BACKGROUND
We have previously shown that disinhibition of the medial prefrontal cortex (mPFC) alter cardiorespiratory and metabolic function. A key finding was the activation of interscapular brown adipose tissue (iBAT), a marker of non shivering thermogenesis. The PFC has major reciprocal connections to the nucleus accumbens. As catecholamines provide a major influence in these limbic regions, we sought to determine the cardiorespriartoy and metabolic effects of dopamine and noradrenaline in the mPFC and NAc with particular focus on the activation of iBAT.
Methods
In vivo electrophysiological experiments were performed in urethane-anaesthetised, artificially ventilated, paralysed, vagotomised, male Sprague-Dawley rats. Microinjections of dopamine hydrochloride (Sigma, 90ug/250nl) and L-norepinephrine hydrochloride (Sigma, 10ug/250nl) were made into the infralimbic cortex of the mPFC and the NAc. Effects on iBAT, heart rate (HR), expired CO2, phrenic nerve amplitude and frequency (PNamp and PNf), mean arterial pressure (MAP), splanchnic and lumbar sympathetic nerve activity (sSNA and lSNA) were determined.
Results
Dopamine altered thermogenic and cardiorespiratory function in both mPFC and NAc. DA evoked significant increases in thermogenic and metabolic outflows (iBAT;2.2±0.3ºC, HR;21±4bpm and expired CO2;0.67±0.11%). Increases in respiratory function were also observed (PNf;11±1bpm, and, PNamp;137±15%) along with minor effects on blood pressure (-11±2mmHg) and SNA (6.1±3.6%) in the mPFC.
Norepinephrine also evoked increases in iBAT (0.8±0.15 ºC), HR (16±2bpm) and expired CO2 (0.35±0.07%). Increased respiratory function and sympathoinhibition were also similar, however, increases in MAP (18±2mmHg) were generated.
Effects from the NAc are currently being analysed.
Conclusions
Two novel sites in the PFC, the ventral mPFC and NAc, are shown to alter thermogenesis and cardiorespiratory function through the actions of dopamine and norepinephrine. Whether these responses are being generated via the distinct interconnectivity of the regions is being investigated.
Disclosure
NA