Impaired GABAergic sympathoinhibition within the paraventricular nucleus via NKCC1 contributes to sympathoexcitation and hypertension in male but not female rats exposed to chronic mild unpredictable stress

Abstract

Psycological stress and depression are established risk factors for the development of cardiovascular disease. To model stress in rats, we use the chronic mild unpredictable stress (CMS) paradigm. We previously showed that male rats exposed to CMS for four weeks develop hypertension and that at least a part of the mechanism involves vasopressinergic signaling via V1a and V1b receptors in the paraventricular nucleus (PVN). The present investigation was designed to further ascertain the mechanistic details of hypertension and increased RSNA responses in CMS rats and to determine the hemodynamic and RSNA perturbations in female Sprague Dawley rats. We hypothesized that the increased sympathetic tone is due at least in part to the impaired GABAergic sympathoinhibition and that blockade of NKCC1 and KCC2 in the PVN will mitigate this response. Male and female Sprague Dawley rats were subjected to the CMS protocol (n = 3/group) for four weeks, while the controls were kept under standard conditions (n = 3/group). All rats were instrumented with brain cannulas directed to the PVN and allowed to recover for three days. Then, the rats were implanted with carotid arterial catheters for blood pressure measurement and a set of silver wire electrodes attached to the renal nerve for the assessment of RSNA. On study day, the rats were allowed to acclimatize to the Plexiglas study chamber for 30 minutes and the PVN was microinjected with vehicle followed by either 9 nmol of muscimol with either NKCC1 (bumetanide) or KCC2 (VU0240551) inhibitors prior to muscimol administration. MAP, heart rate (HR) and RSNA were continuously measured throughout the experiment in conscious awake rats. Male CMS rats had higher baseline MAP (133 ± 6 mmHg) and HR (435 ± 10 BPM) compared to the female CMS rats (MAP 110 ± 6 mmHg, HR 417 ± 6 BPM, P < 0.05). Microinjection of muscimol, a GABA agonist, reduced MAP and HR similarly between the male (13 ± 4 mmHg and 42 ± 16 BPM, respectively) and female (15 ± 3 mmHg and 38 ± 18 BPM, respectively) control rats. Compared to the control rats, microinjection of muscimol resulted in much smaller decrease in MAP (6 ± 5 mmHg) and HR (26 ± 17 BPM) in male rats and virtually no change in MAP (-2 ± 2 mmHg) and a similar decrease in HR (51 ± 14 BPM) in female rats. Administration of bumetanide in the PVN partially rescued the GABAergic responses to muscimol in male rats, decreasing MAP by 10 ± 2 mmHg and HR by 68 ± 31 BPM ( P < 0.001 vs. vehicle treated). Administration of VU0240551 was not effective in rescuing rescuing the muscimol responses as evidenced by a decrease in MAP by 8 ± 3 mmHg and HR by 49 ± 45 BPM (N.S. vs. vehicle treated control). These results indicate that in CMS male Sprague Dawley rats, the deranged neurocardiovascular responses are at least partially mediated by the impaired sympathoinhibitory GABA signaling, unlike in female premenopausal Sprague Dawley rats that appear to be protected from developing hypertension. This study was funded by the Department of Veteran Affairs BX003480. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.