Abstract Title

Enhanced Excitability of Vasopressin Neurons in the Supraoptic Nucleus Following 48 hr. Water Deprivation

RAD Assignment Number

1506

Presenter Name

Gef Farmer

Abstract

Purpose

Arginine vasopressin (AVP) is a neurohypophyseal hormone released from the posterior pituitary by magnocellular neurosecretory cells (MNCs) located within the supraoptic (SON) and paraventricular (PVN) nuclei of the hypothalamus. AVP is involved in the regulation of body fluid homeostasis and influences blood pressure, plasma osmolality, and blood volume. The regulation of AVP release is critical to maintaining body fluid homeostasis and is dependent on the activity of MNCs. The balance of excitatory and inhibitory inputs are important elements of activity, however the mechanisms leading to changes in AVP release are not fully understood. Water deprivation (WD), a physiological challenge, was used to examine changes in excitatory neurotransmission in MNCs using patch-clamp electrophysiology.

Methods

Male Sprague-Dawley rats weighing 250 – 350 g received bilateral SON infusions of an adeno-associated virus (AAV) construct containing mouse AVP gene promoter and EGFP reporter. Two weeks following AAV infusions, rats were water deprived for 24 hr. or 48 hrs. Controls were allowed ad libitum access to water. Following water deprivation, coronal brain slices (300 µm) containing the SON were cut using standard procedures. Whole-cell patch clamp recordings were obtained from slices superfused with aCSF containing tetrodotoxin (TTX; 0.5 µM) and bicuculine methbromide (Bic; 10 µM). Baseline mEPSCs were recorded then NMDAR mediated components were pharmacologically isolated with 5 minutes drug application of AMPA antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 10uM). Parameters measured for mEPSCs were amplitude (pA), rise time (ms), decay time (ms), charge transfer, and mEPSC frequency.

Results

In EGFP labeled SON neurons (i.e. confirmed vasopressinergic neurons), water deprivation increased the frequency of mEPSCs in both the 24 hr. group (p < 0.05) and the 48 hr. group (p < 0.05) when compared to controls. The water deprivation dependent enhancement in mEPSC frequency was independent of changes in mEPSC amplitude, rise time, decay time, or charge transfer.

Conclusion

Although no changes in amplitude, rise time, decay time, or charge transfer were detected, there was an increase in the frequency of mEPSCs following both 24 hr. and 48 hr. WD. It remains unclear how water deprivation leads to enhanced mEPSC frequency in MNC of the SON. Future studies will investigate the mechanisms that underlie this water deprivation dependent plasticity.

Presentation Type

Poster

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Enhanced Excitability of Vasopressin Neurons in the Supraoptic Nucleus Following 48 hr. Water Deprivation

Purpose

Arginine vasopressin (AVP) is a neurohypophyseal hormone released from the posterior pituitary by magnocellular neurosecretory cells (MNCs) located within the supraoptic (SON) and paraventricular (PVN) nuclei of the hypothalamus. AVP is involved in the regulation of body fluid homeostasis and influences blood pressure, plasma osmolality, and blood volume. The regulation of AVP release is critical to maintaining body fluid homeostasis and is dependent on the activity of MNCs. The balance of excitatory and inhibitory inputs are important elements of activity, however the mechanisms leading to changes in AVP release are not fully understood. Water deprivation (WD), a physiological challenge, was used to examine changes in excitatory neurotransmission in MNCs using patch-clamp electrophysiology.

Methods

Male Sprague-Dawley rats weighing 250 – 350 g received bilateral SON infusions of an adeno-associated virus (AAV) construct containing mouse AVP gene promoter and EGFP reporter. Two weeks following AAV infusions, rats were water deprived for 24 hr. or 48 hrs. Controls were allowed ad libitum access to water. Following water deprivation, coronal brain slices (300 µm) containing the SON were cut using standard procedures. Whole-cell patch clamp recordings were obtained from slices superfused with aCSF containing tetrodotoxin (TTX; 0.5 µM) and bicuculine methbromide (Bic; 10 µM). Baseline mEPSCs were recorded then NMDAR mediated components were pharmacologically isolated with 5 minutes drug application of AMPA antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 10uM). Parameters measured for mEPSCs were amplitude (pA), rise time (ms), decay time (ms), charge transfer, and mEPSC frequency.

Results

In EGFP labeled SON neurons (i.e. confirmed vasopressinergic neurons), water deprivation increased the frequency of mEPSCs in both the 24 hr. group (p < 0.05) and the 48 hr. group (p < 0.05) when compared to controls. The water deprivation dependent enhancement in mEPSC frequency was independent of changes in mEPSC amplitude, rise time, decay time, or charge transfer.

Conclusion

Although no changes in amplitude, rise time, decay time, or charge transfer were detected, there was an increase in the frequency of mEPSCs following both 24 hr. and 48 hr. WD. It remains unclear how water deprivation leads to enhanced mEPSC frequency in MNC of the SON. Future studies will investigate the mechanisms that underlie this water deprivation dependent plasticity.