutaneous warm and cold receptors that are relayed to MnPO, respectively, via different subnuclei in the lateral parabrachial nucleus and (iii) input from the medulla associated with baroreceptor and vagal afferents. These afferent signals reach appropriate neurones within the MnPO that enable relevant neural outputs, both excitatory and inhibitory, to be activated or inhibited. The efferent neural pathways that proceed from the MnPO terminate on (i) neuroendocrine cells in the hypothalamic supraoptic and paraventricular nuclei to regulate vasopressin release, while polysynaptic pathways from MnPO to cortical sites may drive thirst and water intake, (ii) thermoregulatory pathways to the dorsomedial hypothalamic nucleus and medullary raphé to regulate shivering, brown adipose tissue and skin vasoconstriction, (iii) parvocellular neurones in the hypothalamic paraventricular nucleus that drive autonomic pathways influencing cardiovascular function. As well, (iv) other efferent pathways from the MnPO to sites in the ventrolateral pre-optic nucleus, perifornical region of the lateral hypothalamic area and midbrain influence sleep mechanisms.

AT1 receptors in the paraventricular nucleus mediate the hyperthermia-induced reflex reduction of renal blood flow in rats

Increasing body core temperature reflexly decreases renal blood flow (RBF), and the hypothalamic paraventricular nucleus (PVN) plays an essential role in this response. ANG II in the brain is involved in the cardiovascular responses to hyperthermia, and ANG II receptors are highly concentrated in the PVN. The present study investigated whether ANG II in the PVN contributes to the cardiovascular responses elicited by hyperthermia. Rats anesthetized with urethane (1-1.4 g/kg iv) were microinjected bilaterally into the PVN (100 nl/side) with saline (n = 5) or losartan (1 nmol/100 nl) (n = 7), an AT1 receptor antagonist. Body core temperature was then elevated from 37°C to 41°C and blood pressure (BP), heart rate (HR), RBF, and renal vascular conductance (RVC) were monitored. In separate groups losartan (n = 4) or saline (n = 4) was microinjected into the PVN, but body core temperature was not elevated. Increasing body core temperature in control rats elicited significant decreases in RBF (-48 ± 5% from a resting level of 14.3 ± 1.4 ml/min) and MVC (-40 ± 4% from a resting level of 0.128 ± 0.013 ml/min·mmHg), and these effects were entirely prevented by pretreatment with losartan. In rats in which body core temperature was not altered, losartan microinjected into the PVN had no significant effects on these variables. The results suggest that endogenous ANG II acts on AT1 receptors in the PVN to mediate the reduction in RBF induced by hyperthermia.

Role of the hypothalamic PVN in the regulation of renal sympathetic nerve activity and blood flow during hyperthermia and in heart failure

The hypothalamic paraventricular nucleus is a key integrative area in the brain involved in influencing sympathetic nerve activity and in the release of hormones or releasing factors that contribute to regulating body fluid homeostasis and endocrine function. The endocrine and hormonal regulatory function of the paraventricular nucleus is well studied, but the regulation of sympathetic nerve activity and blood flow by this region is less clear. Here we review the critical role of the paraventricular nucleus in regulating renal blood blow during hyperthermia and the evidence pointing to an important pathophysiological role of the paraventricular nucleus in the elevated renal sympathetic nerve activity that is a characteristic of heart failure.

Effects of encouraged water drinking on thermoregulatory responses after 20 days of head-down bed rest in humans

We tested the hypothesis that encouraged water drinking according to urine output for 20 days could ameliorate impaired thermoregulatory function under microgravity conditions. Twelve healthy men, aged 24 +/- 1.5 years (mean +/- SE), underwent -6 degrees head-down bed rest (HDBR) for 20 days. During bed rest, subjects were encouraged to drink the same amount of water as the 24-h urine output volume of the previous day. A heat exposure test consisting of water immersion up to the knees at 42 degrees C for 45 min after a 10 min rest (baseline) in the sitting position was performed 2 days before the 20-day HDBR (PRE), and 2 days after the 20-day HDBR (POST). Core temperature (tympanic), skin temperature, skin blood flow and sweat rate were recorded continuously. We found that the -6 degrees HDBR did not increase the threshold temperature for onset of sweating under the encouraged water drinking regime. We conclude that encouraged water drinking could prevent impaired thermoregulatory responses after HDBR.

Role of the hypothalamic PVN in the reflex reduction in mesenteric blood flow elicited by hyperthermia

The hypothalamic paraventricular nucleus (PVN) is an important integrative center in the brain. In the present study, we investigated whether the PVN is a key region in the mesenteric vasoconstriction that normally accompanies an increase in core body temperature. Anesthetized rats were monitored for blood pressure, heart rate, mesenteric blood flow, and vascular conductance. In control rats, elevation of core body temperature to 41 degrees C had no significant effect on blood pressure, increased heart rate, and reduced mesenteric blood flow by 21%. In a separate group of rats, muscimol was microinjected bilaterally (1 nmol/side) into the PVN. Compared with the control group, there was no significant difference in the blood pressure and heart rate responses elicited by the increase in core body temperature. In contrast to control animals, however, mesenteric blood flow did not fall in the muscimol-treated rats in response to the elevation in core body temperature. In a separate group, in which muscimol was microinjected into regions outside the PVN, elevating core body temperature elicited the normal reduction in mesenteric blood flow. The results suggest that the PVN may play a key role in the reflex decrease in mesenteric blood flow elicited by hyperthermia.

Hypothalamic paraventricular nucleus is critical for renal vasoconstriction elicited by elevations in body temperature

Redistribution of blood from the viscera to the peripheral vasculature is the major cardiovascular response designed to restore thermoregulatory homeostasis after an elevation in body core temperature. In this study, we investigated the role of the hypothalamic paraventricular nucleus (PVN) in the reflex decrease in renal blood flow that is induced by hyperthermia, as this brain region is known to play a key role in renal function and may contribute to the central pathways underlying thermoregulatory responses. In anesthetized rats, blood pressure, heart rate, renal blood flow, and tail skin temperature were recorded in response to elevating body core temperature. In the control group, saline was microinjected bilaterally into the PVN; in the second group, muscimol (1 nmol in 100 nl per side) was microinjected to inhibit neuronal activity in the PVN; and in a third group, muscimol was microinjected outside the PVN. Compared with control, microinjection of muscimol into the PVN did not significantly affect the blood pressure or heart rate responses. However, the normal reflex reduction in renal blood flow observed in response to hyperthermia in the control group ( approximately 70% from a resting level of 11.5 ml/min) was abolished by the microinjection of muscimol into the PVN (maximum reduction of 8% from a resting of 9.1 ml/min). This effect was specific to the PVN since microinjection of muscimol outside the PVN did not prevent the normal renal blood flow response. The data suggest that the PVN plays an essential role in the reflex decrease in renal blood flow elicited by hyperthermia.

Exposure to a hot environment can activate rostral ventrolateral medulla-projecting neurones in the hypothalamic paraventricular nucleus in conscious rats

A major integrative site within the brain for autonomic function is the hypothalamic paraventricular nucleus (PVN). Several studies have suggested that the PVN may be involved in the responses regulating body temperature. Hyperthermia elicits redirection of blood flow from the viscera to the periphery and involves changes in sympathetic nerve activity mediated by the central nervous system. The hypothalamic PVN includes neurones that project to the rostral ventrolateral medulla (RVLM), an important autonomic region involved in the tonic regulation of sympathetic nerve activity. This pathway could contribute to the cardiovascular changes induced by hyperthermia. The PVN has a high concentration of nitrergic neurones and it is known that nitric oxide within the brain mediates heat dissipation. Thus the aims of this study were to determine whether RVLM-projecting neurones in the PVN are activated by heat and whether those neurones are also nitrergic. The results show that, compared with control conditions, exposure of conscious rats to a hot environment of 39 degrees C significantly increased the number of neurones containing a Fos-positive nucleus (a marker of activation) and significantly increased the number of activated RVLM-projecting neurones in the PVN. Also, although heating significantly increased the number of activated nitrergic PVN neurones, triple-labelled neurones (i.e. activated, nitrergic and RVLM projecting) in the PVN were rarely observed. The results suggest that RVLM-projecting neurones in the PVN may play a role in responses to heat exposure but these are not nitrergic.

Effects of acute heat exposure on prosencephalic c-Fos expression in normohydrated, water-deprived and salt-loaded rats

In the present study, the distribution pattern of c-Fos protein immunoreactivity (Fos-IR) in prosencephalic areas of the brain involved in thermoregulatory and osmoregulatory responses was investigated, in rats exposed or not exposed to a hyperthermic environment, under three different conditions: normohydration, dehydration induced by water deprivation and hyperosmolarity induced by an acute intragastric salt load. Normohydrated, water-deprived or salt-loaded male Wistar rats (270+/-30 g) were submitted or not to acute heat exposure (33 degrees C for 45 min). A separate group of animals was submitted to the same experimental protocol and had blood samples collected before and after the heating period to measure serum osmolarity and sodium. The brains were processed for c-Fos immunohistochemistry using the avidin-biotin peroxidase method. After analyzing Fos-IR in the brains of animals in the present study, three different types of prosencephalic areas were identified: (1) those that respond to hydrational and to heat conditions, with an interaction between these two factors (PaMP and SON); (2) those that respond to hydrational and to heat conditions, but with no interaction between these factors (MnPO, LSV and OVLT); and (3) those that respond only to hydrational status (SFO and PaLM).

Activation of spinally projecting and nitrergic neurons in the PVN following heat exposure

The present study investigated the effect of acute thermal stimulation in conscious rats on the production of Fos, a marker of increased neuronal activity, in spinally projecting and nitrergic neurons in the hypothalamic paraventricular nucleus (PVN). The PVN contains a high concentration of nitrergic neurons, as well as neurons that project to the intermediolateral cell column (IML) of the spinal cord that can directly influence sympathetic nerve activity (SNA). During thermal stimulation, the PVN is activated, but it is unknown whether spinally projecting PVN neurons and the nitrergic neurons are involved. Compared with controls, rats exposed to an environmental temperature of 39 degrees C for 1 h had a 10-fold increase in the number of cells producing Fos in the PVN (133 +/- 23 vs. 1,336 +/- 43, respectively, P < 0.0001). Of the spinally projecting neurons in the PVN of heated rats (98 +/- 10), over 20% expressed Fos. Additionally, of the nitrergic neurons (NADPH-diaphorase positive) located in the parvocellular PVN (723 +/- 17), 40% also expressed Fos (P < 0.0001 compared with controls). Finally, there was a significant increase in the number of spinally projecting neurons in the PVN that were nitrergic and expressed Fos after heat exposure (12%) compared with controls (0.1%) (P < 0.0001). These results suggest that spinally projecting and nitrergic neurons in the PVN may contribute to the central pathways activated by thermal stimulation.

The median preoptic nucleus is involved in the facilitation of heat-escape/cold-seeking behavior during systemic salt loading in rats

Systemic salt loading has been reported to facilitate operant heat-escape/cold-seeking behavior. In the present study, we hypothesized that the median preoptic nucleus (MnPO) would be involved in this mechanism. Rats were divided into two groups (n = 6 each): one group had the MnPO lesion with ibotenic acid (4.0 mug) and the other was the vehicle control. After subcutaneous injection (10 ml/kg) of either isotonic- (154 mM) or hypertonic-saline (2,500 mM), each rat was placed in a behavior box, where the ambient temperature was changed to 26 degrees C, 35 degrees C, and 40 degrees C every 1 h. The position of a rat in the box and the body core temperature (T(core)) were monitored. A rat could trigger 0 degrees C air for 45 s in the 35 degrees C and 40 degrees C heat when moved in a specific area in the box (operant behavior). In the control group, counts of the operant behavior were greater (P < 0.05) in the hypertonic- than in the isotonic-saline injection (17 +/- 2 and 10 +/- 2 at 35 degrees C, 24 +/- 2 and 18 +/- 1 at 40 degrees C). T(core) remained unchanged throughout the exposure, although the level was lower (P < 0.05) in the hypertonic- than in the isotonic-saline trial (36.6 +/- 0.2 degrees C and 37.4 +/- 0.1 degrees C at 26 degrees C and 36.9 +/- 0.2 degrees C and 37.4 +/- 0.1 degrees C at 40 degrees C, respectively). However, in the MnPO-lesion group, counts of the behavior were similar between the hypertonic- and isotonic-saline injection trials (10 +/- 2 and 8 +/- 1 at 35 degrees C, and 17 +/- 1 and 16 +/- 1 at 40 degrees C, respectively). T(core) increased (P < 0.05) in the heat in both trials (36.8 +/- 0.1 degrees C and 37.4 +/- 0.1 degrees C at 26 degrees C and 37.4 +/- 0.2 degrees C and 37.8 +/- 0.2 degrees C at 40 degrees C in the hypertonic- and isotonic-saline injection trials, respectively). These results may suggest that, at least in part, the MnPO is involved in the facilitation of heat-escape/cold-seeking behavior during osmotic stimulation.

Thermoregulatory role of periventricular tissue surrounding the anteroventral third ventricle (AV3V) during acute heat stress in the rat

1. Thermoregulatory effector mechanisms are strongly influenced by hydration status. Dehydration delays the onset of evaporative heat loss and the redistribution of cardiac output in response to elevations in core temperature, yet very little is known about how and where thermal and non-thermal information is integrated. 2. The anteroventral third ventricular (AV3V) region encompasses several distinct neural structures, including the organum vasculosum of the lamina terminalis, the median preoptic nucleus, the preoptic periventricular nucleus and the medial aspects of the medial preoptic nucleus. In addition to its well-documented role in body fluid and cardiovascular homeostasis, recent anatomical and in vitro evidence has indicated the AV3V region may also be pivotal in the integration of thermal and osmotic information. 3. Electrolytic lesions of the AV3V region produce a markedly reduced thermal tolerance in rats. Elevations in mean arterial pressure, heart rate and mesenteric resistance were all attenuated in the AV3V-lesioned animals in response to a heat stress; however, hindquarter resistance was unaffected. Heat-induced salivation was also attenuated, severely reducing the ability of rats to lose heat via evaporation. 4. The AV3V region clearly has a functional role in thermoregulation, as well as cardiovascular and body fluid homeostasis. These data add further support to the hypothesis that thermal and non-thermal information may be integrated within this region.

Lesions of the anteroventral third ventricle region (AV3V) disrupt cardiovascular responses to an elevation in core temperature

Blood flow is redistributed from the viscera to the periphery during periods of heat stress to maximize heat loss. The heat-induced redistribution of blood flow is strongly influenced by nonthermal inputs such as hydration status. At present, little is known about where thermal and nonthermal information is integrated to generate an appropriate effector response. Recently, the periventricular tissue that surrounds the anteroventral third ventricle (AV3V) has been implicated in the integration of thermal and osmotic information. The purpose of the present study was to determine the effects of electrolytic lesions of the AV3V on the cardiovascular response to a passive heat stress in unanesthetized, free-moving male Sprague-Dawley rats. Core temperature was elevated at a constant rate of approximately 0.03 degrees C/min in sham- and AV3V-lesion rats using an infrared heat lamp. Changes in mesenteric and hindquarter vascular resistance were determined using Doppler flow probes, and heat-induced salivation was estimated using the spit-print technique. The rise in mean arterial pressure (MAP), heart rate (HR), and mesenteric resistance in response to elevations in core temperature were all attenuated in AV3V-lesion rats; however, hindquarter resistance was unaffected. Heat-induced salivation was also diminished. In addition, AV3V-lesion rats were more affected by the novelty of the experimental environment, resulting in a higher basal core temperature, HR, and MAP. These results indicate that AV3V lesions disrupt the cardiovascular and salivatory response to a passive heat stress in rats and produce an exaggerated stress-induced fever triggered by a novel environment.

Central muscarinic receptors signal pilocarpine-induced salivation

Although cholinergic agonists such as pilocarpine injected peripherally can act directly on salivary glands to induce salivation, it is possible that their action in the brain may contribute to salivation. To investigate if the action in the brain is important to salivation, we injected pilocarpine intraperitoneally after blockade of central cholinergic receptors with atropine methyl bromide (atropine-mb). In male Holtzman rats with stainless steel cannulas implanted into the lateral ventricle and anesthetized with ketamine, atropine-mb (8 and 16 nmol) intracerebroventricularly reduced the salivation induced by pilocarpine (4 micro mol/kg) intraperitoneally (133 + 42 and 108 + 22 mg/7 min, respectively, vs. saline, 463 + 26 mg/7 min), but did not modify peripheral cardiovascular responses to intravenous acetylcholine. Similar doses of atropine-mb intraperitoneally also reduced pilocarpine-induced salivation. Therefore, systemically injected pilocarpine also enters the brain and acts on central muscarinic receptors, activating autonomic efferent fibers to induce salivation.

Dual viral transneuronal tracing of central autonomic circuits involved in the innervation of the two kidneys in rat

The neural control of renal function is exerted by the central nervous system via sympathetic innervation of the kidneys. To determine the extent to which the control of the two kidneys is provided by the same brain neurons, the central circuitry involved in the innervation of both kidneys was characterized in individual rats by dual viral transneuronal tracing using isogenic recombinant strains (PRV-152 and BaBlu) of pseudorabies virus. Prior to dual tracing, the neuroinvasive properties of PRV-152 and BaBlu were characterized by conducting parametric studies, using the two kidneys as an anatomical model, and comparing the pattern of infection with that obtained following injection of the parental strain, PRV-Bartha, into the left kidney. Once the optimal concentrations of virus required to obtain equivalent infection were established, PRV-152 and BaBlu were injected into the left and right kidney, respectively, in the same rats. Immunocytochemical localization of viral reporter proteins at different postinoculation times allowed us to determine the sequence of infection in the brain, as well as to quantify dual- and single-labeled neurons in each infected area. Neurons that influence autonomic outflow to one or both kidneys coexist in all brain areas involved in the control of the sympathetic outflow to the kidneys at every hierarchical level of the circuit. The proportions of dual-infected neurons with respect to the number of total infected neurons varied across regions, but they were maintained at different survival times. The pattern of infection suggests that the activity of each kidney is controlled independently by organ-specific neurons, whereas the functional coordination of the two kidneys results from neurons that collaterize to modulate the sympathetic outflow to both organs. The advantages of using an anatomical symmetrical system, such as the two kidneys, as an experimental approach to characterize PRV recombinants in general are also discussed.

Excitatory and inhibitory postsynaptic currents of the superior salivatory nucleus innervating the salivary glands and tongue in the rat

The excitatory and inhibitory synaptic inputs to parasympathetic preganglionic neurons in the superior salivatory (SS) nucleus were investigated in brain slices of neonatal (4-8 days old) rat using the whole-cell patch-clamp technique. The SS neurons innervating the submandibular and sublingual salivary glands and innervating the lingual artery in the anterior region of the tongue were identified by retrograde transport of a fluorescent tracer. Whole-cell currents were evoked by electrical stimulation of tissue surrounding the cell. These evoked postsynaptic currents were completely abolished by antagonists for N-methyl-D-aspartate (NMDA) glutamate, non-NMDA glutamate, gamma-aminobutyric acid type A (GABAA), and glycine receptors, suggesting that SS neurons receive glutamatergic excitatory, and GABAergic and glycinergic inhibitory synaptic inputs. In SS neurons for the salivary glands, the ratio of the NMDA component to the total excitatory postsynaptic current (EPSC) was larger than that of the non-NMDA component. This profile was reversed in the SS neurons for the tongue. In SS neurons for the salivary glands, the ratio of the GABAA component to the total IPSC was larger than the ratio of the glycine component to total inhibitory postsynaptic current (IPSC). The decay time constants of the GABAA component were slower than those for glycine. These characteristics of the excitatory and inhibitory inputs may be involved in determining the firing properties of the SS neurons innervating the salivary glands and the tongue.

Lesions of periventricular tissue surrounding the anteroventral third ventricle (AV3V) attenuate salivation and thermal tolerance in response to a heat stress

The purpose of this study was to determine if ablation of the periventricular tissue that surrounds the anteroventral third ventricle (AV3V) would reduce an animal's ability to withstand a thermal challenge. The results show that AV3V-lesion rats are less capable of withstanding a 37 degrees C heat stress and that this is, at least in part, due to a reduced salivation response.