NMDA receptors in the insular cortex modulate cardiovascular and
autonomic but not neuroendocrine responses to restraint stress in rats
Background and Purpose: The insular cortex (IC) is a brain structure
involved in the modulation of autonomic, cardiovascular and
neuroendocrine adjustments during stress situations. However, the local
neurochemical mechanisms involved in the control of these responses by
the IC are poorly understood. Glutamate is a prominent excitatory
neurotransmitter in the brain. Thus, the current study aimed to
investigate the involvement of glutamatergic neurotransmission within
the IC in cardiovascular, autonomic and neuroendocrine responses to
acute restraint stress. Experimental Approach: The selective NMDA
glutamate receptor antagonist LY235959 (1 nmol/100 nL) and the selective
non-NMDA glutamate receptor antagonist NBQX (1 nmol/100 nL) were
microinjected into the IC 10 min before the onset of restraint stress.
Key Results: The antagonism of NMDA receptors within the IC potentiated
the restraint-evoked increases in both arterial pressure and heart rate,
while non-NMDA blockade had no effect on these parameters. Spontaneous
baroreflex analysis demonstrated that microinjection of LY235959 into
the IC decreased baroreflex activity during restraint stress. The
decrease in tail skin temperature during restraint stress was shifted to
an increase in animals treated with the NMDA receptor antagonist.
Moreover, the blockade of IC glutamate receptors did not affect the
increase in circulating corticosterone levels during restraint stress.
Conclusion and Implications: Overall, our findings provide evidence that
IC glutamatergic signalling, acting via NMDA receptors, plays a
prominent role in the control of autonomic and cardiovascular responses
to restraint stress but does not affect neuroendocrine adjustments.