9th multidisciplinary international

Conference of Biological Psychiatry

«Stress and Behavior»

Proceedings of the 9th International Multidisciplinary Conference «Stress and behavior» Saint-Petersburg, Russia, 16-19 May 2005 Editor: Allan V. Kalueff, PhD

CONFERENCE ABSTRACTS

5. PSYCHONEUROIMMUNOLOGY

IMMUNOHISTOCHEMICAL STUDIES OF THE REACTIONS OF THE NUCLEUS TRACTUS

SOLITARIUS AND PARABRACHIAL COMPLEX NEURONS TO THE VAGUS NERVE STIMULATION

V. Osharina, N. Larnicol, F. Wallois, V. Bagaev Pavlov Institute of Physiology RAS, St. Petersburg, Russia; Picardie University, Amiens, France It is well known that vagal stimulation may be an alternative to therapeutic treatment of inoperable and drug-resistant forms of epilepsy. However the mechanisms of its antiepileptic effects, and the regularity of the transmission of the interoceptive information to the forebrain structures, are poorly understood. Besides it is necessary to carry out the physiological experimental studies to optimize vagal stimulation parameters, in order to reduce side-effects (such as respiratory distress and cardiac abnormalities). The present study analysed spatial organization of the nucleus tractus solitarius and parabrachial complex nitroergic neurons expressing c-Fos proteins (product of the immediate early gene c-fos) in response to the electrical stimulation of the left cervical central cut end of the vagus nerve. The experiments were performed on the Sprague-Dawley adult rats. Double labelling for c-Fos proteins and NADPH-diaphorase was conducted on fixed brain tissue. Serial coronal brainstem sections (40 mkm) across the nucleus tractus solitarius and parabrachial complex areas were collected. Fos immunohistochemistry was conducted according to ABC procedure, using a primary polyclonal antibody against Fos (Santa-Cruz, sc-52) and detection kits including solutions of secondary biotinylated antibody, streptavidin and biotinylated horseradish peroxidase (Novocastra). NADPH-diaphorase was revealed according to standard procedures in the presence of beta-NADPH and nitro blue tetrazolium as substrates. The light microscope for detection of c-Fos and NADPH positive cells was used. Peculiarities of the reflectory changes of intragastric pressure, breathing and heart rates were studied as «autonomic indicators» of efficacy of vagal stimulation. Parameters of the nerve stimulation were related to those used in clinical practice for the treatment of epilepsy (100—300 mA, 0.5—1.0 ms, 1 or 10 Hz for 10 s). Without stimulation, NADPH-positive neurons were identified and the peculiarities of their localization in the commissural, medial and ventrolateral (the area postrema level) subnuclei of the nucleus tractus solitarius and caudal and rostral parts of the lateral and medial subnuclei of the parabrachial complex were studied. In neurons of the same areas the spontaneous c-Fos protein expression was investigated. After the vagus nerve stimulation by restangular pulses of .5 ms at 10 Hz and 200—300 mA for 10 s, the amount of c-Fos positive cells in commissural, medial and ventrolateral subnuclei of the nucleus tractus solitarius rised in 75, 100 and 220%, accordingly. The quantity of these neurons rose in parabrachial complex: in rostral parts of the lateral and medial subnuclei in 130 and 80%, accordingly and in caudal parts of the same subnuclei (40 and 210%). Under the same parameters of the vagus nerve stimulation, the intragastric pressure decreased and the breathing stopped (apnoea during the period of stimulation). The heart rate inhibited under these conditions by 10—50% vs. the baseline. Thus, here we identified nitroergic neurons in the nucleus tractus solitarius (the first synapse level for interoceptive impulses) and the parabrachial complex (the second synapse level) responding by c-Fos protein expression to electrical stimulation of the left cervical vagus nerve. Therefore, the participation of mentioned neurons in mechanisms of the therapeutic action of vagal stimulation has been demonstrated. Also we showed that vagal stimulation is accompanied by the changes in intragastric pressure, heart and

Psychopharmacol. Biol. Narcol. 2005. Vol. 5, N 2. P. 914

Psyhopharmacology & biological narcology

ISSN 1606-8181

breathing rates. Reflectory modifications of the breathing rate are the most sensitive «autonomic indicator» of the vagus nerve stimulation efficacy. The study was supported in part by grant 04-04-48710 from the Russian Foundation for Basic Research and by NATO fellowship (402349H to V.O.).

Psychopharmacol. Biol. Narcol. 2005. Vol. 5, N 2. P. 914

Psyhopharmacology & biological narcology

ISSN 1606-8181