G. Petrosino

Viscerotopic representation of the subdiaphragmatic tracts of the digestive apparatus within the vagus complex in the sheep.

The distribution in the brainstem and cervical spinal cord of neurons supplying the reticulum and the reticular groove, the rumen, the omasum, the abomasum, and the small and large intestine was investigated in the sheep using the fluorescent retrograde tracer technique. Only the reticulum and reticular groove were represented in the dorsal motor nucleus of the vagus nerve (DMNX), in the nucleus ambiguus (NA), and in the nucleus retroambigualis (NRA). The other forestomach, the abomasum and the small intestine were supplied by the DMNX only, with the exception of the rumen which was also innervated by the NRA. Some reticular formation neurons were found labeled after the injection of the tracer into the reticulum, the reticular groove, and the rumen. We present evidence that the reticular groove is the part of the forestomach having the widest representation, and also the richest innervation.

An immunohistochemical study of the distribution of nitric oxide synthase-immunoreactive neurons and fibers in the reticular groove of suckling lambs.

The reticular groove (RG) is a specialized region of ruminant forestomach which, in suckling animals, via a vagovagal reflex, transforms itself into a tube to ensure the direct transport of milk from the esophagus to the abomasum. The nervous mechanism controlling the RG movement is not fully understood; however, at this level, the enteric nervous system (ENS) shows the highest neuronal density when compared with other forestomach compartments. Because nitric oxide is considered the putative major mediator of non‐adrenergic non‐cholinergic smooth muscle relaxation, the aim of the present study was to investigate the ENS of the RG of suckling lambs, both in the floor and in the lip, with particular regard to nitric oxide synthase (NOS)‐immunoreactivity (‐IR), by means of double immunohistochemical staining. NOS antiserum was used in association with some neurochemical markers which have been utilized by many authors in ENS. A rich innervation of fibers extended along the entire length of the RG. Proceeding distally, the number of neurons stained with a pan‐neuronal marker increased; they were more numerous in the lips and lip–floor junction than in the floor itself. However, the percentage of NOS‐IR neurons was the same in the proximal and distal parts. Many NOS‐IR neurons often co‐expressed galanin and dopamine β‐hydroxylase. Neurochemical markers, such as calbindin, calcitonin gene‐related peptide, IB4 and neurofilament 200 kDa, usually used to identify primary sensory neurons were not expressed in RG neurons, and the co‐localization of NOS with tyrosine hydroxylase and substance P was rarely found. When compared with other districts, the RG showed some peculiar aspects, such as the lack of both neurons in the submucosal plexus and the lack of typical sensory neurons.

The Mesencephalic Trigeminal Nucleus of the Duck: Development and Apoptosis

The normal development of the mesencephalic trigeminal nucleus (MesV) of the white Peking duck (Anas platyrhynchos) was studied from the 9th day of incubation until hatching and during adulthood. In the early days of embryonic development, neurons are present in the posterior commissure and in the mesenchymal tissue outside the leptomeninges in addition to those in the tectal commissure (TC) and in the optic tectum. Following the internucleosomal cleavage of DNA, a massive loss of neurons in the MesV starts in the 11-day embryo and continues until the 15th day of incubation. On the 16th day, the nucleus consists of a numerically larger medial division located in the TC and a smaller lateral division within the stratum griseum periventriculare as is found in the adult animal. The programmed cell death occurring in the MesV is discussed herein and correlated with the analogous apoptotic phenomena observed in the trigeminal motor nucleus.

NOS Immunoreactivity in the Reticular Groove of Lamb

Evidence suggests that the reticular groove (RG) may have an important role as the coordination center of reticulo-ruminal motility. The aim of this study was to investigate the presence and distribution of nitric oxide synthase (NOS) neurons and their phenotype in the RG of suckling lamb. Using double immunohistochemistry, many NOS neurons were found along the entire length of the RG and were more abundant in the floor than in the lips. They showed irregular profiles and often colocalized with galanin and dopamine β-hydroxylase but rarely with substance P and tyrosine hydroxylase. We never observed NOS neurons expressing neuropeptides normally found in intrinsic primary sensory neurons, such as calcitonin gene-related peptide, calbindin, IB4, and neurofilament 200kDa. When compared to other districts, the enteric plexuses of the RG showed some peculiar aspects, such as the lack of both neurons in the submucosal plexus and typical sensory neurons.