ABSTRACT
In the experiments on sagittal hypothalamic slices of male Wistar rats, the effect of 10 nM neuropeptide Y on the electrical activity of the suprachiasmatic nucleus neurons and spike information coding parameters were studied. Applications of neuropeptide Y induced a reduction of action potential frequency in 35 of 81 tested neurons, in 8 cells an increase in the parameter was observed; the remaining 38 neurons did not change their spike activity level. The decrease in spike frequency generation by neurons of the suprachiasmatic nucleus accompanied by an increase in both entropy of interspike interval distribution and mutual information between adjacent interspike intervals. These suggest an increased irregularity of the later as well as an increased patterning of spike information induced by neuropeptide Y. The obtained data indicate the ability of neuropeptide Y to modulate a level of activity and influence a spike code in a relatively numerous population of neurons in circadian oscillator of the suprachiasmatic nucleus.
Subject(s)
Circadian Clocks/drug effects , Membrane Potentials/drug effects , Neurons/metabolism , Neuropeptide Y/pharmacology , Suprachiasmatic Nucleus/metabolism , Animals , Male , Neurons/cytology , Rats , Rats, Wistar , Suprachiasmatic Nucleus/cytologyABSTRACT
Experiments on rat brainstem sections in membrane potential clamping conditions addressed the effects of serotonin and GABA on serotoninergic neurons in the nucleus raphe magnus. Local application of serotonin stimulated inhibitory postsynaptic currents (IPSC) in 45% of the serotoninergic neurons studied. This response was not seen in the presence of the fast sodium channel blocker tetrodotoxin. The GABAA receptor antagonist gabazine blocked IPSC in both serotonin-sensitive and serotonin-insensitive neurons. Application of GABA evoked generation of a membrane current (IGABA), which was completely blocked by gabazine. These results indicate self-regulation of the activity of serotoninergic neurons in the nucleus raphe magnus via a negative feedback circuit involving local GABAergic interneurons.
Subject(s)
Neurons/physiology , Raphe Nuclei/physiology , Serotonin/physiology , gamma-Aminobutyric Acid/physiology , Animals , Feedback, Physiological , GABA-A Receptor Antagonists/pharmacology , Ion Channel Gating , Male , Membrane Potentials , Neurons/drug effects , Pyridazines/pharmacology , Raphe Nuclei/drug effects , Rats , Rats, Wistar , Serotonin/pharmacology , Sodium Channels , Tetrodotoxin/pharmacology , gamma-Aminobutyric Acid/pharmacologyABSTRACT
Acute experiments on anesthetized laboratory rats were performed to study the effects microinjections of 10(-4) M leptin into the solitary tract nucleus on the extent of the Hering-Breuer inflation reflex in ventilatory reactions to hypercapnia. Local administration of leptin into this area led to inhibition of the Hering-Breuer reflex. The extent of ventilatory responses to hypercapnia, conversely, increased, which may provide evidence that leptin has a modulatory influence on central chemoreceptors. These physiological mechanisms of action probably play a leading role in mediating the stimulatory respiratory effects of leptin at the level of the solitary tract nucleus.
Subject(s)
Leptin/pharmacology , Respiration/drug effects , Respiratory Center/physiology , Solitary Nucleus/physiology , Animals , Electromyography , Female , Hypercapnia/physiopathology , Leptin/administration & dosage , Leptin/physiology , Male , Microinjections , Rats , Reflex, Stretch/physiology , Respiratory Center/drug effects , Solitary Nucleus/drug effectsABSTRACT
The regulatory peptide leptin has a respiratory stimulating effect along with its well known hypothalamic effects. The present study, performed on anesthetized rats, addressed respiratory responses to microinjections of 10(-10)-10(-4) M leptin into the solitary tract nucleus, which contains a high concentration of leptin receptors. Injections of 10(-8)-10(-4) M leptin led to stimulation of respiration, inducing a dose-dependent increase in the level of pulmonary ventilation and an increase in respiratory volume, accompanied by an increase in bioelectrical activity in the inspiratory muscles; 10(-6) M leptin also induced a transient increase in respiratory rate due to shortening of inhalation and exhalation. A characteristic feature of the response was the appearance of "sighs" - deep, prolonged inhalations accompanied by increased volley activity on the electromyograms of the inspiratory muscles and lengthening of the subsequent intervolley interval. These leptin effects, along with data on the high concentrations of specific leptin receptors (ObRb) in the solitary tract nucleus, suggested that endogenous leptin has a role in controlling respiration at the level of the dorsal segment of the respiratory center.
