Central gray lesions produce estrous behavioral responses in hormonally anestrous cats

Roles of the pontine dorsomedial tegmentum and midbrain central gray in regulating female rat sexual behaviors: effects of p-chlorophenylalanine

Lesions in the midbrain dorsal central gray (MCGL) markedly suppressed both lordosis and soliciting behavior in estradiol benzoate-progesterone (EB-P)-primed castrated female rats. Similarly, the pontine dorsomedial tegmental lesions (PDMTL) caused a severe loss of lordosis behavior. However, the PDMTL females while demonstrating no lordotic response displayed ear-wiggling. These results suggest that the midbrain dorsal central gray plays an important role in regulation of both lordosis and soliciting behaviors. In contrast, the pontine dorsomedial tegmentum appears to participate in regulating the neural mechanism for lordosis only and not for soliciting behavior. Two weeks later prior to a second test, approximately half of the MCGL and PDMTL females that had shown no lordosis in the first test, were injected with p-chlorophenylalanine (PCPA) and primed with EB-P. PCPA significantly increased the lordotic activity of EB-P-primed MCGL females, whereas it failed to potentiate a lordotic response in the PDMTL females. Since PCPA effectively facilitated the display of lordosis in the absence of the neural substrate of the midbrain central gray, this neural structure may not be the minimally necessary component of the neural circuitry regulating the display of lordosis behavior. On the other hand, the pontine dorsomedial tegmentum may be a neural substrate more closely related with the descending pathway controlling the expression of lordosis.

Forebrain influences on brainstem and spinal mechanisms of copulatory behavior: a current perspective on Frank Beach's contribution

In a 1967 Physiological Reviews paper, Frank Beach put forth four propositions regarding forebrain and hormonal control of brainstem-spinal mechanisms of copulatory behavior. Simply stated, he proposed that: 1) the forebrain exerted an inhibitory control over species-typical copulatory reflexes through descending effects on brainstem-spinal mechanisms and 2) gonadal hormones influence these reflexes largely by actions on forebrain control processes rather than by direct effects on the brainstem or spinal cord. This theoretical scheme was of great heuristic significance during the subsequent two decades of research, which has largely supported and delineated in greater mechanistic detail the processes Beach hypothesized to exist. This subsequent research has also shown the central nervous system actions of gonadal hormones to be more widespread and complex than Beach proposed. Some of these recent research findings are presented, with emphasis on neurophysiological studies which have identified hormone-induced functional changes in forebrain and brainstem neurons. It is proposed that these functional changes may represent a mechanism for the behavior-controlling actions of hormones that were hypothesized by Beach.

Lordosis-disrupting tectal lesions alter midbrain unit somatosensory responsiveness in hamsters

Previous research has shown that bilateral deep tectal lesions in golden hamsters abolish the lordosis response, whereas unilateral lesions selectively impair lordosis elicitation by contralateral flank stimulation. The present study analyzed the neural basis of these lesion effects by assessing the somatosensory responsiveness of midbrain neurons in three groups of urethane-anesthetized hamsters: animals with lordosis-abolishing bilateral tectal lesions, animals with lordosis-impairing unilateral lesions, and intact animals. Animals with bilateral lesions differed from the other groups in three aspects of unit sensory responsiveness by showing: (1) the highest percentage of neurons responsive to somatic stimulation, (2) the highest incidence of unit responsiveness to flank stimulation, and (3) the greatest proportion of responsive neurons in the ventral tegmentum. Hamsters with unilateral lesions showed basically normal unit responsiveness apart from elevated unit response to face stimulation. The results suggest that bilateral tectal lesions may eliminate lordosis by the combined effects of enhanced ventral tegmental somatosensory responsiveness and tectal destruction. Unilateral lesions appear to impair lordosis without changing the somatosensory excitability of remaining midbrain neurons.

An autoradiographic study of projections ascending from the midbrain central gray, and from the region lateral to it, in the rat

Ascending projections from the midbrain central gray (CG) and from the region lateral to it were traced in the rat using tritiated amino acid autoradiography. Leucine or a cocktail of amino acids (leucine, proline, lysine, histidine, and tyrosine) were used as tracers. In addition to projections within the midbrain, ascending fibers follow three trajectories. The ventral projection passes through the ventral tegmental region of Tsai and the medial forebrain bundle to reach the hypothalamus, preoptic area, caudoputamen, substantia innominata, stria terminalis, and amygdala. There are labeled fibers in the diagonal bands of Broca and medial septum, and terminal labeling in the lateral septum, nucleus accumbens, olfactory tubercle, and frontal cortex. The dorsal periventricular projection terminates in the midline and intralaminar thalamic nuclei. The ventral periventricular projection follows the ventral component of the third ventricle into the hypothalamus, passing primarily through the dorsal hypothalamic area and labeling the rostral hypothalamus and preoptic area. Projections from the region lateral to the CG are similar, but exhibit stronger proximal, and weaker distal, projections. Rostral levels of the CG send heavier projections to the fields of Forel and the zona incerta, but fewer fibers through the supraoptic decussation, than do caudal levels. Ascending projections from the CG are both strong and widespread. Strong projections to the limbic system and the intralaminar thalamic nuclei provide an anatomical substrate for CG involvement in nociception and affective responses.