- Email: [email protected]
Calmodulin translocation in rat brain regions after PTZ-kindling
02
9thMeeting of the ESN
5
I,
EAA ANTAGONISTS CONSERVE FUNCTIONAL PROPERTIES OF NEURONS EXPOSED TO EAAS.
CALMOOULIN TRANSLOCATION IN RAT BRAIN REGIONS AFTER PTZ-KINDLING.
Aa. Frandsen & A. Schousboe, PharmaBiotec Res. Ctr., School of Pharmacy, DK-2100 Copenhagen, Denmark.
N.S.Popov Institute of Pharaacology cology, Medical Academy, Germany
It is important to assure that drugs proven to be neuroprotective as judged by cell viability tests, e.g. leakage of lactate dehydrogenase (LDH) also conserve the functional properties of the neurons. Therefore, the neuroprotective effect of EAA antagonists against EAA induced toxicity has been evaluated by means of both a biochemical assay (the LDH leakage test) and a functional test based on the ability of the cultures to release neurotransmitter upon depolarization. It was found that exposure to EAAs lead to massive leakage of LDH which
coincided with the loss of depolarization coupled neurotransmitter release. Vice versa, in all cases the neurons were functionaly active if they were exposed to EAAs in the presence of the EAA receptor antagonists under which conditions no leakage of LDH was
observed.
CHANGES IN EXTRACELLULAR N-ACETYLASPARTATE (NM) DURING FOCAL INJURY AND LOCAL APPLICATION OF K’. Urenjak, T.P. J. Obrenovitch, D.A. Richards, S.R. Williams and L. Symon Department of Biophysics, The Royal College of Surgeons, London, U.K. The basal level of NAA in the extracellular fluid (ECF) of the rat striatum was examined microusing dialysis. Dialysate samples were analyzed by HPLC. The effects of focal injury, local K'-stimuli and terminal were ischaemia The measured. data indicated a high intra-/extracellular gradient in NAA, probably maintained by potent uptake mechanism(s). The ECF NAA level did not change during K'-induced local depolarisation (30 min perfusion with an isotonic medium containing 100 mM K'; with or without Ca"). However, on return to control dialysate we consistently observed an significant increase in ECF NAA. These data support the concept that, despite a high intra-/extracellular gradient, NAA is not a neurotransmitter. The delayed increase after K' may reflect an involvement of NAA in mechanisms protecting neurones against marked ionic changes or osmotic stress.
and
Toxi-
Magdsburg
,
Radioimmunologically assayed cytosolic and membrane-bound celmodulin in brain tissue of pentylentetrazol-kindled rate revealed altsrations in content of ccrlmodulin in terms of tranelocation from the cytosolic to the membrane compartment. Thus, in hippocampus, striatum and cortex a decrease in cytosolic celwodulin (30%) wss associated with an increase&in membrane-bound calmodulin 130-35%x;). However, an increase in the‘net synthesis of~calmodulin cannot be ruled out. Theee findings agree with other results using the same kindling model, e.g. alteretions in content of other calciumbinding proteins, increase in glutamate receptor density etc. The results are discussed in light of the current understandin of kindling as a form of neurons 9 plasticity.
RBCBPTOR ACTIVATION MBDIATBS HYPEROSMOLAR BRBACHING OF THE BLOOD-BRAIN BARRIER.
NMDA
H. Koemg, C.Y. Lu, A.D. Goldstone and J.J. Trout, Newologj Service, VA Lakeside Medical Center and Department of Neurology, Northwestern University Medical School. Chicago, II USA. The Bkwd-brain bamer (SBB) openmg by intracarohd infusion 01 hyperosmolar (1.6 M) mamtitol is cnsuaily linked to a rapid increase in brain capillary (BC) polypmines and the activity of their regulatory enzyme omithime decarhoxylase @DC) (H. Koenig et al., Brain Res. 483: 110, 1989). Is&ted BC possess NMDA receptsxs coupled to QDC which upwdulate capillary transport and mediate BBB breakdown foilowmg cold injury (H. Koenig et al. SIX. Neurosci: Abstr. 17:7, 1991). The NMDA receptor antagonist MK-801 .(I-lOmg/kg) effectively blocked the BBB disruption, monitored by -a -[14C] aminoisobutymte and fluorescein leakage, evoked by the intracarotid&w.ion of (1.6 M) mannitol. This is the first indication that overstimulation of capillary NMDA receptors IS involved in triggering the hyperosmolar hreacbing of the BBB.
9thMeeting of the ESN
5
I,
EAA ANTAGONISTS CONSERVE FUNCTIONAL PROPERTIES OF NEURONS EXPOSED TO EAAS.
CALMOOULIN TRANSLOCATION IN RAT BRAIN REGIONS AFTER PTZ-KINDLING.
Aa. Frandsen & A. Schousboe, PharmaBiotec Res. Ctr., School of Pharmacy, DK-2100 Copenhagen, Denmark.
N.S.Popov Institute of Pharaacology cology, Medical Academy, Germany
It is important to assure that drugs proven to be neuroprotective as judged by cell viability tests, e.g. leakage of lactate dehydrogenase (LDH) also conserve the functional properties of the neurons. Therefore, the neuroprotective effect of EAA antagonists against EAA induced toxicity has been evaluated by means of both a biochemical assay (the LDH leakage test) and a functional test based on the ability of the cultures to release neurotransmitter upon depolarization. It was found that exposure to EAAs lead to massive leakage of LDH which
coincided with the loss of depolarization coupled neurotransmitter release. Vice versa, in all cases the neurons were functionaly active if they were exposed to EAAs in the presence of the EAA receptor antagonists under which conditions no leakage of LDH was
observed.
CHANGES IN EXTRACELLULAR N-ACETYLASPARTATE (NM) DURING FOCAL INJURY AND LOCAL APPLICATION OF K’. Urenjak, T.P. J. Obrenovitch, D.A. Richards, S.R. Williams and L. Symon Department of Biophysics, The Royal College of Surgeons, London, U.K. The basal level of NAA in the extracellular fluid (ECF) of the rat striatum was examined microusing dialysis. Dialysate samples were analyzed by HPLC. The effects of focal injury, local K'-stimuli and terminal were ischaemia The measured. data indicated a high intra-/extracellular gradient in NAA, probably maintained by potent uptake mechanism(s). The ECF NAA level did not change during K'-induced local depolarisation (30 min perfusion with an isotonic medium containing 100 mM K'; with or without Ca"). However, on return to control dialysate we consistently observed an significant increase in ECF NAA. These data support the concept that, despite a high intra-/extracellular gradient, NAA is not a neurotransmitter. The delayed increase after K' may reflect an involvement of NAA in mechanisms protecting neurones against marked ionic changes or osmotic stress.
and
Toxi-
Magdsburg
,
Radioimmunologically assayed cytosolic and membrane-bound celmodulin in brain tissue of pentylentetrazol-kindled rate revealed altsrations in content of ccrlmodulin in terms of tranelocation from the cytosolic to the membrane compartment. Thus, in hippocampus, striatum and cortex a decrease in cytosolic celwodulin (30%) wss associated with an increase&in membrane-bound calmodulin 130-35%x;). However, an increase in the‘net synthesis of~calmodulin cannot be ruled out. Theee findings agree with other results using the same kindling model, e.g. alteretions in content of other calciumbinding proteins, increase in glutamate receptor density etc. The results are discussed in light of the current understandin of kindling as a form of neurons 9 plasticity.
RBCBPTOR ACTIVATION MBDIATBS HYPEROSMOLAR BRBACHING OF THE BLOOD-BRAIN BARRIER.
NMDA
H. Koemg, C.Y. Lu, A.D. Goldstone and J.J. Trout, Newologj Service, VA Lakeside Medical Center and Department of Neurology, Northwestern University Medical School. Chicago, II USA. The Bkwd-brain bamer (SBB) openmg by intracarohd infusion 01 hyperosmolar (1.6 M) mamtitol is cnsuaily linked to a rapid increase in brain capillary (BC) polypmines and the activity of their regulatory enzyme omithime decarhoxylase @DC) (H. Koenig et al., Brain Res. 483: 110, 1989). Is&ted BC possess NMDA receptsxs coupled to QDC which upwdulate capillary transport and mediate BBB breakdown foilowmg cold injury (H. Koenig et al. SIX. Neurosci: Abstr. 17:7, 1991). The NMDA receptor antagonist MK-801 .(I-lOmg/kg) effectively blocked the BBB disruption, monitored by -a -[14C] aminoisobutymte and fluorescein leakage, evoked by the intracarotid&w.ion of (1.6 M) mannitol. This is the first indication that overstimulation of capillary NMDA receptors IS involved in triggering the hyperosmolar hreacbing of the BBB.