Estrogen receptor-alpha immunoreactive neurons in the brainstem and spinal cord of the female rhesus monkey: species-specific characteristics

Abstract

The distribution pattern of estrogen receptors in the rodent CNS has been reported extensively, but mapping of estrogen receptors in primates is incomplete. In this study we describe the distribution of estrogen receptor alpha immunoreactive (ER-alpha IR) neurons in the brainstem and spinal cord of the rhesus monkey. In the midbrain, ER-alpha IR neurons were located in the periaqueductal gray, especially the caudal ventrolateral part, the adjacent tegmentum, peripeduncular nucleus, and pretectal nucleus. A few ER-alpha IR neurons were found in the lateral parabrachial nucleus, lateral pontine tegmentum, and pontine gray medial to the locus coeruleus. At caudal medullary levels, ER-alpha IR neurons were present in the commissural nucleus of the solitary complex and the caudal spinal trigeminal nucleus. The remaining regions of the brainstem were devoid of ER-alpha IR neurons. Spinal ER-alpha IR neurons were found in laminae I-V, and area X, and were most numerous in lower lumbar and sacral segments. The lateral collateral pathway and dorsal commissural nuclei of the sacral cord and the thoracic intermediolateral cell column also contained ER-alpha IR neurons. Estrogen treatment did not result in any differences in the distribution pattern of ER-alpha IR neurons. The results indicate that ER-alpha IR neurons in the primate brainstem and spinal cord are concentrated mainly in regions involved in sensory and autonomic processing. Compared with rodent species, the regional distribution of ER-alpha IR neurons is less widespread, and ER-alpha IR neurons in regions such as the spinal dorsal horn and caudal spinal trigeminal nucleus appear to be less abundant. These distinctions suggest a modest role of ER-alpha in estrogen-mediated actions on primate brainstem and spinal systems. These differences may contribute to variations in behavioral effects of estrogen between primate and rodent species.

Figure 1

Line drawings of 50µm thick, transverse sections through the midbrain showing the distribution of ER-α IR neurons in monkey M11. Each dot represents a single ER-α IR neuron. The drawings are taken at intervals of 1mm (levels 8 to 2) or 0.5mm (levels 2, 1.5, and 1). Level 0 is defined as the level at which the aqueduct opens into the 4^th ventricle. For abbreviations, see List of Abbreviations.

Figure 1

Line drawings of 50µm thick, transverse sections through the midbrain showing the distribution of ER-α IR neurons in monkey M11. Each dot represents a single ER-α IR neuron. The drawings are taken at intervals of 1mm (levels 8 to 2) or 0.5mm (levels 2, 1.5, and 1). Level 0 is defined as the level at which the aqueduct opens into the 4^th ventricle. For abbreviations, see List of Abbreviations.

Figure 2

Photomicrographs of ER-α IR neurons in: A: peripeduncular nucleus, level 6 (M18); B: caudal ventrolateral PAG, level 1.5 (M18); C: commissural nucleus of the Sol, level −15 (M18); D: medial part of the dorsal horn of C7 (M12); E: lateral collateral pathway in S1 (M11); and F: dorsal commissural nucleus of S1 (M11). Note that ER-α IR neurons are numerous and densely labeled in the peripeduncular area and ventrolateral caudal PAG. ER-α IR neurons in the remaining areas are less numerous and lightly to moderately labeled. For abbreviations, see List of Abbreviations. Bar: 100µm.

Figure 3

Line drawings of 50µm thick transverse sections through the pons and medulla oblongata showing the distribution of ER-α IR neurons of monkey M12. Each dot represents a single ER-α IR neuron. The drawings are taken at intervals of 2mm. Level 0 is defined as the level at which the aqueduct opens into the 4^th ventricle. Note that ER-α IR neurons are present only in the dorsolateral pons and caudal medulla oblongata. For abbreviations, see List of Abbreviations.

Figure 4

Line drawings of 50µm thick transverse sections through different spinal segments showing the distribution of ER-α IR neurons in monkey M18. In contrast to figures 1 and 3, each drawing is composed of three 50µm sections to obtain a better overview of the laminar distribution. Each dot represents a single ER-α IR neuron. For abbreviations, see List of Abbreviations.

Figure 5

Graphs showing the segmental distribution of spinal ER-α IR neurons in monkeys that did not receive estrogen treatment. The average number of ER-α IR neurons per 50µm transverse section is depicted, as determined in six non-adjacent transverse sections per segment per case (M12, M18: all segments; M15: all segments except C3, T2 and L2; M11: segments L6 and S1). SEM is indicated only for data that represents more than 2 animals.