The Spinal Pattern Generator for Ejaculation Exhibits Oscillatory Activity in the Spinal Male Rat

Research Article

Austin Andrology. 2016; 1(1): 1004.

The Spinal Pattern Generator for Ejaculation Exhibits Oscillatory Activity in the Spinal Male Rat

Carro-Juárez M¹* and Rodríguez-Manzo G²

¹Laboratorio de Comportamiento Reproductivo, Escuela de Medicina Veterinaria y Zootecnia, Universidad Autónoma de Tlaxcala, C.P.90000, Tlaxcala, México

²Departamento de Farmacobiología, Cinvestav-SedeSur , Calzada de los Tenorios 235, Col. Granjas Coapa, Deleg. Tlalpan, México

*Corresponding author: Dr. Miguel Carro-Juárez, Laboratorio de Comportamiento Reproductivo, Escuela de Medicina Veterinaria y Zootecnia, Universidad Autónoma de Tlaxcala, C.P.90000, Tlaxcala, México

Received: June 30, 2016; Accepted: July 27, 2016; Published: July 29, 2016


A spinal pattern generator controls ejaculation in male rats. Spinal pattern generators may display oscillatory bursting activity that shape the rhythmic motor patterns as a result of the intrinsic or conditioned oscillatory properties of its neuronal elements. The spinal pattern generator for ejaculation could exhibit oscillatory activity. The aim of the present study was to show the oscillatory activity of the spinal pattern generator for ejaculation in male rats. To this aim, we analysed the ejaculatory responses of spinal male Wistar rats of different ages, different ejaculatory conditions, subjected to different physiological or pharmacological stimuli within the frame of the theory of oscillatory behaviour. State variables, phases and periods of electromyography recordings of the genital motor patterns of ejaculation were obtained from the bulbospongiosus muscles. Recordings of the spontaneous and sensorially-induced genital motor patterns of ejaculation, obtained under the different physiological conditions or pharmacological treatments, revealed the oscillatory behaviour of the spinal generator for ejaculation which showed striking variations among rats of different ages, ejaculatory conditions and subjected to distinct stimuli, including an intense sexual training scheme. In conclusion, the spinal pattern generator for ejaculation behaves as a neural oscillator whose function can be modified by internal and external demands. The variability in the oscillatory activity of the ejaculation generator is a prominent feature that should be taken into consideration when characterising the most common ejaculatory dysfunctions.

Keywords: Ejaculation Oscillator; Spinal Oscillator; Spinal Pattern Generator; Spinal Cord; Ejaculation; Ejaculatory Dysfunction


Rhythmic motor behaviours such as respiration, locomotion, chewing and ejaculation are controlled by neuronal networks known as central pattern generators (CPG) [1-3]. CPGs are constituted by specialised groups of neurones that act as local control circuits and neural command centres capable of generating organised rhythmic patterns of motor activity [4-9]. CPGs can function in the absence of higher centres influence and sensory feedback and can be activated in a spontaneous manner maintaining a proper rhythm [10,11]. Two major conceptual models have been proposed to account for the source of rhythmicity in CPGs: the pacemaker theory, which suggests the existence of inherent membrane potential oscillations in some neurones of the network that act as leaders in synchronising firing activities of non-pacemaker interneurones and the emergent network theory, in which the rhythm arises from a pool of synaptically interacting excitatory interneurones that synchronize their spiking activities [12]. It has been proposed that the CPG pacemaker neurones serve as the source of the rhythm and their synaptic interactions with other network elements can modify this rhythm, but the inherent activity of the pacemaker neurons to promote rhythmic activity remains dominant [13]. Pacemaker neurones exhibit oscillations that result from the combination of their intrinsic electric properties and their synaptic interactions [14]. In neuronal circuits with excitatory activity at high- or slow-frequency, oscillations occur to finely shape and time the rhythmic motor patterns [14,15]. A tonic excitatory drive is widely accepted to be necessary to generate specific rhythms in CPG networks [12,16] with glutamate playing an essential role, as the main excitatory neurotransmitter, through the activation of N-methyl-D-aspartate (NMDA) receptors located at the CPG [12,16]. However, activation of NMDA receptors alone is not sufficient to lead pacemaker neurones to oscillate and other mechanisms, such as those elicited by afferent inputs, are required to generate neural oscillations [15]. Although in some rhythmic behaviours such as ejaculation [17,18], it has been demonstrated that the rhythmic motor response appears in the electromyogram almost immediately after electrical micro stimulation is applied to CPG neurones, it is not known whether oscillations directly give rise to rhythmic neuronal firing. The doubt arises because the electrically-induced CPGs oscillation frequencies are often lower than those seen in natural or fictive motor responses [16-18]. Nevertheless, the oscillatory properties of neurones of the CPGs might help to shape and time their rhythmic firing rather than to generate the locomotion rhythm [19]. Thus, oscillatory properties of CPGs can control and regulate the locomotor rhythmicity [12] and cycle duration [20] and consolidate the robustness of the rhythmic motor output [12].

In urethane anaesthetised and spinalised rats with intact afferent pathways, the mechanical sensory stimulation applied to genitalia evokes a highly rhythmic motor pattern, synchronically registered in all striated muscles associated with the genital tract [21]. This motor pattern is termed the genital motor pattern of ejaculation (GMPE) and is comprised of two clear components: a first ejaculatory motor train and an after discharge component (Figure 1) [21]. The GMPE is under the control of the spinal generator of ejaculation (SGE) and it drives the rhythmic expulsion of seminal secretions, supports the concomitant mechanical expression of phasic penile erections and promotes changes into the intraurethral pressure [3 and 17, for review]. Although the precise structure, location and function of the spinal generator for ejaculation is poorly understood, several studies suggest that it could be structured by pacemaker cells, [3] located at the lamina X of the spinal cord [21-24], which in addition could exhibit oscillatory activity.