Key result
Epicardial application of bradykinin increased c-Fos expression in the thalamus and PVN, but the cardiac sympathetic afferent reflex was abolished by inhibition of the PVN and not the thalamus.
Absolute Event Rate: 190% vs 101%
p-value: p=<0.05
The paraventricular nucleus of the hypothalamus, but not the thalamus, is critically involved in the central pathway mediating the cardiac sympathetic afferent reflex.
Supports critical PVN involvement in the cardiac sympathetic afferent reflex; hypothesis-generating for central autonomic pathways.
The cardiac sympathetic afferent reflex (CSAR) is induced by stimulating the cardiac sympathetic afferents, which evokes increases in sympathetic outflow and arterial pressure. In the present study, we attempted to identify the contribution of thalamic and hypothalamic nuclei involved in the CSAR. First, we observed that there was an increase in the number of c-Fos-labeled cells in the paraventricular nucleus (PVN) (190 ± 18 vs. 101 ± 15; P < 0.05), the paraventricular nucleus of the thalamus (PVT) (239 ± 23 vs. 151 ± 15; P < 0.05), and the mediodorsal thalamic nucleus (MD) (92 ± 9 vs. 63 ± 6; P < 0.05) following epicardial application of bradykinin (BK) compared with the control group (P < 0.05). Second, using extracellular single-unit recording, we found 25% of spontaneously active neurons in the thalamus were stimulated by epicardial application of BK or capsaicin in intact rats. However, 24% of spontaneously active neurons in the thalamus were still stimulated by epicardial application of BK or capsaicin despite vagotomy and sinoaortic denervation. None of the neurons in the thalamus responded to baroreflex changes in arterial pressure, induced by intravenous injection of phenylephrine or sodium nitroprusside. The CSAR was inhibited by microinjection of muscimol or lidocaine into the PVN. However, it was not inhibited or blocked by microinjection of muscimol or lidocaine into the thalamus. Taken together, these data suggest that the thalamus, while activated, is not critical for autonomic adjustments in response to activation of the CSAR. On the other hand, the PVN is critically involved in the central pathway of the CSAR.
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Xu et al. (2013) studied Cardiac sympathetic afferent reflex. Epicardial application of bradykinin and microinjection of lidocaine or muscimol vs. Saline or artificial cerebrospinal fluid was evaluated on Number of c-Fos-labeled cells in the paraventricular nucleus (PVN) (p=<0.05). Epicardial application of bradykinin increased c-Fos expression in the thalamus and PVN, but the cardiac sympathetic afferent reflex was abolished by inhibition of the PVN and not the thalamus.