Effects of hypothalamic noradrenaline depletion with 6-hydroxydopamine on the body temperature regulation of the rat

Breathing and temperature control disrupted by morphine and stabilized by clonidine in neonatal rats

BACKGROUND

Sedative-analgesics are often given to newborn infants and are known to affect many components of the autonomic nervous system. While morphine is most frequently used, α-2 adrenergic receptor agonists are being increasingly used in this population. Alpha-2 adrenergic receptors agonists also have anti-shivering properties which may make it a desirable drug to give to infants undergoing therapeutic hypothermia. The aim of this study was to systematically compare two different classes of sedative-analgesics, morphine, a μ-opioid receptor agonist, and clonidine an α-2 adrenergic receptor agonist on breathing, metabolism and core body temperature (CBT) in neonatal rodents.

METHODS

Breathing parameters, oxygen consumption (VO2) and carbon dioxide production (VCO2), were measured prior to, 10 and 90 min after intraperitoneal (IP) administration of morphine (2, 10 or 20 mg/kg), clonidine (40, 200 or 400 μg/kg), or saline in Sprague-Dawley rat pups at postnatal day 7 (p7) while continuously monitoring CBT.

RESULTS

Morphine reduced the respiratory rate, VO2 and VCO2 greater than clonidine at all dosages used (p<0.05, morphine vs. clonidine, for all metabolic and respiratory parameters). Furthermore, morphine induced prolonged respiratory pauses, which were not observed in animals treated with clonidine or saline. Morphine caused hypothermia which was dose dependent, while clonidine stabilized CBT in comparison to saline treated animals (p<0.0001).

CONCLUSION

In the newborn rat, morphine causes profound respiratory depression and hypothermia while clonidine causes minimal respiratory depression and stabilizes CBT. All together, we suggest that clonidine promotes autonomic stability and may be a desirable agent to use in infants being treated with therapeutic hypothermia.

GABAA receptors modulate cannabinoid-evoked hypothermia

Cannabinoids evoke hypothermia by stimulating central CB(1) receptors. GABA induces hypothermia via GABA(A) or GABA(B) receptor activation. CB(1) receptor activation increases GABA release in the hypothalamus, a central locus for thermoregulation, suggesting that cannabinoid and GABA systems may be functionally linked in body temperature regulation. We investigated whether GABA receptors modulate the hypothermic actions of [4,5-dihydro-2-methyl-4(4-morpholinylmethyl)-1-(1-naphthalenyl-carbonyl)-6H-pyrrolo[3,2,1ij]quinolin-6-one] (WIN 55212-2), a selective cannabinoid agonist, in male Sprague-Dawley rats. WIN 55212-2 (2.5 mg/kg im) produced a rapid hypothermia that peaked 45-90 min postinjection. The hypothermia was attenuated by bicuculline (2 mg/kg ip), a GABA(A) antagonist. However, SCH 50911 (1-10 mg/kg ip), a GABA(B) blocker, did not antagonize the hypothermia. Neither bicuculline (2 mg/kg) nor SCH 50911 (10 mg/kg) by itself altered body temperature. We also investigated a possible role for CB(1) receptors in GABA-generated hypothermia. Muscimol (2.5 mg/kg ip), a GABA(A) agonist, or baclofen (5 mg/kg ip), a GABA(B) agonist, evoked a significant hypothermia. Blockade of CB(1) receptors with SR141716A (2.5 mg/kg im) did not antagonize muscimol- or baclofen-induced hypothermia, indicating that GABA-evoked hypothermia does not contain a CB(1)-sensitive component. Our results implicate GABA(A) receptors in the hypothermic actions of cannabinoids and provide further evidence of a functional link between cannabinoid and GABA systems.

Astroglial and vascular interactions of noradrenaline terminals in the rat cerebral cortex

Noradrenaline (NA) has been shown to influence astrocytic and vascular functions related to brain homeostasis, metabolism, local blood flow, and blood-brain barrier permeability. In the current study, we investigate the possible associations that exist between NA-immunoreactive nerve terminals and astrocytes and intraparenchymal blood vessels in the rat frontoparietal cortex, both at the light and electron microscopic levels. As a second step, we sought to determine whether the NA innervation around intracortical microvessels arises from peripheral or central structures by means of injections of N-(2-chloroethyl-N-ethyl-2-bromobenzylamine) (DSP-4), a neurotoxin that specifically destroys NA neurons from the locus ceruleus. At the light microscopic level, 6.8% of all NA-immunoreactive nerve terminals in the frontoparietal cortex were associated with vascular walls, and this perivascular noradrenergic input, together with that of the cerebral cortex, almost completely disappeared after DSP-4 administration. When analyzed at the ultrastructural level in control rats, NA terminals in the neuropil had a mean surface area of 0.53 +/- 0.03 micron2 and were rarely junctional (synaptic incidence close to 7%). Perivascular terminals (located within a 3-micron perimeter from the vessel basal lamina) counted at the electron microscopic level represented 8.8% of the total NA terminals in the cortical tissue. They were smaller (0.29 +/- 0.01 micron2, P < 0.05) than their neuronal counterparts and were located, on average, 1.34 +/- 0.08 microns away from intracortical blood vessels, which consisted mostly of capillaries (65%). None of the perivascular NA terminals engaged in junctional contacts with surrounding neuronal or vascular elements. The primary targets of both neuronal and perivascular NA nerve terminals consisted of dendrites, nerve terminals, astrocytes, and axons, whereas in the immediate vicinity (0.25 micron or less) of the microvessels, astrocytic processes represented the major target. The results of the current study show that penetrating arteries and intracortical microvessels receive a central NA input, albeit parasynaptic in its interaction, originating from the locus ceruleus. Particularly, they point to frequent appositions between both neuronal and perivascular NA terminals and astroglial cells and their processes. Such NA neuronal-glial and neuronal-glial-vascular associations could be of significance in the regulation of local metabolic and vascular functions under normal and pathologic situations.

New hybrids of quipazine and trazodone as selective inhibitors of uptake of 5-hydroxytryptamine

Two new congeners, 4-(chloropropyl)-1-(2-quinolyl)piperazine- and 2-[3-[4-[2-(quinolyl)]-1-piperazinyl]propyl]-1,2,4-triazolo] 4,3-a]pyridin-3(2H)-one, of trazodone were synthesized and found to be potent and selective inhibitors of synaptosomal uptake of 5-hydroxytryptamine [5-HT, serotonin; IC50 = norepinephrine greater than 5 microM, 5-HT = 210-890 nM], with minimal effects in antagonizing (-)-apomorphine-induced climbing behavior and suppression of spontaneous locomotor activity in mice (ED50 greater than 50 mg/kg). The two compounds behaved like atypical antidepressants, since they weakly antagonized reserpine-induced hypothermia. The acute toxicity studies have shown that these compounds were less lethal when compared with imipramine or quipazine. Furthermore, chronic treatments (20 mg/kg, daily for 10 and 21 days) significantly decreased the isoprenaline-induced increase in cyclic AMP in the rat brain cortex, suggesting desensitization of beta-adrenoceptors. These findings point to the effects of these compounds as potential antidepressants dealing with specific serotonergic mechanisms.

Rioprostil, a new prostaglandin E1 analogue, in the once-daily treatment of acute duodenal ulcer: a comparison with ranitidine

The efficacy of Rioprostil (a new prostaglandin E1 analogue) is compared with ranitidine in the once-a-day treatment in the evening for 4 or 6 weeks of active uncomplicated duodenal ulcer disease. A total of 255 patients are entered in this study; of these 243 have been statistically evaluated. One hundred and twenty (120) patients receive rioprostil 600 micrograms/daily, and 123 patients receive ranitidine 300 mg/daily. After 4 weeks 63.3% of the patients on rioprostil are endoscopically healed, as compared with 69.1% on ranitidine. After 6 weeks the cumulative cure rates are 87.3% and 89.9%, respectively, the difference not being statistically significant. Pain relief is similar for both drugs. Diarrhoea with rioprostil occurs in about 2% of the treatment days and is generally self-limiting.

Acute effects of a parkinsonism-inducing neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on mouse body temperature

The parkinsonism-inducing neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) given in single systemic doses (i.p.) to mice produced marked hyperthermia, and subsequent long-lasting hypothermia. Administration of MPTP or its oxidized product, 1-methyl-4-phenylpyridinium ion, MPP+, via i.c.v. resulted in only hypothermia. In contrast, i.p. MPP+ administration resulted in only hyperthermia. The MPTP-induced hyperthermia (i.p.) was blocked by quaternary derivatives of anti-cholinergic agents, atropine and scopolamine, but not by the tertiary-derivative of atropine. Duration of this hyperthermic effect was potentiated by neostigmine. Pretreatment with 1-deprenyl did not prevent hypothermia, but nomifensine partially or clorgyline completely prevented the effect without preventing MPTP-induced hyperthermia. The thermic effects by MPTP, unlike its neurotoxicity for the nigrostriatal DA system, may not require metabolism to MPP+. These results indicate that peripheral cholinergic functions are responsible for the MPTP-induced hyperthermia, whereas its hypothermic effect may be centrally mediated via dysregulation of the various neuron systems.

Effects of 2-substituted-4-phenylquinolines on uptake of serotonin and norepinephrine by isolated brain synaptosomes

In this present communication, the in vitro inhibition of the uptake of [3H]-L-norepinephrine ([3H] NE) and [3H]-Serotonin ([3H] 5-HT) by eleven synthesized 2-substituted-4-phenyl quinolines were studied using rat brain synaptosomal preparations. Compounds with an open side chain were relatively weak inhibitors of the synaptosomal uptake of [3H] NE and [3H] 5HT. Compounds having a distance of three atoms between the terminal basic nitrogen of the side chain and the quinoline ring were better inhibitors of serotonin uptake than those compounds having a four-atom distance. The replacement of the side chain with a piperazine ring produced compounds which were more potent and selective inhibitors of the uptake of either [3H] 5-HT or [3H] NE. Further structure-activity relationships are also discussed.

Alterations in the thermic response to chlorpromazine in rats exposed prenatally to central nervous system depressants

The thermic response to acute administration of chlorpromazine (5 mg/kg, i.p.) was assessed in rats exposed prenatally to haloperidol (0.1 mg/kg), phenobarbital (10 mg/kg), nitrazepam (2 mg/kg), propylene glycol (1 ml/kg) or saline, once daily from days 1-21 or 15-21 of gestation. The response in all animals was tested only once. The administration of chlorpromazine to 8- or 13-week-old male and female rats treated with saline (1-21 d) induced marked hypothermia for a 6-hr period of observation. Male and female rats treated with haloperidol (1-21 d) showed a delayed hyperthermic response to chlorpromazine at 8 weeks of age; the males showed an increase in rectal temperature at 3 hr and the females from 3 to 6 hr. Thirteen-week-old males but not females treated with haloperidol (1-21 d) showed a hyperthermic response to chlorpromazine during the first 2 hr. Eight-week-old male and female rats treated with phenobarbital (1-21 d) showed hypothermia, whereas 13-week-old male rats of another group treated with phenobarbital (1-21 d) showed significant hyperthermia after the administration of the chlorpromazine. The hypothermic response of the rats treated with nitrazepam (1-21 d) to chlorpromazine was similar to that in the vehicle (propylene glycol)-treated controls. The male rats treated with phenobarbital (15-21 d) responded to chlorpromazine with significant hyperthermia from 30 min to 1 hr. There was no alteration in thermic response to chlorpromazine in rats born to mothers treated with one tenth of the dose of phenobarbital, haloperidol or nitrazepam.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in body temperature after administration of adrenergic and serotonergic agents and related drugs including antidepressants: II

This survey continues a second series of compilations of data regarding changes in body temperature induced by drugs and related agents. The information listed includes the species used, the route of administration and dose of drug, the environmental temperature at which experiments were performed, the number of tests, the direction and magnitude of change in body temperature and remarks on the presence of special conditions, such as age or brain lesions. Also indicated is the influence of other drugs, such as antagonists, on the response to the primary agent. Most of the papers were published from 1980 to 1984 but data from many earlier papers are also tabulated.

Effects of subdiaphragmatic vagotomy on thermoregulatory responses of rats to different ambient temperatures

Rats 4 weeks after bilateral transections of the subdiaphragmatic vagus nerve displayed a thermoregulatory deficit. Rectal and skin temperatures and metabolic rate were reduced at ambient temperatures of 22 and 8 degrees C. However, these vagotomized animals maintained their body temperatures within the normal limits displayed by normal animals at an ambient temperature of 30 degrees C.

Catecholamine-blocking drugs injected at sites of amine accumulation reverse catecholamine degeneration associated deficits

It has been hypothesized that catecholamine (CA) accumulation in the axons of degenerating neurons may represent areas of functional neurotransmitter, and may be producing some of the consummatory and locomotory deficits which occur after central CA-depleting lesions. To test this hypothesis further, haloperidol (0.5 microliter of a 7 nM sol.), propranolol (0.5 microliter of a 175 nM sol.) or isotonic saline (0.5 microliter) were injected 1.5 h, 24 h and 48 h after the injection of 6-hydroxydopamine (6-OHDA; 2 microliter of 8 micrograms/microliters) into the lateral hypothalamus (LH) of Sprague-Dawley rats to determine if the hypothermia, motor impairment and consummatory deficits could be reversed. Although haloperidol injection significantly enhanced the hypothermia seen 1.5 h after 6-OHDA injection, open field performance and consummatory responses were significantly improved after haloperidol was injected into the LH where accumulation is known to occur. Three consecutive days of intracerebral haloperidol treatment produced a recovery of body weight regulation lasting for 6 days. Treatment with propranolol enhanced open field performance 1 day after 6-OHDA injection but failed to enhance recovery of consummatory behaviour and body weight control. These results suggest that CA released from areas of accumulation act on adjacent CA receptors to participate in the production of behavioural deficits previously attributed only to the loss of functional neurotransmitter in terminal fields in the forebrain.