Effects of Passive Avoidance Training on Calcium Flux in Chick Forebrain.

Chaudhury, Dipesh (1999). Effects of Passive Avoidance Training on Calcium Flux in Chick Forebrain. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000ff3e

Abstract

Calcium flux via voltage sensitive calcium channels (VSCC) was studied after passive avoidance training in the day-old chick. Intracellular free calcium concentration [Ca²⁺]_i, after depolarisation with 70mM KC1> was measured using the calcium chelator fiira-2/AM in the crude membrane preparations from the IMHV and LPO of chicks. Experiments showed a significant increase in KCl-stimulated [Ca²⁺]_i in the left IMHV of birds tested immediately after training compared to quiet birds (Q) and water trained birds (W). This increase was sustained in the left IMHV of birds tested 30 minutes after training. There was no significant difference between any of the groups of birds tested at later times. There was no significant increase in KCl-stimulated [Ca2+]i in the right IMHV of trained birds at any of the times tested. Significant elevation in KCl-stimulated [Ca²⁺]_iwas also detected, in both the left and right LPO, of birds tested 5 minutes after training; which was still evident in birds tested 10 minutes after training. There was no significant difference between any of the treatment groups in the left or right LPO at any of the other times tested.

Addition of different VSCC antagonists; such as co-conotoxin GVIA (N-type blocker), ω-conotoxin MVHC (N/P/Q-type blocker), nimodipine (L-type blocker), and co-agatoxin IVA (P-type blocker), were all shown to inhibit KCl-stimulated [Ca²⁺]_i elevation in the crude membrane preparation from the IMHV of untrained chicks. Addition of ω-conotoxin GVIA, nimodipine or co-conotoxin MVHC into the crude membranes from the left or right IMHV of chicks, tested immediately after training, showed greater inhibition in the left IMHV of trained birds compared to Q- and W-birds. There was no difference in inhibition in the right IMHV between any of the treatment groups.

The GABAergic receptors, GABA_A and GABA_B both inhibited KCl-stimulated [Ca²⁺]_i elevation in crude membranes prepared from the IMHV of untrained chicks. Furthermore, the GABA_B receptor antagonists were shown to exhibit some atypical properties. GABA_B receptors were shown to evoke greater inhibition on KCl-stimulated [Ca²⁺]_i elevation in crude membranes prepared from the IMHV of chicks tested 30 minutes after training compared to untrained birds and birds that were tested 5 minutes after training.