The vigilance promoting drug modafinil increases extracellular glutamate levels in the medial preoptic area and the posterior hypothalamus of the conscious rat: prevention by local GABAA receptor blockade.
The effects of modafinil on glutamatergic and GABAergic transmission in the rat medial preoptic area (MPA) and posterior hypothalamus (PH), are analysed. Modafinil (30-300 mg/kg) increased glutamate and decreased GABA levels in the MPA and PH. Local perfusion with the GABAA agonist muscimol (10 microM), reduced, while the GABAA antagonist bicuculline (1 microM and 10 microM) increased glutamate levels. The modafinil (100 mg/kg)-induced increase of glutamate levels was antagonized by local perfusion with bicuculline (1 microM). When glutamate levels were increased by the local perfusion with the glutamate uptake inhibitor L-trans-PDC (0.5 mM), modafinil produced an additional enhancement of glutamate levels. Modafinil (1-33 microM) failed to affect [3H]glutamate uptake in hypothalamic synaptosomes and slices. These findings show that modafinil increases glutamate and decreases GABA levels in MPA and PH. The evidence that bicuculline counteracts the modafinil-induced increase of glutamate levels strengthens the evidence for an inhibitory GABA/glutamate interaction in the above regions controlling the sleep-wakefulness cycle. (+info)
Nitric oxide-compromised hypertension: facts and enigmas.
NO concentration in the femoral artery and femoral vein of anesthetized dogs was found to be 154.2+/-5.6 nM and 90.0+/-12 nM, respectively. Inhibition of NO synthase (NOS) slightly decreased the basal NO concentration in femoral artery from 154.2+/-5.6 to 137.2+/-3.3 nM. Acetylcholine-induced increase in NO concentration was slightly but still significantly attenuated, suggesting that very probably L-NAME did not inhibit all sources of nitric oxide (NO). Local NOS inhibition in the posterior hypothalamus dose-dependently increased systemic blood pressure (BP) in rats. Short-term general NOS inhibition in anesthetized dogs increased diastolic BP but not systolic BP. The heart rate after one-hour down-fluctuation returned to initial values. Proteosynthesis in the myocardium and both branches of the left coronary artery increased, but this was not supported by polyamines, since the activity of ornithine decarboxylase declined. Long-term general NOS inhibition elicited a sustained BP increase, a decrease in heart rate, cardiac hypertrophy and an increase in wall thickness of the coronary and carotid artery. The results indicate that NO deficiency itself plays a role in proteosynthesis and cardiac hypertrophy, in spite of relatively small increase in diastolic blood pressure and no change in systolic blood pressure, at least after an acute L-NAME administration. The hypotension response to acetylcholine and bradykinin studied in anesthetized NO-compromised rats, was unexpectedly enhanced. The elucidation of this paradoxical phenomenon will require further experiments. (+info)
Studies on the mechanism controlling growth hormone release induced by chlorpromazine in the anesthetized rat.
In intact urethane-anesthetized rats, plasma growth hormone (GH) levels were low but increased significantly following intravenous injection of chlorpromazine. Plasma GH levels were significantly elevated in rats with hypothalamic cuts such as complete deafferentiation, anterior cut and antero-lateral cut, whereas plasma GH levels in rats with posterior cut or postero-lateral cut were not significantly different from those in rats with sham-operation. Intravenous injection of chlorpromazine caused an increase of plasma GH in rats with any type of hypothalamic cut. However, the maximum increments of plasma GH following chlorpromazine were larger in rats with antero-lateral cut and smaller in rats with posterior cut than in rats with sham-operation. These results suggest that extrahypothalamic inhibiting and stimulating neurons influence the regulatory mechanism of rat GH secretion through anterior and posterior routes to the hypothalamus respectively. (+info)
Hypoxic augmentation of fast-inactivating and persistent sodium currents in rat caudal hypothalamic neurons.
Previous work from this laboratory has indicated that TTX-sensitive sodium channels are involved in the hypoxia-induced inward current response of caudal hypothalamic neurons. Since this inward current underlies the depolarization and increased firing frequency observed in these cells during hypoxia, the present study utilized more detailed biophysical methods to specifically determine which sodium currents are responsible for this hypoxic activation. Caudal hypothalamic neurons from approximately 3-wk-old Sprague-Dawley rats were acutely dissociated and patch-clamped in the voltage-clamp mode to obtain recordings from fast-inactivating and persistent (noninactivating) whole cell sodium currents. Using computer-generated activation and inactivation voltage protocols, rapidly inactivating sodium currents were analyzed during normal conditions and during a brief (3-6 min) period of severe hypoxia. In addition, voltage-ramp and extended-voltage-activation protocols were used to analyze persistent sodium currents during normal conditions and during hypoxia. A polarographic oxygen electrode determined that the level of oxygen in this preparation quickly dropped to 10 Torr within 2 min of initiation of hypoxia and stabilized at <0.5 Torr within 4 min. During hypoxia, the peak fast-inactivating sodium current was significantly increased throughout the entire activation range, and both the activation and inactivation values (V(1/2)) were negatively shifted. Furthermore both the voltage-ramp and extended-activation protocols demonstrated a significant increase in the persistent sodium current during hypoxia when compared with normoxia. These results demonstrate that both rapidly inactivating and persistent sodium currents are significantly enhanced by a brief hypoxic stimulus. Furthermore the hypoxic-induced increase in these currents most likely is the primary mechanism for the depolarization and increased firing frequency observed in caudal hypothalamic neurons during hypoxia. Since these neurons are important in modulating cardiorespiratory activity, the oxygen responsiveness of these sodium currents may play a significant role in the centrally mediated cardiorespiratory response to hypoxia. (+info)
Interleukin-1beta and neurogenic control of blood pressure in normal rats and rats with chronic renal failure.
Increased sympathetic nervous system (SNS) activity plays a role in the genesis of hypertension in rats with chronic renal failure (CRF). The rise in central SNS activity is mitigated by increased local expression of neuronal nitric oxide synthase (NOS) mRNA and NO(2)/NO(3) production. Because interleukin (IL)-1beta may activate nitric oxide in the brain, we have tested the hypothesis that IL-1beta may modulate the activity of the SNS via regulation of the local expression of neuronal NOS (nNOS) in the brain of CRF and control rats. To this end, we first found that administration of IL-1beta in the lateral ventricle of control and CRF rats decreased blood pressure and norepinephrine (NE) secretion from the posterior hypothalamus (PH) and increased NOS mRNA expression. Second, we observed that an acute or chronic injection of an IL-1beta-specific antibody in the lateral ventricle raised blood pressure and NE secretion from the PH and decreased NOS mRNA abundance in the PH of control and CRF rats. Finally, we measured the IL-1beta mRNA abundance in the PH, locus coeruleus, and paraventricular nuclei of CRF and control rats by RT-PCR and found it to be greater in CRF rats than in control rats. In conclusion, these studies have shown that IL-1beta modulates the activity of the SNS in the central nervous system and that this modulation is mediated by increased local expression of nNOS mRNA. (+info)
Biophysical characterization of rat caudal hypothalamic neurons: calcium channel contribution to excitability.
Neurons in the caudal hypothalamus (CH) are responsible for the modulation of various processes including respiratory and cardiovascular output. Previous results from this and other laboratories have demonstrated in vivo that these neurons have firing rhythms matched to the respiratory and cardiovascular cycles. The goal of the present study was to characterize the biophysical properties of neurons in the CH with particular emphasis in those properties responsible for rhythmic firing behavior. Whole cell, patch-clamped CH neurons displayed a resting membrane potential of -58.0 +/- 1.1 mV and an input resistance of 319.3 +/- 16.6 MOmega when recorded in current-clamp mode in an in vitro brain slice preparation. A large proportion of these neurons displayed postinhibitory rebound (PIR) that was dependent on the duration and magnitude of hyperpolarizing current as well as the resting membrane potential of the cell. Furthermore these neurons discharged tonically in response to a depolarizing current pulse at a depolarized resting membrane potential (more positive than -65 mV) but switched to a rapid burst of firing to the same stimulus when the resting membrane potential was lowered. The PIR observed in these neurons was calcium dependent as demonstrated by the ability to block its amplitude by perfusion of Ca(2+)-free bath solution or by application of Ni(2+) (0.3-0.5 mM) or nifedipine (10 microM). These properties suggest that low-voltage-activated (LVA) calcium current is involved in the PIR and bursting firing of these CH neurons. In addition, high-voltage-activated calcium responses were detected after blockade of outward potassium current or in Ba(2+)-replacement solution. In addition, almost all of the CH neurons studied showed spike frequency adaptation that was decreased following Ca(2+) removal, indicating the involvement of Ca(2+)-dependent K(+) current (I(K,Ca)) in these cells. In conclusion, CH neurons have at least two different types of calcium currents that contribute to their excitability; the dominant current is the LVA or T-type. This LVA current appears to play a significant role in the bursting characteristics that may underlie the rhythmic firing of CH neurons. (+info)
Cerebellar connections to the dorsomedial and posterior nuclei of the hypothalamus in the rat.
The stimulation or ablation of cerebellar structures has produced a variety of visceral responses, indicating a cerebellar role in visceral functions. Studies using anterograde and retrograde tracing methods have revealed connections between the hypothalamus and cerebellar structures. The aim of this study is to investigate the cerebellar connections of the dorsomedial (DMH) and posterior hypothalamic nuclei using retrograde axonal transport of horseradish peroxidase (HRP). In the present study, micro-injection of HRP restricted within the borders of the DMH showed that the projections of this nucleus are not uniform throughout its extent. The posterior DMH receives projections from the cerebellum, whereas the anterior DMH does not. These projections were from the (greatest to least concentration) lateral (dentate), anterior interposed (emboliform), and medial (fastigial) cerebellar nuclei. In addition, both the anterior and posterior DMH receive projections from various areas of the brainstem which confirms earlier studies and provides detailed descriptions. This study also demonstrates the distribution of labelled neurons to cerebellar and brainstem nuclei following HRP injection into the posterior hypothalamic nucleus. It provides clear evidence for a direct cerebellar nuclei-posterior DMH and cerebellar nuclei-posterior hypothalamic nucleus connections. We suggest that the brainstem reticular nuclei and other connections, such as the solitary, trigeminal and vestibular nuclei, of both DMH and posterior hypothalamus may contribute to the indirect cerebellohypothalamic connections. These observations offer a new perspective on the question of how the cerebellum may influence autonomic activity. (+info)
The afferent connections of the posterior hypothalamic nucleus in the rat using horseradish peroxidase.
The posterior hypothalamic nucleus has been implicated as an area controlling autonomic activity. The afferent input to the nucleus will provide evidence as to its role in autonomic function. In the present study, we aimed to identify the detailed anatomical projections to the posterior hypothalamic nucleus from cortical, subcortical and brainstem structures, using the horseradish peroxidase (HRP) retrograde axonal transport technique in the rat. Subsequent to the injection of HRP into the posterior hypothalamic nucleus, extensive cell labelling was observed bilaterally in various areas of the cerebral cortex including the cingulate, frontal, parietal and insular cortices. At subcortical levels, labelled cells were observed in the medial and lateral septal nuclei, the bed nucleus of stria terminalis, and various thalamic and amygdaloid nuclei. Also axons of the vertical and horizontal limbs of the diagonal band were labelled and labelled cells were localised at the CA1 and CA3 fields of the hippocampus and the dentate gyrus. The brainstem projections were from the medial, lateral and parasolitary nuclei, the intercalated nucleus of the medulla, the sensory nuclei of the trigeminal nerve, and various reticular, vestibular, raphe and central grey nuclei. The posterior hypothalamic nucleus also received projections from the lateral and medial cerebellar nuclei and from upper cervical spinal levels. The results are discussed in relation to the involvement of the posterior hypothalamic nucleus in autonomic function and allows a better understanding of how the brain controls visceral function. (+info)