Mapping of somatostatin-28 (1–12) in the alpaca diencephalon

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Abstract

Using an immunocytochemical technique, we report for the first time the distribution of immunoreactive cell bodies and fibers containing somatostatin-28 (1–12) in the alpaca diencephalon. Somatostatin-28 (1–12)-immunoreactive cell bodies were only observed in the hypothalamus (lateral hypothalamic area, arcuate nucleus and ventromedial hypothalamic nucleus). However, immunoreactive fibers were widely distributed throughout the thalamus and hypothalamus. A high density of such fibers was observed in the central medial thalamic nucleus, laterodorsal thalamic nucleus, lateral habenular nucleus, mediodorsal thalamic nucleus, paraventricular thalamic nucleus, reuniens thalamic nucleus, rhomboid thalamic nucleus, subparafascicular thalamic nucleus, anterior hypothalamic area, arcuate nucleus, dorsal hypothalamic area, around the fornix, lateral hypothalamic area, lateral mammilary nucleus, posterior hypothalamic nucleus, paraventricular hypothalamic nucleus, suprachiasmatic nucleus, supraoptic hypothalamic nucleus, and in the ventromedial hypothalamic nucleus. The widespread distribution of somatostatin-28 (1–12) in the thalamus and hypothalamus of the alpaca suggests that the neuropeptide could be involved in many physiological actions.

Highlights

► Somatostatin-28 (1–12)-immunoreactivity is reported in the alpaca diencephalon. ► Cell bodies were found in the lateral hypothalamic area. ► Perikarya were also found in the arcuate and ventromedial hypothalamic nuclei. ► Immunoreactive fibers were widely distributed throughout thalamus and hypothalamus.

Introduction

Somatostatin has been implicated in numerous physiological effects. After central administration of this peptide, behavioural changes such as difficulty in breathing, excessive grooming, decreased sleep, and hypersensitivity to tactile stimuli have been reported (Reichlin, 1983). Moreover, somatostatin inhibits the release of noradrenalin and growth hormone, stimulates the release of acetylcholine and serotonin, and exerts an important neural effect on the motor cortex, hippocampus and limbic system (Reichlin, 1983). With immunocytochemical and radioimmunoassay techniques, three prosomatostatin-derived peptides (somatostatin-28, somatostatin-28 (1–12) and somatostatin-14) have been described in the central nervous system of rats (Barden et al., 1981, Bennet-Clarke et al., 1980, Benoit et al., 1982, Finley et al., 1981, Guy et al., 1985, Johansson et al., 1984, Palkovits, 1988, Vincent et al., 1985), guinea-pigs (Hökfelt et al., 1974, Tramu et al., 1981), cats (de León et al., 1991, de León et al., 1992, Graybiel and Elde, 1983, Martín et al., 2003), monkeys (Macaca fascicularis, Saimiri sciureus) (Amaral et al., 1989, Campbell et al., 1987, Hendry et al., 1984, Lewis et al., 1986) and humans (Bennet-Clarke and Joseph, 1986, Bouras et al., 1987, Cooper et al., 1981, Hornung et al., 1992, Sorensen, 1982). Somatostatin-14 is a tetradecapeptide originally isolated from the hypothalamus, somatostatin-28 consists of the entire sequence of somatostatin-14 at its carboxyl terminal, followed by a double pair of basic amino acids and then somatostatin-28 (1–12); the peptide corresponding to the first 12 amino acids of somatostatin-28 is named somatostatin-28 (1–12) (see Benoit et al., 1985).

In general, previous research carried out on South America camelids has mainly focused on reproductive mechanisms (Bravo et al., 1996, Correa et al., 1997, Ratto et al., 2005, Ratto et al., 2006). No study has been carried out using immunocytochemical techniques on the distribution of neuropeptides in the central nervous system of camelids, except for two recent studies carried out on the distribution of immunoreactive fibers and cell bodies containing leucine-enkephalin or calcitonin gene-related peptide in the alpaca brainstem (de Souza et al., 2007, de Souza et al., 2008) and another focused on the colocalization of calcitonin gene-related peptide and tyrosine hydroxylase in the alpaca brainstem (Marcos et al., 2011). In this sense, no study addressing the presence of somatostatin-immunoreactive structures in the alpaca diencephalon has been reported. It is known that the thalamus and the hypothalamus are diencephalic regions involved in many physiological actions. Thus, the thalamus receives somatosensorial, nociceptive, visual, auditive, vestibular, taste and olfactory inputs (see Coveñas et al., 2001), whereas the hypothalamus is involved in drinking, food intake, thermoregulation, neuroendocrine control, immunoregulation, circadian rhythms, blood pressure, stress, reproduction and aggressive behaviour (see Swaab, 1997). Accordingly, our aim in this work was to study the distribution of immunoreactive fibers and cell bodies containing somatostatin-28 (1–12) in both important regions of the central nervous of the alpaca, using an immunocytochemical technique. A further aim was to compare our results with the distribution of the pre-prosomatostatin-derived peptides (e.g., somatostatin-14) previously described in the mammalian diencephalon. The neuroanatomical findings reported here will serve in the future to demonstrate the possible involvement of somatostatin-28 (1–12) in the physiological actions mentioned above in the alpaca diencephalon.

Section snippets

Animals

The experimental design, protocols, and procedures of this work were performed under the principles of laboratory animal care and under the guidelines of the ethics and legal recommendations of Peruvian and Spanish legislation. This work was also approved by the research commission of the Cayetano Heredia Peruvian University (Lima, Peru). We used six male adult alpacas (Lama pacos) (70–80 kg) obtained from the Cayetano Heredia Peruvian University (Faculty of Veterinary Medicine and Animal

Results

Table 1 shows the density of the immunoreactive structures containing somatostatin-28 (1–12) in the alpaca diencephalon, whereas Fig. 1 shows the widespread distribution of these structures from rostral (Fig. 1A) to caudal (Fig. 1E) diencephalic regions. In the alpaca diencephalon, the presence of immunoreactive cell bodies was quite restricted, since cell bodies containing somatostatin-28 (1–12) were only observed in three hypothalamic nuclei: a high density of immunoreactive cell bodies was

Discussion

This is the first time that the distribution of immunoreactive structures containing a neuropeptide has been described not only in the alpaca diencephalon, but also in the diencephalon of camelids. Immunoreactive fibers containing somatostatin-28 (1–12) were widely distributed throughout the diencephalon of the camelid studied here, but the presence of immunoreactive cell bodies was quite restricted.

Regarding the distribution of somatostatin-28 (1–12) in the rat diencephalon, our results are in

Acknowledgements

This work has been supported by the Ministerio de Educación y Ciencia (BFU2005-02241/BFI), Spain and the Ministerio de Ciencia e Innovación (BFU2008-03369/BFI), Spain and by the CONCYTEC: PROCYT project 2006, Peru. The authors thank N. Skinner for stylistic revision of the English text and Professor Gerard Tramu (University of Bordeaux I, France) for kindly providing the somatostatin-28 (1–12) antiserum.

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