Dynamic and morphological responses of draining lymph nodes to single and repeated applications of oxazolone to guinea-pig skin

Auricular lymph nodes in guinea-pigs were studied for 3 weeks under continuous stimulation with oxazolone applied to the ear skin. Quantitation of 3H-Tdr labelled paracortical lymphocytes following pulse labeling, demonstrated a marked, but only transitory rise in the proportion of cells in DNA synthesis. In spite of this, the total number of cells in S-phase continued to rise during the remaining part of the observation time, as a result of a steady increase of the paracortical cell mass. The variation in the proportion of large, pyroninophilic blast cells, revealed a pattern similar to that of the labelling index. A high proportion of blast cells was found only in the initial phase of the reaction, while the chronic response was characterized by a low proportion, no different from the starting level. Paracortical enlargement appeared to be the most reliable morphological criterion on which a chronically stimulated paracortex could be distinguished from an "unstimulated". The initial paracortical response, similar to a primary reaction, was followed by an equally pronounced development of germinal centres and plasma cells. These were also persistent features under continued stimulation. The reported changes are most likely specific responses to oxazolone stimulation.     

Vasopressin V1 receptors contribute to hemodynamic and sympathoinhibitory responses evoked by stimulation of adenosine A2a receptors in NTS

Activation of adenosine A2a receptors in the nucleus of the solitary tract (NTS) decreases mean arterial pressure (MAP), heart rate (HR), and renal sympathetic nerve activity (RSNA), whereas increases in preganglionic adrenal sympathetic nerve activity (pre-ASNA) occur, a pattern similar to that observed during hypotensive hemorrhage. Central vasopressin V1 receptors may contribute to posthemorrhagic hypotension and bradycardia. Both V1 and A2a receptors are densely expressed in the NTS, and both of these receptors are involved in cardiovascular control; thus they may interact. The responses elicited by NTS A2a receptors are mediated mostly via nonglutamatergic mechanisms, possibly via release of vasopressin. Therefore, we investigated whether blockade of NTS V1 receptors alters the autonomic response patterns evoked by stimulation of NTS A2a receptors (CGS-21680, 20 pmol/50 nl) in alpha-chloralose-urethane anesthetized male Sprague-Dawley rats. In addition, we compared the regional sympathetic responses to microinjections of vasopressin (0.1-100 ng/50 nl) into the NTS. Blockade of V1 receptors reversed the normal decreases in MAP into increases (-95.6 +/- 28.3 vs. 51.4 +/- 15.7 integralDelta%), virtually abolished the decreases in HR (-258.3 +/- 54.0 vs. 18.9 +/- 57.8 integralDeltabeats/min) and RSNA (-239.3 +/- 47.4 vs. 15.9 +/- 36.1 integralDelta%), and did not affect the increases in pre-ASNA (279.7 +/- 48.3 vs. 233.1 +/- 54.1 integralDelta%) evoked by A2a receptor stimulation. The responses partially returned toward normal values approximately 90 min after the blockade. Microinjections of vasopressin into the NTS evoked dose-dependent decreases in HR and RSNA and variable MAP and pre-ASNA responses with a tendency toward increases. We conclude that the decreases in MAP, HR, and RSNA in response to NTS A2a receptor stimulation may be mediated via release of vasopressin from neural terminals in the NTS. The differential effects of NTS V1 and A2a receptors on RSNA versus pre-ASNA support the hypothesis that these receptor subtypes are differentially located/expressed on NTS neurons/neural terminals controlling different sympathetic outputs.     

Mechanisms mediating regional sympathoactivatory responses to stimulation of NTS A(1) adenosine receptors

Selective activation of adenosine A(1) and A(2a) receptors in the subpostremal nucleus tractus solitarius (NTS) increases and decreases mean arterial pressure (MAP), respectively, and decreases heart rate (HR). We have previously shown that the decreases in MAP evoked by NTS A(2a) receptor stimulation were accompanied with differential sympathetic responses in renal (RSNA), lumbar (LSNA), and preganglionic adrenal sympathetic nerve activity (pre-ASNA). Therefore, now we investigated whether stimulation of NTS A(1) receptors via unilateral microinjection of N(6)-cyclopentyladenosine (CPA) elicits differential activation of the same sympathetic outputs in alpha-chloralose-urethane-anesthetized male Sprague-Dawley rats. CPA (0.33-330.0 pmol in 50 nl) evoked dose-dependent increases in MAP, variable decreases in HR, and differential increases in all recorded sympathetic outputs: upward arrow pre-ASNA > upward arrow RSNA > or = upward arrow LSNA. Sinoaortic denervation + vagotomy abolished the MAP and LSNA responses, reversed the normal increases in RSNA into decreases, and significantly attenuated increases in pre-ASNA. NTS ionotropic glutamatergic receptor blockade with kynurenate sodium (4.4 nmol/100 nl) reversed the responses in MAP, LSNA, and RSNA and attenuated the responses in pre-ASNA. We conclude that afferent inputs and intact glutamatergic transmission in the NTS are necessary to mediate the pressor and differential sympathoactivatory responses to stimulation of NTS A(1) receptors.     

The neuronal electrical responses of the superior cervical ganglion in the rabbit to nociceptive skin stimulation]

The patterns of tonic activity in the neurons of rabbit superior cervical ganglion at rest and during noxious stimulation of the skin were studied using intracellular recording. According to reflex changes in the activity patterns, all neurons studied were classified into three groups. Cardiac rhythmicity is more pronounced in the neurons of the second type than in those of the first type. The magnitude of the cardiac rhythmicity in both types of neurons was reduced after noxious stimulation of the skin. In the third type of neurons the cardiac rhythmicity was absent. In some neurons slow excitatory and inhibitory postsynaptic potentials appeared resulting from skin stimulation.     

Differential role of nitric oxide in regional sympathetic responses to stimulation of NTS A2a adenosine receptors

Our previous studies showed that preganglionic adrenal (pre-ASNA), renal (RSNA), lumbar, and postganglionic adrenal sympathetic nerve activities (post-ASNA) are inhibited after stimulation of arterial baroreceptors, nucleus of the solitary tract (NTS), and glutamatergic and P2x receptors and are activated after stimulation of adenosine A1 receptors. However, stimulation of adenosine A2a receptors inhibited RSNA and post-ASNA, whereas it activated pre-ASNA. Because the effects evoked by NTS A2a receptors may be mediated via activation of nitric oxide (NO) mechanisms in NTS neurons, we tested the hypothesis that NO synthase (NOS) inhibitors would attenuate regional sympathetic responses to NTS A2a receptor stimulation, whereas NO donors would evoke contrasting responses from pre-ASNA versus RSNA and post-ASNA. Therefore, in chloralose/urethane-anesthetized rats, we compared hemodynamic and regional sympathetic responses to microinjections of selective A2a receptor agonist (CGS-21680, 20 pmol/50 nl) after pretreatment with NOS inhibitors Nomega-nitro-L-arginine methyl ester (10 nmol/100 nl) and 1-[2-(trifluoromethyl)phenyl]imidazole (100 pmol/100 nl) versus pretreatment with vehicle (100 nl). In addition, responses to microinjections into the NTS of different NO donors [40 and 400 pmol/50 nl sodium nitroprusside (SNP); 0.5 and 5 nmol/50 nl 3,3-bis(aminoethyl)-1-hydroxy-2-oxo-1-triazene (DETA NONOate, also known as NOC-18), and 2 nmol/50 nl 3-(2-hydroxy-2-nitroso-1-propylhydrazino)-1-propanamine (PAPA NONOate, also known as NOC-15)], the NO precursor L-arginine (10-50 nmol/50 nl), and sodium glutamate (500 pmol/50 nl) were evaluated. SNP, DETA NONOate, and PAPA NONOate activated pre-ASNA and inhibited RSNA and post-ASNA, whereas l-arginine and glutamate microinjected into the same site of the NTS inhibited all these sympathetic outputs. Decreases in heart rate and depressor or biphasic responses accompanied the neural responses. Pretreatment with NOS inhibitors reversed the normal depressor and sympathoinhibitory responses to stimulation of NTS A2a receptors into pressor and sympathoactivatory responses and attenuated the heart rate decreases; however, it did not change the increases in pre-ASNA. We conclude that NTS NO mechanisms differentially affect regional sympathetic outputs and differentially contribute to the pattern of regional sympathetic responses evoked by stimulation of NTS A2a receptors.     

Anandamide modulates carotid sinus nerve afferent activity via TRPV1 receptors increasing responses to heat

Abnormal respiratory chemosensitivity is implicated in recurrent apnea syndromes, with the peripheral chemoreceptors, the carotid bodies, playing a particularly important role. Previous work suggests that supraphysiological concentrations of the endocannabinoid endovanilloid and TASK channel blocker anandamide (ANA) excite carotid bodies, but the mechanism(s) and physiological significance are unknown. Given that carotid body output is temperature-sensitive, we hypothesized that ANA stimulates carotid body chemosensory afferents via temperature-sensitive vanilloid (TRPV1) receptors. To test this hypothesis, we used the dual-perfused in situ rat preparation to confirm that independent perfusion of carotid arteries with supraphysiological concentrations of ANA strongly excites carotid sinus nerve afferents and that this activity is sufficient to increase phrenic activity. Next, using ex vivo carotid body preparations, we demonstrate that these effects are mediated by TRPV1 receptors, not CB1 receptors or TASK channels: in CB1-null mouse preparations, ANA increased afferent activity across all levels of Po(2), whereas in TRPV1-null mouse preparations, the stimulatory effect of ANA was absent. In rat ex vivo preparations, ANA's stimulatory effects were mimicked by olvanil, a nonpungent TRPV1 agonist, and suppressed by the TRPV1 antagonist AMG-9810. The specific CB1 agonist oleamide had no effect. Physiological levels of ANA had no effect alone but increased sensitivity to mild hyperthermia. AMG-9810 blocked ANA's effect on the temperature response. Immunolabeling and RT-PCR demonstrated that TRPV1 receptors are not expressed in carotid body glomus cells but reside in petrosal sensory afferents. Together, these results suggest that ANA plays a physiological role in augmenting afferent responses to mild hyperthermia by activating TRPV1 receptors on petrosal afferents.     

Cardiovascular and thermoregulatory responses to repeated anticholinesterase administration

1. 1.|Pyridostigmine administration decreased resting heart rate by 11 ± 7 beats/min and resting oesophageal temperature by 0.23 ± 12°C after 50 h (P < 0.05). In addition, red blood cell cholinesterase activity was decreased an average of 43 ± 7% after 50 h of pyridostigmine treatment.

2. 2.|The lower heart rates and core temperatures at rest were continued during high intensity exercise in a 35°C environment. Whole body sweating was 12 ± 18% higher (P = 0.20) during exercise in the heat after 50 h of pyridostigmine treatment.

3. 3.|Repeated anticholinesterase administration had little effect on cardiovascular and thermoregulatory responses during high intensity exercise.

Metabolic effects of repeated short-term exposures to heat in the rat

Repeated daily exposures of rats to a hot ambient temperature (40-41 degrees C) for 20 days induced activation of the oxidative enzymes in the thigh muscle and of lactate dehydrogenase in the myocardium. Heat-stressed rats also showed increased tolerance to cold. These changes, it is suggested, are caused by the increased sympathetic activity bouts associated with the heat stresses. The interscapular brown adipose tissue, however, showed adaptive changes similar to those induced by warm acclimation. The activity of oxidative enzymes was decreased and the fat droplets became large and unilocular.