Received September 29, 2005
Revised October 19, 2005
Accepted after revision November 18, 2005
P2X PURINOCEPTOR SUBTYPES ON PARAVENTRICULAR NUCLEUS NEURONS PROJECTING TO THE ROSTRAL VENTROLATERAL MEDULLA IN RAT
Joo Lee Cham 1,
Neil C Owens 1,
Julian Barden 2,
Andrew Lawrence 3,
Emilio Badoer 1*
1 RMIT University
2 University of Sydney
3 Howard Florey Institute
* To whom correspondence should be addressed. E-mail: emilio.badoer{at}rmit.edu.au.
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Abstract |
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The rostral ventrolateral medulla (RVLM) is essential for the generation of sympathetic nerve activity. The RVLM receives a substantial innervation from the hypothalamic paraventricular nucleus (PVN). Activation of P2X purinoceptors via ATP has been shown to mediate fast excitatory synaptic neurotransmission. There is mounting evidence suggesting the presence of P2X purinoceptors in hypothalamic nuclei, including the PVN. In this study, we determined whether P2X1-P2X6 purinoceptor subtypes were present on PVN neurons that projected to the RVLM. Injection of the retrogradely-transported tracer, rhodamine-tagged microspheres, into the pressor region of the RVLM was used to identify the neurons in the PVN that innervated the RVLM. P2X1-P2X6 purinoceptors were detected by immunohistochemistry. Double-labeled neurons were quantitated and expressed as a proportion of the retrogradely labeled neurons. The proportions of double-labeled neurons for each of the P2X purinoceptor subtypes varied, on average, from 14% to 29%. The P2X3 purinoceptor subtype was found to be the dominant purinoceptor subtype present on PVN neurons projecting to the RVLM. Additionally it was apparent that more than one P2X purinoceptor subtype was present on the PVN neurons projecting to the RVLM, since the sum of the average percentages of double-labeled neurons for each P2X purinoceptor subtype exceeded 100%. These findings highlight the presence of the P2X1- P2X6 purinoceptors on PVN neurons projecting to the RVLM. The results suggest a potential role for ATP in the PVN in the regulation of sympathetic nerve activity.
Key Words:
Hypothalamus, P2 purinoceptor, Sympathetic nervous system
