Department of Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260, USA.
Exp Brain Res. 2012 Jul;220(2):121-33. doi: 10.1007/s00221-012-3122-8. Epub 2012 May 24.
Stimulation of vestibular receptors elicits distinct changes in blood flow to the forelimb and hindlimb, showing that the nervous system has the capacity to produce changes in sympathetic outflow which are specific for a particular region of the body. However, it is unclear whether the rostral ventrolateral medulla (RVLM), the primary region of the brainstem that regulates sympathetic outflow to vascular smooth muscle, has the appropriate connectivity with sympathetic preganglionic neurons to generate anatomically patterned responses. To make this determination, the retrograde fluorescent tracer Fast Blue was injected into the T(4) spinal cord segment of cats, which regulates upper body blood flow, whereas Fluoro-Ruby was injected into the T(10) segment to label projections to a region of the spinal cord that regulates lower body blood flow. More neurons were single-labeled by a particular tracer (92 %) than were double labeled by both tracers (8 %), supporting the notion that the RVLM can regulate sympathetic outflow from a limited number of spinal cord segments. Since a large fraction of RVLM neurons that control sympathetic outflow in rodents contain epinephrine, we additionally determined whether the tracer-labeled cells were immunopositive for the enzyme tyrosine hydroxylase (TH), which participates in the synthesis of catecholamines. Double labeling by the two tracers injected into the spinal cord was more common for TH-immunopositive neurons than for the general population of RVLM neurons: 19 % of the TH-positive cells contained both Fast Blue and Fluoro-Ruby, 30 % contained one of the tracers, and 51 % were not labeled by either tracer. Furthermore, many spinally projecting neurons in close proximity to the RVLM catecholaminergic neurons (41 % of the population) were not immunopositive for TH, suggesting that feline RVLM is neurochemically heterogeneous.
前庭感受器的刺激会引起前肢和后肢血流量的明显变化，这表明神经系统有能力产生特定于身体特定区域的交感神经输出变化。然而，尚不清楚调节血管平滑肌交感神经输出的脑干主要区域——腹外侧头端延髓（RVLM）是否与交感节前神经元具有适当的连接，以产生解剖模式的反应。为了确定这一点，将逆行荧光示踪剂 Fast Blue 注入调节上半身血流的猫 T(4)脊髓段，而将 Fluoro-Ruby 注入调节下半身血流的脊髓 T(10)段以标记到脊髓的一个区域的投射。通过特定示踪剂进行单一标记的神经元（92%）比通过两种示踪剂进行双重标记的神经元（8%）多，这支持了 RVLM 可以从有限数量的脊髓段调节交感神经输出的观点。由于控制啮齿动物交感神经输出的 RVLM 神经元中有很大一部分含有肾上腺素，因此我们还确定了示踪剂标记的细胞是否对参与儿茶酚胺合成的酶酪氨酸羟化酶（TH）呈免疫阳性。注入脊髓的两种示踪剂的双重标记在 TH 免疫阳性神经元中比在 RVLM 神经元的一般群体中更为常见：19%的 TH 阳性细胞同时含有 Fast Blue 和 Fluoro-Ruby，30%的细胞含有一种示踪剂，而 51%的细胞不被两种示踪剂中的任何一种标记。此外，RVLM 儿茶酚胺能神经元附近的许多脊髓投射神经元（占群体的 41%）对 TH 不呈免疫阳性，这表明猫的 RVLM 在神经化学上是异质的。
