Objective - The activity of the gastrointestinal tract is strongly regulated through the catecholaminergic system, which acts via the activation of α and β adrenergic receptors (ARs). Since data concerning the distribution of ARs in the horse intestine is virtually absent, we investigated the distribution of β2-AR in the horse ileum. Animals - Four Italian trotter horses, two young females age 2.5 and 3.5 years, and two males age 8 months and 5 years. Procedures - Double-immunofluorescence staining was performed on cryostat sections with primary antibodies against β2-AR, Hu, neuron-specific enolase (NSE), S100 protein and tyrosine hydroxylase (TH). The percentage of double-immunolabeled neurons was determined in the submucosal plexus (SMP) and myenteric plexus (MP). In addition, the relationship between the β2-AR-immunoreactive (IR) cells and the cathecolaminergic fibers showing immunoreactivity for the enzyme tyrosine hydroxylase (TH) was also studied. Results - The β2-AR-immunoreactivity (IR) was observed in the following elements: in most (95%) neurons located mainly in SMP; in few (8%) neurons of the MP; in non-neuronal elements (interstitial cells of Cajal, mast cells and immunocytes). In addition, sympathetic TH-IR fibers were observed close to neurons, ICCs and mast cells expressing β2-AR-IR. Although enteric glial cells were not β2-AR-IR, in the SMP and MP the TH-IR fibers were observed also near glial cells. Conclusion and Clinical Relevance - Since β2-AR is virtually expressed in most neurons located in the horse SMP and in a lower percentage of neurons in the MP, it is reasonable to retain that this adrenergic receptor could regulate the activity of both secretomotor neurons and motor neurons innervating muscle layers and blood vessels. The high density of TH-IR fibers near SMP and MP β2-AR-IR neurons indicates that the excitability of these cells could be directly modulated by the sympathetic system. Consequently, the sympathetic system may regulate the motility, secretion and blood flow of the ileum acting also on β2-ARs. The presence of β2-AR in ICCs, mast cells and immunocytes indicates that catecholamines can regulate the activity of the non-neuronal cells distributed inside the gut wall. The pathogenesis of intestinal dysmotility includes also an imbalance of the sympathetic activity. Thus, the present work provides useful data on the cellular populations potentially involved in these pathological processes.
EXPRESSION OF Β2 ADRENOCEPTORS WITHIN ENTERIC NEURONS OF THE HORSE ILEUM.
GARDINI, ANNA;BOMBARDI, CRISTIANO;GRANDIS, ANNAMARIA;SORTENI, CATERINA;CLAVENZANI, PAOLO;CHIOCCHETTI, ROBERTO
2012
Abstract
Objective - The activity of the gastrointestinal tract is strongly regulated through the catecholaminergic system, which acts via the activation of α and β adrenergic receptors (ARs). Since data concerning the distribution of ARs in the horse intestine is virtually absent, we investigated the distribution of β2-AR in the horse ileum. Animals - Four Italian trotter horses, two young females age 2.5 and 3.5 years, and two males age 8 months and 5 years. Procedures - Double-immunofluorescence staining was performed on cryostat sections with primary antibodies against β2-AR, Hu, neuron-specific enolase (NSE), S100 protein and tyrosine hydroxylase (TH). The percentage of double-immunolabeled neurons was determined in the submucosal plexus (SMP) and myenteric plexus (MP). In addition, the relationship between the β2-AR-immunoreactive (IR) cells and the cathecolaminergic fibers showing immunoreactivity for the enzyme tyrosine hydroxylase (TH) was also studied. Results - The β2-AR-immunoreactivity (IR) was observed in the following elements: in most (95%) neurons located mainly in SMP; in few (8%) neurons of the MP; in non-neuronal elements (interstitial cells of Cajal, mast cells and immunocytes). In addition, sympathetic TH-IR fibers were observed close to neurons, ICCs and mast cells expressing β2-AR-IR. Although enteric glial cells were not β2-AR-IR, in the SMP and MP the TH-IR fibers were observed also near glial cells. Conclusion and Clinical Relevance - Since β2-AR is virtually expressed in most neurons located in the horse SMP and in a lower percentage of neurons in the MP, it is reasonable to retain that this adrenergic receptor could regulate the activity of both secretomotor neurons and motor neurons innervating muscle layers and blood vessels. The high density of TH-IR fibers near SMP and MP β2-AR-IR neurons indicates that the excitability of these cells could be directly modulated by the sympathetic system. Consequently, the sympathetic system may regulate the motility, secretion and blood flow of the ileum acting also on β2-ARs. The presence of β2-AR in ICCs, mast cells and immunocytes indicates that catecholamines can regulate the activity of the non-neuronal cells distributed inside the gut wall. The pathogenesis of intestinal dysmotility includes also an imbalance of the sympathetic activity. Thus, the present work provides useful data on the cellular populations potentially involved in these pathological processes.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
