Rabbit Hypothalamus Research Articles

L-DOPA for the prevention and acceleration of the reversal of neurogenic dystrophic damage to internal organs

This review presents experimental and clinical studies of the effects of the levorotatory isomer of dihydroxyphenylalanine (l-DOPA) on the development and reversal of neurogenic dystrophic changes (neurogenic dystrophy) in the heart, stomach, liver, and pancreas. These changes were induced by stimulation of the reflexogenic zones such as the aortic arch and pyloroduodenal area in rats and rabbits, by tonsillar stimulation in rabbits, by 3-hour electrical stimulation and immobilization in rats, and by central electrical stimulation of the posterior hypothalamus in rabbits. Protective effects of l-DOPA were identified at doses of 30, 50, and 300 mg/kg in terms of the development of biochemical and morphological manifestations of neurogenic dystrophy in the studied organs, including a significant decrease in norepinephrine and creatine phosphate levels and an increase in lactic acid level. The use of l-DOPA during the repair phase accelerated the recovery of adrenergic mediation, energy metabolism, and the resolution of dystrophic morphological manifestations, in particular, hemorrhagic erosions of the gastric mucosa. In clinical settings, preoperative medication of patients with l-DOPA (5 mg/kg) for 3 days before mitral commissurotomy prevented the development of postoperative heart failure. In patients with peptic ulcer disease, the administration of l-DOPA during the early remission phase accelerated the healing of ulcers in the stomach and duodenal wall.

HISTOLOGICAL, HISTOCHEMICAL AND IMMUNOHISTOCHEMICAL STUDIES ON THE PARAVENTRICULAR AND SUPRAOPTIC NUCLEI OF THE HYPOTHALAMUS IN THE ADULT NEW ZEALAND RABBITS

The present investigation aims to give a detailed histomorphological feature of the anterior group of hypothalamus of adult New Zealand rabbits in both sexes. Specimens were prepared to be examined microscopically by using light and transmission electron microscope. The obtained results revealed that, the anterior group of the hypothalamus composed of paraventricular (PVN) and supraoptic nuclei (SON). The paraventricular nucleus was located on either sides of the 3rd ventricle. It consisted of different-shaped neurons which appeared in the form of clusters and irregular groups intermingled with nerve fibers associated with neuroglia cells and permeated by blood capillaries. Ultrastructurally, the neurons appeared polyhedral in shape contained large eccentric euchromatic nucleus and electron lucent cytoplasm contained many mitochondria, rER, Golgi apparatus, numerous ribosomes and some secretory granules. On the other hand, the supraoptic nucleus was located dorsolateral to the optic chiasma and consisted of two portions; thin medial and thick lateral one. The neurons of the thin medial part appeared pyramidal in shape with vesicular oval eccentric nuclei and lightly stained cytoplasm, while that of the thick lateral one showed irregular groups or rows of oval and pyriform shaped cells contained vesicular rounded eccentric nuclei. Ultrastructurally, the neurons of the thick lateral part of SON appeared pyriform in shape with spherical eccentric euchromatic nucleus in electron lucent cytoplasm showed intensive network of rER, many mitochondria, Golgi apparatus, numerous free ribosomes and few secretory granules. The cytoplasmic granules of the PVN and SON neurons gave positive reaction with all nonspecific and specific stains used. Also, they gave positive immunoreactions when subjected to Anti-CGA and Anti-NSE antibodies. There were no microscopic structural differences correlated to neither sex nor age of studied animals.

Expression pattern of Toll-like receptors (TLRs) in different organs and effects of lipopolysaccharide on the expression of TLR 2 and 4 in reproductive organs of female rabbit

Toll-like receptors (TLRs) are vital for innate immunity, and they were expressed in various immune cells, tissues and organs. Moreover, TLRs specific expression pattern in different cells, tissue and organs have been confirmed to have correlation with the ability to resistance to pathogenic challenges. The present study aimed to determine the expression profiles and levels of TLR2, 3, 4, 5, 6, 8 and 10 in the lung, trachea, intestine, stomach, liver, spleen, uterine horn and body, cervix, ovary, oviduct and hypothalamus of female rabbits, and whether the expression level of TLR2 and 4 in the ovary, oviduct, uterine horn and body, and cervix were affected by lipopolyasaccharide (LPS). The tissues of the lung, trachea, intestine, stomach, liver, spleen, uterine horn and body, cervix, ovary, oviduct and hypothalamus were collected from four rabbits which didn’t be treated as 0h. 16 rabbits in LPS group were injected with LPS (according to 0.5mg/kg body weight) and 16 rabbits in control group were injected with saline (LPS carrier), hereafter the tissues of the uterine horn and body, cervix, ovary and oviduct from 32 rabbits were collected after 1.5, 3, 6, and 12h (n=4 each group) postinjection. The expression profiles of TLRs were analyzed by reverse transcriptase polymerase chain reaction (RT-PCR), and expression level of TLRs were examined using quantitative real-time PCR (qRT-PCR). The results shown: TLR2, 3, 4, 5, 6, 8 and 10 were expressed in lung, trachea, intestine, stomach, liver, spleen, uterine horn and body, cervix, ovary, oviduct and hypothalamus of female rabbits, but their expression level had great difference in the same organs, and each TLR has different expression level in the different organs. After LPS-stimulation, the expression of TLR2 in the uterine body and horn was significantly higher than that in control group by 3h and 12h of postinjection (P<0.05) respectively. The expression of TLR4 in ovary and uterine body was significantly higher than that in control group by 3 and 12h of postinjection (P<0.05), and the expression of TLR4 in uterine body was greater than that in control by 3h postinjection (P<0.05). The results suggested LPS upregulated the expression of TLR2 and 4 in uterine body and horn, and the expression of TLR4 in ovary.

Obesity related hypertension: an altered downstream regulation of leptin signaling (682.5)

Background: Short term (3weeks) high fat diet (HFD) consumption leads to an increase in blood pressure (BP) and renal sympathetic nerve activity (RSNA) in rabbits. We suggest there is an altered down‐stream sensitivity of leptin in the hypothalamus which involves altered responses to α‐melanocyte stimulating hormone (α‐MSH) and neuropeptide Y (NPY) when rabbits are fed a HFD.Aim: To investigate the role of α‐MSH and NPY in the hypothalamus in HFD‐fed rabbits.Methods: New Zealand White Rabbits were fed with a normal or a 13.3% HFD for 3 weeks. A bilateral guide cannula into the dorsomedial (DMH) or ventromedial hypothalamus (VMH) and an RSNA recording electrode was implanted. After 3 weeks on the diet, α‐MSH (0.1, 0.3nmol), NPY (0.1, 0.5nmol) or Ringer’s were injected directly into the DMH or VMH.Results: Rabbits exhibited higher BP, HR and RSNA when fed a HFD compared to controls (n=6‐8). α‐MSH injection into the DMH increased BP (5.7%, P&lt;0.05 and 8.3%, P&lt;0.01 with 0.1nmol and 0.3nmol respectively) and RSNA (40%, P&lt;0.05 with 0.3nmol) in HFD rabbits. When α‐MSH was injected into the VMH, BP was unchanged but RSNA was increased (28%, P=0.01 and 38%, P&lt;0.01) in HFD rabbits. NPY injection had no effect in both control and HFD rabbits.Conclusion: Elevated blood pressure and sympatho‐excitation in HFD rabbits are due to increased sensitivity of the leptin signalling pathway which involves a dorsal and ventral hypothalamic projection of α‐MSH activated second order neurons.

Metabolic syndrome induces inflammation and impairs gonadotropin-releasing hormone neurons in the preoptic area of the hypothalamus in rabbits

Rabbits with high fat diet (HFD)-induced metabolic syndrome (MetS) developed hypogonadotropic hypogonadism (HH) and showed a reduced gonadotropin-releasing hormone (GnRH) immunopositivity in the hypothalamus. This study investigated the relationship between MetS and hypothalamic alterations in HFD-rabbits. Gonadotropin levels decreased as a function of MetS severity, hypothalamic gene expression of glucose transporter 4 (GLUT4) and interleukin-6 (IL-6). HFD determined a low-grade inflammation in the hypothalamus, significantly inducing microglial activation, expression and immunopositivity of IL-6, as well as GLUT4 and reduced immunopositivity for KISS1 receptor, whose mRNA expression was negatively correlated to glucose intolerance. Correcting glucose metabolism with obetcholic acid improved hypothalamic alterations, reducing GLUT4 and IL-6 immunopositivity and significantly increasing GnRH mRNA, without, however, preventing HFD-related HH. No significant effects at the hypothalamic level were observed after systemic anti-inflammatory treatment (infliximab). Our results suggest that HFD-induced metabolic derangements negatively affect GnRH neuron function through an inflammatory injury at the hypothalamic level.

Effects of Electric Stimulation of the Hunger Center in the Lateral Hypothalamus on Slow Electric Activity and Spike Activity of Fundal and Antral Stomach Muscles in Rabbits under Conditions of Hunger and Satiation

In chronic experiments on rabbits, the effect of electric stimulation of the hunger center in the lateral hypothalamus on myoelectric activity of the fundal and antral parts of the stomach was studied under conditions of hunger and satiation in the absence of food. Stimulation of the lateral hypothalamus in rabbits subjected to 24-h food deprivation and in previously fed rabbits produced incessant seeking behavior, which was followed by reorganization of the structure of temporal organization of slow wave electric activity of muscles of the stomach body and antrum specific for hungry and satiated animals. Increased hunger motivation during electric stimulation of the lateral hypothalamus manifested in the structure of temporal organization of slow wave electric activity of the stomach body and antrum muscles in rabbits subjected to 24-h food deprivation in the replacement of bimodal distribution of slow wave periods to a trimodal type typical of 2-day deprivation, while transition from satiation to hunger caused by electric stimulation of the lateral hypothalamus was associated with a shift from monomodal distributions of slow wave periods to a bimodal type typical of 24-h deprivation. Reorganization of the structure of temporal organization of slow wave electric activity of the stomach body and antrum muscles during electric stimulation of the lateral hypothalamus was determined by descending inhibitory influences of food motivational excitation on activity of the myogenic pacemaker of the lesser curvature of the stomach.

Reflection of induced and amplified food motivation in impulse activity of the masticatory muscles during electrostimulation of the “hunger center” in the lateral hypothalamus in rabbits

We studied reflection of artificially induced and amplified food motivation in impulse activity of the masticatory muscles during electrostimulation of "hunger center" of the lateral hypothalamus in the absence and presence of food. The threshold stimulation of the lateral hypothalamus in hungry and satiated animals in the absence of food induced incessant food-procuring behavior paralleled by regular generation of spike bursts in masticatory muscles with biomodal distributions of intervals between pulses. This reaction of masticatory muscles during stimulation of the lateral hypothalamus in the absence of food was an example of the anticipatory reaction reflecting characteristics of the action result acceptor. Higher level of hunger motivation during threshold stimulation of the lateral hypothalamus in hungry and satiated rabbits in the course of effective food-procuring behavior increased the incidence of spike burst generation during the food capture phase, but did not modify this parameter during the chewing phase. Impulse activity of the masticatory muscles reflected convergent interactions of food motivation and support excitation on neurons of the central generator of chewing pattern.

Differential responses of sympathetic premotor neurons in the rostral ventrolateral medulla to stimulation of the dorsomedial hypothalamus in rabbits

Electrical stimulation of the posterior dorsomedial hypothalamus (DMH) elicits a defense response, including vasodilation in the skeletal muscles and vasoconstriction in the viscera. To examine whether sympathetic premotor neurons in the rostral ventrolateral medulla (RVLM) participate in these differential vascular responses, RVLM neuron activity, renal sympathetic nerve activity (RSNA), renal vessel conductance (RVC), skeletal muscular vessel conductance (MVC), arterial pressure (AP), and heart rate (HR) were simultaneously measured in urethane-anesthetized, vagotomized, and immobilized rabbits. Electrical stimulation of the DMH increased RSNA, MVC, AP, and HR but decreased RVC. The RVLM neurons were classified into three groups according to their responses to tetanic (10 s) stimulation of the DMH. Twenty neurons (Type I) were excited, 17 (Type II) were inhibited, and 2 (Type III) did not respond. To the short-train (100 ms) stimulation, all of the Type I neurons showed excitation; in contrast, 12 Type II neurons showed biphasic response that was early excitation followed by inhibition. The remainder showed only inhibition. Type III neurons also did not respond to the short-train stimulation. These results indicated that regional differences in responses of sympathetic nerves in the defense response are supported by functional differentiation of sympathetic premotor neurons in the RVLM.

Prenatal Exposure to Vinclozolin Disrupts Selective Aspects of the Gonadotrophin‐Releasing Hormone Neuronal System of the Rabbit

Developmental exposure to the agricultural fungicide vinclozolin can impair reproductive function in male rabbits and was previously found to decrease the number of immunoreactive-gonadotrophin-releasing hormone (GnRH) neurones in the region of the organum vasculosum of the lamina terminalis and rostral preoptic area by postnatal week (PNW) 6. In the present study, in an aim to further examine the disruption of GnRH neurones by foetal vinclozolin exposure, pregnant rabbits were dosed orally with vinclozolin, flutamide or carrot paste vehicle for the last 2 weeks of gestation. Offspring were euthanised at birth (males and females), PNW 6 (females), PNW 26 (adult males) or PNW 30 (adult females) of age. At birth and in adults, brains were sectioned and processed for immunoreactive GnRH. The numbers of immunoreactive GnRH neuronal perikarya were significantly decreased in vinclozolin-treated rabbits at birth and in adult littermates. By contrast, there was an increase in GnRH immunoreactivity in the terminals in the region of the median eminence. Analysis of PNW 6 female brains by radioimmunoassay revealed a two-fold increase in GnRH peptide content in the mediobasal hypothalamus in vinclozolin-treated rabbits. This finding was complemented by immunofluorescence analyses, which revealed a 2.8-fold increase in GnRH immunoreactivity in the median eminence of vinclozolin compared to vehicle-treated females at PNW 30. However, there was no difference between treatment groups in the measures of reproduction that were evaluated: ejaculation latency, conception rates or litter size. These results indicate that sub-acute, prenatal vinclozolin treatment is sufficient to create perdurable alterations in the GnRH neuronal network that forms an important input into the reproductive axis. Finally, the effect of vinclozolin on the GnRH neuronal network was not comparable to that of flutamide, suggesting that vinclozolin was not acting through anti-androgenic mechanisms.

Influence of microinjection of corticosterone into ventromedial hypothalamus on hepatic acetate metabolism in rabbits.

Corticosterone was injected into the ventromedial hypothalamus (VMH) of rabbits, and changes in hepatic acetate metabolism were studied. The microinjection of corticosterone with seasame oil into the VMH of intact rabbits increased the rates of 14C transfer from 14C-1-acetate into CO2, glucose, ketone bodies, triglyceride, free cholesterol, free fatty acids and phospholipids but decreased those of 14C transfer into cholesterol ester. However, corticosterone injected into the VMH of rabbits with VMH lesions or the parietal cortex of intact rabbits was without effect on the hepatic acetate metabolism. From these results it might be suggested that the VMH is an integral part of the corticosterone-sensitive brain regulator system in the hepatic acetate metabolism.

Curcumin inhibits the increase of glutamate, hydroxyl radicals and PGE 2 in the hypothalamus and reduces fever during LPS-induced systemic inflammation in rabbits

Evidence has accumulated to suggest that systemic administration of lipopolysaccharide (LPS), in addition to elevating tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and interleukin-6 (IL-6) as well as fever, induces overproduction of glutamate, hydroxyl radicals and prostaglandin E 2 (PGE 2) in the rabbit's hypothalamus. Current study was attempted to assess whether Curcumin exerts its antipyresis by reducing circulating pro-inflammatory cytokines and hypothalamic glutamate, hydroxyl radicals and PGE 2 in rabbits. The microdialysis probes were stereotaxically and chronically implanted into the preoptic anterior hypothalamus of rabbit brain for determination of glutamate, hydroxyl radicals, and PGE 2 in situ. It was found that systemic administration of LPS (2 µg/kg) induced increased levels of both core temperature and hypothalamic levels of both glutamate and hydroxyl radicals accompanied by increased plasma levels of TNF-α, IL-1β, and IL-6. The rise in both the core temperature and hypothalamic glutamate and hydroxyl radicals could also be induced by direct injection of TNF-α, IL-1β, or IL-6 into the lateral ventricle of rabbit brain. Pretreatment with Curcumin (5–40 mg/kg, i.p.) 1 h before an i.v. dose of LPS significantly reduced the LPS-induced overproduction of circulating TNF-α, IL-1β, and IL-6, and brain glutamate, PGE 2, and hydroxyl radicals. Both the febrile response and overproduction of both glutamate and hydroxyl radicals in the hypothalamus caused by central administration of TNF-α, IL-1β, or IL-6 could be suppressed by Curcumin. These results indicate that systemic injection of Curcumin may exert its antipyresis by inhibiting the glutamate-hydroxyl radicals-PGE 2 pathways in the hypothalamus and circulating TNF-α, IL-1β, and IL-6 accumulation during LPS fever.

The Neuropeptide Y (NPY) Y2 Receptors Are Largely Dimeric in the Kidney, but Monomeric in the Forebrain

The neuropeptide Y(NPY) Y2 receptors are detected largely as dimers in the clonal expressions in CHO cells and in particulates from rabbit kidney cortex. However, in two areas of the forebrain (rat or rabbit piriform cortex and hypothalamus), these receptors are found mainly as monomers. Evidence is presented that this difference relates to large levels of G proteins containing the Gi α -subunit in the forebrain areas. The predominant monomeric status of these Y2 receptors should also be physiologically linked to large synaptic inputs of the agonist NPY. The rabbit kidney and the human CHO cell-expressed Y2 dimers are converted by agonists to monomers in vitro at a similar rate in the presence of divalent cations.

Release of ATP in the central nervous system during systemic inflammation: real‐time measurement in the hypothalamus of conscious rabbits

Receptors for extracellular ATP (both ionotropic and metabotropic) are widely expressed in the CNS both in neurones and glia. ATP can modulate neuronal activity in many parts of the brain and contributes to the central nervous control of several physiological functions. Here we show that during the systemic inflammatory response the extracellular concentrations of ATP increase in the anterior hypothalamus and this has a profound effect on the development of the thermoregulatory febrile response. In conscious rabbits we measured ATP release in real time with novel amperometric biosensors and monitored a marked increase in the concentration of ATP (4.0 ± 0.7 μm) in the anterior hypothalamus in response to intravenous injection of bacterial endotoxin – lipopolysaccharide (LPS). No ATP release was observed in the posterior hypothalamus. The release of ATP coincided with the development of the initial phase of the febrile response, starting 18 ± 2 min and reaching its peak 45 ± 2 min after LPS injection. Application of the ATP receptor antagonists pyridoxal-5′-phosphate-6-azophenyl-2′,4′-disulphonic acid, Brilliant Blue G or periodate oxidized ATP dialdehyde to the site of ATP release in the anterior hypothalamus markedly augmented and prolonged the febrile response. These data indicate that during the development of the systemic inflammation, ATP is released in the anterior hypothalamus to limit the magnitude and duration of fever. This release may also have a profound effect on the hypothalamic control of other physiological functions in which ATP and related purines have been implicated to play modulatory roles, such as food intake, hormone secretion, cardiovascular activity and sleep.

Brain superoxide as a key regulator of the cardiovascular response to emotional stress in rabbits

Cardiovascular reactivity, an abrupt increase in blood pressure and heart rate in response to emotional stress, is a risk factor for hypertension and heart disease. Brain angiotensin II (Ang II) type 1 (AT(1)) receptor is increasingly recognized as an important regulator of cardiovascular reactivity. Given that a wide variety of AT(1) receptor signalling pathways exists in neurones, the precise molecular mechanisms that underlie central cardiovascular actions of Ang II during emotional stress are yet to be determined. Growing evidence, however, indicates that reactive oxygen species, and in particular superoxide (.O(2)(-)), are important intracellular messengers of many actions of brain Ang II. In particular, studies employing microinjection of .O(2)(-) scavengers directly into the rostral ventrolateral medulla (RVLM) and dorsomedial hypothalamus of rabbits have shown that the activation of AT(1) receptor-.O(2)(-) signalling is required for full manifestation of the cardiovascular response to emotional stress. This role of .O(2)(-) appears to be highly specific, because .O(2)(-) scavengers in the RVLM do not alter the sympathoexcitatory response to baroreceptor unloading or sciatic nerve stimulation. The subcellular mechanisms for the stress-induced .O(2)(-) production are likely to include the activation of NADPH oxidase and are essentially independent of nitric oxide. This review summarizes current knowledge of redox-sensitive signalling mechanisms in the brain that regulate cardiovascular effects of stress. Additionally, it presents initial evidence that .O(2)(-) may be less important in the activation of central pressor pathways mediating cardiovascular arousal associated with appetitive events, such as food anticipation and feeding.

Diurnal pattern of clock gene expression in the hypothalamus of the newborn rabbit

In the European rabbit (Oryctolagus cuniculus) nursing acts as a strong non-photic synchronizer of circadian rhythmicity in the newborn young. Rabbits only nurse for a few minutes once every 24 h and previous studies have shown that the pups, blind at birth, display endogenous circadian rhythms in behavior and physiology entrained by this regular daily event. As a further step toward understanding the neural organization of the rabbit’s early circadian system, we investigated the expression of clock genes in the suprachiasmatic nucleus of the hypothalamus (SCN; the principal circadian pacemaker in adult mammals) across the pups’ 24-h day. We used 43 pups from seven litters maintained in constant darkness and entrained non-photically by nursing at the same time each day until P7. After nursing on day 7, pups were killed in the dark at 3-h intervals so as to obtain eight groups (n=5–6 pups/group) distributed evenly across the 24 h before the next scheduled nursing. Profiles in the expression of the clock genes Per1, Per2, Cry1 and Bmal1 were determined using in situ hybridization in brain sections through the hypothalamus at the level of the SCN. We report for the first time: 1) that Per1, Per2, Cry1 and Bmal1 are all expressed in the SCN of the newborn rabbit, 2) that the expression of Per1, Per2 and Bmal1 but not Cry1 shows diurnal rhythmicity similar to that in adult mammals, and 3) that the expression of Per1, Per2 and Bmal1 is consistent with the strong entraining effect of nursing found in previous studies. Unexpectedly, and contrasting somewhat to the pattern in the SCN, we also found diurnal rhythmicity in the expression of Cry1 and Bmal1 but not of Per1 in the anterior ventromedial hypothalamic nucleus. Overall, our findings suggest that the SCN is a functional part of the newborn rabbit’s circadian system and that it can be entrained by non-photic cues associated with the mother’s daily nursing visit.

The antipyretic effects of baicalin in lipopolysaccharide-evoked fever in rabbits

Evidence has accumulated to indicate that systemic administration of lipopolysaccharide (LPS), in addition to elevating tumor necrosis factor-alpha (TNF-α) as well as fever, induces overproduction of both glutamate and hydroxyl radicals in the rabbit's hypothalamus. Current investigation was attempted to determine whether baicalin exerts its antipyresis by suppressing overproduction of circulating TNF-α and hypothalamic glutamate and hydroxyl radicals in rabbits. The microdialysis probes were stereotaxically and chronically implanted into the preoptic anterior hypothalamus of rabbit brain for determination of both glutamate and hydroxyl radicals in situ. It was found that systemic administration of LPS (0.5–10 μg/kg) induced dose-related increased levels of both core temperature and hypothalamic levels of both glutamate and hydroxyl radicals accompanied by increased plasma levels of TNF-α. The rise in both the core temperature and hypothalamic glutamate and hydroxyl radicals could also be induced by direct injection of TNF-α (1–20 ng) into the lateral ventricle of rabbit brain. Pretreatment with baicalin (2–20 mg/kg, i.v.) one hour before an i.v. dose of LPS significantly reduced the LPS-induced overproduction of circulating TNF-α and brain glutamate and hydroxyl radicals. Both the febrile response and overproduction of both glutamate and hydroxyl radicals in the hypothalamus caused by central administration of TNF-α could be suppressed by baicalin. These findings suggest that systemic administration of baicalin may exert its antipyresis by inhibiting the N-methyl- d-aspartate receptor-dependent hydroxyl radicals pathways in the hypothalamus and circulating TNF-α accumulation during LPS-fever.

Correspondence between the time course of cerebral vasospasm and the level of cerebral dopamine-β-hydroxylase in rabbits

The aim of the study was to explore whether the biphasic time course of the vasospastic response following experimental subarachnoid hemorrhage is associated with any concomitant changes in the amount of cerebral dopamine β-hydroxylase in the noradrenergic central nervous system. A single-hemorrhage animal model was used. Rabbits were sacrificed from day 1 to day 8 after subarachnoid hemorrhage. Intimal corrugation of the basilar artery and the amount of cerebral dopamine β-hydroxylase in the hypothalamus and brain stem were measured each day. Vasospastic changes occurred in the biphasic manner following subarachnoid hemorrhage. More profound vasospastic corrugation occurred in the acute phase, followed by a slightly less intense corrugation in the chronic phase (between days 5 and 8 after the subarachnoid hemorrhage). Simultaneously, a clear concomitant biphasic time course developed in the form of an increased amount of dopamine-β-hydroxylase in the noradrenergic nervous system of the rabbit hypothalamus and brain stem during the acute and chronic phases after the subarachnoid hemorrhage. Statistically significant correlation between basilar artery corrugation and the amount of dopamine β-hydroxylase was found. These results suggest the possible role of the central sympathetic system in the pathogenesis of vasospasm. At the same time, this study demonstrates the chronological similarity of the vasospastic development after subarachnoid hemorrhage in the animal experimental model with the human time course of vasospasm.

An NMDA receptor-dependent hydroxyl radical pathway in the rabbit hypothalamus may mediate lipopolysaccharide fever

The aim of this study was to investigate the effects of antioxidants (e.g. α-lipoic acid and N-acetyl- l-cysteine) as well as N-methyl- d-aspartate (NMDA) receptor antagonists (e.g. MK-801 and LY235959) on the changes of both core temperature and hypothalamic levels of 2,3-dihydroxybenzoic acid (2,3-DHBA) induced by systemic administration of lipopolysaccharide (LPS) in rabbits. The measurements of 2,3-DHBA were used as an index of the intrahypothalamic levels of hydroxyl radicals. Intravenous administration of LPS (2–10 μg/kg) elicited a biphasic febrile response, with the core temperature maxima at 80 and 200 min post-injection. Each core temperature rise was accompanied by a distinct wave of cellular concentrations of 2,3-DHBA in the hypothalamus. The rise in both the core temperature and hypothalamic 2,3-DHBA could be induced by direct injection of glutamate (100–400 μg in 10 μl/rabbit) into the cerebroventricular fluid system. Either the early or the late phase of fever rise and increased hypothalamic levels of 2,3-DHBA following systemic injection of LPS were significantly antagonized by pretreatment with injection of α-lipoic acid (5–60 mg/kg, i.v.), N-acetyl- l-cysteine (2–20 mg/kg, i.v.), MK-801 (0.1–1 mg/kg, i.m.), or LY235959 (0.1–1 mg/kg, i.v.) 1 h before LPS injection. The increased levels of prostaglandin E 2 in the hypothalamus induced by LPS could be suppressed by α-lipoic acid or N-acetyl- l-cysteine pretreatment. These findings suggest that an NMDA receptor-dependent hydroxyl radical pathway in the hypothalamus of rabbit brain may mediate both the early and late phases of the fever induced by LPS.

Reticulospinal neurons inactivated by warming of the preoptic area and anterior hypothalamus of rabbits

To identify the premotor neurons for vasoconstrictors of the skin, activities of reticulospinal neurons in the rostroventral medulla, the ear sympathetic nerve (ESNA) and the renal sympathetic nerve (RSNA) were recorded in anesthetized and immobilized Japanese White or New Zealand White rabbits. Two groups of neurons were identified according to their responses to thermal stimulation of the preoptic area and the anterior hypothalamus (POAH) and to electrical stimulation of baroreceptor afferents, the aortic nerve (AN). Neurons (Type I neurons, n = 21) whose activity was inhibited by warm stimulation of the POAH but not inhibited by the AN stimulation were located in sites medial to the rostral ventrolateral medulla (RVLM). The other neurons (Type II neurons, n = 20) whose activity was not inhibited by warm stimulation of the POAH but inhibited by the AN stimulation were located in the RVLM. Because the time course of the inhibitory response of Type I neurons to warm stimulation of the POAH was very similar to that of the inhibitory response of the ESNA and activities of these neurons and the ESNA were not inhibited by the stimulation of the AN, it was suggested the Type I neurons might participate in regulation of activity of the vasoconstrictors of the ear skin. The Type II neurons are considered to be the barosensitive RVLM neurons that regulate systemic arterial pressure by controlling the activity of visceral or muscular sympathetic vasoconstrictors or cardiac sympathetic fibers.

Attenuation of cerebral vasospasm in rabbits using clonidine hydrochloride, a central adrenergic agonist

The aim of this study was to assess, firstly, if exclusion of central noradrenergic areas in the hypothalamus and brain stem with the central sympathetic blocker clonidine hydrochloride could prevent the development of chronic vasospasm following experimental subarachnoid haemorrhage in rabbits and, secondly, if, parallel with the effect on cerebral arteries, changes in dopamine β-hydroxylase concentration in the hypothalamus and brain stem could also be detected. Experimental subarachnoid haemorrhage, in concentrations of 1 ml of autologous arterial blood/1 kg of body weight was carried out on 18 New Zealand rabbits. Histological specimens were obtained by the method of perfusion fixation after the rabbits were sacrificed on day 8 after subarachnoid haemorrhage. The spastic effect of experimentally induced subarachnoid haemorrhage was determined by assessing the intensity of corrugation of the intima of the rabbit basilar artery by the previously developed method of corrugation coefficient and computer image analysis. The concentration and localization of dopamine β-hydroxylase in noradrenaline-containing neurons was immunohistochemically assessed (semiquantitatively as 0, 1 and 2) with anti-dopamine β-hydroxylase, at precisely defined sites of the hypothalamus and brain stem of the same rabbit. The results revealed less corrugated and smoother intima in the basilar artery and significantly lower dopamine β-hydroxylase concentration in the control group of rabbits with sham subarachnoid haemorrhage and without any additional interventions (mean corrugation coefficient=1.123±0.024, P=0.35×10 −3; mean dopamine β-hydroxylase=0.350±0.071, P=0.22×10 −3), and smoother intima in the basilar artery with significantly lower concentration of dopamine β-hydroxylase in the clonidine group (rabbits with subarachnoid haemorrhage and central α 2-blocker clonidine hydrochloride at a daily dose of 0.03 mg/kg of body weight for 8 days; mean corrugation coefficient=1.177±0.058, P=1.7×10 −3; mean dopamine β-hydroxylase=0.583±0.175, P=1.1×10 −3). In comparison, the haemorrhage only group (rabbits with subarachnoid haemorrhage and without medication; mean corrugation coefficient=1.370±0.101; mean dopamine β-hydroxylase=1.214±0.313) displayed intensive corrugation of the intima of the basilar artery and a significantly more intensive accumulation of dopamine β-hydroxylase than did the control group and the clonidine group. The results of this study demonstrated that the central α 2-blocker clonidine hydrochloride effectively prevents vasospasm, and diminishes the concentration of cerebral dopamine β-hydroxylase in the hypothalamus and brain stem after experimental subarachnoid haemorrhage in rabbits.